diff --git a/apps/services/gateway/gateway/db.py b/apps/services/gateway/gateway/db.py
index 85f9444a1..67e0fbacb 100644
--- a/apps/services/gateway/gateway/db.py
+++ b/apps/services/gateway/gateway/db.py
@@ -20,17 +20,29 @@
 from __future__ import annotations
 
 from acb_common.db import (
+    TenantUnbound,
     async_database_url,
+    bind_tenant,
+    clear_tenant,
+    current_tenant,
     engine_connect_args,
     get_db,
     get_engine,
     get_session_factory,
+    release_tenant,
+    tenant_session,
 )
 
 __all__ = [
+    "TenantUnbound",
     "async_database_url",
+    "bind_tenant",
+    "clear_tenant",
+    "current_tenant",
     "engine_connect_args",
     "get_db",
     "get_engine",
     "get_session_factory",
+    "release_tenant",
+    "tenant_session",
 ]
diff --git a/apps/services/gateway/gateway/main.py b/apps/services/gateway/gateway/main.py
index 4b863ffea..09a264ac3 100644
--- a/apps/services/gateway/gateway/main.py
+++ b/apps/services/gateway/gateway/main.py
@@ -8,6 +8,7 @@
 from acb_auth import (UserContext, UserRole, get_current_user,
                       require_authenticated, require_role)
 from acb_common import configure_logging, get_logger, get_settings
+from acb_common.db import clear_tenant, release_tenant
 from fastapi import BackgroundTasks, Depends, FastAPI
 from fastapi.middleware.cors import CORSMiddleware
 from fastapi.responses import StreamingResponse
@@ -553,6 +554,31 @@ def docs_enabled(env: str) -> bool:
     openapi_url="/openapi.json" if _docs_enabled else None,
 )
 
+# ── Tenant scope (MT-1c / H2) ── every HTTP request runs inside its own tenant
+# scope: opened empty here, filled in by `_with_resolved_access` when the auth
+# dependency resolves the caller's organization, released after the response.
+# Pure ASGI (no BaseHTTPMiddleware) so the downstream app runs in THIS task and
+# the contextvar token round-trips — which is what makes "one request can never
+# inherit another's binding" true on any server task model, not just uvicorn's
+# task-per-request. Jobs and consumers get no scope from this; they bind
+# explicitly or fail closed with TenantUnbound (H4).
+class TenantScopeMiddleware:
+    def __init__(self, asgi_app):  # noqa: ANN001 — ASGI protocol shape
+        self.asgi_app = asgi_app
+
+    async def __call__(self, scope, receive, send):  # noqa: ANN001
+        if scope["type"] != "http":
+            await self.asgi_app(scope, receive, send)
+            return
+        token = clear_tenant()
+        try:
+            await self.asgi_app(scope, receive, send)
+        finally:
+            release_tenant(token)
+
+
+app.add_middleware(TenantScopeMiddleware)
+
 # ── CORS ── allow workbench dev server (port 3001) and production origin
 app.add_middleware(
     CORSMiddleware,
diff --git a/apps/services/gateway/gateway/routes/projects/activities.py b/apps/services/gateway/gateway/routes/projects/activities.py
index 04fa5481b..10c92eca1 100644
--- a/apps/services/gateway/gateway/routes/projects/activities.py
+++ b/apps/services/gateway/gateway/routes/projects/activities.py
@@ -24,7 +24,7 @@
 from gateway.routes.projects.core import (
     ActivityModel,
     Page,
-    _get_db,
+    _tenant_session,
     actor,
     emit,
     from_jsonb,
@@ -85,8 +85,7 @@ async def get_timeline(
     never withheld — the history of what happened to a task is not editable by
     the people it happened to.
     """
-    db = await _get_db()
-    try:
+    async with _tenant_session() as db:
         vis = await resolve_visibility(db, user)
         await load_visible_task(db, vis, task_id)
         params = {
@@ -111,8 +110,6 @@ async def get_timeline(
             "rows": [row_to_dict(r, ActivityModel) for r in rows],
             "total": int(total),
         }
-    finally:
-        await db.close()
 
 
 @router.post("/tasks/{task_id}/comments", status_code=201)
@@ -123,8 +120,7 @@ async def add_comment(
     body = (payload.body or "").strip()
     if not body:
         raise HTTPException(status_code=422, detail="A comment needs a body.")
-    db = await _get_db()
-    try:
+    async with _tenant_session() as db:
         vis = await resolve_visibility(db, user)
         await load_visible_task(db, vis, task_id)
         row = await record_activity(
@@ -170,13 +166,10 @@ async def add_comment(
                 task_id=task_id,
                 meta={"mentioned": mention_result["notified"]},
             )
-        await db.commit()
         result = row_to_dict(row, ActivityModel)
         # Surfaced, not swallowed: a mention that reached nobody would
         # otherwise leave the author believing they pulled a colleague in.
         result["not_notified"] = mention_result["skipped"]
-    finally:
-        await db.close()
 
     await emit("pm.task.comment_added", {"task_id": task_id})
     return result
@@ -211,8 +204,7 @@ async def edit_comment(
     body = (payload.body or "").strip()
     if not body:
         raise HTTPException(status_code=422, detail="A comment needs a body.")
-    db = await _get_db()
-    try:
+    async with _tenant_session() as db:
         comment = await _load_own_comment(db, activity_id, user)
         # The task must still be visible: a member removed from a Center keeps
         # authorship of what they wrote but not access to it.
@@ -244,12 +236,9 @@ async def edit_comment(
                 task_id=task_id,
                 meta={"mentioned": mention_result["notified"]},
             )
-        await db.commit()
         result = row_to_dict(row, ActivityModel)
         result["not_notified"] = mention_result["skipped"]
         return result
-    finally:
-        await db.close()
 
 
 @router.delete("/comments/{activity_id}")
@@ -263,17 +252,13 @@ async def delete_comment(
     the row hidden, so "deleted" means the words are gone rather than merely
     filtered out of one read path.
     """
-    db = await _get_db()
-    try:
+    async with _tenant_session() as db:
         await _load_own_comment(db, activity_id, user)
         await update_row(
             db, "pm_activities", activity_id,
             {"deleted_at": now(), "body": None},
         )
-        await db.commit()
         return {"deleted": activity_id}
-    finally:
-        await db.close()
 
 
 def _restore_custom(task: Any, changes: list[dict]) -> dict | None:
@@ -317,8 +302,7 @@ async def revert_change(
     the timeline shows that a revert happened instead of history appearing never
     to have contained the change.
     """
-    db = await _get_db()
-    try:
+    async with _tenant_session() as db:
         row = (await db.execute(
             text(
                 "SELECT * FROM pm_activities WHERE id = CAST(:aid AS uuid) "
@@ -378,7 +362,6 @@ async def revert_change(
             ],
             extra_meta={"reverted_activity_id": activity_id},
         )
-        await db.commit()
         task_id = str(task.id)
         reverted = sorted(
             [k for k in restore if k != "custom_fields"]
@@ -387,8 +370,6 @@ async def revert_change(
                 if str(c.get("field") or "").startswith(_CUSTOM_PREFIX)
             ]
         )
-    finally:
-        await db.close()
 
     await emit("pm.task.updated", {"task_id": task_id})
     return {"task_id": task_id, "reverted": reverted, "skipped": skipped}
diff --git a/apps/services/gateway/gateway/routes/projects/admin.py b/apps/services/gateway/gateway/routes/projects/admin.py
index 7caab7e69..6b9b94e67 100644
--- a/apps/services/gateway/gateway/routes/projects/admin.py
+++ b/apps/services/gateway/gateway/routes/projects/admin.py
@@ -28,7 +28,7 @@
     STATUS_CATEGORIES,
     StatusModel,
     TypeModel,
-    _get_db,
+    _tenant_session,
     clean_payload,
     count_where,
     load_visible_project,
@@ -93,8 +93,7 @@ async def _clear_other_defaults(db: Any, table: str, root: str, keep: str) -> No
 async def list_statuses(
     project_id: str, user: UserContext = Depends(get_current_user),
 ) -> dict:
-    db = await _get_db()
-    try:
+    async with _tenant_session() as db:
         vis = await resolve_visibility(db, user)
         root = await _root_for(db, vis, project_id)
         rows = (await db.execute(
@@ -107,8 +106,6 @@ async def list_statuses(
         return {
             "rows": [row_to_dict(r, StatusModel) for r in rows], "total": len(rows),
         }
-    finally:
-        await db.close()
 
 
 @router.post("/nodes/{project_id}/statuses", status_code=201)
@@ -123,8 +120,7 @@ async def create_status(
     category = values.get("category") or "todo"
     validate_choice(category, STATUS_CATEGORIES, "status category")
 
-    db = await _get_db()
-    try:
+    async with _tenant_session() as db:
         vis = await resolve_visibility(db, user)
         root = await _root_for(db, vis, project_id)
         row = (await db.execute(
@@ -144,10 +140,7 @@ async def create_status(
         )).fetchone()
         if row.is_default:
             await _clear_other_defaults(db, "pm_task_statuses", root, str(row.id))
-        await db.commit()
         return row_to_dict(row, StatusModel)
-    finally:
-        await db.close()
 
 
 @router.patch("/statuses/{status_id}")
@@ -157,8 +150,7 @@ async def patch_status(
 ) -> dict:
     values = clean_payload(payload)
     validate_choice(values.get("category"), STATUS_CATEGORIES, "status category")
-    db = await _get_db()
-    try:
+    async with _tenant_session() as db:
         existing = await require_row(db, "pm_task_statuses", status_id, "Status")
         vis = await resolve_visibility(db, user)
         await load_visible_project(db, vis, str(existing.project_id))
@@ -169,10 +161,7 @@ async def patch_status(
             await _clear_other_defaults(
                 db, "pm_task_statuses", str(row.project_id), status_id,
             )
-        await db.commit()
         return row_to_dict(row, StatusModel)
-    finally:
-        await db.close()
 
 
 @router.delete("/statuses/{status_id}")
@@ -186,8 +175,7 @@ async def delete_status(
     that into a 409 naming how many tasks are in the way, which is the number
     the caller needs to decide what to do next.
     """
-    db = await _get_db()
-    try:
+    async with _tenant_session() as db:
         existing = await require_row(db, "pm_task_statuses", status_id, "Status")
         vis = await resolve_visibility(db, user)
         await load_visible_project(db, vis, str(existing.project_id))
@@ -204,10 +192,7 @@ async def delete_status(
             text("DELETE FROM pm_task_statuses WHERE id = CAST(:sid AS uuid)"),
             {"sid": status_id},
         )
-        await db.commit()
         return {"deleted": status_id, "tasks_affected": 0}
-    finally:
-        await db.close()
 
 
 # ── Types ───────────────────────────────────────────────────────────────────
@@ -216,8 +201,7 @@ async def delete_status(
 async def list_types(
     project_id: str, user: UserContext = Depends(get_current_user),
 ) -> dict:
-    db = await _get_db()
-    try:
+    async with _tenant_session() as db:
         vis = await resolve_visibility(db, user)
         root = await _root_for(db, vis, project_id)
         rows = (await db.execute(
@@ -230,8 +214,6 @@ async def list_types(
         return {
             "rows": [row_to_dict(r, TypeModel) for r in rows], "total": len(rows),
         }
-    finally:
-        await db.close()
 
 
 @router.post("/nodes/{project_id}/types", status_code=201)
@@ -244,8 +226,7 @@ async def create_type(
     if not name:
         raise HTTPException(status_code=422, detail="A task type needs a name.")
 
-    db = await _get_db()
-    try:
+    async with _tenant_session() as db:
         vis = await resolve_visibility(db, user)
         root = await _root_for(db, vis, project_id)
         row = (await db.execute(
@@ -266,10 +247,7 @@ async def create_type(
         # second root-only type — or, worse, a type that claims Epic's exemption.
         if row.is_default:
             await _clear_other_defaults(db, "pm_task_types", root, str(row.id))
-        await db.commit()
         return row_to_dict(row, TypeModel)
-    finally:
-        await db.close()
 
 
 @router.patch("/types/{type_id}")
@@ -278,8 +256,7 @@ async def patch_type(
     user: UserContext = Depends(get_current_user),
 ) -> dict:
     values = clean_payload(payload)
-    db = await _get_db()
-    try:
+    async with _tenant_session() as db:
         existing = await require_row(db, "pm_task_types", type_id, "Task type")
         vis = await resolve_visibility(db, user)
         await load_visible_project(db, vis, str(existing.project_id))
@@ -298,10 +275,7 @@ async def patch_type(
             await _clear_other_defaults(
                 db, "pm_task_types", str(row.project_id), type_id,
             )
-        await db.commit()
         return row_to_dict(row, TypeModel)
-    finally:
-        await db.close()
 
 
 @router.delete("/types/{type_id}")
@@ -315,8 +289,7 @@ async def delete_type(
     lane. The count is reported (R7/R8) because "12 tasks became untyped" is
     not something to discover from a board.
     """
-    db = await _get_db()
-    try:
+    async with _tenant_session() as db:
         existing = await require_row(db, "pm_task_types", type_id, "Task type")
         vis = await resolve_visibility(db, user)
         await load_visible_project(db, vis, str(existing.project_id))
@@ -330,7 +303,4 @@ async def delete_type(
             text("DELETE FROM pm_task_types WHERE id = CAST(:tid AS uuid)"),
             {"tid": type_id},
         )
-        await db.commit()
         return {"deleted": type_id, "tasks_untyped": affected}
-    finally:
-        await db.close()
diff --git a/apps/services/gateway/gateway/routes/projects/agent_dispatch.py b/apps/services/gateway/gateway/routes/projects/agent_dispatch.py
index 95c93b167..e443d0d0c 100644
--- a/apps/services/gateway/gateway/routes/projects/agent_dispatch.py
+++ b/apps/services/gateway/gateway/routes/projects/agent_dispatch.py
@@ -29,7 +29,20 @@
 from typing import Any
 
 from acb_common import get_logger
-from gateway.routes.projects.core import _get_db, record_activity
+
+# ⚠️ H4, DELIBERATELY NOT H2 (`saas_multitenancy_handover.md`): this module is
+# an EVENT CONSUMER, not a request handler — `on_event` fires from
+# `emit_event`'s sink fan-out and `_run_and_record` outlives the request that
+# scheduled it. The runbook's rule for that category is "do not let a job
+# inherit an ambient tenant", so converting these sites to the ambient
+# `tenant_session()` would be exactly the inheritance it forbids. They stay on
+# the unbound `get_db()` until H4 threads an EXPLICIT tenant through the event
+# payload (`tenant_session(org_id)`), and the H2 ratchet in
+# `test_db_engine_seam.py` carries this module as its one named exemption.
+# Sequencing is safe: RLS phase 4 (which would starve these reads) is gated on
+# H2+H4 both being complete.
+from gateway.db import get_db as _get_db
+from gateway.routes.projects.core import record_activity
 from sqlalchemy import text
 
