refactor(session): drop dead task-scoped session columns (v41)

Sessions have been agent-scoped since v34, but the schema kept four
dead task-scoped columns that every session code path had to pretend
were meaningful:

  - tasks.active_session_id     (mirrored agents.session_id)
  - tasks.session_json          (superseded by task_sessions.session_params_json)
  - tasks.session_display_id    (superseded by task_sessions.session_display_id)
  - task_sessions.task_id       (always empty-string on new rows)

v41 drops all four via SQLite table rebuild — the only safe path when
multiple columns need to go in one step and indexes / FK directions
need to be preserved. `PRAGMA foreign_keys = OFF` spans the swap
window so cascade-delete does not fire mid-rebuild. The migration is
idempotent and also backfills the optional task columns
(task_type / requires_user_review / retry_count / last_failure_at /
started_at / completed_at / cancelled_at / checkout_run_id /
execution_locked_at) before rebuilding so it works whether or not
`ensureOptionalColumns` has run yet on this install.

Along with the schema change, every code path that read or wrote
those columns has been rewired to the agent-scoped equivalents:

- task-sessions-crud.ts: deleted updateTaskSession,
  getTaskSession, getActiveTaskSession, updateTasksActiveSessionForAgent;
  added updateSessionParams(sessionId, ...) for the worker's
  finalizer. ensureAgentSession and createNewSession no longer touch
  task_id.
- database-base.ts: facade drops the now-unused pass-throughs.
- snapshot.ts / task-queries.ts / tasks-status.ts / entity-crud.ts:
  SELECT projections no longer pull session_json / session_display_id
  / active_session_id from tasks.
- tasks-crud.ts (TaskRow) and shared/types/records-core.ts
  (TaskRecord): sessionJson / sessionDisplayId fields removed.
- TaskSessionRecord: taskId field removed.
- turn-context.ts::resolveSession: no more
  updateTasksActiveSessionForAgent mirror; sessionParams read directly
  from the current session via getSessionById.
- run-finished-helpers.ts::finalizeRun: stamps sessionParams via
  updateSessionParams on the agent's current session, resolved through
  agents.session_id.
- session-management-service.ts: rotateSession stops calling
  updateTasksActiveSessionForAgent.

Test suite updated to use the new session-id API. Existing tests used
`getActiveTaskSession(taskId)` and `createNewSession({ taskId, ...})`
as probes; they now use `getSessionById(sessionId)` and the taskId-less
createNewSession input.

Tests: 603/603 green. Typecheck clean. Migration tested on fresh DB
(runs v1→v41 cleanly) and idempotent re-apply (detects absent dead
columns, skips).

tests/unit/edge-case-session.test.ts

@@ -116,7 +116,6 @@ describe("Edge Case: Session Rotation During Execution (D-05.3)", () => {
 
     // Create a session
     const sessionId = db.createNewSession({
-      taskId,
       companyId,
       agentId,
       adapterType: "gemini-cli",
@@ -130,7 +129,7 @@ describe("Edge Case: Session Rotation During Execution (D-05.3)", () => {
     }
 
     // Get the updated session from DB
-    const session = db.getActiveTaskSession(taskId);
+    const session = db.getSessionById(sessionId);
     expect(session).not.toBeNull();
     expect(session!.runCount).toBe(DEFAULT_THRESHOLDS.maxRuns);
 
@@ -145,7 +144,6 @@ describe("Edge Case: Session Rotation During Execution (D-05.3)", () => {
     const sessionService = createSessionManagementService({ db, logger: mockLogger });
 
     const sessionId = db.createNewSession({
-      taskId,
       companyId,
       agentId,
       adapterType: "gemini-cli",
@@ -157,7 +155,7 @@ describe("Edge Case: Session Rotation During Execution (D-05.3)", () => {
     // DEFAULT_THRESHOLDS.maxTokens = 500_000 (total input + output)
     db.incrementSessionUsage(sessionId, 300000, 250000, "big-run");
 
