docs(changelog): scope breaking-change to the LangGraph handler only

Address Greptile review: the breaking-change entry listed
create_pydantic_ai_tracing_handler as removed, but that handler is still
exported here and is only removed in the following PR. Narrow this entry to
the LangGraph handler actually removed in this change.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: declan-scale

CHANGELOG.md

@@ -4,7 +4,7 @@
 
 ### ⚠ BREAKING CHANGES
 
-* **harness:** removed the deprecated bespoke tracing handlers `create_langgraph_tracing_handler` / `create_pydantic_ai_tracing_handler` (and their `AgentexLangGraphTracingHandler` / `AgentexPydanticAITracingHandler` classes) from the public `agentex.lib.adk` surface. Span tracing is now derived from the canonical `StreamTaskMessage*` stream by `UnifiedEmitter` — wrap your run in the harness `*Turn` and drive `UnifiedEmitter.yield_turn` / `auto_send_turn`. The `agentex init` templates were migrated accordingly.
+* **harness:** removed the deprecated bespoke LangGraph tracing handler `create_langgraph_tracing_handler` (and its `AgentexLangGraphTracingHandler` class) from the public `agentex.lib.adk` surface. Span tracing is now derived from the canonical `StreamTaskMessage*` stream by `UnifiedEmitter` — wrap your run in the harness `*Turn` and drive `UnifiedEmitter.yield_turn` / `auto_send_turn`. The `agentex init` templates were migrated accordingly.
 * **harness:** each harness now exposes exactly `_<harness>_sync.py` + `_<harness>_turn.py` under `agentex.lib.adk._modules`. The OpenAI harness `OpenAITurn` and `convert_openai_to_agentex_events` moved to `agentex.lib.adk._modules._openai_turn` / `_openai_sync`; back-compat shims remain at `agentex.lib.adk.providers._modules.{openai_turn,sync_provider}` for one release. Public facade names (`stream_pydantic_ai_events`, `stream_langgraph_events`, `emit_langgraph_messages`, etc.) are unchanged.
 
 ### Features