 _log = get_logger("projects.agent_dispatch")
diff --git a/apps/services/gateway/gateway/routes/projects/attachments.py b/apps/services/gateway/gateway/routes/projects/attachments.py
index e7eaa482c..59339568d 100644
--- a/apps/services/gateway/gateway/routes/projects/attachments.py
+++ b/apps/services/gateway/gateway/routes/projects/attachments.py
@@ -39,7 +39,7 @@
 from fastapi.responses import FileResponse
 from gateway.routes.projects.core import (
     ListResponse,
-    _get_db,
+    _tenant_session,
     actor,
     emit,
     load_visible_task,
@@ -90,8 +90,7 @@ async def attach_file(
     would mean an unauthorised caller could still make the server do the work.
     """
     email = actor(user)
-    db = await _get_db()
-    try:
+    async with _tenant_session() as db:
         vis = await resolve_visibility(db, user)
         task = await load_visible_task(db, vis, task_id)
 
@@ -138,7 +137,6 @@ async def attach_file(
             meta={"attachment_id": att_id, "name": name, "mime": mime,
                   "size": len(content)},
         )
-        await db.commit()
         result = {
             "attachment_id": att_id, "name": name, "mime": mime,
             "size": len(content), "added_by": email,
@@ -146,8 +144,6 @@ async def attach_file(
             "url": f"/api/projects/attachments/{att_id}/{name}",
         }
         project_id = str(task.project_id)
-    finally:
-        await db.close()
 
     await emit("pm.task.updated", {"task_id": task_id, "project_id": project_id,
                                    "attachment_added": att_id})
@@ -158,8 +154,7 @@ async def attach_file(
 async def list_attachments(
     task_id: str, user: UserContext = Depends(get_current_user),
 ) -> ListResponse:
-    db = await _get_db()
-    try:
+    async with _tenant_session() as db:
         vis = await resolve_visibility(db, user)
         await load_visible_task(db, vis, task_id)
         rows = (await db.execute(
@@ -173,8 +168,6 @@ async def list_attachments(
             ),
             {"tid": task_id},
         )).fetchall()
-    finally:
-        await db.close()
     items = [descriptor(r) for r in rows]
     return ListResponse(rows=items, total=len(items))
 
@@ -194,8 +187,7 @@ async def serve_attachment(
     404 for "not attached to anything you can see" as well as "no such file"
     (R5). A 403 here would confirm the file exists.
     """
-    db = await _get_db()
-    try:
+    async with _tenant_session() as db:
         vis = await resolve_visibility(db, user)
         params: dict[str, Any] = {"aid": attachment_id}
         clauses = ["ta.attachment_id = CAST(:aid AS uuid)"]
@@ -216,8 +208,6 @@ async def serve_attachment(
             ),
             params,
         )).fetchone()
-    finally:
-        await db.close()
     if row is None or not Path(row.path).is_file():
         raise HTTPException(status_code=404, detail="Attachment not found")
     return FileResponse(
@@ -243,8 +233,7 @@ async def detach_file(
     half-failed request safe.
     """
     email = actor(user)
-    db = await _get_db()
-    try:
+    async with _tenant_session() as db:
         vis = await resolve_visibility(db, user)
         await load_visible_task(db, vis, task_id)
         result = await db.execute(
@@ -262,7 +251,4 @@ async def detach_file(
                 task_id=task_id, body="Removed an attachment",
                 meta={"attachment_id": attachment_id, "removed": True},
             )
-        await db.commit()
-    finally:
-        await db.close()
     return {"task_id": task_id, "attachment_id": attachment_id, "removed": removed}
diff --git a/apps/services/gateway/gateway/routes/projects/bulk.py b/apps/services/gateway/gateway/routes/projects/bulk.py
index 877bacc18..4a90926a9 100644
--- a/apps/services/gateway/gateway/routes/projects/bulk.py
+++ b/apps/services/gateway/gateway/routes/projects/bulk.py
@@ -40,7 +40,7 @@
     apply_task_patch,
 )
 from gateway.routes.projects.core import (
-    _get_db,
+    _tenant_session,
     actor,
     emit,
     load_visible_task,
@@ -341,8 +341,7 @@ async def bulk_edit(
     newly_assigned: dict[str, list[str]] = {}
     changed_ids: list[str] = []
 
-    db = await _get_db()
-    try:
+    async with _tenant_session() as db:
         vis = await resolve_visibility(db, user)
         for task_id in ids:
             try:
@@ -383,9 +382,6 @@ async def bulk_edit(
                     f"and {len(tasks) - 1} other task(s)" if len(tasks) > 1 else None
                 ),
             )
-        await db.commit()
-    finally:
-        await db.close()
 
     # Emitted after the commit, and per task: `emit` is best-effort by
     # construction, so an automation that fails cannot roll back a re-triage.
diff --git a/apps/services/gateway/gateway/routes/projects/calendar.py b/apps/services/gateway/gateway/routes/projects/calendar.py
index b0ce9baec..b79c37e07 100644
--- a/apps/services/gateway/gateway/routes/projects/calendar.py
+++ b/apps/services/gateway/gateway/routes/projects/calendar.py
@@ -51,7 +51,7 @@
 from fastapi import Depends, HTTPException, Query
 from gateway.routes.projects.core import (
     TaskModel,
-    _get_db,
+    _tenant_session,
     load_visible_project,
     resolve_visibility,
     router,
@@ -218,8 +218,7 @@ async def get_calendar(
     """
     window_from, window_to = window_bounds(date_from, date_to)
 
-    db = await _get_db()
-    try:
+    async with _tenant_session() as db:
         vis = await resolve_visibility(db, user)
         clauses: list[str] = [task_visibility_clause(vis)]
         params: dict[str, Any] = dict(vis.params)
@@ -289,8 +288,6 @@ async def get_calendar(
             # has no dependencies" must not be confused with "nobody asked".
             "links": await window_links(db, window_rows) if include_links else [],
         }
-    finally:
-        await db.close()
 
 
 __all__ = [
diff --git a/apps/services/gateway/gateway/routes/projects/core.py b/apps/services/gateway/gateway/routes/projects/core.py
index ce7b065c6..3d6ded7e8 100644
--- a/apps/services/gateway/gateway/routes/projects/core.py
+++ b/apps/services/gateway/gateway/routes/projects/core.py
@@ -44,7 +44,15 @@
 from acb_auth import UserContext, require_feature_router
 from acb_common import get_logger
 from fastapi import APIRouter, HTTPException, Query
-from gateway.db import get_db as _get_db  # noqa: F401  — the shared seam (BO-10)
+
+# The shared seam (BO-10 → MT-1c/H2). `_tenant_session` IS
+# `acb_common.db.tenant_session`, aliased per-package for the same reason
+# `_get_db` was: every submodule imports it from here BY NAME, which is the
+# seam `tests/unit/_projects_fakes.bind_db` patches per module. The tenant
+# comes from the request context — bound once in `_with_resolved_access` —
+# so no call site passes one (H2). A call outside a bound request raises
+# `TenantUnbound` rather than defaulting: fail closed, never "the usual org".
+from gateway.db import tenant_session as _tenant_session
 from pydantic import BaseModel
 from sqlalchemy import text
 
diff --git a/apps/services/gateway/gateway/routes/projects/custom_fields.py b/apps/services/gateway/gateway/routes/projects/custom_fields.py
index 71c73ffbc..e94c7ff56 100644
--- a/apps/services/gateway/gateway/routes/projects/custom_fields.py
+++ b/apps/services/gateway/gateway/routes/projects/custom_fields.py
@@ -29,7 +29,7 @@
 from acb_auth import UserContext, get_current_user
 from fastapi import Depends, HTTPException
 from gateway.routes.projects.core import (
-    _get_db,
+    _tenant_session,
     actor,
     clean_payload,
     load_visible_project,
@@ -366,14 +366,11 @@ async def _count_with_key(db: Any, root: str, key: str) -> int:
 async def list_fields(
     project_id: str, user: UserContext = Depends(get_current_user),
 ) -> dict:
-    db = await _get_db()
-    try:
+    async with _tenant_session() as db:
         vis = await resolve_visibility(db, user)
         root = await _root_for(db, vis, project_id)
         rows = await load_definitions(db, root)
         return {"rows": rows, "total": len(rows)}
-    finally:
-        await db.close()
 
 
 @router.post("/nodes/{project_id}/fields", status_code=201)
@@ -394,8 +391,7 @@ async def create_field(
     key = validate_key(str(values.get("field_key") or slugify_key(name)))
     options = clean_options(field_type, values.get("options"))
 
-    db = await _get_db()
-    try:
+    async with _tenant_session() as db:
         vis = await resolve_visibility(db, user)
         root = await _root_for(db, vis, project_id)
         existing = await load_definitions(db, root)
@@ -428,10 +424,7 @@ async def create_field(
                 "by": actor(user),
             },
         )).fetchone()
-        await db.commit()
         return _definition_row(row)
-    finally:
-        await db.close()
 
 
 @router.patch("/fields/{field_id}")
@@ -465,8 +458,7 @@ async def patch_field(
                    f"One of: {list(FIELD_TYPES)}.",
         )
 
-    db = await _get_db()
-    try:
+    async with _tenant_session() as db:
         existing = await require_row(db, "pm_custom_fields", field_id, "Custom field")
         vis = await resolve_visibility(db, user)
         await load_visible_project(db, vis, str(existing.project_id))
@@ -501,10 +493,7 @@ async def patch_field(
             values["options"] = _json(options)
 
         row = await update_row(db, "pm_custom_fields", field_id, values)
-        await db.commit()
         return _definition_row(row)
-    finally:
-        await db.close()
 
 
 @router.delete("/fields/{field_id}")
@@ -523,8 +512,7 @@ async def delete_field(
     The count is reported (R7/R8), for the same reason ``delete_view`` reports
     its cascade: losing data silently is what makes people distrust a delete.
     """
-    db = await _get_db()
-    try:
+    async with _tenant_session() as db:
         existing = await require_row(db, "pm_custom_fields", field_id, "Custom field")
         vis = await resolve_visibility(db, user)
         await load_visible_project(db, vis, str(existing.project_id))
@@ -541,14 +529,11 @@ async def delete_field(
             text("DELETE FROM pm_custom_fields WHERE id = CAST(:fid AS uuid)"),
             {"fid": field_id},
         )
-        await db.commit()
         return {
             "deleted": field_id,
             "field_key": existing.field_key,
             "cascaded": {"values_cleared": int(cleared)},
         }
-    finally:
-        await db.close()
 
 
 async def _options_in_use(
diff --git a/apps/services/gateway/gateway/routes/projects/import_clickup.py b/apps/services/gateway/gateway/routes/projects/import_clickup.py
index 31ef79a0b..e4e73d25e 100644
--- a/apps/services/gateway/gateway/routes/projects/import_clickup.py
+++ b/apps/services/gateway/gateway/routes/projects/import_clickup.py
@@ -37,7 +37,7 @@ class this app cannot make silently. The plan is a read; the import writes only
 from acb_common import get_logger
 from fastapi import Depends, HTTPException
 from gateway.routes.projects.core import (
-    _get_db,
+    _tenant_session,
     actor,
     insert_row,
     record_activity,
@@ -121,8 +121,7 @@ async def _resolve_provider(account_id: str) -> Any:
     from gateway.routes.tasks.core import _key_store
     from gateway.routes.tasks.providers import build_provider
 
-    db = await _get_db()
-    try:
+    async with _tenant_session() as db:
         row = (await db.execute(
             text(
                 "SELECT provider, workspace_id, credentials_encrypted "
@@ -130,8 +129,6 @@ async def _resolve_provider(account_id: str) -> Any:
             ),
             {"id": account_id},
         )).mappings().first()
-    finally:
-        await db.close()
     if row is None:
         raise HTTPException(status_code=404, detail="Task account not found")
     if row["provider"] != "clickup":
@@ -213,8 +210,7 @@ async def plan_import(
     workspace_id = getattr(provider, "_workspace_id", None)
     facts = await _gather(provider, str(workspace_id))
 
-    db = await _get_db()
-    try:
+    async with _tenant_session() as db:
         centers = await load_centers(db)
         group_members = await load_group_members(db)
         existing = await _existing_mappings(db)
@@ -249,8 +245,6 @@ async def plan_import(
                     else suggestion.as_dict()
                 ),
             })
-    finally:
-        await db.close()
 
     return {
         "account_id": payload.account_id,
@@ -291,8 +285,7 @@ async def import_clickup(
     facts = await _gather(provider, workspace_id)
     chosen = {m.space_id: m.center for m in payload.mappings}
 
-    db = await _get_db()
-    try:
+    async with _tenant_session() as db:
         centers = await load_centers(db)
         unknown = sorted(
             {c for c in chosen.values() if c and c not in centers}
@@ -318,10 +311,7 @@ async def import_clickup(
             # Nothing is committed, and the caller is told so in the response
             # rather than left to infer it from a counts-only payload.
             return {"dry_run": True, **summary.as_dict(facts)}
-        await db.commit()
         return {"dry_run": False, **summary.as_dict(facts)}
-    finally:
-        await db.close()
 
