fix(web): blink the terminal cursor again

[StiensWout]

What

The web terminal's cursor stopped blinking when the renderer moved from xterm.js to libghostty-vt. This restores it.

Why it broke

The old renderer was constructed with cursorBlink: true, so every T3 terminal blinked regardless of what the program inside it wanted. libghostty-vt's built-in default is a steady cursor, and the Canvas renderer only toggles the cursor while the terminal reports cursorBlinking — that is, when a program turns blinking on through DECSCUSR (CSI 5/3/1 q) or DEC mode 12. A plain shell prompt does neither, so the cursor sat still.

What changed

• GhosttyTerminalCore sets GHOSTTY_TERMINAL_OPT_DEFAULT_CURSOR_BLINK when it creates a terminal, so a session starts blinking and returns to blinking on CSI 0 q. Programs still own the cursor: a steady DECSCUSR style or CSI ?12l turns the blink off, and CSI ?12h turns it back on.
• The option is applied again in resetAndWrite, because RIS restores Ghostty's built-in steady default. That is the path a reattach to an existing session takes, so without it a reconnected terminal came back steady.
• The blink phase machinery in GhosttyTerminalSurface was already in place (500ms half-cycle, reset to the visible phase on write and focus). It now runs through one predicate, shouldBlinkTerminalCursor, which also holds the cursor steady when the reader prefers reduced motion, next to the existing unfocused and hidden-cursor cases.

Tests

• runtimeAbi.test.ts exercises the real vendored WASM: the default is steady, option 23 makes it blink, CSI 2 q / CSI ?12l override it, CSI 0 q / CSI ?12h restore it, and RIS drops back to steady (the reason for the second apply).
• renderer.test.ts covers the off phase repainting the cell without the inverted cursor glyph.
• surface.test.ts covers the blink predicate.

Verified in a dev environment — the GIF above is the terminal drawer in that build.

Note

apps/mobile's Android and iOS terminal views gate on the same cursorBlinking flag, so they blink only when a program asks. Matching them to this default is a separate change, not included here.

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Note

Low Risk
Terminal UI and embedder default cursor option only; no auth, data, or API surface changes beyond local terminal behavior.

Overview
Restores blinking cursor behavior in the Ghostty web terminal after the move from xterm.js, which always blinked, to libghostty-vt whose default is steady.

GhosttyTerminalCore now sets terminal option 23 (embedder default cursor blink) when a terminal is created and again after resetAndWrite, because RIS resets Ghostty’s built-in steady default—important for session reattach. Programs still override via DECSCUSR and DEC mode 12.

Blink scheduling in GhosttyTerminalSurface goes through shouldBlinkTerminalCursor, which also keeps the cursor steady when the surface is unfocused, the cursor is hidden, or prefers-reduced-motion: reduce is set; the surface listens for that media query and resets to the visible phase when it changes.

Tests cover WASM blink semantics, renderer off-phase repaint, and the blink predicate.

^{Reviewed by Cursor Bugbot for commit 0988f07. Bugbot is set up for automated code reviews on this repo. Configure here.}

Note

Fix terminal cursor blinking with reduced-motion and focus awareness

• Enables cursor blinking by default by setting Ghostty option 23 immediately after terminal creation and after any terminal reset.
• Adds shouldBlinkTerminalCursor to centralize blink logic, requiring the surface to be focused, cursor to be visible and blinking, and prefers-reduced-motion to be false.
• Watches the prefers-reduced-motion media query at runtime and restarts the blink cycle on change.
• Replaces the hardcoded 500ms interval with CURSOR_BLINK_INTERVAL_MS and gates blink scheduling through the new blinkEnabled() helper.
• After resetAndWrite, forces cursorOn=true so the cursor starts visible rather than mid-blink.

^{Macroscope summarized 0988f07.}

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[cursor]

Cursor Bugbot has reviewed your changes using high effort and found 1 potential issue.

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[macroscopeapp]

Approvability

Verdict: Approved 0988f07

Bug fix to restore terminal cursor blinking, with comprehensive test coverage. The author owns these terminal files and the changes are self-contained with clear accessibility considerations (reduced motion support).

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