fix(desktop): upgrade xterm.js to 6.1.0-beta to fix renderer crashes

[Kitenite]

Summary

• Upgrade @xterm/xterm and @xterm/headless from 6.0.0 to 6.1.0-beta.145
• Upgrade all @xterm/addon-* packages to matching beta versions
• Fixes multiple known crash bugs in the WebGL renderer that shipped with 6.0.0

Why beta?

xterm.js 6.0.0 has several confirmed crash-level bugs with no stable patch release (no 6.0.1 exists). All fixes are only available in the 6.1.0-beta series. VS Code ships these betas internally.

Bugs fixed by this upgrade

Issue	Severity	Description
#5585	Crash	Stack overflow in WebGL glyph rasterizer
#5586	Crash	dimensions undefined on mouse events during terminal kill
#5622	Crash	substring undefined in glyph rasterizer
#5606	Visual	WebGL wrong dimensions at 125% DPI scaling (Windows)
#5620	UX	Scrollbar jumping with AI CLI tools (Claude Code, etc.)
#5548	Perf	DOM renderer layout thrashing
#5570	Crash	OOM with CommitMono font + ligatures

Package versions

Package	Old	New
@xterm/xterm	^6.0.0	6.1.0-beta.145
@xterm/headless	^6.0.0	6.1.0-beta.145
@xterm/addon-clipboard	^0.2.0	0.3.0-beta.145
@xterm/addon-fit	^0.11.0	0.12.0-beta.145
@xterm/addon-image	^0.9.0	0.10.0-beta.145
@xterm/addon-ligatures	^0.10.0	0.11.0-beta.145
@xterm/addon-search	^0.16.0	0.17.0-beta.145
@xterm/addon-serialize	^0.14.0	0.15.0-beta.145
@xterm/addon-unicode11	^0.9.0	0.10.0-beta.145
@xterm/addon-webgl	^0.19.0	0.20.0-beta.144

Note: @xterm/headless Vite alias workaround in electron.vite.config.ts is still needed — the packaging bug persists in the beta.

Test plan

• Verify terminal renders correctly on startup
• Test WebGL renderer works (check console for renderer type)
• Test DOM fallback works (localStorage.setItem('terminal-renderer', 'dom'))
• Verify scrolling behavior (especially with AI CLI tools)
• Test copy/paste functionality
• Test at non-100% DPI scaling if possible
• Verify Option+Left/Right word navigation still works on macOS

Summary by CodeRabbit

• Chores
  • Pinned terminal core and addon packages to specific prerelease (beta) versions for consistent installs.
• Bug Fixes
  • Added an environment polyfill and a preload step to improve terminal compatibility and stability in non-browser runtimes.
  • Adjusted daemon startup behavior to ensure more reliable process startup and I/O handling during tests.

[coderabbitai]

📝 Walkthrough

Walkthrough

Pins multiple @xterm packages to exact beta prerelease versions and introduces a Bun preload polyfill plus test startup changes so @xterm/headless is safe to load in Bun by preloading xterm-env-polyfill.ts before the daemon.

Changes

Cohort / File(s)	Summary
Xterm dependency pins apps/desktop/package.json	Replaced caret ranges with exact beta prerelease versions for @xterm packages (addons, headless, xterm). No script changes.
Bun polyfill file apps/desktop/src/main/terminal-host/xterm-env-polyfill.ts	New polyfill that assigns globalThis.window = globalThis when window is absent to satisfy @xterm/headless runtime checks in Bun/Node environments.
Daemon startup & tests apps/desktop/src/main/terminal-host/daemon.test.ts, apps/desktop/src/main/terminal-host/session-lifecycle.test.ts	Tests add XTERM_POLYFILL_PATH and spawn Bun with --preload the polyfill before the daemon; stdio and detached options moved into the spawn configuration.
Bun test config apps/desktop/bunfig.toml	Updated test preload configuration to include xterm-env-polyfill.ts before test-setup.ts with explanatory comments.

Sequence Diagram(s)

sequenceDiagram
  participant Test as Test Process
  participant Bun as Bun (runner)
  participant Polyfill as xterm-env-polyfill
  participant Daemon as Terminal Daemon
  participant Xterm as `@xterm/headless`

  Test->>Bun: spawn("bun", ["run", "--preload", "xterm-env-polyfill.ts", "daemon"], {stdio, detached})
  Bun->>Polyfill: preload & execute
  Polyfill-->>Bun: set globalThis.window if absent
  Bun->>Daemon: start daemon process
  Daemon->>Xterm: import/require `@xterm/headless`
  Xterm-->>Daemon: initialize (safe due to polyfill)
  Daemon-->>Test: ready / emits expected signals

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Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Possibly related PRs

• chore(desktop): upgrade xterm.js to v6.0.0 #1125: Also addresses runtime entry for @xterm/headless by altering how the headless entry is resolved/loaded.
• feat(desktop): use headless xterm for terminal scrollback storage #686: Integrates @xterm/headless into the desktop app — closely related to the polyfill and test adjustments here.
• add xterm addons #124: Adds/updates xterm addon dependencies similar to the package.json pins in this PR.

Poem

🐰 I hopped in with a tiny patch,
Preloaded a blanket for a terminal match.
Betas snug, no headless fright,
Window found in Bun tonight.
Thump-thump — tests pass bright.

🚥 Pre-merge checks | ✅ 3

✅ Passed checks (3 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately summarizes the main change: upgrading xterm.js to fix renderer crashes, which is the primary objective of the PR.
Description check	✅ Passed	The PR description includes a comprehensive summary, detailed rationale, linked issues table, package version changes, test plan, and additional notes about the workaround. While not strictly following the template format, it provides all essential information and exceeds typical requirements.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.

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✨ Finishing touches

• 📝 Generate docstrings

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch kitenite/investigate-release-66-renderer-issues-possible-xt

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[github-actions]

🧹 Preview Cleanup Complete

The following preview resources have been cleaned up:

• ✅ Neon database branch
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