fix: resolve false-positive rate limit and one-message-behind in chat sessions

The Claude Code CLI v2.1.45+ emits a `rate_limit_event` message type that
the Python SDK v0.1.19 cannot parse, raising MessageParseError. Two bugs
resulted:

1. **False-positive rate limit**: check_rate_limit_error() matched
   "rate_limit" in the exception string "Unknown message type:
   rate_limit_event" via both an explicit type check and a regex fallback,
   triggering 15-19s backoff + query re-send on every session.

2. **One-message-behind**: The MessageParseError killed the
   receive_response() async generator, but the CLI subprocess was still
   alive with buffered response data. Catching and returning meant the
   response was never consumed. The next send_message() would read the
   previous response first, creating a one-behind offset.

Changes:

- chat_constants.py: check_rate_limit_error() now returns (False, None)
  for any MessageParseError, blocking both false-positive paths. Added
  safe_receive_response() helper that retries receive_response() on
  MessageParseError — the SDK's decoupled producer/consumer architecture
  (anyio memory channel) allows the new generator to continue reading
  remaining messages without data loss. Removed calculate_rate_limit_backoff
  re-export and MAX_CHAT_RATE_LIMIT_RETRIES constant.

- spec_chat_session.py, assistant_chat_session.py, expand_chat_session.py:
  Replaced retry-with-backoff loops with safe_receive_response() wrapper.
  Removed asyncio.sleep backoff, query re-send, and rate_limited yield.
  Cleaned up unused imports (asyncio, calculate_rate_limit_backoff,
  MAX_CHAT_RATE_LIMIT_RETRIES).

- agent.py: Added inner retry loop around receive_response() with same
  MessageParseError skip-and-restart pattern. Removed early-return that
  truncated responses.

- types.ts: Removed SpecChatRateLimitedMessage,
  AssistantChatRateLimitedMessage, and their union entries.

- useSpecChat.ts, useAssistantChat.ts, useExpandChat.ts: Removed dead
  'rate_limited' case handlers.

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

agent.py

@@ -74,46 +74,65 @@ async def run_agent_session(
         await client.query(message)
 
         # Collect response text and show tool use
+        # Retry receive_response() on MessageParseError — the SDK raises this for
+        # unknown CLI message types (e.g. "rate_limit_event") which kills the async
+        # generator.  The subprocess is still alive so we restart to read remaining
+        # messages from the buffered channel.
         response_text = ""
-        async for msg in client.receive_response():
-            msg_type = type(msg).__name__
+        max_parse_retries = 50
+        parse_retries = 0
+        while True:
+            try:
+                async for msg in client.receive_response():
+                    msg_type = type(msg).__name__
 
-            # Handle AssistantMessage (text and tool use)
-            if msg_type == "AssistantMessage" and hasattr(msg, "content"):
-                for block in msg.content:
-                    block_type = type(block).__name__
+                    # Handle AssistantMessage (text and tool use)
+                    if msg_type == "AssistantMessage" and hasattr(msg, "content"):
+                        for block in msg.content:
+                            block_type = type(block).__name__
 
-                    if block_type == "TextBlock" and hasattr(block, "text"):
-                        response_text += block.text
-                        print(block.text, end="", flush=True)
-                    elif block_type == "ToolUseBlock" and hasattr(block, "name"):
-                        print(f"\n[Tool: {block.name}]", flush=True)
-                        if hasattr(block, "input"):
-                            input_str = str(block.input)
-                            if len(input_str) > 200:
-                                print(f"   Input: {input_str[:200]}...", flush=True)
-                            else:
-                                print(f"   Input: {input_str}", flush=True)
+                            if block_type == "TextBlock" and hasattr(block, "text"):
+                                response_text += block.text
+                                print(block.text, end="", flush=True)
+                            elif block_type == "ToolUseBlock" and hasattr(block, "name"):
+                                print(f"\n[Tool: {block.name}]", flush=True)
+                                if hasattr(block, "input"):
+                                    input_str = str(block.input)
+                                    if len(input_str) > 200:
+                                        print(f"   Input: {input_str[:200]}...", flush=True)
+                                    else:
+                                        print(f"   Input: {input_str}", flush=True)
 
-            # Handle UserMessage (tool results)
-            elif msg_type == "UserMessage" and hasattr(msg, "content"):
-                for block in msg.content:
-                    block_type = type(block).__name__
+                    # Handle UserMessage (tool results)
+                    elif msg_type == "UserMessage" and hasattr(msg, "content"):
+                        for block in msg.content:
+                            block_type = type(block).__name__
 
-                    if block_type == "ToolResultBlock":
-                        result_content = getattr(block, "content", "")
-                        is_error = getattr(block, "is_error", False)
+                            if block_type == "ToolResultBlock":
+                                result_content = getattr(block, "content", "")
+                                is_error = getattr(block, "is_error", False)
 
-                        # Check if command was blocked by security hook
-                        if "blocked" in str(result_content).lower():
-                            print(f"   [BLOCKED] {result_content}", flush=True)
-                        elif is_error:
-                            # Show errors (truncated)
-                            error_str = str(result_content)[:500]
-                            print(f"   [Error] {error_str}", flush=True)
-                        else:
-                            # Tool succeeded - just show brief confirmation
-                            print("   [Done]", flush=True)
+                                # Check if command was blocked by security hook
+                                if "blocked" in str(result_content).lower():
+                                    print(f"   [BLOCKED] {result_content}", flush=True)
+                                elif is_error:
+                                    # Show errors (truncated)
+                                    error_str = str(result_content)[:500]
+                                    print(f"   [Error] {error_str}", flush=True)
+                                else:
+                                    # Tool succeeded - just show brief confirmation
+                                    print("   [Done]", flush=True)
+
+                break  # Normal completion
+            except Exception as inner_exc:
+                if type(inner_exc).__name__ == "MessageParseError":
+                    parse_retries += 1
+                    if parse_retries > max_parse_retries:
+                        print(f"Too many unrecognized CLI messages ({parse_retries}), stopping")
+                        break
+                    print(f"Ignoring unrecognized message from Claude CLI: {inner_exc}")
+                    continue
+                raise  # Re-raise to outer except
 
         print("\n" + "-" * 70 + "\n")
         return "continue", response_text