refactor(harness): move OpenAI harness into adk/_modules + facade export

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Summary

Sixth slice of #425. Consolidates the OpenAI harness into the canonical adk/_modules layout and makes it a first-class facade export.

• Move into _modules — OpenAITurn → _modules/_openai_turn.py, the sync tap (convert_openai_to_agentex_events) → _modules/_openai_sync.py, matching every other harness.
• Back-compat shims kept at providers/_modules/{openai_turn,sync_provider}.py, so existing import paths (tutorials, sync-openai-agents template, services) keep working. The larger Temporal/MCP provider stays under adk.providers.
• Facade export (Greptile follow-up) — OpenAITurn, openai_usage_to_turn_usage, and convert_openai_to_agentex_events are now exported from agentex.lib.adk, parallel to ClaudeCodeTurn / CodexTurn. The new default-openai-agents template (next PR) imports from the package facade rather than a private module path.

Test plan

• pytest tests/lib/adk/providers/test_openai_turn.py test_openai_activities.py — 27 passed
• facade + back-compat shim imports verified
• ruff check on all changed source — clean

Notes

Stacked on #431. Retarget to next after the chain merges.

🤖 Generated with Claude Code

Greptile Summary

This PR moves the OpenAI harness implementation (OpenAITurn, convert_openai_to_agentex_events, openai_usage_to_turn_usage) from providers/_modules/ into the canonical adk/_modules/ layout, matching every other harness (LangGraph, PydanticAI, ClaudeCode, Codex), and exposes the three symbols as first-class exports from agentex.lib.adk.

• _modules/_openai_turn.py and _modules/_openai_sync.py are lifted verbatim from their old locations; the old files become thin back-compat shims that re-export unchanged.
• providers/_modules/openai_turn.py now re-exports both OpenAITurn and openai_usage_to_turn_usage (fixing the gap flagged in the previous review), while sync_provider.py re-exports convert_openai_to_agentex_events via the explicit-alias pattern.

Confidence Score: 5/5

Safe to merge — this is a pure structural lift with no logic changes; both back-compat shims are in place and the previous gap (missing openai_usage_to_turn_usage in the shim) is now resolved.

The implementation code is moved verbatim; the facade export and both shims have been verified to expose the full original surface. Tests continue to pass against the new canonical paths and the old shim paths remain importable.

No files require special attention. The two minor style issues in _openai_sync.py (unused counter, inline imports) are pre-existing carry-overs and do not affect correctness.

Important Files Changed

Filename	Overview
src/agentex/lib/adk/init.py	Adds facade imports and all entries for OpenAITurn, openai_usage_to_turn_usage, and convert_openai_to_agentex_events from the new _modules paths; consistent with ClaudeCode and Codex patterns already in the file.
src/agentex/lib/adk/_modules/_openai_sync.py	New canonical home for convert_openai_to_agentex_events and its helpers; code is a faithful lift from sync_provider.py with two minor pre-existing style issues (unused event_count counter, import json inside function branches).
src/agentex/lib/adk/_modules/_openai_turn.py	New canonical home for OpenAITurn, openai_usage_to_turn_usage, and _aggregate_usage; clean lift from the old providers/_modules/openai_turn.py with updated intra-package import path.
src/agentex/lib/adk/providers/_modules/openai_turn.py	Replaced with a back-compat shim; now correctly re-exports both OpenAITurn and openai_usage_to_turn_usage (addressing the previous review comment), using noqa: F401 to suppress unused-import warnings.
src/agentex/lib/adk/providers/_modules/sync_provider.py	Implementation of convert_openai_to_agentex_events removed; re-exported from _openai_sync via the explicit alias pattern for back-compat; SyncStreamingModel deprecation notice updated to the new canonical path.
src/agentex/lib/core/services/adk/providers/openai.py	Minor comment housekeeping only — ticket reference stripped from an inline comment; no functional change.
tests/lib/adk/providers/test_openai_turn.py	Import paths updated to point at the new canonical module (_modules._openai_turn); test coverage and logic unchanged.
tests/lib/adk/providers/test_openai_activities.py	Ticket reference removed from one docstring; no functional or coverage change.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    facade["agentex.lib.adk\n(__init__.py)\nFacade export"]

    subgraph NEW ["New canonical locations (_modules)"]
        ot["_modules/_openai_turn.py\nOpenAITurn\nopenai_usage_to_turn_usage\n_aggregate_usage"]
        os["_modules/_openai_sync.py\nconvert_openai_to_agentex_events\n_extract_tool_call_info\n_extract_tool_response_info"]
    end

    subgraph SHIMS ["Back-compat shims (providers/_modules)"]
        shimT["providers/_modules/openai_turn.py\n(re-exports OpenAITurn +\nopenai_usage_to_turn_usage)"]
        shimS["providers/_modules/sync_provider.py\n(re-exports convert_openai_to_agentex_events)"]
    end

    svc["lib/core/services/adk/providers/openai.py\n(OpenAIService)"]
    tests["tests/lib/adk/providers/\ntest_openai_turn.py\ntest_openai_activities.py"]

    facade -->|imports from| ot
    facade -->|imports from| os
    shimT -->|re-exports from| ot
    shimS -->|re-exports from| os
    ot -->|imports from| os
    svc -->|uses| ot
    tests -->|imports directly from| ot

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%%{init: {'theme': 'base', 'themeVariables': {"darkMode": true, "background": "#0d1117", "primaryColor": "#21262d", "primaryTextColor": "#e6edf3", "primaryBorderColor": "#8b949e", "lineColor": "#8b949e", "textColor": "#e6edf3", "edgeLabelBackground": "#161b22", "actorBkg": "#21262d", "actorBorder": "#8b949e", "actorTextColor": "#e6edf3", "actorLineColor": "#8b949e", "signalColor": "#8b949e", "signalTextColor": "#e6edf3", "noteBkgColor": "#373320", "noteBorderColor": "#d4a72c", "noteTextColor": "#f0e6c0", "labelBoxBkgColor": "#21262d", "labelBoxBorderColor": "#8b949e", "labelTextColor": "#e6edf3", "loopTextColor": "#e6edf3", "activationBkgColor": "#30363d", "activationBorderColor": "#8b949e"}}}%%
flowchart TD
    facade["agentex.lib.adk\n(__init__.py)\nFacade export"]

    subgraph NEW ["New canonical locations (_modules)"]
        ot["_modules/_openai_turn.py\nOpenAITurn\nopenai_usage_to_turn_usage\n_aggregate_usage"]
        os["_modules/_openai_sync.py\nconvert_openai_to_agentex_events\n_extract_tool_call_info\n_extract_tool_response_info"]
    end

    subgraph SHIMS ["Back-compat shims (providers/_modules)"]
        shimT["providers/_modules/openai_turn.py\n(re-exports OpenAITurn +\nopenai_usage_to_turn_usage)"]
        shimS["providers/_modules/sync_provider.py\n(re-exports convert_openai_to_agentex_events)"]
    end

    svc["lib/core/services/adk/providers/openai.py\n(OpenAIService)"]
    tests["tests/lib/adk/providers/\ntest_openai_turn.py\ntest_openai_activities.py"]

    facade -->|imports from| ot
    facade -->|imports from| os
    shimT -->|re-exports from| ot
    shimS -->|re-exports from| os
    ot -->|imports from| os
    svc -->|uses| ot
    tests -->|imports directly from| ot

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