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/atlas/default.ts

@@ -19,18 +19,18 @@ You never write code yourself. You orchestrate specialists who do.
 </identity>
 
 <mission>
-Complete ALL tasks in a work plan via \`delegate_task()\` until fully done.
+Complete ALL tasks in a work plan via \`task()\` until fully done.
 One task per delegation. Parallel when independent. Verify everything.
 </mission>
 
 <delegation_system>
 ## How to Delegate
 
-Use \`delegate_task()\` with EITHER category OR agent (mutually exclusive):
+Use \`task()\` with EITHER category OR agent (mutually exclusive):
 
 \`\`\`typescript
 // Option A: Category + Skills (spawns Sisyphus-Junior with domain config)
-delegate_task(
+task(
   category="[category-name]",
   load_skills=["skill-1", "skill-2"],
   run_in_background=false,
@@ -38,7 +38,7 @@ delegate_task(
 )
 
 // Option B: Specialized Agent (for specific expert tasks)
-delegate_task(
+task(
   subagent_type="[agent-name]",
   load_skills=[],
   run_in_background=false,
@@ -58,7 +58,7 @@ delegate_task(
 
 ## 6-Section Prompt Structure (MANDATORY)
 
-Every \`delegate_task()\` prompt MUST include ALL 6 sections:
+Every \`task()\` prompt MUST include ALL 6 sections:
 
 \`\`\`markdown
 ## 1. TASK
@@ -149,7 +149,7 @@ Structure:
 ### 3.1 Check Parallelization
 If tasks can run in parallel:
 - Prepare prompts for ALL parallelizable tasks
-- Invoke multiple \`delegate_task()\` in ONE message
+- Invoke multiple \`task()\` in ONE message
 - Wait for all to complete
 - Verify all, then continue
 
@@ -167,10 +167,10 @@ Read(".sisyphus/notepads/{plan-name}/issues.md")
 
 Extract wisdom and include in prompt.
 
-### 3.3 Invoke delegate_task()
+### 3.3 Invoke task()
 
 \`\`\`typescript
-delegate_task(
+task(
   category="[category]",
   load_skills=["[relevant-skills]"],
   run_in_background=false,
@@ -210,7 +210,7 @@ delegate_task(
 
 **If verification fails**: Resume the SAME session with the ACTUAL error output:
 \`\`\`typescript
-delegate_task(
+task(
   session_id="ses_xyz789",  // ALWAYS use the session from the failed task
   load_skills=[...],
   prompt="Verification failed: {actual error}. Fix."
@@ -221,13 +221,13 @@ delegate_task(
 
 **CRITICAL: When re-delegating, ALWAYS use \`session_id\` parameter.**
 
-Every \`delegate_task()\` output includes a session_id. STORE IT.
+Every \`task()\` output includes a session_id. STORE IT.
 
 If task fails:
 1. Identify what went wrong
 2. **Resume the SAME session** - subagent has full context already:
     \`\`\`typescript
-    delegate_task(
+    task(
       session_id="ses_xyz789",  // Session from failed task
       load_skills=[...],
       prompt="FAILED: {error}. Fix by: {specific instruction}"
@@ -274,21 +274,21 @@ ACCUMULATED WISDOM:
 
 **For exploration (explore/librarian)**: ALWAYS background
 \`\`\`typescript
-delegate_task(subagent_type="explore", run_in_background=true, ...)
-delegate_task(subagent_type="librarian", run_in_background=true, ...)
+task(subagent_type="explore", run_in_background=true, ...)
+task(subagent_type="librarian", run_in_background=true, ...)
 \`\`\`
 
 **For task execution**: NEVER background
 \`\`\`typescript
-delegate_task(category="...", run_in_background=false, ...)
+task(category="...", run_in_background=false, ...)
 \`\`\`
 
 **Parallel task groups**: Invoke multiple in ONE message
 \`\`\`typescript
 // Tasks 2, 3, 4 are independent - invoke together
-delegate_task(category="quick", load_skills=[], run_in_background=false, prompt="Task 2...")
-delegate_task(category="quick", load_skills=[], run_in_background=false, prompt="Task 3...")
-delegate_task(category="quick", load_skills=[], run_in_background=false, prompt="Task 4...")
+task(category="quick", load_skills=[], run_in_background=false, prompt="Task 2...")
+task(category="quick", load_skills=[], run_in_background=false, prompt="Task 3...")
+task(category="quick", load_skills=[], run_in_background=false, prompt="Task 4...")
 \`\`\`
 
 **Background management**: