feat(theme): add a default terminal theme that follows terminal colors

[dhh]

Problem

Every built-in theme paints Hunk with a fixed editor color scheme, so Hunk never matches the terminal it runs in. On setups where the terminal theme changes (Omarchy theme switching, light/dark toggles, herdr/tmux theme sync) Hunk also can't follow along without a restart.

What this does

New terminal theme, now the default. At startup Hunk queries the terminal's foreground, background, and 16-color ANSI palette (OSC 10/11/4) and derives the whole theme from them:

• diff rows: green additions, red removals, blue accent, with tints blended against the real background and the existing contrast rescue rules applied
• syntax: keywords magenta, strings green, functions blue, types yellow, constants cyan, comments bright black, everything else the terminal foreground
• the syntax scopes replace the base Shiki theme's rules (new syntaxScopesReplaceBase) so no bundled editor palette leaks through
• terminals that don't answer get a stand-in xterm light/dark palette

The probe ends with a DA1 query as a sentinel, so responsive terminals finish immediately instead of waiting out the timeout. auto keeps meaning GitHub light/dark, explicit themes are unchanged, and terminal is reserved from custom-theme ids.

Live refresh. HunkSessionHost runs a watcher that re-probes through OpenTUI's renderer-owned getPalette() and republishes through ThemeController when the colors changed:

• on mode 2031 color-scheme notifications (CSI ? 997 ; n n), which OpenTUI already opts into and Ghostty/kitty/herdr send; the handler leaves the sequence for OpenTUI's own light/dark tracking
• on SIGWINCH, which tmux-aware theme tools send after rewriting pane colors (OpenTUI skips its resize path when the size is unchanged)
• once after mount when startup never probed (explicit-theme launches), so switching to terminal later shows the real palette

OpenTUI only clears its palette cache on a light↔dark flip, so the watcher clears it before each probe to catch dark→dark switches. Probes are debounced, and only changed reports repaint.

Tradeoffs

• Themes with syntax scope overrides are highlighted inline rather than on the worker (existing documentWorkerEligibility rule), which now applies to the default theme on very large diffs.
• SIGWINCH also fires on ordinary resizes; those cost one palette query and repaint nothing.

Verification

• bun run typecheck, lint, format:check, deps:check, check:docs
• bun run test: passes except Jujutsu source reading > logs unexpected source failures…, which fails identically on main locally
• bun run test:integration: passes. PTY tests that assert exact GitHub hex colors now pin --theme github-dark-default; tests that assert the default id or selector order now expect terminal.
• New unit coverage: OSC 4/10/11 parsing and the DA1-terminated probe, terminal theme derivation and fallback, controller color updates, the watcher's triggers/debounce/disposal, and selector repaint (including a terminal preview across a dark→dark switch).
• End-to-end in a PTY against a scripted terminal that answers color queries: Hunk enables mode 2031, renders palette A, and after the palette changes and a 997 notification arrives, repaints entirely in palette B.

Not yet verified by hand in a real terminal session across an actual theme switch.

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[benvinegar]

Reviewed the startup OSC probe, terminal palette derivation and fallback, OpenTUI watcher lifecycle, controller/selector repaint path, syntax-theme replacement, docs, and compatibility updates. I did not find a blocking correctness issue.

Validation: bun run test, bun run typecheck, bun run lint, bun run deps:check, bun run check:docs, and the changed-file format check pass. bun run test:integration had one unrelated watch-start process-cleanup failure; that test passed immediately when rerun alone.

Non-blocking: the scripted palette-switch PTY scenario described in the PR body would be valuable as a checked-in regression test; the current watcher coverage mocks the renderer boundary.

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Posted in error; no review was requested to be submitted.

[benvinegar]

Thanks! I tried this on my desktop Omarchy (by switching through some themes) and it looked pretty nice

As a follow-up I'd love to have hunk detect the theme switch somehow (vs having to restart today)

[dhh]

It'll do the update in Omarchy when it gets SIGWINCH. We'll get that setup on our side.

[dhh]

Follow-up on the Omarchy side: omacom/omarchy#13518 adds omarchy-theme-set-hunk, which sends SIGWINCH to running hunk processes when the Omarchy theme changes, so the terminal theme repaints even in terminals that don't send a mode 2031 color-scheme notification when their palette is reloaded.

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