refactor: migrate delegate_task to task tool with metadata fixes

- Rename delegate_task tool to task across codebase (100 files)
- Update model references: claude-opus-4-6 → 4-5, gpt-5.3-codex → 5.2-codex
- Add tool-metadata-store to restore metadata overwritten by fromPlugin()
- Add session ID polling for BackgroundManager task sessions
- Await async ctx.metadata() calls in tool executors
- Add ses_ prefix guard to getMessageDir for performance
- Harden BackgroundManager with idle deferral and error handling
- Fix duplicate task key in sisyphus-junior test object literals
- Fix unawaited showOutputToUser in ast_grep_replace
- Fix background=true → run_in_background=true in ultrawork prompt
- Fix duplicate task/task references in docs and comments

src/hooks/prometheus-md-only/index.test.ts

@@ -227,11 +227,11 @@ describe("prometheus-md-only", () => {
       ).resolves.toBeUndefined()
     })
 
-    test("should inject read-only warning when Prometheus calls delegate_task", async () => {
+    test("should inject read-only warning when Prometheus calls task", async () => {
       // given
       const hook = createPrometheusMdOnlyHook(createMockPluginInput())
       const input = {
-        tool: "delegate_task",
+        tool: "task",
         sessionID: TEST_SESSION_ID,
         callID: "call-1",
       }
@@ -289,7 +289,7 @@ describe("prometheus-md-only", () => {
       // given
       const hook = createPrometheusMdOnlyHook(createMockPluginInput())
       const input = {
-        tool: "delegate_task",
+        tool: "task",
         sessionID: TEST_SESSION_ID,
         callID: "call-1",
       }
@@ -330,11 +330,11 @@ describe("prometheus-md-only", () => {
       ).resolves.toBeUndefined()
     })
 
-    test("should not inject warning for non-Prometheus agents calling delegate_task", async () => {
+    test("should not inject warning for non-Prometheus agents calling task", async () => {
       // given
       const hook = createPrometheusMdOnlyHook(createMockPluginInput())
       const input = {
-        tool: "delegate_task",
+        tool: "task",
         sessionID: TEST_SESSION_ID,
         callID: "call-1",
       }