diff --git a/.github/workflows/rust-ci.yml b/.github/workflows/rust-ci.yml
index adfc9202..1c93514b 100644
--- a/.github/workflows/rust-ci.yml
+++ b/.github/workflows/rust-ci.yml
@@ -4,6 +4,7 @@ on:
   pull_request:
     paths:
       - 'src-rust/**'
+      - 'scripts/test-headless-schemas.py'
       - '.github/workflows/rust-ci.yml'
   workflow_dispatch:
 
@@ -18,6 +19,22 @@ env:
   CARGO_TERM_COLOR: always
 
 jobs:
+  headless-schemas:
+    name: Headless JSON Schema constraints
+    runs-on: ubuntu-latest
+    timeout-minutes: 5
+    steps:
+      - uses: actions/checkout@v5
+        with:
+          persist-credentials: false
+      - uses: actions/setup-python@v6
+        with:
+          python-version: '3.12'
+      - name: Validate runtime fixtures and cross-field constraints
+        run: |
+          python -m pip install jsonschema==4.25.1
+          python scripts/test-headless-schemas.py
+
   rust:
     name: Format, lint, and test
     runs-on: ubuntu-latest
diff --git a/docs/headless-contract.md b/docs/headless-contract.md
index cba95c69..4719248e 100644
--- a/docs/headless-contract.md
+++ b/docs/headless-contract.md
@@ -6,22 +6,26 @@ The runtime also accepts version `2` briefs during the coven-github migration
 and echoes `"2"` in their result envelopes. Version `3` remains the normative
 schema; all other major versions are rejected.
 
-This document is the single source of truth for the interface between
-`coven-github` (the GitHub ingress adapter) and `coven-code` (the execution
-runtime) when the runtime is invoked in headless mode.
-
-It is normative. Where the prose in [`COVEN-GITHUB.md`](../COVEN-GITHUB.md) or any
-other doc disagrees with this file, **this file wins**. Both repositories MUST
-implement exactly what is specified here, and changes require a contract version
-bump (see [Versioning](#versioning)).
-
-The contract is enforced on the `coven-github` side by golden fixtures in
-[`docs/contracts/`](contracts/) and a conformance test
-(`crates/github/tests/contract.rs`) that round-trips those fixtures through the
-Rust types. `coven-code` MUST validate its emitted `result.json` against
-[`docs/contracts/result.schema.json`](contracts/result.schema.json) and its
-accepted `session-brief.json` against
-[`docs/contracts/session-brief.schema.json`](contracts/session-brief.schema.json).
+This document specifies the runtime's version 3 interface. The adapter's
+[upstream contract](https://github.com/OpenCoven/coven-github/blob/main/docs/headless-contract.md)
+and fixtures currently describe version 2. The local fixtures include v3
+review-memory provenance and are not verbatim upstream copies.
+
+Where [`COVEN-GITHUB.md`](../COVEN-GITHUB.md) disagrees with this runtime
+specification, this file wins. Coordinate breaking changes with the adapter
+and bump the contract version (see [Versioning](#6-versioning)).
+
+The runtime fixtures live in
+[`src-rust/crates/cli/tests/headless_contract/`](../src-rust/crates/cli/tests/headless_contract/).
+Rust tests round-trip those fixtures through runtime types. Run
+`uv run scripts/test-headless-schemas.py` to validate the v3 fixtures and
+cross-field constraints with a Draft 2020-12 JSON Schema validator.
+
+Accepting a v2 brief and echoing its version does not prove strict adapter-v2
+schema conformance: the runtime also emits `review.memory`, which the current
+adapter-v2 schema does not accept. That migration requires coordinated work
+in both repositories. This document does not claim adapter memory-grant or
+memory-write governance support.
 
 The key words MUST, MUST NOT, SHOULD, and MAY are used as in RFC 2119.
 
