feat(subagents): make subagent timeout configurable via config.yaml (#897)

* feat(subagents): make subagent timeout configurable via config.yaml

- Add SubagentsAppConfig supporting global and per-agent timeout_seconds
- Load subagents config section in AppConfig.from_file()
- Registry now applies config.yaml overrides without mutating builtin defaults
- Polling safety-net in task_tool is now dynamic (execution timeout + 60s buffer)
- Document subagents section in config.example.yaml
- Add make test command and enforce TDD policy in CLAUDE.md
- Add 38 unit tests covering config validation, timeout resolution, registry
  override behavior, and polling timeout formula

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

* feat(subagents): add logging for subagent timeout config and execution

- Log loaded timeout config (global default + per-agent overrides) on startup
- Log debug message in registry when config.yaml overrides a builtin timeout
- Include timeout in executor's async execution start log
- Log effective timeout and polling limit when a task is dispatched
- Fix UnboundLocalError: move max_poll_count assignment before logger.info

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

* ci(backend): add lint step and run all unit tests via Makefile

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

* fix lint

---------

Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/src/tools/builtins/task_tool.py

@@ -115,12 +115,15 @@ def task_tool(
     # Start background execution (always async to prevent blocking)
     # Use tool_call_id as task_id for better traceability
     task_id = executor.execute_async(prompt, task_id=tool_call_id)
-    logger.info(f"[trace={trace_id}] Started background task {task_id}, polling for completion...")
 
     # Poll for task completion in backend (removes need for LLM to poll)
     poll_count = 0
     last_status = None
     last_message_count = 0  # Track how many AI messages we've already sent
+    # Polling timeout: execution timeout + 60s buffer, checked every 5s
+    max_poll_count = (config.timeout_seconds + 60) // 5
+
+    logger.info(f"[trace={trace_id}] Started background task {task_id} (subagent={subagent_type}, timeout={config.timeout_seconds}s, polling_limit={max_poll_count} polls)")
 
     writer = get_stream_writer()
     # Send Task Started message'
@@ -176,9 +179,10 @@ def task_tool(
         poll_count += 1
 
         # Polling timeout as a safety net (in case thread pool timeout doesn't work)
-        # Set to 16 minutes (longer than the default 15-minute thread pool timeout)
+        # Set to execution timeout + 60s buffer, in 5s poll intervals
         # This catches edge cases where the background task gets stuck
-        if poll_count > 192:  # 192 * 5s = 16 minutes
+        if poll_count > max_poll_count:
+            timeout_minutes = config.timeout_seconds // 60
             logger.error(f"[trace={trace_id}] Task {task_id} polling timed out after {poll_count} polls (should have been caught by thread pool timeout)")
             writer({"type": "task_timed_out", "task_id": task_id})
-            return f"Task polling timed out after 16 minutes. This may indicate the background task is stuck. Status: {result.status.value}"
+            return f"Task polling timed out after {timeout_minutes} minutes. This may indicate the background task is stuck. Status: {result.status.value}"