fix: expose raw error messages and flatten tool schemas for OpenAI

[larryro]

Summary

• Add rawMessage field to SanitizedError so the chat UI displays the original provider error beneath the translated i18n hint, giving users more debugging context
• Add AI SDK middleware to flatten oneOf/anyOf tool input schemas into a single object schema, working around OpenAI's strict schema validation (OpenAI-compatible providers fail with tools - missing 'type: object' in JSON Schema vercel/ai#7924)

Closes #1253
Closes #1254

Test plan

• Verify chat error messages show both the i18n hint and the raw provider error
• Verify agent tools with z.discriminatedUnion() schemas work correctly with OpenAI models (ChatGPT 5.2, 5.2 Pro, GPT-5.2 Instant)
• Run sanitize-chat-error unit tests

Summary by CodeRabbit

• Improvements
  • Chat error messages now display additional raw error details with improved formatting, including better text wrapping and visual hierarchy for secondary content.
  • Enhanced tool schema handling in language model resolution for improved compatibility and processing.

[greptile-apps]

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[coderabbitai]

Caution

Review failed

Pull request was closed or merged during review

📝 Walkthrough

Walkthrough

The PR extends error handling across the chat feature by adding a rawMessage field to the SanitizedError type to preserve original error text. The message bubble component is updated to display both sanitized i18n translations and raw error messages with distinct styling. Corresponding tests for the sanitization utility are updated to validate the new field. Additionally, model resolution logic introduces middleware with a schema flattening helper that transforms JSON Schemas containing root-level oneOf/anyOf unions into flat object schemas by merging properties and computing intersection requirements.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Possibly related PRs

• feat(chat): render agent-generated files as download cards #811: Modifies error block and retry UI in message-bubble.tsx alongside error rendering changes.
• refactor(chat): enhance chat interface and message bubble components #21: Refactors and memoizes MessageBubble component and its message-rendering logic paths.
• feat: show error details on failed messages and fix RAG retry status #799: Updates message error rendering in message-bubble.tsx to add errorDetails and isFailed state handling.

🚥 Pre-merge checks | ✅ 2 | ❌ 3

❌ Failed checks (3 warnings)

Check name	Status	Explanation	Resolution
Linked Issues check	⚠️ Warning	The PR changes do not implement the linked issue #1187 requirements for displaying source citations inline after individual pieces of information.	Review if issue #1187 requirements are actually in scope for this PR or if a separate issue should track citation display functionality.
Out of Scope Changes check	⚠️ Warning	The PR includes changes to error message handling and tool schema flattening, which are unrelated to the source citations requirements stated in linked issue #1187.	Clarify whether issue #1187 is correctly linked or if this PR addresses a different issue that was mislabeled.
Docstring Coverage	⚠️ Warning	Docstring coverage is 50.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (2 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately describes the two main changes: exposing raw error messages in the chat UI and flattening tool schemas for OpenAI compatibility.

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✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/chat-errors-and-tool-schema-middleware

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