@@ -197,7 +201,7 @@ the file MAY be absent.
 | `summary` | string | One-line familiar-voice summary. Used in the Check Run and PR title. |
 | `pr_body` | string | Full PR body, **authored by the familiar** in its own voice — not a template. |
 | `review` | object | Structured review evidence and findings. Required even when `mode` is `none`. See [3.2](#32-review). |
-| `exit_reason` | string enum \| null | `null` on success; otherwise the terminal cause. See [3.4](#34-exit_reason). |
+| `exit_reason` | string enum \| null | `null` or absent on success; required for `failure` and `needs_input`; optional for `partial`. See [3.4](#34-exit_reason). |
 
 > **Drift note (supersedes `COVEN-GITHUB.md`):** the prose result envelope listed
 > an `events` array. Progress/event streaming is **not** part of the v3 result
@@ -241,7 +245,9 @@ and `needs_input` do not open a PR by themselves.
 
 ### 3.4 `exit_reason`
 
-`null` on success. Otherwise one of:
+For `success`, omit this field or set it to `null`. For `failure` and
+`needs_input`, provide one of the causes below. A `partial` result may omit
+the field, set it to `null`, or provide a cause when one is known.
 
 | Value | Meaning |
 |---|---|
@@ -319,11 +325,11 @@ must accept the new required nullable provenance fields and `provenance` arrays.
 
 | Artifact | Purpose |
 |---|---|
-| [`docs/contracts/session-brief.schema.json`](contracts/session-brief.schema.json) | JSON Schema for the input brief. |
-| [`docs/contracts/result.schema.json`](contracts/result.schema.json) | JSON Schema for the output envelope. |
-| [`docs/contracts/session-brief.example.json`](contracts/session-brief.example.json) | Golden input fixture. |
-| [`docs/contracts/result.example.json`](contracts/result.example.json) | Golden output fixture. |
-| `crates/github/tests/contract.rs` | Round-trips the golden fixtures through the Rust types — fails the build if the adapter drifts from this contract. |
+| [`session-brief.schema.json`](../src-rust/crates/cli/tests/headless_contract/session-brief.schema.json) | JSON Schema for the input brief. |
+| [`result.schema.json`](../src-rust/crates/cli/tests/headless_contract/result.schema.json) | JSON Schema for the output envelope. |
+| [`session-brief.example.json`](../src-rust/crates/cli/tests/headless_contract/session-brief.example.json) | Golden input fixture. |
+| [`result.example.json`](../src-rust/crates/cli/tests/headless_contract/result.example.json) | Golden output fixture. |
+| `scripts/test-headless-schemas.py` | Validates runtime fixtures and cross-field schema constraints. |
 
