fix(engine): prevent auto-merge cooldown loop on unresolvable conflicts

Tasks were getting stuck in `in-review` forever when auto-merge could not
resolve conflicts within MAX_AUTO_MERGE_RETRIES. The conflict-exhaustion
branch silently cleared `status` (no error, no log entry, no comment),
and the 30-min cooldown sweep would reset retries and re-attempt the
same impossible merge — looping silently with no user-facing surface.

Why:
- FN-2918 and FN-2903 both spent hours in this loop with no error/comment
  visible on the task. The only log evidence was repeated
  "Auto-merge retry cooldown elapsed (30m idle)" entries with no
  follow-up outcome.

How to apply:
- Every merge failure now writes a `<Manual|Auto>-merge failed: <msg>`
  entry to the task log so the dashboard surfaces the reason.
- Conflict-retry exhaustion now bounces the task back to `in-progress`
  with a comment + log entry so the executor re-rebases against main
  and retries — mirroring the verification-failure-bounce pattern.
- New `mergeConflictBounceCount` task field caps outer bounces
  (`MAX_MERGE_CONFLICT_BOUNCES = 2`); past the cap, the task is parked
  in `in-review` with `status="failed"` and a follow-up triage task is
  created so a human can resolve the conflict manually.
- Non-conflict and non-direct-strategy errors now also set
  `status="failed"` so the cooldown sweep can't re-pick them up.
- `canMergeTask` skips tasks with `status="failed"` so terminal
  failures (verification cap, bounce cap, non-conflict error) are no
  longer eligible for cooldown re-attempts.

Schema migration v52 adds the `mergeConflictBounceCount` column.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

packages/core/src/__tests__/db.test.ts

@@ -131,7 +131,7 @@ describe("Database", () => {
     });
 
     it("seeds schema version", () => {
-      expect(db.getSchemaVersion()).toBe(51);
+      expect(db.getSchemaVersion()).toBe(52);
     });
 
     it("seeds lastModified", () => {
@@ -154,7 +154,7 @@ describe("Database", () => {
 
     it("is idempotent - calling init() twice does not fail", () => {
       expect(() => db.init()).not.toThrow();
-      expect(db.getSchemaVersion()).toBe(51);
+      expect(db.getSchemaVersion()).toBe(52);
     });
 
     it("does not overwrite existing config on re-init", () => {
@@ -761,7 +761,7 @@ describe("schema migrations", () => {
     db.init();
 
     // Verify version bumped to 29 (includes v1→v2 through v26→v29)
-    expect(db.getSchemaVersion()).toBe(51);
+    expect(db.getSchemaVersion()).toBe(52);
 
     // Verify new columns exist and existing data is intact
     const cols = db.prepare("PRAGMA table_info(tasks)").all() as Array<{ name: string }>;
@@ -786,11 +786,11 @@ describe("schema migrations", () => {
     const db = new Database(fusionDir);
     db.init();
 
-    expect(db.getSchemaVersion()).toBe(51);
+    expect(db.getSchemaVersion()).toBe(52);
 
     // Re-init should not fail
     db.init();
-    expect(db.getSchemaVersion()).toBe(51);
+    expect(db.getSchemaVersion()).toBe(52);
 
     db.close();
   });
@@ -825,7 +825,7 @@ describe("schema migrations", () => {
 
     db.init();
 
-    expect(db.getSchemaVersion()).toBe(51);
+    expect(db.getSchemaVersion()).toBe(52);
 
     const cols = db.prepare("PRAGMA table_info(tasks)").all() as Array<{ name: string }>;
     expect(cols.map((col) => col.name)).toContain("priority");
@@ -866,7 +866,7 @@ describe("schema migrations", () => {
 
     db.init();
 
-    expect(db.getSchemaVersion()).toBe(51);
+    expect(db.getSchemaVersion()).toBe(52);
 
     const cols = db.prepare("PRAGMA table_info(tasks)").all() as Array<{ name: string }>;
     const colNames = cols.map((col) => col.name);
@@ -935,7 +935,7 @@ describe("schema migrations", () => {
 
     db.init();
 
-    expect(db.getSchemaVersion()).toBe(51);
+    expect(db.getSchemaVersion()).toBe(52);
 
     const cols = db.prepare("PRAGMA table_info(tasks)").all() as Array<{ name: string }>;
     const colNames = cols.map((col) => col.name);
@@ -994,7 +994,7 @@ describe("schema migrations", () => {
 
     db.init();
 
-    expect(db.getSchemaVersion()).toBe(51);
+    expect(db.getSchemaVersion()).toBe(52);
 
     const cols = db.prepare("PRAGMA table_info(chat_messages)").all() as Array<{ name: string }>;
     expect(cols.map((col) => col.name)).toContain("attachments");
@@ -1016,7 +1016,7 @@ describe("schema migrations", () => {
 
     db.init();
 
