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/agent-usage-reminder/constants.ts

@@ -24,7 +24,7 @@ export const TARGET_TOOLS = new Set([
 export const AGENT_TOOLS = new Set([
   "task",
   "call_omo_agent",
-  "delegate_task",
+  "task",
 ]);
 
 export const REMINDER_MESSAGE = `
@@ -32,13 +32,13 @@ export const REMINDER_MESSAGE = `
 
 You called a search/fetch tool directly without leveraging specialized agents.
 
-RECOMMENDED: Use delegate_task with explore/librarian agents for better results:
+RECOMMENDED: Use task with explore/librarian agents for better results:
 
 \`\`\`
 // Parallel exploration - fire multiple agents simultaneously
-delegate_task(agent="explore", prompt="Find all files matching pattern X")
-delegate_task(agent="explore", prompt="Search for implementation of Y") 
-delegate_task(agent="librarian", prompt="Lookup documentation for Z")
+task(agent="explore", prompt="Find all files matching pattern X")
+task(agent="explore", prompt="Search for implementation of Y") 
+task(agent="librarian", prompt="Lookup documentation for Z")
 
 // Then continue your work while they run in background
 // System will notify you when each completes
@@ -50,5 +50,5 @@ WHY:
 - Specialized agents have domain expertise
 - Reduces context window usage in main session
 
-ALWAYS prefer: Multiple parallel delegate_task calls > Direct tool calls
+ALWAYS prefer: Multiple parallel task calls > Direct tool calls
 `;