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/shared/agent-tool-restrictions.ts

@@ -8,7 +8,6 @@ const EXPLORATION_AGENT_DENYLIST: Record<string, boolean> = {
   write: false,
   edit: false,
   task: false,
-  delegate_task: false,
   call_omo_agent: false,
 }
 
@@ -21,7 +20,6 @@ const AGENT_RESTRICTIONS: Record<string, Record<string, boolean>> = {
     write: false,
     edit: false,
     task: false,
-    delegate_task: false,
     call_omo_agent: false,
   },
 
@@ -29,14 +27,12 @@ const AGENT_RESTRICTIONS: Record<string, Record<string, boolean>> = {
     write: false,
     edit: false,
     task: false,
-    delegate_task: false,
   },
 
   momus: {
     write: false,
     edit: false,
     task: false,
-    delegate_task: false,
   },
 
   "multimodal-looker": {
@@ -45,7 +41,6 @@ const AGENT_RESTRICTIONS: Record<string, Record<string, boolean>> = {
 
   "sisyphus-junior": {
     task: false,
-    delegate_task: false,
   },
 }