feat(terminal): upgrade xterm.js to 6.1.0 with synchronized output support

[sgeraldes]

Summary

Upgrades xterm.js from 5.5.0 to 6.1.0-beta.106, enabling Synchronized Output (DEC mode 2026) support. This eliminates visual tearing and flickering in TUI applications.

Key Changes

• Synchronized Output: TUI apps (npm progress bars, htop, spinners) now render in-place without scrolling artifacts
• FitAddon Refactor: Uses public terminal.dimensions API instead of private internals
• VS Code Scrollbar: New scrollbar implementation with updated CSS
• PowerShell Fix (Windows): Build system and shell launches use pwsh -NoProfile to prevent profile interference

Commits

1. refactor(fitaddon): Update to xterm.js 6.1.0 public API
2. chore(deps): Upgrade xterm.js to 6.1.0-beta.106
3. style(terminal): Update CSS for xterm.js 6.1.0 scrollbar
4. fix(terminal): Address code review findings
5. fix(windows): Use pwsh with -NoProfile for build and shell

New Features from xterm.js 6.x

• Synchronized Output (DEC mode 2026)
• Shadow DOM support in WebGL
• Detailed ligatures and variants
• OSC 52 clipboard support
• Search performance improvements
• Overview ruler borders

Breaking Changes Handled

Change	Resolution
Canvas renderer removed	Already using WebGL
Overview ruler restructured	Updated config path
New scrollbar implementation	Added CSS for .xterm-scrollable-element

Test plan

• Terminal renders correctly on startup
• npm install progress bars animate in-place
• htop or btop renders without tearing
• Scrollbar appears on hover with correct styling
• Copy/paste, search, resize all functional
• Windows: Build completes without PowerShell profile output

🤖 Generated with Claude Code

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Walkthrough

This PR upgrades xterm.js and related addons to 6.1.0-beta and updates package.json accordingly. FitAddon was migrated to the public xterm 6.1 API, adding a public noScrollbar field and removing private core access. New scrollbar styling was added in SCSS/CSS. Build automation Taskfile entries and Windows-targeted commands were standardized to PowerShell Core using pwsh -NoProfile -Command. Go shell-launching code (pkg/shellexec/shellexec.go) now inserts -NoProfile before -ExecutionPolicy. BUILD.md Windows prerequisites were expanded to include PowerShell 7+ instructions. No other public/exported APIs were changed.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~25 minutes

🚥 Pre-merge checks | ✅ 2 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (2 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately describes the main feature—upgrading xterm.js to 6.1.0 with synchronized output support—which aligns with the primary objective of the changeset.
Description check	✅ Passed	The description provides comprehensive context about the xterm.js upgrade, synchronized output feature, refactored FitAddon, scrollbar changes, and PowerShell fixes, all directly related to the changeset.

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Actionable comments posted: 1

🤖 Fix all issues with AI agents

In `@Taskfile.yml`:
- Around line 11-12: The Taskfile.yml change replaced PowerShell usage with pwsh
in the RMRF and DATE variables (symbols RMRF and DATE), which will break Windows
hosts without PowerShell Core; update Taskfile.yml to either (a) use a fallback
that tries pwsh and falls back to powershell (e.g. conditional/ternary around
pwsh vs powershell for the RMRF and DATE commands) or (b) revert to using
powershell -NoProfile if no pwsh-specific features are required, and if you
intentionally require pwsh add a note to BUILD.md declaring PowerShell Core as a
prerequisite; apply this change to the RMRF and DATE definitions and any other
places where pwsh was introduced.

🧹 Nitpick comments (4)

frontend/app/view/term/xterm.css (3)

195-202: Inconsistent indentation: tabs used instead of spaces.

Lines 196-197 and 201 use tab characters for indentation while the rest of the file uses spaces. Consider normalizing to spaces for consistency.