-    expect(db.getSchemaVersion()).toBe(51);
+    expect(db.getSchemaVersion()).toBe(52);
 
     const tables = db.prepare("SELECT name FROM sqlite_master WHERE type='table' AND name = 'agentRatings'").all() as Array<{ name: string }>;
     expect(tables).toEqual([{ name: "agentRatings" }]);
@@ -1040,7 +1040,7 @@ describe("schema migrations", () => {
 
     db.init();
 
-    expect(db.getSchemaVersion()).toBe(51);
+    expect(db.getSchemaVersion()).toBe(52);
 
     const tables = db.prepare("SELECT name FROM sqlite_master WHERE type='table' AND name = 'mission_events'").all() as Array<{ name: string }>;
     expect(tables).toEqual([{ name: "mission_events" }]);
@@ -1144,7 +1144,7 @@ describe("schema migrations", () => {
     db.init();
 
     // Verify version bumped to 29
-    expect(db.getSchemaVersion()).toBe(51);
+    expect(db.getSchemaVersion()).toBe(52);
 
     // Verify new columns exist and existing data is intact
     const cols = db.prepare("PRAGMA table_info(tasks)").all() as Array<{ name: string }>;
@@ -1595,7 +1595,7 @@ describe("createDatabase factory", () => {
     const db = createDatabase(fusionDir);
     db.init();
 
-    expect(db.getSchemaVersion()).toBe(51);
+    expect(db.getSchemaVersion()).toBe(52);
     expect(db.getLastModified()).toBeGreaterThan(0);
 
     db.close();

packages/core/src/__tests__/insight-store.test.ts

@@ -779,7 +779,7 @@ describe("Migration: pre-33 DB upgrade", () => {
       // Step 1: Create a fresh database at v33 (runs all migrations up to 33)
       const db1 = createDatabase(legacyDir);
       db1.init();
-      expect(db1.getSchemaVersion()).toBe(51);
+      expect(db1.getSchemaVersion()).toBe(52);
       db1.close();
 
       // Step 2: Manually downgrade to version 32 and drop insight tables
@@ -814,7 +814,7 @@ describe("Migration: pre-33 DB upgrade", () => {
       expect(tableNamesBefore).not.toContain("project_insight_runs");
       // Now run init — this triggers the v32→v33 migration
       db3.init();
-      expect(db3.getSchemaVersion()).toBe(51);
+      expect(db3.getSchemaVersion()).toBe(52);
 
       // Step 4: Verify insight tables exist after migration
       const tablesAfter = db3.prepare(
@@ -845,12 +845,12 @@ describe("Migration: pre-33 DB upgrade", () => {
     try {
       const db1 = createDatabase(testDir);
       db1.init();
-      expect(db1.getSchemaVersion()).toBe(51);
+      expect(db1.getSchemaVersion()).toBe(52);
       db1.close();
 
       const db2 = createDatabase(testDir);
       expect(() => db2.init()).not.toThrow();
-      expect(db2.getSchemaVersion()).toBe(51);
+      expect(db2.getSchemaVersion()).toBe(52);
       db2.close();
     } finally {
       rmSync(testDir, { recursive: true, force: true });

packages/core/src/__tests__/mission-store.test.ts

@@ -2629,7 +2629,7 @@ describe("MissionStore", () => {
 
   describe("Loop State & Validator Run Schema (v31)", () => {
     it("schema version is 40 after migration", () => {
-      expect(db.getSchemaVersion()).toBe(51);
+      expect(db.getSchemaVersion()).toBe(52);
     });
 
     it("mission_features table has loop state columns", () => {

packages/core/src/__tests__/roadmap-store.test.ts

@@ -742,7 +742,7 @@ describe("RoadmapStore", () => {
 
   describe("schema version", () => {
     it("schema version is 40 after init", () => {
-      expect(db.getSchemaVersion()).toBe(51);
+      expect(db.getSchemaVersion()).toBe(52);
     });
   });
 

packages/core/src/__tests__/run-audit.test.ts

@@ -465,7 +465,7 @@ describe("Run Audit", () => {
     });
 
     it("schema version is bumped to 40", () => {
-      expect(db.getSchemaVersion()).toBe(51);
+      expect(db.getSchemaVersion()).toBe(52);
     });
   });
 });

packages/core/src/__tests__/task-documents.test.ts

@@ -51,7 +51,7 @@ describe("TaskStore task documents", () => {
 
     expect(tableNames.has("task_documents")).toBe(true);
     expect(tableNames.has("task_document_revisions")).toBe(true);
-    expect(db.getSchemaVersion()).toBe(51);
+    expect(db.getSchemaVersion()).toBe(52);
 
     const index = db
       .prepare(