Skip empty Gemini thought parts instead of emitting empty reasoning

[PratikDhanave]

Problem

In buildResponsePart (provider/geminiprovider/agent.go), a response part with Thought=true is appended as TextReasoningContent unconditionally, while the sibling text branch guards on part.Text != "":

if part.Thought {
    // ... always appends TextReasoningContent
} else if part.Text != "" {
    // only appends TextContent when non-empty
}

So a thought part carrying neither thinking text nor a ThoughtSignature produces an empty, information-free TextReasoningContent{Text:"", ProtectedData:""} in the response message.

Fix

Guard the thought branch on part.Text != "" || len(part.ThoughtSignature) > 0, mirroring the text guard. A signature-only thought (empty text, non-empty signature) is still emitted so the signature round-trips via ProtectedData in multi-turn requests — only the fully-empty thought part is skipped.

Test

TestResponseWithEmptyThoughtPartOmitted (black-box, in agent_test.go) returns a candidate with an empty {"thought": true} part alongside a normal text part, and asserts no TextReasoningContent is produced. Fails on main (empty reasoning content emitted), passes with the fix. The existing thinking-content and thought-signature tests are unchanged.

[Copilot]

Pull request overview

This PR updates the Gemini provider’s response-part translation so that “thought” parts that carry no useful information (no thinking text and no thought signature) are omitted rather than being converted into an empty TextReasoningContent, aligning behavior with the existing “skip empty text parts” logic.

Changes:

• Skip emitting TextReasoningContent for thought=true parts when both Text and ThoughtSignature are empty.
• Add a black-box test covering an empty thought-only part in the response.
• Minor formatting change to a test call site for RunText(...).

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
provider/geminiprovider/agent.go	Adds a guard to avoid appending empty reasoning content for fully-empty thought parts while still preserving signature-only thoughts.
provider/geminiprovider/agent_test.go	Adds a regression test for omitting empty thought parts and includes a minor formatting adjustment in an existing test.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[PratikDhanave]

Done — the test now also asserts the non-thought text part ("The answer is 42.") is emitted, so it fails if the provider drops all response parts, not just the reasoning content.