refactor(harness)!: consolidate the LangGraph harness + remove tracing handler

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Summary

Fourth slice of #425. Consolidates the LangGraph harness filesystem and removes the deprecated tracing handler.

Breaking

• Removed create_langgraph_tracing_handler (and its handler class). Span tracing is now derived from the canonical stream by UnifiedEmitter.

Consolidation

• _langgraph_async.py + _langgraph_messages.py + _langgraph_tracing.py collapsed into _langgraph_sync.py (emit_langgraph_messages, convert_langgraph_to_agentex_events) and _langgraph_turn.py (stream_langgraph_events).
• adk/__init__.py re-wired (langgraph imports only; pydantic untouched here).
• Comment-only refresh in core/harness/auto_send.py / tracer.py; harness.md + CHANGELOG.

Public facade names are unchanged apart from the removed handler. All in-repo consumers (tutorials, templates) were migrated in #428/#429.

Test plan

• pytest langgraph sync/async/temporal + conformance — 45 passed
• import agentex.lib.adk clean; handler gone from __all__

Notes

Stacked on #429. Retarget to next after the chain merges.

🤖 Generated with Claude Code

Greptile Summary

Collapses five LangGraph harness files (_langgraph_async.py, _langgraph_messages.py, _langgraph_tracing.py, plus the pre-existing _langgraph_sync.py and _langgraph_turn.py) into two canonical modules, and removes the deprecated create_langgraph_tracing_handler as a hard breaking change. All public facade names (stream_langgraph_events, emit_langgraph_messages, convert_langgraph_to_agentex_events, LangGraphTurn) are preserved.

• stream_langgraph_events moves from _langgraph_async.py → _langgraph_turn.py; emit_langgraph_messages moves from _langgraph_messages.py → _langgraph_sync.py; both implementations are byte-for-byte identical to the deleted originals.
• AgentexLangGraphTracingHandler / create_langgraph_tracing_handler are deleted entirely; span tracing is now derived from the canonical stream by UnifiedEmitter.
• Test deduplication: three copies of the in-memory _FakeTracing test double are consolidated into a new tests/lib/core/harness/_fakes.py; test_langgraph_sync_unified.py is absorbed into test_langgraph_sync.py.

Confidence Score: 5/5

Safe to merge — all moved functions are byte-for-byte identical to their deleted originals, the public facade is unchanged, and the full test suite (45 tests) passes.

This is a pure filesystem consolidation: no logic was altered, only file locations changed. Each moved symbol (stream_langgraph_events, emit_langgraph_messages) is identical to what it replaces. The only net-new code is the _fakes.py test helper consolidation and the addition of stream_langgraph_events to _langgraph_turn.py. The single comment to fix is a misleading docstring in a test file.

No files require special attention.

Important Files Changed

Filename	Overview
src/agentex/lib/adk/init.py	Re-wires LangGraph imports: stream_langgraph_events now sourced from _langgraph_turn, emit_langgraph_messages from _langgraph_sync; create_langgraph_tracing_handler removed from public surface and __all__.
src/agentex/lib/adk/_modules/_langgraph_turn.py	Absorbs stream_langgraph_events from the deleted _langgraph_async.py; implementation is identical — LangGraphTurn + UnifiedEmitter.auto_send_turn with workflow_now_if_in_workflow(). Module-level doc comment cleaned up (ticket refs removed).
src/agentex/lib/adk/_modules/_langgraph_sync.py	Absorbs emit_langgraph_messages verbatim from the deleted _langgraph_messages.py; logic is unchanged. Module now owns both the streaming converter and the non-streaming message emitter.
src/agentex/lib/adk/_modules/_langgraph_async.py	Deleted — stream_langgraph_events moved to _langgraph_turn.py.
src/agentex/lib/adk/_modules/_langgraph_messages.py	Deleted — emit_langgraph_messages moved to _langgraph_sync.py.
src/agentex/lib/adk/_modules/_langgraph_tracing.py	Deleted — AgentexLangGraphTracingHandler and create_langgraph_tracing_handler removed as a documented breaking change; no replacement needed since UnifiedEmitter derives spans from the canonical stream.
tests/lib/adk/test_langgraph_sync.py	Merges test_langgraph_sync_unified.py (passthrough + span derivation tests) into this file; replaces the deleted TestLangGraphTracingHandlerBackwardCompat. Module-level autouse=True _real_langchain_core fixture correctly covers the new test classes.
tests/lib/adk/test_langgraph_sync_unified.py	Deleted — content absorbed into test_langgraph_sync.py.
tests/lib/core/harness/_fakes.py	New shared module extracting FakeTracing/FakeSpan from three duplicated test-local implementations; exposes convenience properties started_names, started_pairs, ended_outputs to keep shape-2/shape-3 assertions clean.
tests/lib/core/harness/test_harness_langgraph_async.py	Removes local _FakeTracing/_FakeSpan; imports FakeTracing from _fakes. Doc updated to reflect that Full tool events now produce spans (previously asserted they didn't).
tests/lib/core/harness/test_harness_langgraph_sync.py	Same _FakeTracing dedup as the async harness test; logic unchanged.
tests/lib/core/harness/test_harness_langgraph_temporal.py	Import of stream_langgraph_events updated to its new home in _langgraph_turn; one docstring phrase about "Redis-streaming code" is misleading but harmless.
tests/lib/adk/test_langgraph_async.py	Single-line import path update: stream_langgraph_events now from _langgraph_turn instead of the deleted _langgraph_async.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    subgraph before["Before (5 files)"]
        A1[_langgraph_async.py\nstream_langgraph_events]
        A2[_langgraph_messages.py\nemit_langgraph_messages]
        A3[_langgraph_tracing.py\ncreate_langgraph_tracing_handler\nAgentexLangGraphTracingHandler]
        A4[_langgraph_sync.py\nconvert_langgraph_to_agentex_events]
        A5[_langgraph_turn.py\nLangGraphTurn]
    end

    subgraph after["After (2 files)"]
        B1[_langgraph_turn.py\nLangGraphTurn\nstream_langgraph_events]
        B2[_langgraph_sync.py\nconvert_langgraph_to_agentex_events\nemit_langgraph_messages]
        B3[REMOVED\ncreate_langgraph_tracing_handler]
    end

    A1 -->|moved to| B1
    A5 -->|stays in| B1
    A2 -->|moved to| B2
    A4 -->|stays in| B2
    A3 -->|deleted| B3

    B1 & B2 --> C[adk/__init__.py\npublic surface unchanged]

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flowchart TD
    subgraph before["Before (5 files)"]
        A1[_langgraph_async.py\nstream_langgraph_events]
        A2[_langgraph_messages.py\nemit_langgraph_messages]
        A3[_langgraph_tracing.py\ncreate_langgraph_tracing_handler\nAgentexLangGraphTracingHandler]
        A4[_langgraph_sync.py\nconvert_langgraph_to_agentex_events]
        A5[_langgraph_turn.py\nLangGraphTurn]
    end

    subgraph after["After (2 files)"]
        B1[_langgraph_turn.py\nLangGraphTurn\nstream_langgraph_events]
        B2[_langgraph_sync.py\nconvert_langgraph_to_agentex_events\nemit_langgraph_messages]
        B3[REMOVED\ncreate_langgraph_tracing_handler]
    end

    A1 -->|moved to| B1
    A5 -->|stays in| B1
    A2 -->|moved to| B2
    A4 -->|stays in| B2
    A3 -->|deleted| B3

    B1 & B2 --> C[adk/__init__.py\npublic surface unchanged]

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