Python: fix(python/openai): use full-history mode by default to fix tool call streaming with OpenRouter

[Bash892]

Summary

Fixes #5105 — streaming crashes after tool execution when using OpenRouter or any provider that doesn't support previous_response_id.

Root cause: _get_conversation_id returned response.id by default (when store was not explicitly False). This caused the executor to enter server-managed continuation mode — clearing the full conversation history and sending only the tool result in the next request. Providers like OpenRouter ignore previous_response_id and received a bare function_call_output at position 0 → HTTP 400.

Fix: _get_conversation_id now returns None unless store=True is explicitly set. Server-managed conversation mode is opt-in; the default is full-history mode, which is universally compatible.

Users who want the server-managed optimization (OpenAI native only) should set store=True in their chat options.

Changes

• python/packages/openai/agent_framework_openai/_chat_client.py: changed if store is False → if store is not True in _get_conversation_id
• python/packages/openai/tests/openai/test_openai_chat_client.py: updated streaming event tests to cover both store=True and store=None; added test_parse_response_with_store_none_returns_none as a regression test

Test plan

• uv run pytest packages/openai/tests/ -m "not integration" — 270 passed, 0 failures
• Verify streaming with OpenRouter no longer raises HTTP 400 after tool execution
• Verify store=True still enables server-managed conversation mode for OpenAI native

[Bash892]

@microsoft-github-policy-service agree

[chetantoshniwal]

Automated Code Review

Reviewers: 4 | Confidence: 90%

✓ Correctness

This PR fixes a correctness issue where _get_conversation_id would return a conversation ID when store=None (the default), causing providers that don't support previous_response_id (e.g. OpenRouter) to fail. The fix changes the guard from if store is False to if store is not True, so only an explicit store=True opt-in enables server-managed conversation mode. The logic change is correct and the tests are well-structured. One note: the same _get_conversation_id method in _responses_client.py (line 448) still uses the old if store is False guard, but this may be intentional since the Responses API is OpenAI-native and always supports previous_response_id.

✓ Security Reliability

This PR fixes a reliability issue (GitHub #5105) where _get_conversation_id would return a conversation ID when store=None (the default), causing failures with OpenAI-compatible providers (e.g., OpenRouter) that don't support previous_response_id. The fix correctly changes the guard from if store is False to if store is not True, ensuring only explicit opt-in via store=True enables server-managed conversation mode. The code change is minimal and well-tested. No security issues are introduced. Note that the sibling _responses_client.py still uses the old if store is False check, but this is likely intentional since the Responses API is OpenAI-native and always supports conversation IDs.

✓ Test Coverage

The test coverage for this behavioral change is solid. The new test test_parse_response_with_store_none_returns_none directly validates the regression fix (issue #5105) by asserting that both store=None and store=False return None from _get_conversation_id. The streaming tests (test_streaming_response_created_type and test_streaming_response_in_progress_type) were properly updated to verify both store=True (returns conversation_id) and store=None (returns None) paths. One minor gap: the non-streaming _get_conversation_id path lacks a direct store=True with-conversation positive test in this diff, though this is likely covered by a pre-existing test. A store=False case for streaming is untested but is functionally identical to store=None under the new is not True guard. Overall the tests are meaningful — they assert specific return values rather than just exercising code paths.

✓ Design Approach

The change correctly inverts the semantics of _get_conversation_id from opt-out (return None only when store=False) to opt-in (return non-None only when store=True). Previously, store=None (the default when a caller omits the field) would fall through the guard and return a previous_response_id-based conversation ID, which breaks providers like OpenRouter that don't support that parameter. The fix properly treats store=None the same as store=False, making server-managed conversation mode strictly opt-in. The change is minimal, addresses the root cause rather than masking it, and the updated tests adequately cover all three store states. No blocking design issues found.

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Automated review by chetantoshniwal's agents

[chetantoshniwal]

This test covers the store=None and store=False negative cases well, but doesn't verify the positive case (store=True returning conv_456). Adding assert client._get_conversation_id(mock_response, store=True) == 'conv_456' would make this a complete tri-state test and guard against future regressions that might accidentally break the store=True path.

Suggested change

	def test_parse_response_uses_response_id_when_no_conversation() -> None:
	assert client._get_conversation_id(mock_response, store=None) is None
	assert client._get_conversation_id(mock_response, store=False) is None
	assert client._get_conversation_id(mock_response, store=True) == "conv_456"