feat(FN-1146): add configurable AI session cleanup lifecycle

- Add aiSessionTtlMs and aiSessionCleanupIntervalMs project settings with defaults and bounds for cleanup scheduling
- Extend AiSessionStore cleanup to expire stale in-progress sessions, emit deletion events, and support start/stop scheduled cleanup loops
- Wire server startup/shutdown to load cleanup settings and manage the scheduled ai_sessions sweep lifecycle
- Align planning, subtask breakdown, and mission interview in-memory session retention to a 7-day TTL with shared deletion-driven cleanup
- Update schema/tests/docs for migration v15 ai_sessions indexing and end-to-end cleanup/TTL behavior stability

packages/core/src/db.test.ts

@@ -96,7 +96,7 @@ describe("Database", () => {
     });
 
     it("seeds schema version", () => {
-      expect(db.getSchemaVersion()).toBe(14);
+      expect(db.getSchemaVersion()).toBe(15);
     });
 
     it("seeds lastModified", () => {
@@ -119,7 +119,7 @@ describe("Database", () => {
 
     it("is idempotent - calling init() twice does not fail", () => {
       expect(() => db.init()).not.toThrow();
-      expect(db.getSchemaVersion()).toBe(14);
+      expect(db.getSchemaVersion()).toBe(15);
     });
 
     it("does not overwrite existing config on re-init", () => {
@@ -726,7 +726,7 @@ describe("schema migrations", () => {
     db.init();
 
     // Verify version bumped to 5 (includes v1→v2, v2→v3, v3→v4, and v4→v5 migrations)
-    expect(db.getSchemaVersion()).toBe(14);
+    expect(db.getSchemaVersion()).toBe(15);
 
     // Verify new columns exist and existing data is intact
     const cols = db.prepare("PRAGMA table_info(tasks)").all() as Array<{ name: string }>;
@@ -751,16 +751,16 @@ describe("schema migrations", () => {
     const db = new Database(kbDir);
     db.init();
 
-    expect(db.getSchemaVersion()).toBe(14);
+    expect(db.getSchemaVersion()).toBe(15);
 
     // Re-init should not fail
     db.init();
-    expect(db.getSchemaVersion()).toBe(14);
+    expect(db.getSchemaVersion()).toBe(15);
 
     db.close();
   });
 
-  it("applies migration 14 by creating agentRatings table and indexes", () => {
+  it("applies migration 14+15 by creating agentRatings and ai_sessions indexes", () => {
     tmpDir = makeTmpDir();
     const kbDir = join(tmpDir, ".fusion");
 
@@ -771,7 +771,7 @@ describe("schema migrations", () => {
 
     db.init();
 
-    expect(db.getSchemaVersion()).toBe(14);
+    expect(db.getSchemaVersion()).toBe(15);
 
     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" }]);
@@ -874,7 +874,7 @@ describe("schema migrations", () => {
     db.init();
 
     // Verify version bumped to 5
-    expect(db.getSchemaVersion()).toBe(14);
+    expect(db.getSchemaVersion()).toBe(15);
 
     // Verify new columns exist and existing data is intact
     const cols = db.prepare("PRAGMA table_info(tasks)").all() as Array<{ name: string }>;
@@ -1084,7 +1084,7 @@ describe("createDatabase factory", () => {
     const db = createDatabase(kbDir);
     db.init();
 
-    expect(db.getSchemaVersion()).toBe(14);
+    expect(db.getSchemaVersion()).toBe(15);
     expect(db.getLastModified()).toBeGreaterThan(0);
 
     db.close();

packages/core/src/db.ts

@@ -59,7 +59,7 @@ export function fromJson<T>(json: string | null | undefined): T | undefined {
 
 // ── Schema Definition ────────────────────────────────────────────────
 
-const SCHEMA_VERSION = 14;
+const SCHEMA_VERSION = 15;
 
 function normalizeTaskComments(
   steeringComments: SteeringComment[] | undefined,
@@ -516,6 +516,14 @@ export class Database {
         this.db.exec(`CREATE INDEX IF NOT EXISTS idxAgentRatingsCreatedAt ON agentRatings(createdAt)`);
       });
     }
+
+    if (version < 15) {
+      this.applyMigration(15, () => {
+        if (this.hasTable("ai_sessions")) {
+          this.db.exec(`CREATE INDEX IF NOT EXISTS idxAiSessionsUpdatedAt ON ai_sessions(updatedAt)`);
+        }
+      });
+    }
   }
 
   /**
@@ -530,6 +538,16 @@ export class Database {
       .run(String(targetVersion));
   }
 
+  /**
+   * Check whether a table exists.
+   */
+  private hasTable(table: string): boolean {
+    const row = this.db
+      .prepare("SELECT name FROM sqlite_master WHERE type = 'table' AND name = ?")
+      .get(table) as { name: string } | undefined;
+    return Boolean(row);
+  }
+
   /**
    * Check whether a table has a given column.
    */

packages/core/src/types.ts

@@ -863,6 +863,15 @@ export interface ProjectSettings {
    *  than this duration, the task is considered stuck and will be terminated and retried.
    *  Default: undefined (disabled). Suggested value: 600000 (10 minutes). */
   taskStuckTimeoutMs?: number;
+  /** TTL in milliseconds for persisted AI planning/subtask/mission interview sessions.
+   *  Sessions older than this cutoff are expired by the dashboard session cleanup loop.
+   *  Valid range: 600000 (10 minutes) to 2592000000 (30 days).
+   *  Default: 604800000 (7 days). */
+  aiSessionTtlMs?: number;
+  /** Interval in milliseconds for scheduled AI session cleanup sweeps.
+   *  Valid range: 60000 (1 minute) to 86400000 (24 hours).
+   *  Default: 3600000 (1 hour). */
+  aiSessionCleanupIntervalMs?: number;
   /** When true, automatically unpause after rate-limit-triggered globalPause using
    *  escalating backoff. Allows unattended recovery from transient API rate limits.
    *  Default: true. */
@@ -1035,6 +1044,8 @@ export const DEFAULT_PROJECT_SETTINGS: ProjectSettings = {
   buildTimeoutMs: 300_000,
   requirePlanApproval: false,
   taskStuckTimeoutMs: undefined,
+  aiSessionTtlMs: 7 * 24 * 60 * 60 * 1000,
+  aiSessionCleanupIntervalMs: 60 * 60 * 1000,
   autoUnpauseEnabled: true,
   autoUnpauseBaseDelayMs: 300_000,
   autoUnpauseMaxDelayMs: 3_600_000,
@@ -1126,6 +1137,8 @@ export const PROJECT_SETTINGS_KEYS: ReadonlyArray<keyof ProjectSettings> = [
   "smartConflictResolution",
   "requirePlanApproval",
   "taskStuckTimeoutMs",
+  "aiSessionTtlMs",
+  "aiSessionCleanupIntervalMs",
   "maxStuckKills",
   "autoUpdatePrStatus",
   "autoCreatePr",