fix(tools): persist idle promotion prune after fold

Fold already drops execute-promoted schemas off the wire. Persist that
empty set to run.json and the crash handle so resume cannot restore them.

Author: TheGreatAxios

docs/MCP.md

@@ -93,9 +93,12 @@ Tools from connected servers are not advertised to the model up front; they are
 registered for dispatch as soon as the server connects (including later in the
 same turn) and surfaced on demand through dynamic tool discovery
 (`tool_search`). A match is a ranked handful of names plus capped
-descriptions — not full input schemas. Names activated via `tool_search`
-join the next inference tool list (no wait for compact), persist in the
-session's `run.json`, and are re-advertised on resume and after rebuilds.
+descriptions — not full input schemas. `tool_search` does not promote
+names onto the next inference or into `run.json`. Calling a discovered
+name declares that one schema on the next infer (promote-on-execute),
+persists it in the session's `run.json`, and re-advertises it on resume
+and after rebuilds. Fold drops idle execute-promoted schemas and persists
+that empty set so a crash or resume does not restore them.
 
 For integrations a project calls constantly, `pinnedTools` in local
 `.corbits/settings.json` keeps those names on the wire permanently — no

src/exec/runner.ts

@@ -128,6 +128,7 @@ import {
   assembleSessionGate,
   assembleSessionLifecycle,
   assembleSessionTrust,
+  commitIdlePromotionPrune,
   createAdvertisedToolset,
   loadSessionLocalSettings,
   resolveLiveSessionSources,
@@ -944,14 +945,21 @@ export async function runExec(config: Config): Promise<ExecResult> {
           telemetry: liveTelemetry,
           onFolded: () => {
             // Fold restarts the cached prefix — drop idle execute-promoted
-            // schemas rather than carrying them forever.
-            if (pruneIdlePromotions()) {
-              directorHolder.instance?.updateToolDefinitions(
-                computeAdvertised(
-                  agentToolset.dynamicRunner.currentDefinitions(),
-                ),
-              );
-            }
+            // schemas rather than carrying them forever, and persist so a
+            // crash resume cannot re-flush the pruned names.
+            commitIdlePromotionPrune({
+              pruneIdlePromotions,
+              refreshAdvertised: () => {
+                directorHolder.instance?.updateToolDefinitions(
+                  computeAdvertised(
+                    agentToolset.dynamicRunner.currentDefinitions(),
+                  ),
+                );
+              },
+              persist: () => {
+                void persist("running");
+              },
+            });
           },
         }),
       getCacheWriteSeed: () =>

src/session/active-run.ts

@@ -22,9 +22,10 @@ export interface RunStateHandle {
   startedAt: number;
   turnsUsed: number;
   model?: string;
-  // Latest tool_search-activated tool names, synced on every snapshot so the
+  // Latest execute-promoted tool names, synced on every snapshot so the
   // crash/signal terminal write can carry them into run.json for the resume
-  // seed.
+  // seed. Fold prune syncs an empty list so that write cannot restore
+  // dropped schemas.
   activatedTools?: string[];
   // Last Anthropic-protocol cache write, and the run-record model that wrote
   // it. The crash path copies the stamp so a killed process can still fold

src/session/assemble-runtime.test.ts

@@ -1,5 +1,5 @@
 import { describe, expect, test } from "bun:test";
-import { mkdtemp } from "node:fs/promises";
+import { mkdtemp, rm } from "node:fs/promises";
 import { tmpdir } from "node:os";
 import { join } from "node:path";
 import type { Agent, DirectorRegistry } from "@intx/agent";
@@ -13,11 +13,14 @@ import type {
 import { withMockedModuleDuring } from "../../testkit/mock-module.js";
 import type { ChatDirector } from "../agent/director.js";
 import { authzParityDefinitions } from "../agent/tool-aliases.js";
+import { syncRunStateHandle, type RunStateHandle } from "./active-run.js";
 import {
+  commitIdlePromotionPrune,
   createAdvertisedToolset,
   loadSessionLocalSettings,
   type ChatAgentWiring,
 } from "./assemble-runtime.js";
+import { loadState, saveState } from "./state.js";
 
 function def(name: string): ToolDefinition {
   return {
@@ -182,6 +185,102 @@ describe("createAdvertisedToolset", () => {
     expect(pruneIdlePromotions()).toBe(false);
   });
 