 
 @dataclass
diff --git a/apps/services/gateway/gateway/routes/projects/import_tasks.py b/apps/services/gateway/gateway/routes/projects/import_tasks.py
index e464a411e..d5ba8f0b9 100644
--- a/apps/services/gateway/gateway/routes/projects/import_tasks.py
+++ b/apps/services/gateway/gateway/routes/projects/import_tasks.py
@@ -52,7 +52,7 @@
 from acb_common import get_logger
 from fastapi import Depends
 from gateway.routes.projects.core import (
-    _get_db,
+    _tenant_session,
     actor,
     insert_row,
     next_task_number,
@@ -377,8 +377,7 @@ async def import_from_tasks(
     tally = _Tally()
     department = (payload.department or "Company").strip() or "Company"
 
-    db = await _get_db()
-    try:
+    async with _tenant_session() as db:
         organization_id = await require_organization_of(db, who.lower())
         root_id = await _root_department(
             db, department, who, tally, payload.dry_run,
@@ -465,9 +464,6 @@ async def import_from_tasks(
                     f"ClickUp mirror into '{department}'"
                 ),
             )
-            await db.commit()
-    finally:
-        await db.close()
 
     return tally.as_dict(department=department, dry_run=payload.dry_run)
 
diff --git a/apps/services/gateway/gateway/routes/projects/intake.py b/apps/services/gateway/gateway/routes/projects/intake.py
index 34e8d653e..5f9d02f39 100644
--- a/apps/services/gateway/gateway/routes/projects/intake.py
+++ b/apps/services/gateway/gateway/routes/projects/intake.py
@@ -54,7 +54,7 @@
     TRIAGE_CATEGORY,
     Page,
     TaskModel,
-    _get_db,
+    _tenant_session,
     actor,
     apply_status_transition,
     emit,
@@ -270,8 +270,7 @@ async def capture_intake(
         raise HTTPException(status_code=422, detail="A capture needs a project_id.")
 
     source = (payload.source or "").strip() or None
-    db = await _get_db()
-    try:
+    async with _tenant_session() as db:
         vis = await resolve_visibility(db, user)
         # R5 — capturing INTO a project requires seeing it; an unreadable id
         # answers 404, never 403.
@@ -306,10 +305,7 @@ async def capture_intake(
             meta={"intake": "captured", "source": source,
                   "source_ref": getattr(wrapper, "source_ref", None)},
         )
-        await db.commit()
         result = _shape(task, wrapper)
-    finally:
-        await db.close()
 
     await emit("pm.intake.captured", {
         "task_id": result["task"]["id"],
@@ -335,8 +331,7 @@ async def list_intake(
     not open, and a `project_id` the caller cannot see is a 404 (R5) rather
     than an empty queue that confirms the project exists.
     """
-    db = await _get_db()
-    try:
+    async with _tenant_session() as db:
         vis = await resolve_visibility(db, user)
         params: dict[str, Any] = dict(vis.params)
         scope = ""
@@ -373,8 +368,6 @@ async def list_intake(
             }
             out.append(item)
         return {"rows": out, "total": int(total)}
-    finally:
-        await db.close()
 
 
 # ── The four rulings ────────────────────────────────────────────────────────
@@ -391,8 +384,7 @@ async def accept_intake(
     `status_change` activity a board drag would. The wrapper flips to
     `accepted` and stays forever.
     """
-    db = await _get_db()
-    try:
+    async with _tenant_session() as db:
         vis = await resolve_visibility(db, user)
         task = await load_visible_task(db, vis, task_id)
         wrapper = await _load_wrapper(db, task_id)
@@ -424,10 +416,7 @@ async def accept_intake(
             task_id=task_id, body="Accepted from intake",
             meta={"intake": "accepted", "status_id": str(destination.id)},
         )
-        await db.commit()
         result = _shape(moved["row"], wrapper)
-    finally:
-        await db.close()
 
     await emit("pm.intake.accepted", {"task_id": task_id})
     return result
@@ -442,8 +431,7 @@ async def decline_intake(
     Archived, not deleted — the standing soft-delete, so a decline is
     revertible the way any archive is, and the capture's timeline survives.
     """
-    db = await _get_db()
-    try:
+    async with _tenant_session() as db:
         vis = await resolve_visibility(db, user)
         await load_visible_task(db, vis, task_id)
         wrapper = await _load_wrapper(db, task_id)
@@ -458,10 +446,7 @@ async def decline_intake(
             task_id=task_id, body="Declined at intake",
             meta={"intake": "declined"},
         )
-        await db.commit()
         result = _shape(task, wrapper)
-    finally:
-        await db.close()
 
     await emit("pm.intake.declined", {"task_id": task_id})
     return result
@@ -483,8 +468,7 @@ async def duplicate_intake(
         raise HTTPException(
             status_code=422, detail="A task cannot be a duplicate of itself.",
         )
-    db = await _get_db()
-    try:
+    async with _tenant_session() as db:
         vis = await resolve_visibility(db, user)
         await load_visible_task(db, vis, task_id)
         await load_visible_task(db, vis, original)
@@ -501,10 +485,7 @@ async def duplicate_intake(
             task_id=task_id, body="Marked duplicate at intake",
             meta={"intake": "duplicate", "duplicate_of_task_id": original},
         )
-        await db.commit()
         result = _shape(task, wrapper)
-    finally:
-        await db.close()
 
     await emit("pm.intake.duplicate", {
         "task_id": task_id, "duplicate_of_task_id": original,
@@ -529,8 +510,7 @@ async def snooze_intake(
         raise HTTPException(
             status_code=422, detail="'until' must be in the future.",
         )
-    db = await _get_db()
-    try:
+    async with _tenant_session() as db:
         vis = await resolve_visibility(db, user)
         task = await load_visible_task(db, vis, task_id)
         wrapper = await _load_wrapper(db, task_id)
@@ -544,10 +524,7 @@ async def snooze_intake(
             task_id=task_id, body="Snoozed at intake",
             meta={"intake": "snoozed", "until": until.isoformat()},
         )
-        await db.commit()
         result = _shape(task, wrapper)
-    finally:
-        await db.close()
 
     await emit("pm.intake.snoozed", {
         "task_id": task_id, "until": until.isoformat(),
diff --git a/apps/services/gateway/gateway/routes/projects/me.py b/apps/services/gateway/gateway/routes/projects/me.py
index fd4fff530..e195baafa 100644
--- a/apps/services/gateway/gateway/routes/projects/me.py
+++ b/apps/services/gateway/gateway/routes/projects/me.py
@@ -23,7 +23,7 @@
     ListResponse,
     Page,
     TaskModel,
-    _get_db,
+    _tenant_session,
     actor,
     resolve_organization_id,
     router,
@@ -77,8 +77,7 @@ async def assigned_to_me(
         )
     where = " WHERE " + " AND ".join(clauses)
 
-    db = await _get_db()
-    try:
+    async with _tenant_session() as db:
         # A caller the directory does not know binds NULL and matches nothing,
         # which is the same fail-closed shape every other read here has.
         scope = {"who": email, "vis_org": await resolve_organization_id(db, email)}
@@ -96,5 +95,3 @@ async def assigned_to_me(
         return ListResponse(
             rows=[row_to_dict(r, TaskModel) for r in rows], total=int(total),
         )
-    finally:
-        await db.close()
diff --git a/apps/services/gateway/gateway/routes/projects/notifications.py b/apps/services/gateway/gateway/routes/projects/notifications.py
index 0d5434c74..8c6128f63 100644
--- a/apps/services/gateway/gateway/routes/projects/notifications.py
+++ b/apps/services/gateway/gateway/routes/projects/notifications.py
@@ -35,7 +35,7 @@
 from fastapi import Depends, Query
 from gateway.routes.projects.core import (
     Page,
-    _get_db,
+    _tenant_session,
     actor,
     insert_row,
     resolve_visibility,
@@ -292,8 +292,7 @@ async def list_notifications(
     address (R3).
     """
     me = actor(user).lower()
-    db = await _get_db()
-    try:
+    async with _tenant_session() as db:
         vis = await resolve_visibility(db, user)
         clause = vis.project_clause("t.root_project_id")
         sql = _LIST_SQL.format(
@@ -319,8 +318,6 @@ async def list_notifications(
             ),
             {"me": me, **vis.params},
         )).fetchone()
-    finally:
-        await db.close()
     return {
         "rows": [_row(r) for r in rows],
         "total": len(rows),
@@ -351,8 +348,7 @@ async def mark_read(
     me = actor(user).lower()
     if not payload.all and not payload.ids:
         return {"marked": 0}
-    db = await _get_db()
-    try:
+    async with _tenant_session() as db:
         if payload.all:
             sql = (
                 "UPDATE pm_notifications SET read_at = now() "
@@ -367,9 +363,6 @@ async def mark_read(
             )
             params = {"me": me, "ids": list(payload.ids)}
         result = await db.execute(text(sql), params)
-        await db.commit()
-    finally:
-        await db.close()
     return {"marked": int(getattr(result, "rowcount", 0) or 0)}
 
 
diff --git a/apps/services/gateway/gateway/routes/projects/personal.py b/apps/services/gateway/gateway/routes/projects/personal.py
index 7506bf62c..dac80ec2d 100644
--- a/apps/services/gateway/gateway/routes/projects/personal.py
+++ b/apps/services/gateway/gateway/routes/projects/personal.py
@@ -38,7 +38,7 @@
     ListResponse,
     Page,
     TaskModel,
-    _get_db,
+    _tenant_session,
     actor,
     clean_payload,
     coerce_write_values,
@@ -202,26 +202,19 @@ async def ensure_personal_project(db: Any, email: str) -> Any:
 async def get_my_project(user: UserContext = Depends(get_current_user)) -> dict:
     """My personal project, or 404 if I have never captured anything."""
     email = actor(user).lower()
-    db = await _get_db()
-    try:
+    async with _tenant_session() as db:
         row = await _load_personal_project(db, email)
         if row is None:
             raise HTTPException(status_code=404, detail="No personal project yet")
         return {"id": str(row.id), "name": row.name}
-    finally:
-        await db.close()
 
 
 @router.post("/my/project", status_code=201)
 async def create_my_project(user: UserContext = Depends(get_current_user)) -> dict:
     email = actor(user).lower()
-    db = await _get_db()
-    try:
+    async with _tenant_session() as db:
         row = await ensure_personal_project(db, email)
-        await db.commit()
         return {"id": str(row.id), "name": row.name}
-    finally:
-        await db.close()
 
 
 @router.post("/my/tasks", status_code=201)
@@ -240,8 +233,7 @@ async def capture(
         raise HTTPException(status_code=422, detail="A task needs a title.")
 
     email = actor(user).lower()
-    db = await _get_db()
-    try:
+    async with _tenant_session() as db:
         project = await ensure_personal_project(db, email)
         project_id = str(project.id)
         status = await load_default_status(db, project_id)
@@ -273,10 +265,7 @@ async def capture(
             db, activity_type="system", created_by=email, task_id=task_id,
             body="Captured",
         )
-        await db.commit()
         result = row_to_dict(task, TaskModel)
-    finally:
-        await db.close()
 
     await emit("pm.task.created", {"task_id": task_id, "project_id": project_id,
                                    "title": title})
@@ -333,8 +322,7 @@ async def set_personal(
         )
 
     email = actor(user).lower()
-    db = await _get_db()
-    try:
+    async with _tenant_session() as db:
         vis = await resolve_visibility(db, user)
         # Seeing the task is the floor. Assignment already satisfies it
         # (`load_visible_task`), so a task delegated across a Center boundary is
@@ -347,10 +335,7 @@ async def set_personal(
         # member looking at it.
         values["clarified_at"] = now()
         row = await _upsert_personal(db, task_id, email, values)
-        await db.commit()
         return _personal_to_dict(row)
-    finally:
-        await db.close()
 
 
 def _personal_to_dict(row: Any) -> dict[str, Any]:
@@ -452,12 +437,9 @@ async def my_inbox(
         params["context"] = context.strip().lower()
 
     sql = _MY_TASKS_SQL + ("".join(f" AND {c}" for c in clauses))
-    db = await _get_db()
-    try:
+    async with _tenant_session() as db:
         params["vis_org"] = await resolve_organization_id(db, email)
         rows = (await db.execute(text(sql), params)).fetchall()
-    finally:
-        await db.close()
 
     items: list[dict[str, Any]] = []
     for row in rows:
@@ -495,8 +477,7 @@ async def my_contexts(user: UserContext = Depends(get_current_user)) -> dict:
     and GTD contexts are personal by nature.
     """
     email = actor(user).lower()
-    db = await _get_db()
-    try:
+    async with _tenant_session() as db:
         rows = (await db.execute(
             text(
                 "SELECT p.context AS context, count(*) AS total "
@@ -514,8 +495,6 @@ async def my_contexts(user: UserContext = Depends(get_current_user)) -> dict:
             ],
             "total": len(rows),
         }
-    finally:
-        await db.close()
 