 A `coven-code` change is contract-conformant when its emitted `result.json`
 validates against `result.schema.json` and it accepts any brief that validates
diff --git a/scripts/test-headless-schemas.py b/scripts/test-headless-schemas.py
new file mode 100644
index 00000000..dfbf0100
--- /dev/null
+++ b/scripts/test-headless-schemas.py
@@ -0,0 +1,71 @@
+# /// script
+# requires-python = ">=3.10"
+# dependencies = ["jsonschema==4.25.1"]
+# ///
+"""Validate the runtime v3 fixtures and their cross-field constraints.
+
+Run from any directory: uv run scripts/test-headless-schemas.py
+"""
+import copy
+import json
+from pathlib import Path
+import unittest
+
+from jsonschema import Draft202012Validator
+
+FIXTURES = Path(__file__).resolve().parents[1] / "src-rust/crates/cli/tests/headless_contract"
+
+
+class HeadlessSchemas(unittest.TestCase):
+    def setUp(self):
+        self.brief = json.loads((FIXTURES / "session-brief.example.json").read_text())
+        self.result = json.loads((FIXTURES / "result.example.json").read_text())
+        self.validators = {}
+        for name in ("session-brief", "result"):
+            schema = json.loads((FIXTURES / f"{name}.schema.json").read_text())
+            Draft202012Validator.check_schema(schema)
+            self.validators[name] = Draft202012Validator(schema)
+
+    def test_golden_fixtures(self):
+        self.validators["session-brief"].validate(self.brief)
+        self.validators["result"].validate(self.result)
+
+    def test_brief_requires_version(self):
+        del self.brief["contract_version"]
+        self.assertFalse(self.validators["session-brief"].is_valid(self.brief))
+
+    def test_result_status_and_exit_reason(self):
+        for status in ("success", "failure", "needs_input", "partial"):
+            for reason in (None, "test_failure", "ambiguous_spec", "git_conflict", "infra_error"):
+                with self.subTest(status=status, reason=reason):
+                    value = copy.deepcopy(self.result)
+                    value.update(status=status, exit_reason=reason)
+                    expected = (
+                        reason is None if status == "success"
+                        else status == "partial" or reason is not None
+                    )
+                    self.assertEqual(self.validators["result"].is_valid(value), expected)
+        for status in ("failure", "needs_input"):
+            with self.subTest(status=status, reason="absent"):
+                value = copy.deepcopy(self.result)
+                value["status"] = status
+                value.pop("exit_reason", None)
+                self.assertFalse(self.validators["result"].is_valid(value))
+
+    def test_review_mode_and_evidence(self):
+        for mode in ("none", "pull_request", "review_comment"):
+            for evidence in ("not_applicable", "complete", "partial", "missing"):
+                for files in ([], ["src/example.rs"]):
+                    with self.subTest(mode=mode, evidence=evidence, files=files):
+                        value = copy.deepcopy(self.result)
+                        value["review"].update(mode=mode, evidence_status=evidence, reviewed_files=files)
+                        expected = (
+                            evidence == "not_applicable" if mode == "none"
+                            else evidence != "not_applicable"
+                            and (bool(files) or evidence == "missing")
+                        )
+                        self.assertEqual(self.validators["result"].is_valid(value), expected)
+
+
+if __name__ == "__main__":
+    unittest.main()
diff --git a/src-rust/crates/cli/src/main.rs b/src-rust/crates/cli/src/main.rs
index 1e173857..1ec9fcac 100644
--- a/src-rust/crates/cli/src/main.rs
+++ b/src-rust/crates/cli/src/main.rs
@@ -546,7 +546,7 @@ async fn main() -> anyhow::Result<()> {
         .with_writer(std::io::stderr)
         .init();
 
-    // --context loads a coven-github session brief (headless contract v1). It
+    // --context loads a coven-github session brief (headless contract v3). It
     // implies full headless + skip-permissions and overrides model/cwd from the
     // brief. A brief with an unsupported major version is rejected here.
     let github_context = SessionBrief::load(cli.context.as_ref())?;
diff --git a/src-rust/crates/cli/tests/headless_contract/README.md b/src-rust/crates/cli/tests/headless_contract/README.md
index 3c0d0508..55847145 100644
--- a/src-rust/crates/cli/tests/headless_contract/README.md
+++ b/src-rust/crates/cli/tests/headless_contract/README.md
@@ -1,27 +1,31 @@
-# Vendored headless-contract fixtures
+# Runtime headless-contract fixtures
 
-These four files are **verbatim copies** of the locked headless execution
-contract artifacts owned by the `coven-github` repository:
+These fixtures describe Coven Code's version 3 headless interface:
 
 - `session-brief.schema.json`
 - `result.schema.json`
 - `session-brief.example.json`
 - `result.example.json`
 
-Canonical source (single source of truth):
-`OpenCoven/coven-github` → `docs/headless-contract.md` + `docs/contracts/`.
+Run the JSON Schema regression tests from the repository root:
 
-**Contract version: `1`.**
+```sh
+uv run scripts/test-headless-schemas.py
+```
 
-`coven-code` is the *consumer* of the session brief and the *producer* of the
-result envelope. The conformance tests in `crates/cli/src/headless.rs` round-trip
-these golden fixtures through the runtime types and assert that:
+The script pins its validator dependency and tests both golden fixtures,
+required version declarations, review evidence, and result exit reasons.
+Rust tests in `crates/cli/src/headless.rs` separately exercise runtime parsing,
+serialization, and selected schema properties.
 
