perf(agent-manager): optimize tab switching and context transition latency

[marius-kilocode]

Problem

Switching between contexts (Local and Worktrees) or switching session tabs in Agent Manager suffered from noticeable latency and main-thread hitching:

1. ChatView unmount/remount on context changes: <ChatView> was conditionally rendered under <Show when={!contextEmpty()}>. When transitioning between an empty context (such as Local with 0 open tabs) and a populated worktree, the entire <ChatView> component tree, its providers, Virtualizer, PromptInput, and DOM were destroyed and recreated, producing over 13,000 transient DOM nodes, 7,300 layout objects, and a ~190ms main-thread freeze.
2. Style recalculation and layout thrashing from tooltips: Tooltip triggers across buttons and tabs mounted <KobalteTooltip.Portal> and <KobalteTooltip.Content> unconditionally. Kobalte's createPresence invoked getComputedStyle(element) to read animationName on every reactive tick, and each tooltip attached a dedicated MutationObserver. getAnimationName was the top CPU hotspot in traces.
3. Synchronous prompt history seeding and unconditional draft writes: PromptInput synchronously scanned all user message parts on every tab switch to seed prompt history, while saveDraft executed Map writes even when drafts were empty or unchanged.
4. Multi-frame layout delay and reactive cascading: MessageList deferred scroll restoration across two nested requestAnimationFrame cycles (introducing a 33-50ms visual delay), while session and selection actions dispatched multiple unbatched reactive signal updates.

Solution

• Persistent ChatView layer: Replaced <Show when={!contextEmpty()}> around <ChatView> with a persistent container toggled via .am-chat-wrapper-hidden (display: none;). The ChatView instance and virtualizer stay warm in memory across context switches.
• Lazy and lightweight tooltips: Render a lightweight <div> trigger when idle and closed, lazily mounting KobalteTooltip only on pointer enter / focus in or when forceOpen is set. Guarded the portal with <Show when={local.forceOpen || state.open}> to completely bypass createPresence style calculations when tooltips are closed, and made MutationObserver registration conditional.
• Deferred history seeding and guarded draft writes: Moved history.seed to an idle timeout and guarded saveDraft against unnecessary Map allocations for empty/unmodified drafts.
• Synchronous batching and single-frame scroll restoration: Wrapped tab selection and context switching operations in Solid's batch(() => ...) to coalesce reactive updates. Pre-hydrated the visible tail messages (last 15 messages) directly into store.parts on load, and reduced scroll restoration in MessageList to a single frame.

Performance Measurements

Metric / Scenario	Baseline	Optimized	Improvement
Local to Worktree Switch: Longest Main-Thread Task	191.2 ms	59.4 ms	69% reduction
Local to Worktree Switch: Total Long Tasks	315.0 ms	59.5 ms	81% reduction
Local to Worktree Switch: Total Task Duration	467.7 ms	230.0 ms	51% faster
Local to Worktree Switch: Transient DOM Nodes	+13,158 nodes	+1,158 nodes	91% reduction
Local to Worktree Switch: Layout Objects Created	+7,346 objects	+688 objects	91% reduction
Local to Worktree Switch: getAnimationName Self-Time	77.5 ms	19.8 ms	75% reduction
Local to Worktree Switch: getBoundingClientRect Self-Time	48.3 ms	18.5 ms	62% reduction
Warm Local Tab Switch: Long Tasks (>50ms)	1 task (53.5 ms)	0 tasks (0 ms)	100% eliminated
Warm Local Tab Switch: Script Execution Delta	0.13 ms	0.12 ms	Instantaneous (<0.2ms)
Warm Worktree Sidebar Switch: Style Recalc Duration	73.6 ms	39.9 ms	46% reduction
Warm Worktree Tab Switch: Script Self-Time	<0.5 ms	<0.5 ms	Instantaneous (<0.2ms)

[kilo-code-bot]

Code Review Summary

Status: No Issues Found | Recommendation: Merge

Files Reviewed (8 files)

• .changeset/optimize-agent-manager-tab-latency.md
• packages/kilo-vscode/webview-ui/agent-manager/AgentManagerApp.tsx
• packages/kilo-vscode/webview-ui/agent-manager/agent-manager.css
• packages/kilo-vscode/webview-ui/agent-manager/selection-actions.ts
• packages/kilo-vscode/webview-ui/src/components/chat/MessageList.tsx
• packages/kilo-vscode/webview-ui/src/components/chat/PromptInput.tsx
• packages/kilo-vscode/webview-ui/src/context/session.tsx
• packages/ui/src/components/tooltip.tsx

Previous Review Summaries (2 snapshots, latest commit 14dcfba)

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

Previous review (commit 14dcfba)

Status: No Issues Found | Recommendation: Merge

Files Reviewed (8 files)

• .changeset/optimize-agent-manager-tab-latency.md
• packages/kilo-vscode/webview-ui/agent-manager/AgentManagerApp.tsx
• packages/kilo-vscode/webview-ui/agent-manager/agent-manager.css
• packages/kilo-vscode/webview-ui/agent-manager/selection-actions.ts
• packages/kilo-vscode/webview-ui/src/components/chat/MessageList.tsx
• packages/kilo-vscode/webview-ui/src/components/chat/PromptInput.tsx
• packages/kilo-vscode/webview-ui/src/context/session.tsx
• packages/ui/src/components/tooltip.tsx

Previous review (commit fae399b)

Status: 2 Issues Found | Recommendation: Address before merge

Overview

Severity	Count
CRITICAL	0
WARNING	1
SUGGESTION	1

Issue Details (click to expand)

WARNING

File	Line	Issue
packages/ui/src/components/tooltip.tsx	119	Lazy-mounting on focusin swaps the Switch branch after focus has moved into a child, detaching the focused node — keyboard users lose focus on first Tab into any tooltip-wrapped control; the swap also recreates the trigger subtree each hover cycle, resetting child state

SUGGESTION

File	Line	Issue
packages/ui/src/components/tooltip.tsx	94	MutationObserver is only installed if an [aria-expanded]/[data-expanded] child exists at activation time; late-mounted expandables are never observed

The persistent ChatView wrapper, batched selection/session actions, guarded draft writes, deferred history seeding, tail pre-hydration, and single-frame scroll restore all look correct — semantics of selectLocalAction/selectWorktreeAction are preserved, the stash/store interplay in handleMessagesLoaded stays consistent (hydrateParts skips pre-hydrated ids), timers/observers are cleaned up, and no memory leaks were introduced. The findings above are limited to the tooltip lazy-mount path.

Files Reviewed (8 files)

• .changeset/optimize-agent-manager-tab-latency.md
• packages/kilo-vscode/webview-ui/agent-manager/AgentManagerApp.tsx
• packages/kilo-vscode/webview-ui/agent-manager/agent-manager.css
• packages/kilo-vscode/webview-ui/agent-manager/selection-actions.ts
• packages/kilo-vscode/webview-ui/src/components/chat/MessageList.tsx
• packages/kilo-vscode/webview-ui/src/components/chat/PromptInput.tsx
• packages/kilo-vscode/webview-ui/src/context/session.tsx
• packages/ui/src/components/tooltip.tsx - 2 issues

Fix these issues in Kilo Cloud

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

[hdcodedev]

@marius-kilocode We found out that messages don’t auto-scroll anymore. The most likely reason for this is the removal of double-rAF. Should we investigate further and see if we can fix it without using double-rAF?

https://discord.com/channels/1349288496988160052/1349288496988160055/1539696538325098656
https://discord.com/channels/1349288496988160052/1391109167275577464/1539874684693254144