 
 # ── Completion, from the personal side ──────────────────────────────────────
@@ -536,8 +515,7 @@ async def complete_task(
     from gateway.routes.projects.core import apply_status_transition
 
     email = actor(user).lower()
-    db = await _get_db()
-    try:
+    async with _tenant_session() as db:
         vis = await resolve_visibility(db, user)
         task = await load_visible_task(db, vis, task_id)
         done = (await db.execute(
@@ -559,10 +537,7 @@ async def complete_task(
         # And the member's own view of it follows, so a completed task does not
         # sit in their Next list contradicting the board.
         await _upsert_personal(db, task_id, email, {"disposition": "DONE"})
-        await db.commit()
         result = row_to_dict(moved["row"], TaskModel)
-    finally:
-        await db.close()
 
     await emit("pm.task.status_changed", {
         "task_id": task_id, "from": moved["from"].name, "to": moved["to"].name,
@@ -584,14 +559,10 @@ async def defer_task(
     unaffected, because deferring is a statement about my attention, not about
     the work."""
     email = actor(user).lower()
-    db = await _get_db()
-    try:
+    async with _tenant_session() as db:
         vis = await resolve_visibility(db, user)
         await load_visible_task(db, vis, task_id)
         row = await _upsert_personal(db, task_id, email, {
             "defer_until": payload.until, "disposition": "SOMEDAY",
         })
-        await db.commit()
         return _personal_to_dict(row)
-    finally:
-        await db.close()
diff --git a/apps/services/gateway/gateway/routes/projects/recurrence.py b/apps/services/gateway/gateway/routes/projects/recurrence.py
index fd975c420..652457e97 100644
--- a/apps/services/gateway/gateway/routes/projects/recurrence.py
+++ b/apps/services/gateway/gateway/routes/projects/recurrence.py
@@ -31,7 +31,7 @@
 from acb_auth import UserContext, get_current_user
 from fastapi import Depends, HTTPException
 from gateway.routes.projects.core import (
-    _get_db,
+    _tenant_session,
     actor,
     clean_payload,
     insert_row,
@@ -387,8 +387,7 @@ async def spawn_successor(db: Any, task: Any, *, actor_id: str) -> str | None:
 async def get_recurrence(
     task_id: str, user: UserContext = Depends(get_current_user),
 ) -> dict:
-    db = await _get_db()
-    try:
+    async with _tenant_session() as db:
         vis = await resolve_visibility(db, user)
         task = await load_visible_task(db, vis, task_id)
         if task.recurrence_id is None:
@@ -398,8 +397,6 @@ async def get_recurrence(
             {"rid": str(task.recurrence_id)},
         )).fetchone()
         return {"rule": rule_of(row) if row else None}
-    finally:
-        await db.close()
 
 
 @router.put("/tasks/{task_id}/recurrence")
@@ -413,8 +410,7 @@ async def set_recurrence(
     "change the cadence" is the same act as "give it one".
     """
     rule = validate_rule(clean_payload(payload))
-    db = await _get_db()
-    try:
+    async with _tenant_session() as db:
         vis = await resolve_visibility(db, user)
         task = await load_visible_task(db, vis, task_id)
         root = str(task.root_project_id)
@@ -431,10 +427,7 @@ async def set_recurrence(
             await update_row(
                 db, "pm_tasks", task_id, {"recurrence_id": str(row.id)},
             )
-        await db.commit()
         return {"rule": rule_of(row)}
-    finally:
-        await db.close()
 
 
 @router.delete("/tasks/{task_id}/recurrence")
@@ -447,8 +440,7 @@ async def clear_recurrence(
     some of it finished, and a "stop repeating this" button that swept away
     three months of completed reports would be the last time anybody pressed it.
     """
-    db = await _get_db()
-    try:
+    async with _tenant_session() as db:
         vis = await resolve_visibility(db, user)
         task = await load_visible_task(db, vis, task_id)
         if task.recurrence_id is None:
@@ -467,10 +459,7 @@ async def clear_recurrence(
             text("DELETE FROM pm_recurrences WHERE id = CAST(:rid AS uuid)"),
             {"rid": rule_id},
         )
-        await db.commit()
         return {"cleared": True, "cascaded": {"tasks_detached": detached}}
-    finally:
-        await db.close()
 
 
 __all__ = [
diff --git a/apps/services/gateway/gateway/routes/projects/relations.py b/apps/services/gateway/gateway/routes/projects/relations.py
index c54d569db..57b09fe7c 100644
--- a/apps/services/gateway/gateway/routes/projects/relations.py
+++ b/apps/services/gateway/gateway/routes/projects/relations.py
@@ -38,7 +38,7 @@
 from gateway.routes.projects.core import (
     CLOSING_CATEGORIES,
     MAX_DEPTH,
-    _get_db,
+    _tenant_session,
     load_visible_task,
     resolve_visibility,
     router,
@@ -200,8 +200,7 @@ async def get_relations(
     and three round trips to fill one block is three chances to paint a
     half-drawn dependency section.
     """
-    db = await _get_db()
-    try:
+    async with _tenant_session() as db:
         vis = await resolve_visibility(db, user)
         await load_visible_task(db, vis, task_id)
         visible = task_visibility_clause(vis)
@@ -238,8 +237,6 @@ async def get_relations(
             "links": links,
             "blocked_by": blocked_by_open(blockers),
         }
-    finally:
-        await db.close()
 
 
 __all__ = [
diff --git a/apps/services/gateway/gateway/routes/projects/search.py b/apps/services/gateway/gateway/routes/projects/search.py
index 39e74cf07..8410c8cf3 100644
--- a/apps/services/gateway/gateway/routes/projects/search.py
+++ b/apps/services/gateway/gateway/routes/projects/search.py
@@ -54,7 +54,7 @@
 from fastapi import Depends
 from gateway.routes.projects.core import (
     MAX_DEPTH,
-    _get_db,
+    _tenant_session,
     load_visible_task,
     resolve_visibility,
     router,
@@ -231,8 +231,7 @@ async def search_tasks(
     cap = max(1, min(int(limit), MAX_HITS))
     escaped = like_escape(term)
 
-    db = await _get_db()
-    try:
+    async with _tenant_session() as db:
         vis = await resolve_visibility(db, user)
         exclude_sql = ""
         exclude_params: dict[str, Any] = {}
@@ -286,8 +285,6 @@ async def search_tasks(
             "truncated": len(rows) > cap,
             "query": term,
         }
-    finally:
-        await db.close()
 
 
 __all__ = ["MAX_HITS", "MIN_QUERY", "relative_task_ids", "task_number"]
diff --git a/apps/services/gateway/gateway/routes/projects/tags.py b/apps/services/gateway/gateway/routes/projects/tags.py
index fafc79d96..8945b1560 100644
--- a/apps/services/gateway/gateway/routes/projects/tags.py
+++ b/apps/services/gateway/gateway/routes/projects/tags.py
@@ -36,7 +36,7 @@
 from acb_auth import UserContext, get_current_user
 from fastapi import Depends, HTTPException
 from gateway.routes.projects.core import (
-    _get_db,
+    _tenant_session,
     actor,
     clean_payload,
     load_visible_project,
@@ -270,8 +270,7 @@ async def list_tags(
     you which of two near-duplicate tags to merge into the other, and computing
     it per row in the browser would mean shipping every task to get it.
     """
-    db = await _get_db()
-    try:
+    async with _tenant_session() as db:
         vis = await resolve_visibility(db, user)
         root = await _root_for(db, vis, project_id)
         rows = (await db.execute(
@@ -292,8 +291,6 @@ async def list_tags(
             "rows": [_row(r, int(r.task_count or 0)) for r in rows],
             "total": len(rows),
         }
-    finally:
-        await db.close()
 
 
 @router.post("/nodes/{project_id}/tags", status_code=201)
@@ -305,8 +302,7 @@ async def create_tag(
     name = normalise_tag(values.get("name"))
     if name is None:
         raise HTTPException(status_code=422, detail="A tag needs a name.")
-    db = await _get_db()
-    try:
+    async with _tenant_session() as db:
         vis = await resolve_visibility(db, user)
         root = await _root_for(db, vis, project_id)
         registry = await load_registry(db, root)
@@ -330,10 +326,7 @@ async def create_tag(
             row = await update_row(db, "pm_tags", str(row.id), {
                 k: v for k, v in values.items() if k in ("color", "description")
             })
-        await db.commit()
         return _row(row, 0)
-    finally:
-        await db.close()
 
 
 @router.patch("/tags/{tag_id}")
@@ -353,8 +346,7 @@ async def patch_tag(
     if "name" in values and new_name is None:
         raise HTTPException(status_code=422, detail="A tag needs a name.")
 
-    db = await _get_db()
-    try:
+    async with _tenant_session() as db:
         existing = await require_row(db, "pm_tags", tag_id, "Tag")
         vis = await resolve_visibility(db, user)
         await load_visible_project(db, vis, str(existing.project_id))
@@ -376,10 +368,7 @@ async def patch_tag(
         if new_name:
             write["name"] = new_name
         row = await update_row(db, "pm_tags", tag_id, write) if write else existing
-        await db.commit()
         return {**_row(row), "retagged": renamed}
-    finally:
-        await db.close()
 
 
 @router.post("/tags/{tag_id}/merge")
@@ -394,8 +383,7 @@ async def merge_tag(
     ends with the target **once** — `merged_tags` is where that is decided, and
     it is pure so the case can be asserted directly.
     """
-    db = await _get_db()
-    try:
+    async with _tenant_session() as db:
         source = await require_row(db, "pm_tags", tag_id, "Tag")
         target = await require_row(db, "pm_tags", payload.into_tag_id, "Tag")
         vis = await resolve_visibility(db, user)
@@ -418,12 +406,9 @@ async def merge_tag(
             text("DELETE FROM pm_tags WHERE id = CAST(:tid AS uuid)"),
             {"tid": tag_id},
         )
-        await db.commit()
         return {
             "merged": source.name, "into": target.name, "retagged": moved,
         }
-    finally:
-        await db.close()
 
 
 @router.delete("/tags/{tag_id}")
@@ -437,8 +422,7 @@ async def delete_tag(
     recreates the name. The count is reported (R7/R8), because losing data
     silently is what makes people distrust a delete.
     """
-    db = await _get_db()
-    try:
+    async with _tenant_session() as db:
         existing = await require_row(db, "pm_tags", tag_id, "Tag")
         vis = await resolve_visibility(db, user)
         await load_visible_project(db, vis, str(existing.project_id))
@@ -454,13 +438,10 @@ async def delete_tag(
             text("DELETE FROM pm_tags WHERE id = CAST(:tid AS uuid)"),
             {"tid": tag_id},
         )
-        await db.commit()
         return {
             "deleted": tag_id, "name": existing.name,
             "cascaded": {"tasks_untagged": int(stripped)},
         }
-    finally:
-        await db.close()
 
 
 async def _rewrite(db: Any, root: str, before: str, after: str) -> int:
diff --git a/apps/services/gateway/gateway/routes/projects/tasks.py b/apps/services/gateway/gateway/routes/projects/tasks.py
index b37d5094c..f0236e919 100644
--- a/apps/services/gateway/gateway/routes/projects/tasks.py
+++ b/apps/services/gateway/gateway/routes/projects/tasks.py
@@ -32,7 +32,7 @@
     Page,
     TaskIn,
     TaskModel,
-    _get_db,
+    _tenant_session,
     actor,
     apply_status_transition,
     assert_epic_has_no_parent,
@@ -164,8 +164,7 @@ async def list_tasks(
             detail=f"Unknown sort direction '{direction}'. One of: asc, desc.",
         )
 
-    db = await _get_db()
-    try:
+    async with _tenant_session() as db:
         vis = await resolve_visibility(db, user)
         clauses: list[str] = [task_visibility_clause(vis)]
         params: dict[str, Any] = dict(vis.params)
@@ -228,16 +227,13 @@ async def list_tasks(
         await attach_assignees(db, page_rows)
         await attach_relation_counts(db, page_rows)
         return ListResponse(rows=page_rows, total=int(total))
-    finally:
-        await db.close()
 
 
 @router.get("/tasks/{task_id}")
 async def get_task(
     task_id: str, user: UserContext = Depends(get_current_user),
 ) -> dict:
-    db = await _get_db()
-    try:
+    async with _tenant_session() as db:
         vis = await resolve_visibility(db, user)
         row = await load_visible_task(db, vis, task_id)
         result = row_to_dict(row, TaskModel)
@@ -250,8 +246,6 @@ async def get_task(
         )).fetchall()
         result["assignees"] = [r.assignee for r in assignees]
         return result
-    finally:
-        await db.close()
 
 
 # ── Writes ──────────────────────────────────────────────────────────────────
@@ -271,8 +265,7 @@ async def create_task(
     values["title"] = title
     values["created_by"] = actor(user)
 
-    db = await _get_db()
-    try:
+    async with _tenant_session() as db:
         vis = await resolve_visibility(db, user)
         await load_visible_project(db, vis, str(project_id))
         root = await root_project_id(db, str(project_id))
@@ -309,10 +302,7 @@ async def create_task(
         # WS-27j author-hears-about-comments behaviour once the audience is
         # watchers ∪ assignees (migration 165 seeds the same for older tasks).
         await ensure_watchers(db, task_id, [actor(user)], by=actor(user))
-        await db.commit()
         result = row_to_dict(row, TaskModel)
-    finally:
-        await db.close()
 
     await emit("pm.task.created", {
         "task_id": task_id, "project_id": str(project_id), "title": title,
@@ -347,8 +337,7 @@ async def patch_task(
     new_status = values.pop("status_id", None)
     custom = values.pop("custom_fields", None)
 
-    db = await _get_db()
-    try:
+    async with _tenant_session() as db:
         vis = await resolve_visibility(db, user)
         before = await load_visible_task(db, vis, task_id)
 
@@ -423,10 +412,7 @@ async def patch_task(
                 db, task_id, mentioned["notified"], by=actor(user),
             )
 
