fix(openai-chat): classify and fingerprint malformed tool calls

[Wibias]

Summary

• classify structurally malformed OpenAI-compatible upstream tool calls as provider/protocol failures with HTTP 502 / upstream_error instead of misleading client 400s
• keep malformed tool calls fail-closed: do not coerce object-valued names, invent dispatch targets, select arbitrary object properties, or recover semantically unknowable tool names
• surface the existing value-free compatibility reason through the normal failure message so request logs and the Logs dashboard identify the rejected shape without raw tool payloads
• add debug-only structural fingerprints for the rejected field: objects expose only allowlisted key names and their value types plus hasUnknownKeys; arrays expose only length; unknown key names and all field values remain private
• cover both streamed and buffered OpenAI-compatible responses and track the live OpenCode Free / DeepSeek V4 Flash reproduction in [Provider] OpenCode Free DeepSeek V4 Flash streams object-valued function.name #1824

Verification

• branch starts from upstream dev at b81314cd29b78fecb447df882dc4fc1a987434b9; dev was rechecked and had not advanced during implementation
• TDD RED regressions reproduced the observed streamed object-valued tool_calls[0].function.name failure and the new fingerprint expectations before the production helper was added
• the normal error contract remains value-free: upstream response contained invalid tool calls (tool_call_function_name_invalid; callIndex=0; valueType=object)
• debug-only fieldShape is not included in the adapter error/request-history message
• object fingerprint tests verify only allowlisted structural keys/types are retained and arbitrary unknown key names collapse to hasUnknownKeys: true
• array fingerprint tests verify only array length is retained, with no element values
• privacy regressions assert raw malformed values, tool arguments, tool-call ids, and attacker-controlled unknown key names do not reach diagnostics
• streaming and buffered-response paths use the same privacy boundary
• existing OpenAI-chat hardening expectations now pin the 502 / upstream_error contract and exact value-free structural reason while retaining usage, terminal-error, and [회귀] OpenAI Chat 스트림의 tool_calls id/name=null 후속 청크를 invalid tool calls로 거부 #1731 null-padding coverage
• CodeRabbit's test-union narrowing finding was fixed and its review thread resolved
• final diff is limited to src/adapters/openai-chat.ts, tests/openai-chat-hardening.test.ts, and tests/openai-chat-invalid-tool-call-diagnostics.test.ts
• on current head 65dac3fe651ea091f4ccf924b6691929002789fc: React Doctor passes; Cross-platform CI is still running

Checklist

• Scope stays focused and avoids unrelated provider routing or recovery changes.
• No end-user documentation change is needed; this corrects error classification and diagnostics and is tracked in [Provider] OpenCode Free DeepSeek V4 Flash streams object-valued function.name #1824.
• Security-sensitive logging reviewed: no prompt, reasoning, credentials, raw tool-call payload, tool arguments, call id, request id, conversation id, arbitrary object key name, or malformed field value is added to diagnostics.
• Structural fingerprinting is provider-debug-only and does not change normal request-log/dashboard payloads beyond the existing bounded compatibility reason.

Refs #1824

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📝 Walkthrough

Walkthrough

The OpenAI chat adapter now reports structured diagnostics for invalid streamed and non-streamed tool calls. These errors use 502 upstream_error metadata. Tests verify validation details, sanitized output, array fingerprinting, and null-padding behavior.

Changes

Invalid tool-call diagnostics

Layer / File(s)	Summary
Structured diagnostic error construction src/adapters/openai-chat.ts	invalidToolCallsEvent now includes the malformed shape, optional call index, and value type. It returns a 502 error classified as upstream_error.
Validation-path propagation src/adapters/openai-chat.ts	Streaming and response validation failures pass the raw payload and mode to invalidToolCallsEvent.
Diagnostic regression coverage tests/openai-chat-invalid-tool-call-diagnostics.test.ts, tests/openai-chat-hardening.test.ts	Tests verify case-specific reasons, indexes, value types, 502 status, upstream_error classification, sanitized output, object fingerprinting, array-length handling, and null padding.

Estimated code review effort: 3 (Moderate) | ~20 minutes

Merge Risk: 🔵 Low · up to 93e11

The change classifies malformed upstream tool calls as provider failures and exposes only privacy-safe structural diagnostics, reducing incorrect client-error reporting without logging raw payloads. The remaining bounded risk is a test assertion that does not narrow to an error event before reading its message; the PR is mergeable with explicit follow-up to strengthen that assertion.

Possibly related PRs

• lidge-jun/opencodex#1332: Both changes update OpenAI Chat tool-call validation and malformed-payload handling.
• lidge-jun/opencodex#1530: Both changes update OpenAI Chat tool-call diagnostics for streaming and response validation.
• lidge-jun/opencodex#1754: Both changes cover streamed tool-call validation and diagnostic reporting.

Suggested labels: review-ready

Suggested reviewers: ingwannu, lidge-jun

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely describes the main changes: classification and fingerprinting of malformed tool calls.

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Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

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Inline comments:
In `@tests/openai-chat-invalid-tool-call-diagnostics.test.ts`:
- Line 84: Update the assertions around events[0]?.message at the affected
checks to first narrow or locate an event with type “error,” asserting that the
error event exists, then inspect its message for the expected content. Apply the
same narrowing to both message assertions and preserve the existing diagnostic
expectations.

Apply the same fix in `@tests/openai-chat-invalid-tool-call-diagnostics.test.ts`
around lines 18 - 25.

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