feat(telemetry): add diagnostic properties to Gemini API error telemetry

[daniel-lxs]

Summary

When Gemini API errors occur (like INVALID_ARGUMENT with code 400), the error messages are too vague to diagnose the root cause. This PR adds diagnostic properties to the captureException() call in the Gemini handler's createMessage() method.

Problem

A PostHog error showed only:

ApiProviderError: {
  "error": {
    "code": 400,
    "message": "Request contains an invalid argument.",
    "status": "INVALID_ARGUMENT"
  }
}

This provides no information about which argument is invalid or what caused the issue.

See original PostHog issue: https://us.posthog.com/error_tracking/019bb205-1968-7581-b2c9-9b7f27537d3d

Solution

Add diagnostic properties to the telemetry capture:

Property	Purpose
messageCount	Number of input messages
geminiContentsCount	Number of converted Gemini contents
hasToolUseBlocks	Whether messages contain tool_use blocks
hasToolResultBlocks	Whether messages contain tool_result blocks
hasImageBlocks	Whether messages contain image blocks
emptyPartsCount	Count of contents with empty parts (likely cause of INVALID_ARGUMENT)
toolIdToNameSize	Size of tool ID→name mapping
hasThinkingConfig	Whether thinking configuration is enabled
usingNativeTools	Whether native tools are in use
includeThoughtSignatures	Whether thought signatures are included

Testing

• All 17 Gemini tests pass
• Full test suite passes (371 passed, 4 skipped)

Linear Issue

Resolves ROO-515

---

Important

Adds diagnostic properties to GeminiHandler.createMessage() telemetry for better error context in API errors.

• Behavior:
  • Adds diagnostic properties to captureException() in GeminiHandler.createMessage() for better error context.
  • Properties include messageCount, geminiContentsCount, hasToolUseBlocks, hasToolResultBlocks, hasImageBlocks, emptyPartsCount, toolIdToNameSize, hasThinkingConfig, usingNativeTools, includeThoughtSignatures.
• Testing:
  • Updates gemini.spec.ts to verify diagnostic properties in telemetry capture for createMessage errors.
  • All 17 Gemini tests pass; full suite: 371 passed, 4 skipped.

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[roomote]

Rooviewer   See task on Roo Cloud

Review complete. No issues identified.

The PR correctly adds diagnostic properties to the Gemini error telemetry. All variables are properly scoped, the telemetry service signature is compatible, and test coverage is adequate.

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