fix(agent-manager): remove unsafe WebGL terminal renderer

[marius-kilocode]

What Problem This Solves

Agent Manager mounted one WebGL renderer for every terminal, including terminals hidden in inactive tabs. Chromium limits the number of live WebGL contexts in a document. The pinned xterm WebGL addon also has known context-disposal and shared glyph-atlas reliability problems. With enough concurrent terminals, or after repeated terminal creation and disposal, a visible terminal could lose its renderer or display stale and corrupted glyphs.

This is especially risky in Agent Manager because terminal instances remain mounted so they can continue receiving PTY output while users switch tabs.

Why This Change Was Made

Agent Manager terminals now use xterm’s DOM renderer instead of allocating one scarce WebGL context per mounted terminal. This removes the browser-level context exhaustion and xterm WebGL atlas risks while preserving the other performance improvements from the original change:

• PTY output is batched by animation frame instead of causing one xterm write and render schedule per WebSocket message.
• Hidden terminal slots remain mounted but are moved outside the viewport so xterm can suspend their render work.
• Terminal hosts remain mounted while History is open, preventing unnecessary xterm and WebSocket teardown and recreation.
• Local connection and exit status messages use the same output batch as PTY data, preserving output order.

The scope was intentionally reduced after review. No shared PTY, server, CLI, transport-protocol, or bun-pty changes are included. No new kilocode_change markers are required.

User Impact

Users can run many Agent Manager terminals concurrently without consuming one WebGL context per terminal. Switching between terminals continues to preserve each terminal’s output and buffer. Opening and closing History does not recreate the existing terminal instances. The tradeoff is that terminal rendering uses the DOM path rather than WebGL; this favors predictable behavior and correctness over the unsafe GPU optimization.

Review Follow-up

Automated review identified three issues. The hidden History stack originally covered the tab bar and could change the terminal height; its bounds now start below the 36px tab bar. Replay overflow could leave buffered keystrokes available to a later reconnect; failed replay now clears the input buffer and closes the connection. The changeset now describes the user-facing WebGL stability fix rather than only the batching change.

There are no unresolved review threads. The bot summary is a non-thread issue comment, so GitHub does not expose a resolve action for it. No reply was posted.

Evidence

Local validation passed for the extension typecheck, lint, Knip, compile, focused terminal tests, conflict-marker check, and formatting checks. GitHub CI passed, including TypeScript analysis, unit tests, source-link validation, visual regression tests, and Kilo Code Review.

The isolated VS Code stress test created 20 simultaneously mounted terminals, streamed 10,000 verified output lines through each terminal, and cycled through the terminal tabs. All 200,000 lines were received without xterm discard errors or terminal-specific console errors. The same test opened and closed History while the terminals were alive and confirmed that the terminal DOM instances were preserved. The final renderer inventory showed 20 DOM renderers and zero WebGL canvases.

The implementation is limited to Agent Manager and dependency metadata. It does not change PTY transport behavior for other clients.

[kilo-code-bot]

Code Review Summary

Status: 1 Issue Found | Recommendation: Address before merge

Overview

Severity	Count
CRITICAL	0
WARNING	1
SUGGESTION	0

Issue Details (click to expand)

WARNING

File	Line	Issue
packages/kilo-vscode/webview-ui/agent-manager/terminal/TerminalTab.tsx	337	WebSocket.close(1009) throws in Chromium, so overflow never disconnects

Files Reviewed (6 files)

• .changeset/agent-manager-terminal-render-performance.md
• packages/kilo-vscode/tests/unit/agent-manager-terminal-layout.test.ts
• packages/kilo-vscode/tests/unit/agent-manager-terminal-replay.test.ts
• packages/kilo-vscode/webview-ui/agent-manager/agent-manager.css
• packages/kilo-vscode/webview-ui/agent-manager/terminal/TerminalTab.tsx - 1 issue
• packages/kilo-vscode/webview-ui/agent-manager/terminal/replay.ts

Fix these issues in Kilo Cloud

Previous Review Summary (commit db40b6d)

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

Previous review (commit db40b6d)

Status: 3 Issues Found | Recommendation: Address before merge

Overview

Severity	Count
CRITICAL	0
WARNING	1
SUGGESTION	2

Issue Details (click to expand)

WARNING

File	Line	Issue
packages/kilo-vscode/webview-ui/agent-manager/agent-manager.css	4914	Hidden History stack uses inset: 0 on .am-detail, so opening History makes the still-active terminal ~2 rows taller and ResizeObserver resizes the PTY

SUGGESTION

File	Line	Issue
packages/kilo-vscode/webview-ui/agent-manager/terminal/replay.ts	186	8 MiB fail-open drops queued replay and skips flush(), so buffered keystrokes can land on a later reconnect
.changeset/agent-manager-terminal-render-performance.md	5	Changeset describes rAF batching instead of the user-visible WebGL stability fix

Files Reviewed (13 files)

• .changeset/agent-manager-terminal-render-performance.md - 1 issue
• bun.lock
• packages/kilo-vscode/package.json
• packages/kilo-vscode/tests/unit/agent-manager-ambient-setup.test.ts
• packages/kilo-vscode/tests/unit/agent-manager-terminal-layout.test.ts
• packages/kilo-vscode/tests/unit/agent-manager-terminal-replay.test.ts
• packages/kilo-vscode/webview-ui/agent-manager/AgentManagerApp.tsx
• packages/kilo-vscode/webview-ui/agent-manager/agent-manager.css - 1 issue
• packages/kilo-vscode/webview-ui/agent-manager/terminal/TerminalTab.tsx
• packages/kilo-vscode/webview-ui/agent-manager/terminal/ambient.ts
• packages/kilo-vscode/webview-ui/agent-manager/terminal/index.ts
• packages/kilo-vscode/webview-ui/agent-manager/terminal/render.tsx
• packages/kilo-vscode/webview-ui/agent-manager/terminal/replay.ts - 1 issue

Fix these issues in Kilo Cloud

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_{Reviewed by grok-4.6 · Input: 170K · Output: 17.4K · Cached: 710.1K}

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