-        await db.commit()
         result = row_to_dict(after, TaskModel)
-    finally:
-        await db.close()
 
     await emit("pm.task.updated", {"task_id": task_id})
     if moved is not None:
@@ -449,8 +435,7 @@ async def move_task(
     the status, because statuses are per-root: carrying the old status across
     would leave the task in a lane the destination board does not render.
     """
-    db = await _get_db()
-    try:
+    async with _tenant_session() as db:
         vis = await resolve_visibility(db, user)
         task = await load_visible_task(db, vis, task_id)
         values: dict[str, Any] = {}
@@ -489,10 +474,7 @@ async def move_task(
             meta={"from_project": str(task.project_id),
                   "from_number": getattr(task, "task_number", None)},
         )
-        await db.commit()
         result = row_to_dict(row, TaskModel)
-    finally:
-        await db.close()
 
     await emit("pm.task.moved", {"task_id": task_id})
     return result
@@ -510,8 +492,7 @@ async def delete_task(
     the exact class of lie the N8 purge shipped: a count that reassures in the
     wrong direction.
     """
-    db = await _get_db()
-    try:
+    async with _tenant_session() as db:
         vis = await resolve_visibility(db, user)
         await load_visible_task(db, vis, task_id)
         promoted = await count_where(db, "pm_tasks", "parent_task_id", task_id)
@@ -536,9 +517,6 @@ async def delete_task(
             text("DELETE FROM pm_tasks WHERE id = CAST(:tid AS uuid)"),
             {"tid": task_id},
         )
-        await db.commit()
-    finally:
-        await db.close()
 
     await emit("pm.task.deleted", {"task_id": task_id})
     return DeleteResponse(
@@ -571,8 +549,7 @@ async def archive_task(
 
     WS-27z's sweeper depends on this guard shipping first.
     """
-    db = await _get_db()
-    try:
+    async with _tenant_session() as db:
         vis = await resolve_visibility(db, user)
         task = await load_visible_task(db, vis, task_id)
         status = await require_row(
@@ -596,10 +573,7 @@ async def archive_task(
             db, activity_type="system", created_by=actor(user),
             task_id=task_id, body="Task archived",
         )
-        await db.commit()
         result = row_to_dict(row, TaskModel)
-    finally:
-        await db.close()
 
     await emit("pm.task.archived", {"task_id": task_id})
     return result
@@ -617,8 +591,7 @@ async def unarchive_task(
     writes ``archived_at``, and the PATCH surface deliberately does not accept
     it.
     """
-    db = await _get_db()
-    try:
+    async with _tenant_session() as db:
         vis = await resolve_visibility(db, user)
         task = await load_visible_task(db, vis, task_id)
         if getattr(task, "archived_at", None) is None:
@@ -628,10 +601,7 @@ async def unarchive_task(
             db, activity_type="system", created_by=actor(user),
             task_id=task_id, body="Task restored from the archive",
         )
-        await db.commit()
         result = row_to_dict(row, TaskModel)
-    finally:
-        await db.close()
 
     await emit("pm.task.unarchived", {"task_id": task_id})
     return result
@@ -654,8 +624,7 @@ async def set_assignees(
     off, so it carries the added assignees rather than the whole set: a
     re-assert of an existing assignee must not re-dispatch a run.
     """
-    db = await _get_db()
-    try:
+    async with _tenant_session() as db:
         vis = await resolve_visibility(db, user)
         await load_visible_task(db, vis, task_id)
 
@@ -717,9 +686,6 @@ async def set_assignees(
         # dispatched, never subscribed), and the rows survive a later
         # unassignment — having held the work is a reason to keep hearing.
         await ensure_watchers(db, task_id, sorted(added), by=actor(user))
-        await db.commit()
-    finally:
-        await db.close()
 
     if added:
         await emit("pm.task.assigned", {
@@ -753,8 +719,7 @@ async def create_link(
         raise HTTPException(
             status_code=422, detail="A task cannot be linked to itself.",
         )
-    db = await _get_db()
-    try:
+    async with _tenant_session() as db:
         vis = await resolve_visibility(db, user)
         await load_visible_task(db, vis, task_id)
         # Both ends must be visible: a link is readable from either side, so
@@ -783,14 +748,11 @@ async def create_link(
             db, activity_type="link", created_by=actor(user), task_id=task_id,
             meta={"target": str(payload.target_task_id), "type": payload.link_type},
         )
-        await db.commit()
         return {
             "id": str(row.id), "source_task_id": task_id,
             "target_task_id": str(payload.target_task_id),
             "link_type": payload.link_type,
         }
-    finally:
-        await db.close()
 
 
 @router.delete("/tasks/{task_id}/links/{link_id}")
@@ -798,8 +760,7 @@ async def delete_link(
     task_id: str, link_id: str,
     user: UserContext = Depends(get_current_user),
 ) -> dict:
-    db = await _get_db()
-    try:
+    async with _tenant_session() as db:
         vis = await resolve_visibility(db, user)
         await load_visible_task(db, vis, task_id)
         row = (await db.execute(
@@ -812,7 +773,4 @@ async def delete_link(
         )).fetchone()
         if row is None:
             raise HTTPException(status_code=404, detail="Link not found")
-        await db.commit()
         return {"deleted": link_id}
-    finally:
-        await db.close()
diff --git a/apps/services/gateway/gateway/routes/projects/tree.py b/apps/services/gateway/gateway/routes/projects/tree.py
index abedeee04..1b11868f8 100644
--- a/apps/services/gateway/gateway/routes/projects/tree.py
+++ b/apps/services/gateway/gateway/routes/projects/tree.py
@@ -33,7 +33,7 @@
     GrantModel,
     ProjectIn,
     ProjectModel,
-    _get_db,
+    _tenant_session,
     actor,
     assert_no_project_cycle,
     clean_payload,
@@ -152,11 +152,8 @@ async def get_tree(user: UserContext = Depends(get_current_user)) -> dict:
     as a root here — that is not a bug to fix by hiding it, it is the shape of a
     subtree granted to a Center without its parent department.
     """
-    db = await _get_db()
-    try:
+    async with _tenant_session() as db:
         rows = await _visible_projects(db, user)
-    finally:
-        await db.close()
 
     nodes = {str(r.id): {**row_to_dict(r, ProjectModel), "children": []} for r in rows}
     roots: list[dict] = []
@@ -168,11 +165,8 @@ async def get_tree(user: UserContext = Depends(get_current_user)) -> dict:
 
 @router.get("/nodes")
 async def list_nodes(user: UserContext = Depends(get_current_user)) -> dict:
-    db = await _get_db()
-    try:
+    async with _tenant_session() as db:
         rows = await _visible_projects(db, user)
-    finally:
-        await db.close()
     return {"rows": [row_to_dict(r, ProjectModel) for r in rows], "total": len(rows)}
 
 
@@ -180,13 +174,10 @@ async def list_nodes(user: UserContext = Depends(get_current_user)) -> dict:
 async def get_node(
     project_id: str, user: UserContext = Depends(get_current_user),
 ) -> dict:
-    db = await _get_db()
-    try:
+    async with _tenant_session() as db:
         vis = await resolve_visibility(db, user)
         row = await load_visible_project(db, vis, project_id)
         return row_to_dict(row, ProjectModel)
-    finally:
-        await db.close()
 
 
 # ── Writes ──────────────────────────────────────────────────────────────────
@@ -239,8 +230,7 @@ async def create_node(
     values["name"] = name
     values["created_by"] = actor(user)
 
-    db = await _get_db()
-    try:
+    async with _tenant_session() as db:
         vis = await resolve_visibility(db, user)
         parent_id = values.get("parent_project_id")
         if parent_id:
@@ -279,10 +269,7 @@ async def create_node(
             db, activity_type="system", created_by=actor(user),
             project_id=project_id, body=f"Project '{name}' created",
         )
-        await db.commit()
         result = row_to_dict(row, ProjectModel)
-    finally:
-        await db.close()
 
     await emit("pm.project.created", {"project_id": project_id, "name": name})
     return result
@@ -305,8 +292,7 @@ async def patch_node(
             detail="Use POST /projects/nodes/{id}/move to re-parent a project.",
         )
 
-    db = await _get_db()
-    try:
+    async with _tenant_session() as db:
         vis = await resolve_visibility(db, user)
         before = await load_visible_project(db, vis, project_id)
         _refuse_lifecycle_on_child(
@@ -325,10 +311,7 @@ async def patch_node(
                 db, created_by=actor(user), project_id=project_id,
                 changes=changes,
             )
-        await db.commit()
         result = row_to_dict(after, ProjectModel)
-    finally:
-        await db.close()
 
     await emit("pm.project.updated", {"project_id": project_id})
     return result
@@ -346,8 +329,7 @@ async def move_node(
     move that left it stale would leave tasks pointing at another project's
     status rows — visible immediately as lanes that do not exist on the board.
     """
-    db = await _get_db()
-    try:
+    async with _tenant_session() as db:
         vis = await resolve_visibility(db, user)
         await load_visible_project(db, vis, project_id)
         new_parent = payload.parent_project_id
@@ -378,10 +360,7 @@ async def move_node(
             db, activity_type="system", created_by=actor(user),
             project_id=project_id, body="Project moved",
         )
-        await db.commit()
         result = row_to_dict(row, ProjectModel)
-    finally:
-        await db.close()
 
     await emit("pm.project.moved", {"project_id": project_id})
     return result
@@ -397,8 +376,7 @@ async def delete_node(
     and the honest number is unobtainable, which is how a destructive route ends
     up reporting zero.
     """
-    db = await _get_db()
-    try:
+    async with _tenant_session() as db:
         vis = await resolve_visibility(db, user)
         await load_visible_project(db, vis, project_id)
 
@@ -431,9 +409,6 @@ async def delete_node(
             text("DELETE FROM pm_projects WHERE id = CAST(:pid AS uuid)"),
             {"pid": project_id},
         )
-        await db.commit()
-    finally:
-        await db.close()
 
     await emit("pm.project.deleted", {"project_id": project_id})
     return DeleteResponse(
@@ -455,8 +430,7 @@ async def delete_node(
 async def list_grants(
     project_id: str, user: UserContext = Depends(get_current_user),
 ) -> dict:
-    db = await _get_db()
-    try:
+    async with _tenant_session() as db:
         vis = await resolve_visibility(db, user)
         await load_visible_project(db, vis, project_id)
         rows = (await db.execute(
@@ -469,8 +443,6 @@ async def list_grants(
         return {
             "rows": [row_to_dict(r, GrantModel) for r in rows], "total": len(rows),
         }
-    finally:
-        await db.close()
 
 
 @router.post("/nodes/{project_id}/grants", status_code=201)
@@ -486,8 +458,7 @@ async def create_grant(
     fixture INSERT proving nothing about the API.
     """
     subject = validate_grant_subject(payload.subject)
-    db = await _get_db()
-    try:
+    async with _tenant_session() as db:
         vis = await resolve_visibility(db, user)
         await load_visible_project(db, vis, project_id)
         row = (await db.execute(
@@ -503,10 +474,7 @@ async def create_grant(
             db, activity_type="system", created_by=actor(user),
             project_id=project_id, body=f"Granted to {subject}",
         )
-        await db.commit()
         return row_to_dict(row, GrantModel)
-    finally:
-        await db.close()
 
 
 @router.delete("/nodes/{project_id}/grants/{grant_id}")
@@ -514,8 +482,7 @@ async def delete_grant(
     project_id: str, grant_id: str,
     user: UserContext = Depends(get_current_user),
 ) -> dict:
-    db = await _get_db()
-    try:
+    async with _tenant_session() as db:
         vis = await resolve_visibility(db, user)
         await load_visible_project(db, vis, project_id)
         row = (await db.execute(
@@ -532,7 +499,4 @@ async def delete_grant(
             db, activity_type="system", created_by=actor(user),
             project_id=project_id, body=f"Revoked {row.subject}",
         )
-        await db.commit()
         return {"deleted": grant_id, "subject": row.subject}
-    finally:
-        await db.close()
diff --git a/apps/services/gateway/gateway/routes/projects/views.py b/apps/services/gateway/gateway/routes/projects/views.py
index 14d12f6bb..92c0dba4d 100644
--- a/apps/services/gateway/gateway/routes/projects/views.py
+++ b/apps/services/gateway/gateway/routes/projects/views.py
@@ -24,7 +24,7 @@
 from fastapi import Depends, HTTPException
 from gateway.routes.projects.core import (
     ViewModel,
-    _get_db,
+    _tenant_session,
     actor,
     clean_payload,
     insert_row,
@@ -69,8 +69,7 @@ class PositionsIn(BaseModel):
 async def list_views(
     project_id: str, user: UserContext = Depends(get_current_user),
 ) -> dict:
-    db = await _get_db()
-    try:
+    async with _tenant_session() as db:
         vis = await resolve_visibility(db, user)
         await load_visible_project(db, vis, project_id)
         rows = (await db.execute(
@@ -83,8 +82,6 @@ async def list_views(
         return {
             "rows": [row_to_dict(r, ViewModel) for r in rows], "total": len(rows),
         }
-    finally:
-        await db.close()
 
 
 @router.post("/nodes/{project_id}/views", status_code=201)
@@ -102,8 +99,7 @@ async def create_view(
             status_code=422,
             detail=f"Unknown view type '{view_type}'. One of: {list(VIEW_TYPES)}.",
         )
-    db = await _get_db()
-    try:
+    async with _tenant_session() as db:
         vis = await resolve_visibility(db, user)
         await load_visible_project(db, vis, project_id)
         row = await insert_row(db, "pm_views", {
@@ -115,10 +111,7 @@ async def create_view(
             "position": values.get("position"),
             "created_by": actor(user),
         })
-        await db.commit()
         return row_to_dict(row, ViewModel)
-    finally:
-        await db.close()
 
 
 @router.patch("/views/{view_id}")
@@ -133,8 +126,7 @@ async def patch_view(
             detail=f"Unknown view type '{values['view_type']}'. "
                    f"One of: {list(VIEW_TYPES)}.",
         )
-    db = await _get_db()
-    try:
+    async with _tenant_session() as db:
         existing = await require_row(db, "pm_views", view_id, "View")
         vis = await resolve_visibility(db, user)
         await load_visible_project(db, vis, str(existing.project_id))
@@ -145,10 +137,7 @@ async def patch_view(
         if "config" in values:
             values["config"] = normalise_view_config(values["config"])
         row = await update_row(db, "pm_views", view_id, values)
-        await db.commit()
         return row_to_dict(row, ViewModel)
-    finally:
-        await db.close()
 