♻️ Suggested fix

 .xterm-screen .xterm-decoration-container .xterm-decoration {
-	z-index: 6;
-	position: absolute;
+    z-index: 6;
+    position: absolute;
 }
 
 .xterm-screen .xterm-decoration-container .xterm-decoration.xterm-decoration-top-layer {
-	z-index: 7;
+    z-index: 7;
 }

---

227-230: Consider documenting or avoiding !important.

The !important on font-size (line 229) may be necessary to override VS Code's scrollbar defaults, but it's generally a code smell. If it's required for the override to work, adding a brief comment explaining why would help future maintainers.

---

232-241: Minor formatting inconsistency.

Line 236 is missing a space after the colon in background:rgba(0,0,0,0). For consistency with the rest of the file, add a space.

♻️ Suggested fix

 .xterm .xterm-scrollable-element > .visible {
 	opacity: 1;
 
 	/* Background rule added for IE9 - to allow clicks on dom node */
-	background:rgba(0,0,0,0);
+	background: rgba(0,0,0,0);
 
 	transition: opacity 100ms linear;
 	/* In front of peek view */
 	z-index: 11;
 }

Taskfile.yml (1)

588-599: Consider consolidating into a single PowerShell script block.

These 12 separate pwsh invocations will spawn 12 processes, adding overhead compared to the Unix equivalent. For a build script this is likely acceptable, but if build performance on Windows becomes a concern, these could be consolidated into a single script block.

♻️ Optional: Consolidated script block

-            - pwsh -NoProfile -Command New-Item -ItemType Directory -Force -Path scaffold
-            - pwsh -NoProfile -Command Copy-Item -Path ../templates/package.json.tmpl -Destination scaffold/package.json
-            - pwsh -NoProfile -Command "Set-Location scaffold; npm install"
-            - pwsh -NoProfile -Command Move-Item -Path scaffold/node_modules -Destination scaffold/nm
-            - pwsh -NoProfile -Command Copy-Item -Recurse -Force -Path dist -Destination scaffold/
-            - pwsh -NoProfile -Command New-Item -ItemType Directory -Force -Path scaffold/dist/tw
-            - pwsh -NoProfile -Command Copy-Item -Path '../templates/*.go.tmpl' -Destination scaffold/
-            - pwsh -NoProfile -Command Copy-Item -Path ../templates/tailwind.css -Destination scaffold/
-            - pwsh -NoProfile -Command Copy-Item -Path ../templates/gitignore.tmpl -Destination scaffold/.gitignore
-            - pwsh -NoProfile -Command Copy-Item -Path 'src/element/*.tsx' -Destination scaffold/dist/tw/
-            - pwsh -NoProfile -Command Copy-Item -Path '../ui/*.go' -Destination scaffold/dist/tw/
-            - pwsh -NoProfile -Command Copy-Item -Path ../engine/errcomponent.go -Destination scaffold/dist/tw/
+            - |
+              pwsh -NoProfile -Command {
+                New-Item -ItemType Directory -Force -Path scaffold
+                Copy-Item -Path ../templates/package.json.tmpl -Destination scaffold/package.json
+                Set-Location scaffold; npm install
+                Move-Item -Path node_modules -Destination nm
+                Set-Location ..
+                Copy-Item -Recurse -Force -Path dist -Destination scaffold/
+                New-Item -ItemType Directory -Force -Path scaffold/dist/tw
+                Copy-Item -Path '../templates/*.go.tmpl' -Destination scaffold/
+                Copy-Item -Path ../templates/tailwind.css -Destination scaffold/
+                Copy-Item -Path ../templates/gitignore.tmpl -Destination scaffold/.gitignore
+                Copy-Item -Path 'src/element/*.tsx' -Destination scaffold/dist/tw/
+                Copy-Item -Path '../ui/*.go' -Destination scaffold/dist/tw/
+                Copy-Item -Path ../engine/errcomponent.go -Destination scaffold/dist/tw/
+              }