Good fix for a real breakage with Gemini 3.0 Pro thinking mode. The thought_signature round-trip is necessary per Google's docs — without it, the API returns 400 on subsequent tool call requests.

Suggestions (non-blocking):

1. Duplicate types: ExtraContent / GoogleExtraContent are defined identically in both pkg/providers/types.go and pkg/tools/types.go. Consider defining once and importing to avoid drift.

2. Future-proofing: Consider using json.RawMessage for extra_content to generically round-trip any provider's extra fields without needing struct changes per vendor.

3. Tests: This is a critical code path — a unit test parsing a sample Gemini response with thought_signature and verifying round-trip would prevent regressions.

LGTM — approving as the fix is correct and urgent.

Good fix for Gemini 3.0 Pro thought_signature requirement. The approach of passing ExtraContent through the ToolCall chain is correct.

A few observations:

1. Duplicated types: ExtraContent and GoogleExtraContent are defined in both pkg/providers/types.go and pkg/tools/types.go. This is a maintenance risk -- if Google adds more fields, you need to update both. Consider having one package import from the other, or defining a shared types package.

2. Hardcoded to Google: The ExtraContent struct only has a Google field. If other providers adopt similar patterns, you would need to keep adding top-level fields. An alternative approach would be map[string]interface{} for ExtraContent to make it provider-agnostic, though the struct approach is safer for type-checking.

3. No tests: This PR lacks unit tests for the thought_signature roundtrip. A test that verifies parseResponse correctly extracts thought_signature from a Gemini response and that it survives through to assistantMsg.ToolCalls would increase confidence.

4. Forward compatibility: If Google adds new required fields, the current approach requires a code change each time. Worth considering a more flexible ExtraContent representation for future iterations.

Overall, this addresses a real issue blocking Gemini 3.0 Pro users. The approach is reasonable.