 
 @router.delete("/views/{view_id}")
@@ -162,8 +151,7 @@ async def delete_view(
     losing a hand-arranged board silently is exactly the surprise that makes
     people distrust a delete button.
     """
-    db = await _get_db()
-    try:
+    async with _tenant_session() as db:
         existing = await require_row(db, "pm_views", view_id, "View")
         vis = await resolve_visibility(db, user)
         await load_visible_project(db, vis, str(existing.project_id))
@@ -178,10 +166,7 @@ async def delete_view(
             text("DELETE FROM pm_views WHERE id = CAST(:vid AS uuid)"),
             {"vid": view_id},
         )
-        await db.commit()
         return {"deleted": view_id, "cascaded": {"positions": int(positions)}}
-    finally:
-        await db.close()
 
 
 # ── Manual order ────────────────────────────────────────────────────────────
@@ -197,8 +182,7 @@ async def _load_visible_view(db: Any, user: UserContext, view_id: str) -> Any:
 async def get_positions(
     view_id: str, user: UserContext = Depends(get_current_user),
 ) -> dict:
-    db = await _get_db()
-    try:
+    async with _tenant_session() as db:
         await _load_visible_view(db, user, view_id)
         rows = (await db.execute(
             text(
@@ -218,8 +202,6 @@ async def get_positions(
             ],
             "total": len(rows),
         }
-    finally:
-        await db.close()
 
 
 @router.put("/views/{view_id}/positions")
@@ -240,8 +222,7 @@ async def set_positions(
             detail=f"At most {MAX_POSITIONS} positions per request; "
                    f"got {len(payload.positions)}.",
         )
-    db = await _get_db()
-    try:
+    async with _tenant_session() as db:
         await _load_visible_view(db, user, view_id)
         for entry in payload.positions:
             await db.execute(
@@ -259,7 +240,4 @@ async def set_positions(
                     "pos": entry.position, "grp": entry.group_key,
                 },
             )
-        await db.commit()
         return {"view_id": view_id, "written": len(payload.positions)}
-    finally:
-        await db.close()
diff --git a/apps/services/gateway/gateway/routes/projects/watchers.py b/apps/services/gateway/gateway/routes/projects/watchers.py
index 092cdfaf1..322e963f3 100644
--- a/apps/services/gateway/gateway/routes/projects/watchers.py
+++ b/apps/services/gateway/gateway/routes/projects/watchers.py
@@ -27,7 +27,7 @@
 from acb_auth import UserContext, get_current_user
 from fastapi import Depends
 from gateway.routes.projects.core import (
-    _get_db,
+    _tenant_session,
     actor,
     load_visible_task,
     resolve_visibility,
@@ -106,17 +106,13 @@ async def watch_task(
     accepted a ``watcher`` parameter would let anyone subscribe anyone else to
     a stream of that task's titles.
     """
-    db = await _get_db()
-    try:
+    async with _tenant_session() as db:
         vis = await resolve_visibility(db, user)
         # R5: an invisible task is 404, never 403 — "not yours" and "no such
         # task" must be one answer, or this endpoint becomes an oracle for
         # which ids exist.
         await load_visible_task(db, vis, task_id)
         await ensure_watchers(db, task_id, [actor(user)], by=actor(user))
-        await db.commit()
-    finally:
-        await db.close()
     return {"task_id": task_id, "watching": True}
 
 
@@ -130,8 +126,7 @@ async def unwatch_task(
     assignees, so somebody who holds the work keeps hearing about it. That is
     the contract's own shape, not an oversight.
     """
-    db = await _get_db()
-    try:
+    async with _tenant_session() as db:
         vis = await resolve_visibility(db, user)
         await load_visible_task(db, vis, task_id)
         await db.execute(
@@ -141,9 +136,6 @@ async def unwatch_task(
             ),
             {"tid": task_id, "who": actor(user).lower()},
         )
-        await db.commit()
-    finally:
-        await db.close()
     return {"task_id": task_id, "watching": False}
 
 
@@ -153,13 +145,10 @@ async def list_watchers(
 ) -> dict:
     """Who watches this task, and whether the caller does — one read, so the
     panel's toggle can render without a second round trip."""
-    db = await _get_db()
-    try:
+    async with _tenant_session() as db:
         vis = await resolve_visibility(db, user)
         await load_visible_task(db, vis, task_id)
         watchers = await watchers_of(db, task_id)
-    finally:
-        await db.close()
     return {
         "watchers": watchers,
         "watching": actor(user).lower() in set(watchers),
diff --git a/packages/acb_auth/acb_auth/deps.py b/packages/acb_auth/acb_auth/deps.py
index 17c174355..5a1803edd 100644
--- a/packages/acb_auth/acb_auth/deps.py
+++ b/packages/acb_auth/acb_auth/deps.py
@@ -62,6 +62,7 @@ async def pull_sales(req: PullRequest):
 from fastapi import Depends, Header, HTTPException, Request
 
 from acb_common import get_logger
+from acb_common.db import bind_tenant
 
 from acb_auth.access import SERVICE_ACCESS, resolve_access, resolve_identity
 from acb_auth.permissions import NO_ACCESS
@@ -274,6 +275,19 @@ async def _with_resolved_access(user: UserContext) -> UserContext:
         access, user_id=user_id, organization_id=organization_id
     )
 
+    # MT-1c / H2 — the ONE place a request binds its tenant
+    # (`saas_multitenancy_handover.md` H2: "bind once, centrally, from the
+    # authenticated session", never from a header/query/body — R11; the
+    # organization_id above came from the app_user row, not from the caller).
+    # `tenant_session()` then needs no argument anywhere on the request path.
+    # No release here: the gateway's TenantScopeMiddleware opened this
+    # request's scope and releases it after the response, so the binding
+    # cannot outlive the request even on servers that reuse a task. An
+    # unresolved identity (no app_user row) binds nothing, and a converted
+    # handler then fails closed with TenantUnbound rather than defaulting.
+    if enriched.organization_id:
+        bind_tenant(enriched.organization_id)
+
     # Keep the legacy coarse role consistent with the org model, so a member
     # promoted to `admin` in the members UI immediately passes the
     # require_role(EXECUTIVE) routes that have not migrated to permissions yet.
diff --git a/packages/acb_common/acb_common/db.py b/packages/acb_common/acb_common/db.py
index 76e3ba09b..ae078af3c 100644
--- a/packages/acb_common/acb_common/db.py
+++ b/packages/acb_common/acb_common/db.py
@@ -177,8 +177,20 @@ def bind_tenant(organization_id: str) -> Token[str | None]:
     return _TENANT.set(str(organization_id))
 
