[codex] Stream native providers for first-token deadlines

[MuncleUscles]

Summary

• Add native streaming backends for Anthropic Messages, Google Gemini streamGenerateContent, and Bedrock ConverseStream.
• Use native streaming internally for non-streaming provider calls whenever first_token_timeout_ms is present, so native providers can satisfy the same first-output deadline contract as OpenAI-compatible routes.
• Wire native stream adapters through the provider registry and serve.py instead of returning streaming unsupported for native api kinds.
• Add focused tests for native stream aggregation, non-stream calls switching to stream under first-token timeout, provider registry wiring, and pre-output timeout behavior.

Notes

This is stacked on #62 (codex/first-token-wall-clock). #62 defines the wall-clock first-token contract; this PR extends that contract to native Anthropic, Gemini, and Bedrock paths.

For native streams, the timeout stops once the provider produces text or tool-call output. Text deltas are emitted immediately; tool-only starts are aggregated and returned for pseudo-streaming/final response handling if no text delta was emitted.

Validation

• .venv/bin/python -m pytest tests/test_native_providers.py tests/test_providers.py tests/test_streaming.py tests/test_codex.py tests/test_antseed_concurrency.py::test_first_token_timeout_uses_internal_streaming_for_json_calls -q (54 passed; pytest cache warning only because checkout is outside writable sandbox root)
• .venv/bin/python -m pytest tests/test_live_wiring.py -q (11 passed)
• .venv/bin/python -m pytest tests/test_native_providers.py tests/test_providers.py -q (19 passed; after cleanup)
• git diff --check
• PYTHONPYCACHEPREFIX=/private/tmp/unhardcoded-pycache .venv/bin/python -m py_compile provider_adapters/common.py provider_adapters/anthropic.py provider_adapters/google.py provider_adapters/bedrock.py providers.py serve.py tests/test_native_providers.py tests/test_providers.py

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Review details

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: b36294c1-13c8-45aa-ac50-bd3bd381c82a

📥 Commits

Reviewing files that changed from the base of the PR and between 0d06b88 and 4e32cb2.

📒 Files selected for processing (8)

• provider_adapters/anthropic.py
• provider_adapters/bedrock.py
• provider_adapters/common.py
• provider_adapters/google.py
• providers.py
• serve.py
• tests/test_native_providers.py
• tests/test_providers.py

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch codex/native-provider-streaming

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