fix(coding-agent/hindsight): reacted to live bank scope changes and flushed before dispose

Mid-session edits to hindsight.bankId / bankIdPrefix / scoping kept the
active HindsightSessionState pinned to the bank selected at session
start, so retain/recall/reflect calls landed in the stale bank. Settings
hooks now fire onHindsightScopeChanged; the backend rebuilds the
primary state against the recomputed scope, disposing the previous one
after flushing its queue so queued tool-initiated retains still land in
the bank they were enqueued for.

Also:
- Renamed ensureBankMission to ensureBankExists. The old version
  skipped creation entirely when bankMission was blank, so the first
  mental-model POST (auto-seed) could land against a never-PUT bank.
  Bank creation is now idempotent and unconditional, and runs before
  mental-model bootstrap.
- Fixed AgentSession.dispose to flush the retain queue BEFORE clearing
  the session state pointer. Reversed, HindsightRetainQueue.#doFlush's
  identity guard would see the cleared pointer and drop the spliced
  batch with a 'session vanished' warning.
- Snapshotted hindsightScopeCallbacks before iterating because each
  rebuild subscribes a fresh callback inside the same fire; iterating
  the live Set would spin.

Fixes #1902

packages/coding-agent/src/tools/memory-reflect.ts

@@ -1,7 +1,7 @@
 import type { AgentTool, AgentToolResult } from "@oh-my-pi/pi-agent-core";
 import { logger, untilAborted } from "@oh-my-pi/pi-utils";
 import * as z from "zod/v4";
-import { ensureBankMission } from "../hindsight/bank";
+import { ensureBankExists } from "../hindsight/bank";
 import reflectDescription from "../prompts/tools/reflect.md" with { type: "text" };
 import type { ToolSession } from ".";
 
@@ -67,7 +67,7 @@ export class MemoryReflectTool implements AgentTool<typeof memoryReflectSchema>
 			}
 
 			try {
-				await ensureBankMission(state.client, state.bankId, state.config, state.missionsSet);
+				await ensureBankExists(state.client, state.bankId, state.config, state.banksSet);
 				const response = await state.client.reflect(state.bankId, params.query, {
 					context: params.context,
 					budget: state.config.recallBudget,