 
+def clear_tenant() -> Token[str | None]:
+    """Open a fresh, empty tenant scope. Returns a reset token.
+
+    The gateway's request middleware calls this at the top of every HTTP
+    request and :func:`release_tenant` after the response, so one request can
+    never inherit another's binding — whatever the server's task model does
+    with context propagation. Inside the scope, the auth dependency's
+    :func:`bind_tenant` is what fills it in.
+    """
+    return _TENANT.set(None)
+
+
 def release_tenant(token: Token[str | None] | None) -> None:
-    """Undo :func:`bind_tenant`. Never raises."""
+    """Undo :func:`bind_tenant` / :func:`clear_tenant`. Never raises."""
     if token is None:
         return
     try:
@@ -232,8 +244,19 @@ async def tenant_session(organization_id: str | None = None) -> AsyncIterator[An
     session = get_session_factory()()
     try:
         await session.begin()
+        # ``set_config(..., is_local := true)`` IS ``SET LOCAL`` — same
+        # transaction-scoped reset on commit/rollback — but it is a function
+        # call, so the tenant can be a BOUND parameter. The literal
+        # ``SET LOCAL app.tenant_id = :tenant`` form is a Postgres syntax
+        # error through the extended protocol (``SET`` takes no bind
+        # parameters), which every hermetic test missed because a Python fake
+        # does not parse SQL; the first live run found it (2026-08-10, the
+        # same lesson as WS-27r's CAST). Interpolating the id into the
+        # statement instead would be the injection seam this module exists to
+        # avoid handing out.
         await session.execute(
-            text("SET LOCAL app.tenant_id = :tenant"), {"tenant": str(tenant)}
+            text("SELECT set_config('app.tenant_id', :tenant, true)"),
+            {"tenant": str(tenant)},
         )
         yield session
         await session.commit()
diff --git a/project-docs/specs/saas_multitenancy.md b/project-docs/specs/saas_multitenancy.md
index 105414e62..7717eb62f 100644
--- a/project-docs/specs/saas_multitenancy.md
+++ b/project-docs/specs/saas_multitenancy.md
@@ -428,6 +428,15 @@ async def get_db(tenant_id: str | None = None) -> AsyncSession:
     await s.execute(text("SET LOCAL app.tenant_id = :t"), {"t": tenant_id or _ctx_tenant()})
     return s
 ```
+> ⚠️ **Correction (2026-08-10, found by the first live H2 run):** the literal
+> `SET LOCAL app.tenant_id = :t` is a Postgres **syntax error** through the extended
+> protocol — `SET` cannot take a bind parameter. Every hermetic test was green with it;
+> real Postgres refused it on the first converted handler. The shipped encoding in
+> `acb_common.db.tenant_session()` is `SELECT set_config('app.tenant_id', :tenant, true)`
+> — identical transaction-local semantics (`is_local = true` IS `SET LOCAL`), but
+> parameterizable. The warning below still binds; only the spelling changed.
+> `test_tenant_session.py` pins the `set_config` form and refuses both the literal and
+> an `is_local = false` variant.
 > ⚠️ **`SET LOCAL`, never `SET`.** The pool recycles connections across requests
 > (`pool_size` + `max_overflow`, `db.py:114-120`). A session-scoped `SET` survives the
 > connection's return to the pool and becomes a cross-tenant read on the next borrower.
diff --git a/project-docs/specs/saas_multitenancy_handover.md b/project-docs/specs/saas_multitenancy_handover.md
index 769606de4..521a05e33 100644
--- a/project-docs/specs/saas_multitenancy_handover.md
+++ b/project-docs/specs/saas_multitenancy_handover.md
@@ -187,6 +187,46 @@ stated values, **and** the baseline test set still passes.
 
 ## H2 · Convert 561 session-acquisition sites to `tenant_session()` · 🟢 AGENT-SAFE · **the long pole**
 
+> ### ◐ H2 STARTED 2026-08-10 — central binding SHIPPED + the Projects slice converted
+>
+> **The "do this first" step is done:** `_with_resolved_access` (acb_auth/deps.py) calls
+> `bind_tenant(organization_id)` when identity resolves — the one place, from the
+> `app_user` row, never a header (R11) — and the gateway's `TenantScopeMiddleware`
+> (main.py) opens a fresh scope per request and releases it after the response.
+> `tests/unit/test_tenant_request_binding.py` pins both, including
+> "`system:internal` binds nothing" and no-leak-across-sequential-requests.
+>
+> **`routes/projects` is converted** (84 sites, the largest single package): every
+> handler is `async with _tenant_session() as db:` where `_tenant_session` IS the
+> shared seam (identity asserted in `test_db_engine_seam.py`). One named exemption:
+> `agent_dispatch.py` (2 sites) is an **event consumer**, so per this document's own
+> rule it stays on `get_db()` until H4 threads an explicit tenant through the event
+> payload — inheriting the ambient one is exactly what H4 forbids.
+>
+> **Ratchets** (test_db_engine_seam.py): `routes/projects` must stay at ZERO
+> unconverted sites; the remainder elsewhere is frozen at **`H2_BASELINE_ELSEWHERE =
+> 494`** and only ratchets down (progress must be banked by lowering the constant).
+>
+> ⚠️ **A live run found a defect in `tenant_session()` itself:** the literal
+> `SET LOCAL app.tenant_id = :tenant` is a Postgres syntax error through the extended
+> protocol — `SET` cannot bind a parameter, and every hermetic test was green with it.
+> Fixed to `SELECT set_config('app.tenant_id', :tenant, true)` (identical
+> transaction-local semantics), pinned by `test_tenant_session.py`, and proven by a
+> live scratch-Postgres smoke: unbound → `TenantUnbound`; converted handlers write
+> under the GUC; rows stamped with the bound org. **Converters of the remaining
+> packages: the runbook below stands unchanged** — but test against real Postgres at
+> least once per package; this class of defect is invisible to fakes.
+>
+> Conversion notes that generalize (learned on the Projects slice): handlers' explicit
+> `await db.commit()` goes away (the wrapper commits on clean exit — and a mid-block
+> commit would END the transaction and drop the GUC for everything after it, so a
+> handler that genuinely needs two transactions needs two `async with` blocks);
+> read-only endpoints now commit an empty transaction, so tests asserting
+> `committed == 0` as a "writes nothing" proxy must assert on statements/rows instead;
+> hermetic fakes swap in via an `asynccontextmanager` patched over the package's
+> `_tenant_session` alias, commit-on-clean-exit so one-transaction contracts stay
+> observable.
+
 `acb_common.db.tenant_session()` exists and is tested. `get_db()` still exists, is
 documented as **not** tenant-bound, and every one of the 561 sites still uses it.
 
diff --git a/project-docs/specs/saas_multitenancy_implementation.md b/project-docs/specs/saas_multitenancy_implementation.md
index 94b16d1c0..caa83ed53 100644
--- a/project-docs/specs/saas_multitenancy_implementation.md
+++ b/project-docs/specs/saas_multitenancy_implementation.md
@@ -168,7 +168,10 @@ async def tenant_session(tenant_id: str | None = None):
     try:
         await session.begin()                       # SET LOCAL needs a transaction
         await session.execute(
-            text("SET LOCAL app.tenant_id = :t"), {"t": str(tid)})
+            # ⚠️ corrected 2026-08-10: the SET LOCAL literal cannot bind a
+            # parameter (extended-protocol syntax error, found live);
+            # set_config(..., true) is the same transaction-local semantics.
+            text("SELECT set_config('app.tenant_id', :t, true)"), {"t": str(tid)})
         yield session
         await session.commit()
     except Exception:
diff --git a/project-docs/work_plan.md b/project-docs/work_plan.md
index cc4df0368..96768d685 100644
--- a/project-docs/work_plan.md
+++ b/project-docs/work_plan.md
@@ -195,7 +195,7 @@ owning specs are the archive; this file owns ordering, gates and states only.
 
 | WS | Workstream | State | Owning spec · record | Gates · next (verified) |
 |---|---|---|---|---|
-| WS-29 | **Multi-tenancy — turning CommandCenter into a product sold to other companies** | ◐ H1 done · H2 next | **`specs/saas_multitenancy.md`** (architecture; §11 tickets) · ⭐ **`specs/saas_multitenancy_handover.md`** (H1→H8 runbook — hand THIS to the executing agent) · `specs/saas_multitenancy_implementation.md` (shapes) · board record 2026-08-09 in the parent spec | **Phase 0 ✅** (MT-0a · 0b · 0c-1 · 0d, pending review) · **H1 ✅ CLOSED**: scratch-verified 2026-08-09, **PR #404 merged and migrations 157/158/159 CONFIRMED on prod the same day** (ledger line "157 already recorded"; box self-applied via pull timer). · MT-1: 1a schema ✅ (identity cutover = H6, open) · 1b generated ✅ · 1c seam + ratchets ✅ — **561 call sites across 138 files unconverted = H2, the long pole** · 1e wrapper ✅ (~58 key sites unconverted = H5) · 1i ✅ (two-org DB fixture owed) · **MT-2/MT-3/MT-4 owner inputs ALL ANSWERED — final pricing shape D23/D24 2026-08-10 (§2.4b Center packages; ladder 600/1200/1800/2400/3000)** — MT-2's scope includes `center_package` + `plan_catalog` + seat `source` + the one-assignment act; spec detailing may start on all three; the customer console is WS-30 · 🔴 MT-0c-2 parked (D16; §6 first blockquote) · §5.1 cutover trigger **ADOPTED 2026-08-09** — owner checks monthly · ⚠️ **#399 (MERGED 2026-08-09) carried a second WS-29 thread** (`specs/multi_tenancy.md`, superseded for architecture — measured record only): migration **161** keys all 17 `pm_*` + a parent-consistency trigger, **162** makes `app_user` unique on `lower(email)`, S1-1 fixed a cross-tenant **write** into access control, S1-4 removed the process-global agent identity, plus a 14-finding leak audit. **It also found a defect in MT-1b:** the generator scoped `crm_contacts`/`crm_deals`/`crm_activities` by column name, but their `organization_id` references `crm_organizations` — phase 2 would have aborted mid-window. Gated at generation time now (`HOMONYM_BLOCKED`); those three tables carry **no isolation** pending a rename — 🔴 owner call. **Next: dispatch H2.** (2026-08-10) |
+| WS-29 | **Multi-tenancy — turning CommandCenter into a product sold to other companies** | ◐ H1 done · H2 next | **`specs/saas_multitenancy.md`** (architecture; §11 tickets) · ⭐ **`specs/saas_multitenancy_handover.md`** (H1→H8 runbook — hand THIS to the executing agent) · `specs/saas_multitenancy_implementation.md` (shapes) · board record 2026-08-09 in the parent spec | **Phase 0 ✅** (MT-0a · 0b · 0c-1 · 0d, pending review) · **H1 ✅ CLOSED**: scratch-verified 2026-08-09, **PR #404 merged and migrations 157/158/159 CONFIRMED on prod the same day** (ledger line "157 already recorded"; box self-applied via pull timer). · MT-1: 1a schema ✅ (identity cutover = H6, open) · 1b generated ✅ · 1c seam + ratchets ✅ — **561 call sites across 138 files unconverted = H2, the long pole** · 1e wrapper ✅ (~58 key sites unconverted = H5) · 1i ✅ (two-org DB fixture owed) · **MT-2/MT-3/MT-4 owner inputs ALL ANSWERED — final pricing shape D23/D24 2026-08-10 (§2.4b Center packages; ladder 600/1200/1800/2400/3000)** — MT-2's scope includes `center_package` + `plan_catalog` + seat `source` + the one-assignment act; spec detailing may start on all three; the customer console is WS-30 · 🔴 MT-0c-2 parked (D16; §6 first blockquote) · §5.1 cutover trigger **ADOPTED 2026-08-09** — owner checks monthly · ⚠️ **#399 (MERGED 2026-08-09) carried a second WS-29 thread** (`specs/multi_tenancy.md`, superseded for architecture — measured record only): migration **161** keys all 17 `pm_*` + a parent-consistency trigger, **162** makes `app_user` unique on `lower(email)`, S1-1 fixed a cross-tenant **write** into access control, S1-4 removed the process-global agent identity, plus a 14-finding leak audit. **It also found a defect in MT-1b:** the generator scoped `crm_contacts`/`crm_deals`/`crm_activities` by column name, but their `organization_id` references `crm_organizations` — phase 2 would have aborted mid-window. Gated at generation time now (`HOMONYM_BLOCKED`); those three tables carry **no isolation** pending a rename — 🔴 owner call. ◐ **H2 STARTED 2026-08-10**: central `bind_tenant` binding + `TenantScopeMiddleware` SHIPPED; `routes/projects` converted (84 sites; `agent_dispatch` H4-exempt by name); ratchets in `test_db_engine_seam.py` (projects=0, elsewhere frozen at 494, bank-your-progress rule). ⚠️ **The first live run found `tenant_session()` itself broken** — `SET LOCAL … = :param` is a Postgres syntax error (SET can't bind); fixed to `set_config(..., true)`, pinned + live-proven. See the handover's H2 box. **Next: convert the remaining 494 sites package-by-package (email/wa/crm/tasks/notes/workflows…), each with one live-Postgres smoke.** (2026-08-10) |
 
 | — | **Future modules roadmap** (KB · Marketing · Support · dashboards-colour · Builder/Workflows slicing rule) *(named 2026-08-09, D21)* | 🔴 not dispatchable | `specs/future_modules_roadmap.md` | No WS rows until each earns a §1-contract spec; Dashboards colour lands in WS-15's acceptance; the Builder/Workflows visibility-tier-at-creation rule binds reviews now (D12). |
 | WS-30 | **Subscription Console — customer-facing billing surface** *(minted 2026-08-09)* | 🔴 MT-2 first | **`specs/subscription_console.md`** | Manage-only at launch: **Centers & add-ons panel · users × Centers seat grid (D23)** · credit monitor · seat writes under D19.3's hard cap · role presets (D24.5) · change-request flow (fulfilment 🔴 OWNER-GATE during silo phase). Sequencing: MT-2 tables → SC-1 → SC-2/SC-3 → SC-4 with MT-4. Business inputs answered (D19 + D23 + **D24** — framing closed); blockers: MT-2's substrate and the MT-2/MT-3 ticket contracts. (2026-08-10) |
diff --git a/tests/unit/_projects_fakes.py b/tests/unit/_projects_fakes.py
index f2ab3933d..bf44a74ec 100644
--- a/tests/unit/_projects_fakes.py
+++ b/tests/unit/_projects_fakes.py
@@ -47,6 +47,7 @@
 from __future__ import annotations
 
 import re
+from contextlib import asynccontextmanager
 from datetime import UTC, datetime, timedelta
 from types import SimpleNamespace
 from typing import Any
@@ -1571,16 +1572,40 @@ def page(number: int = 1, size: int = 50) -> Any:
 
 
 def bind_db(monkeypatch: Any, fake: FakeProjectsDB, modules: tuple[Any, ...]) -> None:
-    """Point each submodule's ``_get_db`` seam at ``fake``.
+    """Point each submodule's ``_tenant_session`` seam at ``fake``.
 
-    Per-module and not per-package because each module imports ``_get_db`` from
+    Per-module and not per-package because each module imports the seam from
     ``core`` by name, so patching ``core`` alone would not reach them.
+
+    H2 note: the real seam is ``acb_common.db.tenant_session`` — an async
+    context manager that begins a transaction, issues ``SET LOCAL
+    app.tenant_id`` and commits on exit. The fake mirrors only the SHAPE
+    (``async with … as db``); transaction semantics stay out of the mirror
+    exactly as ``commit``/``close`` no-ops did before, because what these
+    tests pin is SQL behaviour, not the GUC plumbing —
+    ``test_tenant_session.py`` owns that.
     """
+    @asynccontextmanager
+    async def _tenant_session(organization_id: str | None = None) -> Any:
+        # Commit-on-clean-exit, exactly like the real wrapper — so "these
+        # writes share one transaction" stays an OBSERVABLE fact
+        # (`db.committed == 1`) rather than a comment, and a handler that
+        # raises mid-block commits nothing here just as it commits nothing
+        # against Postgres.
+        yield fake
+        await fake.commit()
+
     async def _get_db() -> FakeProjectsDB:
         return fake
 
     for module in modules:
-        monkeypatch.setattr(module, "_get_db", _get_db)
+        if hasattr(module, "_tenant_session"):
+            monkeypatch.setattr(module, "_tenant_session", _tenant_session)
+        else:
+            # The one H4 exemption: `agent_dispatch` is an event consumer and
+            # deliberately stays on the unbound `get_db` seam until H4 threads
+            # an explicit tenant through the event payload.
+            monkeypatch.setattr(module, "_get_db", _get_db)
 
 
 def silence_events(monkeypatch: Any, modules: tuple[Any, ...]) -> list[tuple[str, dict]]:
diff --git a/tests/unit/test_db_engine_seam.py b/tests/unit/test_db_engine_seam.py
index 21d402df5..77e51ba35 100644
--- a/tests/unit/test_db_engine_seam.py
+++ b/tests/unit/test_db_engine_seam.py
@@ -39,6 +39,7 @@
 from __future__ import annotations
 
 import ast
+import re
 from functools import cache
 from pathlib import Path
 
@@ -265,6 +266,11 @@ def test_route_packages_resolve_to_the_shared_factory(module_path: str) -> None:
         "_get_session_factory": shared.get_session_factory,
         "get_db": shared.get_db,
         "_get_db": shared.get_db,
+        # H2 (MT-1c): a converted package drops `_get_db` for the tenant-bound
+        # context manager — which must still BE the shared seam, not a wrapper
+        # with its own pool or its own GUC discipline.
+        "tenant_session": shared.tenant_session,
+        "_tenant_session": shared.tenant_session,
     }
     found = [n for n in expected if hasattr(mod, n)]