-- every brief that validates against `session-brief.schema.json` is accepted,
-- every `result.json` the runtime emits validates against `result.schema.json`.
+The [upstream adapter contract](https://github.com/OpenCoven/coven-github/blob/main/docs/headless-contract.md)
+and its `docs/contracts/` fixtures currently use version 2. These runtime
+fixtures use version 3 and include `review.memory` provenance. They are not
+verbatim copies. The runtime still accepts v2 briefs and echoes that version,
+but its extra review provenance needs reconciliation with the strict adapter-v2
+schema before claiming cross-repository conformance.
 
-If a test here fails, the runtime drifted from the contract **or** the contract
-changed. Do not "bless" the fixtures — re-copy them from `coven-github` only as
-part of a deliberate, version-bumped contract change (see the contract doc's
-Versioning section). A breaking change MUST bump `contract_version` on both
-sides.
+See the [runtime contract](../../../../../docs/headless-contract.md) for the
+normative v3 behavior. Coordinate breaking changes and version bumps with
+both repositories; do not overwrite these fixtures with an older upstream
+schema.
diff --git a/src-rust/crates/cli/tests/headless_contract/result.schema.json b/src-rust/crates/cli/tests/headless_contract/result.schema.json
index 663d813e..18ed3d8e 100644
--- a/src-rust/crates/cli/tests/headless_contract/result.schema.json
+++ b/src-rust/crates/cli/tests/headless_contract/result.schema.json
@@ -165,11 +165,23 @@
             "required": ["mode"]
           },
           "then": {
+            "properties": {
+              "evidence_status": { "enum": ["complete", "partial", "missing"] }
+            },
             "anyOf": [
               { "properties": { "reviewed_files": { "minItems": 1 } }, "required": ["reviewed_files"] },
               { "properties": { "evidence_status": { "const": "missing" } }, "required": ["evidence_status"] }
             ]
           }
+        },
+        {
+          "if": {
+            "properties": { "mode": { "const": "none" } },
+            "required": ["mode"]
+          },
+          "then": {
+            "properties": { "evidence_status": { "const": "not_applicable" } }
+          }
         }
       ]
     },
@@ -177,5 +189,33 @@
       "type": ["string", "null"],
       "enum": ["test_failure", "ambiguous_spec", "git_conflict", "infra_error", null]
     }
-  }
+  },
+  "allOf": [
+    {
+      "if": {
+        "properties": { "status": { "const": "success" } },
+        "required": ["status"]
+      },
+      "then": {
+        "properties": {
+          "exit_reason": { "const": null }
+        }
+      }
+    },
+    {
+      "if": {
+        "properties": { "status": { "enum": ["failure", "needs_input"] } },
+        "required": ["status"]
+      },
+      "then": {
+        "properties": {
+          "exit_reason": {
+            "type": "string",
+            "enum": ["test_failure", "ambiguous_spec", "git_conflict", "infra_error"]
+          }
+        },
+        "required": ["exit_reason"]
+      }
+    }
+  ]
 }
diff --git a/src-rust/crates/cli/tests/headless_contract/session-brief.schema.json b/src-rust/crates/cli/tests/headless_contract/session-brief.schema.json
index bd06bc0c..750cf189 100644
--- a/src-rust/crates/cli/tests/headless_contract/session-brief.schema.json
+++ b/src-rust/crates/cli/tests/headless_contract/session-brief.schema.json
@@ -5,7 +5,7 @@
   "description": "Tokenless read-context payload the adapter writes for coven-code --headless --context. Contract version 3.",
   "type": "object",
   "additionalProperties": false,
-  "required": ["trigger", "repo", "task", "familiar", "workspace"],
+  "required": ["contract_version", "trigger", "repo", "task", "familiar", "workspace"],
   "properties": {
     "contract_version": {
       "type": "string",