docs(harness): changelog for the harness-cleanup breaking changes; fix stale tutorial refs

Documents the deprecated-tracing-handler removal and the _modules consolidation /
openai relocation (with back-compat shim window) under CHANGELOG Unreleased, and
updates the sync_provider deprecation note to the renamed openai tutorial slots.

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

Author: declan-scale

CHANGELOG.md

@@ -2,6 +2,11 @@
 
 ## Unreleased
 
+### ⚠ 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:** 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
 
 * **tracing:** emit OTel metrics for async span queue depth, batch drain, and SGP export success/failure (HTTP status labels). Disable SDK-side recording with ``AGENTEX_TRACING_METRICS=0``.

src/agentex/lib/adk/providers/_modules/sync_provider.py

@@ -71,8 +71,8 @@ class SyncStreamingModel(Model):
         wrap a ``Runner.run_streamed`` result in
         ``agentex.lib.adk._modules._openai_turn.OpenAITurn`` and drive
         delivery + tracing through ``UnifiedEmitter`` (see the
-        ``060_harness_openai`` / ``130_harness_openai`` / ``140_harness_openai``
-        tutorials). This per-model tracing wrapper predates the harness and is
+        ``050_openai_agents`` / ``120_openai_agents`` tutorials). This
+        per-model tracing wrapper predates the harness and is
         retained only for backwards compatibility; it will be removed in a
         future release. No runtime warning is emitted.
     """