fix(vscode): keep background subagent cards collapsed and cap reasoning

[marius-kilocode]

What Problem This Solves

Background subagent task cards opened while the task was starting and briefly showed Starting..., then collapsed once the task finished. That open-then-close cycle flickered the transcript. Reasoning blocks inside a background agent transcript also re-expanded and collapsed while the agent streamed.

Why This Change Was Made

• TaskToolExpanded derived auto-open from taskRunning(status), which is true during pending while the tool arguments, including background, are still streaming. The card therefore opened before it could know the task was asynchronous, and BasicTool seeds its open state only once.
• The card's open state is now controlled and settles after the input arrives. It auto-opens only when the status is running and the task is not a background task. Background cards stay collapsed and never render the Starting... item. A stored preference, a search forceOpen, or a manual toggle still wins over the automatic state.
• Foreground agents still need the display-driven collapse, so reasoningCapped renders reasoning in a background agent transcript as the existing 120px capped preview that starts open and never auto-expands.

User Impact

• Background task cards stay as a single collapsed header (description plus status) and no longer flicker; they can be expanded manually once the task is done.
• Background agent reasoning shows a compact preview instead of animating open and closed. Click to collapse it to the header, or expand the full body.
• Foreground task cards, their Starting... status, and reasoning behavior are unchanged.

Evidence

• bun run typecheck (host and webview): 0 errors.
• bun run lint: 0 errors.
• bun run bundle: 0 errors.
• bun test in packages/kilo-vscode: 5529 pass, 0 fail, including new backgroundChildren unit tests.
• VS Code self-test of the live background-task flow was not run because it requires a paid model request.

[kilo-code-bot]

Code Review Summary

Status: No Issues Found | Recommendation: Merge

Files Reviewed (1 files)

• packages/kilo-vscode/src/SubAgentViewerProvider.ts

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Incremental review of 4902593e (fix: refresh subagent viewer reasoning cap on panel reuse). The previously reported suggestion (reused panels ignored the new background argument) is resolved: openPanel now tracks the flag in a backgrounds map and re-posts viewSubAgentSession when it changes, which the webview handles by updating subAgentCapped. The new map is cleaned up on panel dispose and provider dispose, so it does not retain entries.

Previous Review Summary (commit 3c040da)

Current summary above is authoritative. Previous snapshots are kept for context only.

Previous review (commit 3c040da)

Status: 1 Issue Found | Recommendation: Address before merge

Overview

Severity	Count
CRITICAL	0
WARNING	0
SUGGESTION	1

Issue Details (click to expand)

SUGGESTION

File	Line	Issue
packages/kilo-vscode/src/SubAgentViewerProvider.ts	24	Reused panels ignore the new background argument, so subAgentCapped can stay stale when the same subagent is opened again with a different background state.

Files Reviewed (18 files)

• .changeset/background-subagent-reasoning-preview.md - ok
• packages/kilo-ui/src/components/message-part.tsx - ok
• packages/kilo-vscode/src/KiloProvider.ts - ok
• packages/kilo-vscode/src/SubAgentViewerProvider.ts - 1 suggestion
• packages/kilo-vscode/src/extension.ts - ok
• packages/kilo-vscode/tests/unit/background-agents.test.ts - ok
• packages/kilo-vscode/webview-ui/agent-manager/SubagentPanel.tsx - ok
• packages/kilo-vscode/webview-ui/src/App.tsx - ok
• packages/kilo-vscode/webview-ui/src/components/chat/AssistantMessage.tsx - ok
• packages/kilo-vscode/webview-ui/src/components/chat/BackgroundAgents.tsx - ok
• packages/kilo-vscode/webview-ui/src/components/chat/ChatView.tsx - ok
• packages/kilo-vscode/webview-ui/src/components/chat/MessageList.tsx - ok
• packages/kilo-vscode/webview-ui/src/components/chat/TaskToolExpanded.tsx - ok
• packages/kilo-vscode/webview-ui/src/components/chat/TranscriptRow.tsx - ok
• packages/kilo-vscode/webview-ui/src/components/chat/background-agents.ts - ok
• packages/kilo-vscode/webview-ui/src/components/chat/open-subagent.ts - ok
• packages/kilo-vscode/webview-ui/src/types/messages/extension-messages.ts - ok
• packages/kilo-vscode/webview-ui/src/types/messages/webview-messages.ts - ok

Fix these issues in Kilo Cloud

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_{Reviewed by deepseek-v4.1-flash · Input: 0 · Output: 0 · Cached: 0}

_{Review guidance: REVIEW.md from base branch main}