+  test("fold prune persist omits activatedTools from run.json and the crash handle", async () => {
+    const cwd = await mkdtemp(join(tmpdir(), "fold-prune-persist-cwd-"));
+    const home = await mkdtemp(join(tmpdir(), "fold-prune-persist-home-"));
+    try {
+      const {
+        activated,
+        computeAdvertised,
+        flushPromotions,
+        pruneIdlePromotions,
+      } = createAdvertisedToolset(wiring());
+      const defs = [def("read_file"), def("mcp__acme__do")];
+      activated.activate(["mcp__acme__do"]);
+      expect(flushPromotions()).toBe(true);
+
+      const sessionId = "fold-prune-persist";
+      const base = {
+        status: "running" as const,
+        turnsUsed: 2,
+        task: "task",
+        startedAt: 1,
+      };
+      await saveState(
+        cwd,
+        sessionId,
+        { ...base, activatedTools: activated.list() },
+        home,
+      );
+      const handle: RunStateHandle = {
+        sessionId,
+        cwd,
+        task: base.task,
+        startedAt: base.startedAt,
+        turnsUsed: base.turnsUsed,
+        activatedTools: activated.list(),
+      };
+
+      let refreshed = false;
+      let persistWrite: Promise<void> | undefined;
+      expect(
+        commitIdlePromotionPrune({
+          pruneIdlePromotions,
+          refreshAdvertised: () => {
+            refreshed = true;
+            expect(computeAdvertised(defs).map((d) => d.name)).not.toContain(
+              "mcp__acme__do",
+            );
+          },
+          persist: () => {
+            const tools = activated.list();
+            syncRunStateHandle(handle, {
+              turnsUsed: base.turnsUsed,
+              task: base.task,
+              startedAt: base.startedAt,
+              activatedTools: tools,
+            });
+            persistWrite = saveState(
+              cwd,
+              sessionId,
+              {
+                ...base,
+                ...(tools.length > 0 ? { activatedTools: tools } : {}),
+              },
+              home,
+            );
+          },
+        }),
+      ).toBe(true);
+      expect(refreshed).toBe(true);
+      expect(handle.activatedTools).toEqual([]);
+      if (persistWrite === undefined) {
+        throw new Error("fold prune persist did not write");
+      }
+      await persistWrite;
+
+      const loaded = await loadState(cwd, sessionId, home);
+      expect(loaded.kind).toBe("ok");
+      if (loaded.kind !== "ok") return;
+      expect(loaded.state.activatedTools).toBeUndefined();
+
+      expect(
+        commitIdlePromotionPrune({
+          pruneIdlePromotions,
+          refreshAdvertised: () => {
+            throw new Error("idle prune must not refresh twice");
+          },
+          persist: () => {
+            throw new Error("idle prune must not persist twice");
+          },
+        }),
+      ).toBe(false);
+    } finally {
+      await rm(cwd, { recursive: true, force: true });
+      await rm(home, { recursive: true, force: true });
+    }
+  });
+
   test("pinned tools are advertised before any activation and survive clear", () => {
     const { activated, computeAdvertised } = createAdvertisedToolset(
       wiring({ pinnedTools: ["mcp__linear__save_issue"] }),

src/session/assemble-runtime.ts

@@ -495,6 +495,22 @@ export function createAdvertisedToolset(args: {
   };
 }
 
+/**
+ * Fold already broke the cache prefix. Drop idle execute-promoted schemas,
+ * refresh the advertised wire, and persist so resume/crash cannot restore
+ * the pruned names from run.json.
+ */
+export function commitIdlePromotionPrune(args: {
+  pruneIdlePromotions: () => boolean;
+  refreshAdvertised: () => void;
+  persist: () => void;
+}): boolean {
+  if (!args.pruneIdlePromotions()) return false;
+  args.refreshAdvertised();
+  args.persist();
+  return true;
+}
+
 // ---------------------------------------------------------------------------
 // 7. Chat agent: director def, agent def, live builder
 // ---------------------------------------------------------------------------

src/session/state.ts

@@ -46,9 +46,10 @@ const RunStateSchema = type({
   // MCP servers connected during the session, with the tool count each
   // contributed. Empty until the first server finishes connecting.
   "mcpServers?": ConnectedMcpServerSchema.array(),
-  // Tool names promoted via tool_search this session. Persisted
-  // so a resume can re-activate them before the first post-resume inference —
-  // the transcript still tells the model they are callable.
+  // Tool names promoted on execute this session. Persisted so a resume can
+  // re-activate them before the first post-resume inference — the transcript
+  // still tells the model they are callable. Fold prune omits this field so
+  // a crash cannot restore dropped schemas.
   "activatedTools?": "string[]",
   // Wall time of the last Anthropic-protocol inference. A later process
   // folds before its first infer once this is at least the published TTL old.

src/tui/resume-seed.test.ts

@@ -64,4 +64,10 @@ describe("resolveResumeSeed", () => {
 
     expect(seed.activatedTools).toEqual([]);
   });
+
+  test("an empty activatedTools list from a crash write does not re-activate pruned names", () => {
+    expect(
+      resolveResumeSeed(pickedState({ activatedTools: [] })).activatedTools,
+    ).toEqual([]);
+  });
 });

src/tui/runner/session.ts

@@ -47,6 +47,7 @@ import {
   assembleChatAgent,
   assembleSessionGate,
   assembleSessionLifecycle,
+  commitIdlePromotionPrune,
   createAdvertisedToolset,
   loadSessionLocalSettings,
   resolveLiveSessionSources,
@@ -713,12 +714,19 @@ export async function assembleTUISession(
           // Main-session folds only — exec runner and subagents stay silent.
           onFolded: (info) => {
             // Fold restarts the cached prefix — drop idle execute-promoted
-            // schemas rather than carrying them forever.
-            if (pruneIdlePromotions()) {
-              directorHolder.instance?.updateToolDefinitions(
-                computeAdvertised(toolset.dynamicRunner.currentDefinitions()),
-              );
-            }
+            // schemas rather than carrying them forever, and persist so a
+            // crash resume cannot re-flush the pruned names.
+            commitIdlePromotionPrune({
+              pruneIdlePromotions,
+              refreshAdvertised: () => {
+                directorHolder.instance?.updateToolDefinitions(
+                  computeAdvertised(toolset.dynamicRunner.currentDefinitions()),
+                );
+              },
+              persist: () => {
+                void state.persistRunSnapshot?.("running");
+              },
+            });
             emitter.emit("compaction", info);
           },
         }),