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/agents/sisyphus-junior/default.ts

@@ -24,7 +24,6 @@ Execute tasks directly. NEVER delegate or spawn other agents.
 <Critical_Constraints>
 BLOCKED ACTIONS (will fail if attempted):
 - task tool: BLOCKED
-- delegate_task tool: BLOCKED
 
 ALLOWED: call_omo_agent - You CAN spawn explore/librarian agents for research.
 You work ALONE for implementation. No delegation of implementation tasks.

src/agents/sisyphus-junior/gpt.ts

@@ -50,7 +50,6 @@ BLOCKED (will fail if attempted):
 | Tool | Status |
 |------|--------|
 | task | BLOCKED |
-| delegate_task | BLOCKED |
 
 ALLOWED:
 | Tool | Usage |

src/agents/sisyphus-junior/index.test.ts

@@ -143,13 +143,12 @@ describe("createSisyphusJuniorAgentWithOverrides", () => {
     })
   })
 
-  describe("tool safety (task/delegate_task blocked, call_omo_agent allowed)", () => {
-    test("task and delegate_task remain blocked, call_omo_agent is allowed via tools format", () => {
+  describe("tool safety (task blocked, call_omo_agent allowed)", () => {
+    test("task remains blocked, call_omo_agent is allowed via tools format", () => {
       // given
       const override = {
         tools: {
           task: true,
-          delegate_task: true,
           call_omo_agent: true,
           read: true,
         },
@@ -163,25 +162,22 @@ describe("createSisyphusJuniorAgentWithOverrides", () => {
       const permission = result.permission as Record<string, string> | undefined
       if (tools) {
         expect(tools.task).toBe(false)
-        expect(tools.delegate_task).toBe(false)
         // call_omo_agent is NOW ALLOWED for subagents to spawn explore/librarian
         expect(tools.call_omo_agent).toBe(true)
         expect(tools.read).toBe(true)
       }
       if (permission) {
         expect(permission.task).toBe("deny")
-        expect(permission.delegate_task).toBe("deny")
         // call_omo_agent is NOW ALLOWED for subagents to spawn explore/librarian
         expect(permission.call_omo_agent).toBe("allow")
       }
     })
 
-    test("task and delegate_task remain blocked when using permission format override", () => {
+    test("task remains blocked when using permission format override", () => {
       // given
       const override = {
         permission: {
           task: "allow",
-          delegate_task: "allow",
           call_omo_agent: "allow",
           read: "allow",
         },
@@ -190,17 +186,15 @@ describe("createSisyphusJuniorAgentWithOverrides", () => {
       // when
       const result = createSisyphusJuniorAgentWithOverrides(override as Parameters<typeof createSisyphusJuniorAgentWithOverrides>[0])
 
-      // then - task/delegate_task blocked, but call_omo_agent allowed for explore/librarian spawning
+      // then - task blocked, but call_omo_agent allowed for explore/librarian spawning
       const tools = result.tools as Record<string, boolean> | undefined
       const permission = result.permission as Record<string, string> | undefined
       if (tools) {
         expect(tools.task).toBe(false)
-        expect(tools.delegate_task).toBe(false)
         expect(tools.call_omo_agent).toBe(true)
       }
       if (permission) {
         expect(permission.task).toBe("deny")
-        expect(permission.delegate_task).toBe("deny")
         expect(permission.call_omo_agent).toBe("allow")
       }
     })

src/agents/sisyphus-junior/index.ts

@@ -28,7 +28,7 @@ const MODE: AgentMode = "subagent"
 
 // Core tools that Sisyphus-Junior must NEVER have access to
 // Note: call_omo_agent is ALLOWED so subagents can spawn explore/librarian
-const BLOCKED_TOOLS = ["task", "delegate_task"]
+const BLOCKED_TOOLS = ["task"]
 
 export const SISYPHUS_JUNIOR_DEFAULTS = {
   model: "anthropic/claude-sonnet-4-5",