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  - tasks.session_json          (superseded by task_sessions.session_params_json)
  - tasks.session_display_id    (superseded by task_sessions.session_display_id)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).

src/main/worker/handlers/run-finished-helpers.ts

@@ -66,11 +66,19 @@ export function finalizeRun(
     }
   }
 
-  if (task) {
-    // Pi-mono sessions are persisted through SqliteSessionStore via RuntimeBridge;
-    // worker-reported sessionParams is an opaque JSON snapshot of whatever the
-    // orchestrator wants to stamp onto the task_sessions row.
-    db.updateTaskSession(task.id, event.sessionParams, event.sessionDisplayId ?? null);
+  // Stamp pi-ai's transient per-turn state (session resume params,
+  // display id) onto the agent's current session row. Sessions are
+  // agent-scoped, so the session id comes from agents.session_id —
+  // not from a task pointer (that indirection was dropped in v41).
+  try {
+    const agent = db.getAgent(run.agentId);
+    if (agent.sessionId) {
+      db.updateSessionParams(agent.sessionId, event.sessionParams, event.sessionDisplayId ?? null);
+    }
+  } catch (error) {
+    logger.warn(
+      `[finalizeRun] updateSessionParams failed for run ${event.runId}: ${error instanceof Error ? error.message : String(error)}`,
+    );
   }
 
   leaseRenewalMap.delete(event.runId);