step-2: add agent streaming and tool result capture (agent_registry.py)

- ChatAgent.__init__: adds tool_results: list[dict] = []
- _tool_loop: wraps execution in a result collector; populates
  self.tool_results with raw execute_on_client dicts after each run
- _tool_loop_stream: streaming variant — uses ainvoke for tool-call
  iterations, llm.astream() for the final answer; same result capture
- ws_context.py: adds _tool_result_collector ContextVar +
  set/clear helpers; execute_on_client appends to collector when set

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

V3_MIGRATION_PLAN.md

@@ -7,6 +7,18 @@
 
 ---
 
+## General Rules
+
+**Code Cleanup**: As you implement each step, remove any code that becomes unused or obsolete. This includes:
+- Old functions/methods that are superseded by new ones
+- Deprecated imports or modules
+- Dead code paths
+- Old test files no longer needed
+
+This keeps the codebase clean and prevents confusion. When removing code, note it in the commit message if significant.
+
+---
+
 ## Decisions Log
 
 | Topic | Decision |
@@ -74,7 +86,7 @@ pytest tests/test_agent_streaming.py
 ```
 
 **Status**:
-- [ ] Step 2 complete
+- [x] Step 2 complete
 
 **Commit**: After tests pass, commit with:
 ```
@@ -222,8 +234,9 @@ git commit -m "step-4: add output formatting layer (output_formatter.py)"
   - Each request gets a `request_id` (UUID) for frame correlation.
   - Concurrent requests from same client are supported (each runs as an async task).
 - `app/api/routes/chat.py`:
-  - Remove `chat_stream` WS endpoint.
+  - Remove `chat_stream` WS endpoint and any related helper functions that were only used by it.
   - Keep `POST /chat` endpoint unchanged (REST fallback).
+  - Clean up any unused imports.
 - `app/main.py`:
   - No change needed (device_ws router already registered).