[Bug]: Settled turn folding swallows substantive response when followed by background task or follow-up message (antigravity) #10991

Before submitting

• I searched existing issues and did not find a duplicate.
• I included enough detail to reproduce or investigate the problem.

Area

apps/desktop

Steps to reproduce

1. In T3 Code desktop using an agent provider (such as Antigravity / Gemini 3.8 Flash), ask a query that performs multiple tool calls and launches a background task or receives a subsequent event.
2. The agent finishes analyzing and writes a complete, substantive multi-paragraph response to the user.
3. Later in the turn (or via background task completion / reactive system message notification), a subsequent tool event occurs (e.g. background task timeout/completion notification) prompting a brief concluding follow-up message from the agent (e.g. "Everything is verified and ready...").
4. Let the turn settle and observe the rendered chat timeline.

Expected behavior

The substantive assistant response should remain visible in the main timeline. Folding should only collapse tool call details and intermediate progress/commentary, or should keep prior assistant answers visible so the user doesn't miss the actual response.

Actual behavior

The entire primary answer is swallowed and folded away inside the "Worked for 11m 33s" accordion. Only the trailing 1-line assistant message ("Everything is verified and ready...") is rendered in the chat view.
The user is left with no visible answer to their prompt and has to manually expand the "Worked for 11m 33s" toggle to discover that the agent actually answered the question.

Impact

Major degradation or frequent failure

Users reasonably assume the agent failed, hallucinated, or gave an empty 1-line non-answer, unless they discover the answer hidden inside the collapsed "Worked for" accordion.

Version or commit

T3 Code (Nightly) v0.0.41-nightly.20260909.1461

Environment

• macOS 26.5.1 (Build 25F80, darwin-arm64)
• T3 Code (Nightly) 0.0.41-nightly.20260909.1461
• Electron 41.5.0
• Provider: Antigravity harness (antigravity-acp), model Gemini 3.8 Flash (High)

Screenshots, recordings, or supporting files

(Screenshots to be attached manually)

1. Collapsed state (what the user initially sees): Only the trailing single sentence is shown below Worked for 11m 33s.
2. Expanded state (top): Expanding Worked for 11m 33s reveals the entire substantive answer that was hidden.
3. Expanded state (bottom): Shows the transition where the earlier answer ends, followed by a tool notification / final turn boundary.

Workaround

Manually expand the "Worked for Xm Xs" collapsible accordion to read the hidden response.

Related issues

• [Bug]: Settled turns hide substantive response under Worked for ... #7518 / [Bug]: The "Worked for …" fold eats every assistant message except the last one #7529 (Settled turns hide substantive response under Worked for ...)
• Turn folding hides the substantive answer when a provider ends a turn with a short progress note (Grok) #8879 (Turn folding hides substantive answer when provider ends turn with short note)
• [Bug]: A response that pauses and resumes is folded as several separate responses #8945 (A response that pauses and resumes is folded as several separate responses)