-    const session = db.getActiveTaskSession(taskId);
+    const session = db.getSessionById(sessionId);
     expect(session).not.toBeNull();
     const totalTokens = session!.totalInputTokens + session!.totalOutputTokens;
     expect(totalTokens).toBe(550000);
@@ -172,7 +170,6 @@ describe("Edge Case: Session Rotation During Execution (D-05.3)", () => {
     const sessionService = createSessionManagementService({ db, logger: mockLogger });
 
     const sessionId = db.createNewSession({
-      taskId,
       companyId,
       agentId,
       adapterType: "gemini-cli",
@@ -205,7 +202,7 @@ describe("Edge Case: Session Rotation During Execution (D-05.3)", () => {
       unattributedCost: false,
     });
 
-    const session = db.getActiveTaskSession(taskId)!;
+    const session = db.getSessionById(sessionId)!;
     // generateHandoff is agent-scoped: it walks the agent's runs across
     // all tasks + taskless heartbeats, not a single task.
     const handoff = sessionService.generateHandoff(session);
@@ -230,7 +227,6 @@ describe("Edge Case: Session Rotation During Execution (D-05.3)", () => {
 
     // Create initial session
     const oldSessionId = db.createNewSession({
-      taskId,
       companyId,
       agentId,
       adapterType: "gemini-cli",
@@ -246,7 +242,6 @@ describe("Edge Case: Session Rotation During Execution (D-05.3)", () => {
 
     // Create new session
     const newSessionId = db.createNewSession({
-      taskId,
       companyId,
       agentId,
       adapterType: "gemini-cli",
@@ -255,7 +250,7 @@ describe("Edge Case: Session Rotation During Execution (D-05.3)", () => {
     });
 
     // Get the new active session
-    const newSession = db.getActiveTaskSession(taskId);
+    const newSession = db.getSessionById(newSessionId);
     expect(newSession).not.toBeNull();
     expect(newSession!.id).toBe(newSessionId);
     expect(newSession!.id).not.toBe(oldSessionId);
@@ -271,7 +266,6 @@ describe("Edge Case: Session Rotation During Execution (D-05.3)", () => {
     const sessionService = createSessionManagementService({ db, logger: mockLogger });
 
     const sessionId = db.createNewSession({
-      taskId,
       companyId,
       agentId,
       adapterType: "claude-pro",
@@ -284,7 +278,7 @@ describe("Edge Case: Session Rotation During Execution (D-05.3)", () => {
       db.incrementSessionUsage(sessionId, 30000, 20000, `run-${i}`);
     }
 
-    const session = db.getActiveTaskSession(taskId)!;
+    const session = db.getSessionById(sessionId)!;
     // Pi-mono delegates compaction to pi-agent-core; AgentCompany still applies rotation uniformly.
     const result = sessionService.evaluateRotation(session, "claude-pro");
     expect(result.shouldRotate).toBe(true);
@@ -296,7 +290,6 @@ describe("Edge Case: Session Rotation During Execution (D-05.3)", () => {
     const sessionService = createSessionManagementService({ db, logger: mockLogger });
 
     const sessionId = db.createNewSession({
-      taskId,
       companyId,
       agentId,
       adapterType: "openai-codex",
@@ -309,7 +302,7 @@ describe("Edge Case: Session Rotation During Execution (D-05.3)", () => {
       db.incrementSessionUsage(sessionId, 30000, 20000, `run-${i}`);
     }
 
-    const session = db.getActiveTaskSession(taskId)!;
+    const session = db.getSessionById(sessionId)!;
     // Pi-mono delegates compaction to pi-agent-core; AgentCompany still applies rotation uniformly.
     const result = sessionService.evaluateRotation(session, "openai-codex");
     expect(result.shouldRotate).toBe(true);
@@ -322,7 +315,6 @@ describe("Edge Case: Session Rotation During Execution (D-05.3)", () => {
 
     // Create session and add usage
     const sessionId = db.createNewSession({
-      taskId,
       companyId,
       agentId,
       adapterType: "gemini-cli",
@@ -352,7 +344,7 @@ describe("Edge Case: Session Rotation During Execution (D-05.3)", () => {
     });
 
     // Rotate the session (archives old, creates new)
-    const oldSession = db.getActiveTaskSession(taskId)!;
+    const oldSession = db.getSessionById(sessionId)!;
     sessionService.rotateSession(oldSession);
 
     // After rotation, the handoff should be retrievable for the next run