fix deadlock

Author: campagnola

CLAUDE.md

@@ -4,7 +4,7 @@ This file provides guidance to Claude Code (claude.ai/code) when working with co
 
 ## Commands
 
-All commands likely require running python from a particular environment. If this is not specified in an agent instruction file, then prompt the user.
+All commands likely require running python from a particular environment. If this is not specified in an agent instruction file, then prompt the user. Run `python` directly from the requested environment (don't use `conda run` since it eats stdout from its subprocesses).
 
 ### Testing
 - **Run all tests**: `python -m pytest coorx/tests`

coorx/events.py

@@ -24,7 +24,7 @@ class CallbackRegistry:
     def __init__(self):
         # List of (is_weakref, callback or weakref) tuples
         self._callbacks: list[tuple[bool, Callable]] = []
-        self.lock = threading.Lock()
+        self.lock = threading.RLock()  # Use reentrant lock to allow add() to call remove()
 
     def _real_callbacks(self):
         """Return (callback, is_weakref, maybe_weakref) tuples for all live callbacks."""