     assert found, f"{module_path} exposes no DB seam name at all"
@@ -284,3 +290,71 @@ def test_acb_auth_shares_the_pool() -> None:
     from acb_common import db as shared
 
     assert access._get_session_factory is shared.get_session_factory
+
+
+# ── H2 ratchet — get_db() call sites only go DOWN ───────────────────────────
+#
+# `saas_multitenancy_handover.md` H2: every `await get_db()` is a session that
+# will read ZERO rows once the RLS phase-4 policies apply, so the workstream's
+# done-when is "the grep returns 0". Converting 500+ sites takes many PRs;
+# this pair of tests is what stops the number creeping back up in between.
+
+_GET_DB_CALL = re.compile(r"await _?get_db\(\)")
+
+#: Sites that are ALLOWED to stay on the unbound seam, each with the reason.
+#: An entry here is a decision, not a grandfathering — H4 owns retiring them.
+H2_EXEMPT_FILES: dict[str, str] = {
+    "apps/services/gateway/gateway/routes/projects/agent_dispatch.py":
+        "event consumer, not a request handler — H4 threads an explicit "
+        "tenant through the event payload; ambient inheritance is forbidden",
+}
+
+#: The unconverted remainder OUTSIDE routes/projects at the time the Projects
+#: slice landed (2026-08-10). Lower it as packages convert; never raise it.
+H2_BASELINE_ELSEWHERE = 494
+
+
+def _get_db_sites() -> dict[str, int]:
+    out: dict[str, int] = {}
+    for base in ("apps", "packages"):
+        for path in (_REPO / base).rglob("*.py"):
+            n = len(_GET_DB_CALL.findall(path.read_text(encoding="utf-8")))
+            if n:
+                out[str(path.relative_to(_REPO)).replace("\\", "/")] = n
+    return out
+
+
+def test_routes_projects_is_converted_and_stays_converted() -> None:
+    """The Projects package acquires sessions ONLY through `tenant_session`.
+
+    A new `get_db()` here is a handler whose queries will silently return
+    nothing under RLS — the fail-closed symptom H2's runbook warns about.
+    """
+    sites = _get_db_sites()
+    offenders = {
+        f: n for f, n in sites.items()
+        if f.startswith("apps/services/gateway/gateway/routes/projects/")
+        and f not in H2_EXEMPT_FILES
+    }
+    assert offenders == {}, (
+        f"unbound get_db() in converted package: {offenders} — use "
+        f"`async with _tenant_session() as db:` (core.py) instead"
+    )
+
+
+def test_get_db_sites_elsewhere_only_ratchet_down() -> None:
+    total = sum(
+        n for f, n in _get_db_sites().items()
+        if not f.startswith("apps/services/gateway/gateway/routes/projects/")
+    )
+    assert total <= H2_BASELINE_ELSEWHERE, (
+        f"{total} unbound get_db() sites outside routes/projects — above the "
+        f"frozen H2 baseline of {H2_BASELINE_ELSEWHERE}. New code must use "
+        f"tenant_session(); see saas_multitenancy_handover.md H2."
+    )
+    if total < H2_BASELINE_ELSEWHERE:
+        # Progress must be BANKED, or the headroom becomes new-debt budget.
+        assert total > H2_BASELINE_ELSEWHERE - 25, (
+            f"H2 progress: {total} sites remain — lower H2_BASELINE_ELSEWHERE "
+            f"to {total} in this PR to bank it"
+        )
diff --git a/tests/unit/test_projects_attachments.py b/tests/unit/test_projects_attachments.py
index ff8965ff5..762155deb 100644
--- a/tests/unit/test_projects_attachments.py
+++ b/tests/unit/test_projects_attachments.py
@@ -20,6 +20,7 @@
 
 import asyncio
 import re
+from contextlib import asynccontextmanager
 from pathlib import Path
 from types import SimpleNamespace
 from typing import Any
@@ -111,8 +112,12 @@ def db() -> FakeDB:
 
 @pytest.fixture(autouse=True)
 def wiring(monkeypatch, db, tmp_path):
-    async def _get_db():
-        return db
+    # H2: the module's seam is `_tenant_session` (an async context manager),
+    # mirrored commit-on-clean-exit like `_projects_fakes.bind_db`.
+    @asynccontextmanager
+    async def _tenant_session(organization_id=None):
+        yield db
+        await db.commit()
 
     async def _resolve(_db, _user):
         from gateway.routes.projects.core import Visibility
@@ -130,7 +135,7 @@ async def _record(*_a, **_k):
     async def _emit(*_a, **_k):
         return None
 
-    monkeypatch.setattr(pm_attachments, "_get_db", _get_db)
+    monkeypatch.setattr(pm_attachments, "_tenant_session", _tenant_session)
     monkeypatch.setattr(pm_attachments, "resolve_visibility", _resolve)
     monkeypatch.setattr(pm_attachments, "load_visible_task", _load_visible)
     monkeypatch.setattr(pm_attachments, "record_activity", _record)
diff --git a/tests/unit/test_projects_import_mapping.py b/tests/unit/test_projects_import_mapping.py
index b7add1c74..7cff66a3c 100644
--- a/tests/unit/test_projects_import_mapping.py
+++ b/tests/unit/test_projects_import_mapping.py
@@ -158,7 +158,11 @@ async def test_the_plan_writes_nothing(
         if s.split(None, 1)[0].upper() in ("INSERT", "UPDATE", "DELETE")
     ]
     assert writes == []
-    assert db.committed == 0
+    # H2 note: the session wrapper now commits on every clean exit — including
+    # a read-only transaction, exactly as `tenant_session` does against
+    # Postgres — so a commit COUNT no longer distinguishes a write from a
+    # read. "Writes nothing" is the two assertions around this comment: no
+    # write statement was issued, and no row appeared.
     assert db.rows("pm_projects") == []
 
 
@@ -562,8 +566,9 @@ async def test_a_dry_run_writes_nothing_and_says_so(
 
     assert result["dry_run"] is True
     assert result["projects"]["created"] > 0
+    # H2: commit count no longer distinguishes reads from writes (see the
+    # plan-writes-nothing test) — the absence of rows IS the dry-run proof.
     assert db.rows("pm_projects") == []
-    assert db.committed == 0
 
 
 # ── Gating ──────────────────────────────────────────────────────────────────
@@ -615,8 +620,11 @@ async def test_a_non_clickup_account_is_refused(
 ) -> None:
     """The importer speaks ClickUp's shapes; handed an Asana account it would
     silently import nothing rather than say why."""
-    async def _fake_db() -> FakeProjectsDB:
-        return db
+    from contextlib import asynccontextmanager
+
+    @asynccontextmanager
+    async def _fake_session(organization_id=None):
+        yield db
 
     class _Row(dict):
         pass
@@ -634,7 +642,7 @@ async def _execute(sql, params=None):
                      "credentials_encrypted": "x"})
 
     monkeypatch.setattr(db, "execute", _execute)
-    monkeypatch.setattr(pm_import, "_get_db", _fake_db)
+    monkeypatch.setattr(pm_import, "_tenant_session", _fake_session)
 
     with pytest.raises(HTTPException) as exc:
         await pm_import._resolve_provider("acct-9")
diff --git a/tests/unit/test_projects_import_tasks.py b/tests/unit/test_projects_import_tasks.py
index 6d688f825..c681eaa98 100644
--- a/tests/unit/test_projects_import_tasks.py
+++ b/tests/unit/test_projects_import_tasks.py
@@ -262,10 +262,15 @@ def gtd_item(**over) -> SimpleNamespace:
 @pytest.fixture()
 def bind(monkeypatch):
     def _bind(db: FakeDB):
-        async def _get_db():
-            return db
+        # H2: the module's seam is `_tenant_session`, commit-on-clean-exit.
+        from contextlib import asynccontextmanager
 
-        monkeypatch.setattr(sut, "_get_db", _get_db, raising=False)
+        @asynccontextmanager
+        async def _tenant_session(organization_id=None):
+            yield db
+            await db.commit()
+
+        monkeypatch.setattr(sut, "_tenant_session", _tenant_session)
         # `_seed_root` lives in tree.py and writes its own rows; it is exercised
         # by the tree suite, and stubbing it keeps this suite about the import.
         async def _seed(*_a, **_k):
diff --git a/tests/unit/test_projects_notifications.py b/tests/unit/test_projects_notifications.py
index 2516dcb76..e2fecc338 100644
--- a/tests/unit/test_projects_notifications.py
+++ b/tests/unit/test_projects_notifications.py
@@ -249,11 +249,16 @@ def _user(email: str, *grants: str) -> UserContext:
 
 
 def bind(monkeypatch, db: FakeDB, *modules) -> None:
-    async def _get_db():
-        return db
+    # H2: the seam is `_tenant_session`, commit-on-clean-exit.
+    from contextlib import asynccontextmanager
+
+    @asynccontextmanager
+    async def _tenant_session(organization_id=None):
+        yield db
+        await db.commit()
 
     for module in modules or (pm_notify,):
-        monkeypatch.setattr(module, "_get_db", _get_db, raising=False)
+        monkeypatch.setattr(module, "_tenant_session", _tenant_session)
 
 
 # ── Rule 3: nobody hears about a task they cannot open ──────────────────────
diff --git a/tests/unit/test_tenant_request_binding.py b/tests/unit/test_tenant_request_binding.py
new file mode 100644
index 000000000..2c3e79283
--- /dev/null
+++ b/tests/unit/test_tenant_request_binding.py
@@ -0,0 +1,139 @@
+"""MT-1c / H2 — the request path binds its tenant once, centrally.
+
+`saas_multitenancy_handover.md` H2: *"Add `bind_tenant(user.organization_id)`
+in the gateway middleware / the app-wide dependency that already resolves
+`UserContext`, and release it after the response. Then the 561 sites need no
+tenant argument at all."*
+
+The claims pinned here are the ones a refactor could silently lose:
+
+* resolving an authenticated identity BINDS the tenant contextvar — this is
+  what lets every converted `tenant_session()` call site take no argument;
+* the tenant comes from the `app_user` row (`resolve_identity`), NEVER from a
+  header the caller controls (R11) — asserted by construction: the fake
+  resolver ignores the asserted role header entirely;
+* an identity with no organization binds NOTHING, so a converted handler fails
+  closed with `TenantUnbound` instead of defaulting to "the usual tenant";
+* the `system:internal` service identity binds nothing — jobs bind their own
+  tenant explicitly (H4) or fail closed;
+* the gateway middleware opens a fresh scope per request and releases it after
+  the response, so a binding cannot leak from one request into the next even
+  on a server that reuses one task for sequential requests.
+
+Hermetic: `resolve_access` / `resolve_identity` are monkeypatched; no DB.
+"""
+
+from __future__ import annotations
+
+import pytest
+from acb_common.db import bind_tenant, clear_tenant, current_tenant, release_tenant
+
+import acb_auth.deps as deps
+from acb_auth.permissions import NO_ACCESS
+
+ORG = "11111111-1111-1111-1111-111111111111"
+
+
+@pytest.fixture(autouse=True)
+def _fresh_scope():
+    """Every test runs in its own empty tenant scope, released afterwards."""
+    token = clear_tenant()
+    yield
+    release_tenant(token)
+
+
+@pytest.fixture
+def identity(monkeypatch: pytest.MonkeyPatch):
+    """Resolve every email to (user-id, ORG) without a database."""
+    async def fake_access(email, legacy_role=None, record_request=False):
+        return NO_ACCESS
+
+    async def fake_identity(email):
+        return ("22222222-2222-2222-2222-222222222222", ORG)
+
+    monkeypatch.setattr(deps, "resolve_access", fake_access)
+    monkeypatch.setattr(deps, "resolve_identity", fake_identity)
+    monkeypatch.setattr(deps, "_get_internal_token", lambda: "tok")
+
+
+async def test_an_authenticated_request_binds_its_organization(identity):
+    user = await deps.get_current_user(
+        x_user_email="priya@fracktal.in",
+        x_user_role="employee",
+        authorization="Bearer tok",
+    )
+    assert user.organization_id == ORG
+    assert current_tenant() == ORG
+
+
+async def test_the_tenant_comes_from_identity_resolution_not_the_caller(identity):
+    """R11 by construction: the resolver saw only the email; the asserted role
+    header (the only other caller-controlled input) cannot steer the tenant."""
+    await deps.get_current_user(
+        x_user_email="priya@fracktal.in",
+        x_user_role="executive",
+        authorization="Bearer tok",
+    )
+    assert current_tenant() == ORG
+
+
+async def test_an_unresolved_identity_binds_nothing(monkeypatch):
+    async def fake_access(email, legacy_role=None, record_request=False):
+        return NO_ACCESS
+
+    async def fake_identity(email):
+        return (None, None)
+
+    monkeypatch.setattr(deps, "resolve_access", fake_access)
+    monkeypatch.setattr(deps, "resolve_identity", fake_identity)
+    monkeypatch.setattr(deps, "_get_internal_token", lambda: "tok")
+
+    user = await deps.get_current_user(
+        x_user_email="stranger@fracktal.in",
+        x_user_role="employee",
+        authorization="Bearer tok",
+    )
+    assert user.organization_id is None
+    assert current_tenant() is None
+
+
+async def test_the_service_identity_binds_nothing(identity):
+    """`system:internal` has no organization. A job that needs one binds it
+    explicitly from its own record (H4) — never inherits an ambient one."""
+    user = await deps.get_current_user(authorization="Bearer tok")
+    assert user.email == "system:internal"
+    assert current_tenant() is None
+
+
+async def test_the_middleware_scope_does_not_leak_across_requests(identity):
+    """Two sequential requests in ONE task: the second starts empty even
+    though the first bound a tenant and never explicitly unbound it."""
+    from gateway.main import TenantScopeMiddleware
+
+    seen: list[str | None] = []
+
+    async def app(scope, receive, send):
+        seen.append(current_tenant())
+        bind_tenant(ORG)  # what _with_resolved_access does mid-request
+
+    mw = TenantScopeMiddleware(app)
+    http = {"type": "http"}
+    await mw(http, None, None)
+    await mw(http, None, None)
+    assert seen == [None, None]
+    assert current_tenant() is None
+
+
+async def test_a_non_http_scope_is_passed_through_untouched(identity):
+    from gateway.main import TenantScopeMiddleware
+
+    called: list[str] = []
+
+    async def app(scope, receive, send):
+        called.append(scope["type"])
+
+    bind_tenant(ORG)
+    await TenantScopeMiddleware(app)({"type": "lifespan"}, None, None)
+    assert called == ["lifespan"]
+    # a lifespan passthrough neither opens nor closes a scope
+    assert current_tenant() == ORG
diff --git a/tests/unit/test_tenant_session.py b/tests/unit/test_tenant_session.py
index beb6d786a..031cd8f7a 100644
--- a/tests/unit/test_tenant_session.py
+++ b/tests/unit/test_tenant_session.py
@@ -70,19 +70,30 @@ def calls(monkeypatch):
 # ==========================================================================
 # 1 — SET LOCAL, not SET.
 # ==========================================================================
-def test_the_seam_uses_set_local_not_set() -> None:
+def test_the_seam_uses_transaction_local_set_config() -> None:
     """A string assertion, deliberately.
 
-    ``SET`` vs ``SET LOCAL`` is a one-word difference whose only symptom is a
-    cross-tenant read under connection reuse. No behavioural unit test
-    reproduces that reliably, so the source is pinned instead.
+    Transaction-local vs session-scoped is a one-argument difference whose
+    only symptom is a cross-tenant read under connection reuse. No behavioural
+    unit test reproduces that reliably, so the source is pinned instead.
+
+    ⚠️ The encoding is ``set_config('app.tenant_id', :tenant, true)`` and NOT
+    the literal ``SET LOCAL app.tenant_id = :tenant`` — the latter is a
+    Postgres SYNTAX ERROR through the extended protocol (``SET`` cannot take
+    a bind parameter). Every hermetic run was green with the broken literal;
+    the first live handler run failed on it (2026-08-10). ``set_config``'s
+    third argument ``true`` is what makes it ``SET LOCAL`` semantics; ``false``
+    (or omitting it) is the session-scoped poison this test exists to refuse.
     """
     src = inspect.getsource(tenant_session.__wrapped__)  # type: ignore[attr-defined]
-    assert "SET LOCAL app.tenant_id" in src
-    assert "SET app.tenant_id" not in src.replace("SET LOCAL app.tenant_id", ""), (
-        "a session-scoped SET survives the connection's return to the pool — "
-        "the next borrower reads the previous tenant"
-    )
+    assert "set_config('app.tenant_id', :tenant, true)" in src
+    # Pin the EXECUTED statement, not the prose around it: no text("SET ...")
+    # may reappear (the literal form cannot bind a parameter — it only ever
+    # worked against fakes), and no is_local=false variant may sneak in (a
+    # session-scoped set survives the connection's return to the pool and the
+    # next borrower reads the previous tenant).
+    assert 'text("SET' not in src and "text('SET" not in src
+    assert "set_config('app.tenant_id', :tenant, false" not in src
 
 
 @pytest.mark.asyncio
@@ -92,7 +103,7 @@ async def test_binding_is_issued_as_a_bound_parameter(calls) -> None:
     sets = [c for c in calls if c[0] == "execute"]
     assert len(sets) == 1
     sql, params = sets[0][1]
-    assert "SET LOCAL app.tenant_id" in sql
+    assert "set_config('app.tenant_id'" in sql
     assert params == {"tenant": _ORG_A}
     assert _ORG_A not in sql, "the tenant id was interpolated into the statement"