fix(ui-tui): a skin owns the terminal's DEFAULT foreground (OSC-10) — kills the invisible-text class

[OutThisLife]

Follow-up to #69616, hit one demo later: composer themed, but the agent's response body went black-on-black the same way. Same class, different call site — and the class is the thing to kill.

The class

The skin repaints the terminal background via OSC-11, but every token rendered without an explicit color — markdown body, borders, anything default-fg — falls back to the terminal's default foreground, which belongs to the HOST profile's polarity, not the skin's. Dark skin + light terminal ⇒ near-black text on pure black. Everything the theming engine explicitly paints (headers, accents, status colors, the placeholder) flips perfectly; the hole is precisely the tokens it doesn't paint. Chasing every <Text> (what #69616 did for the input) is unwinnable one call site at a time.

Fix — own the default itself

When a skin authors a background (the existing opt-in), applySkin now paints the terminal's default foreground from the resolved theme's text color via OSC-10, beside the OSC-11 background it already painted. Every default-fg token — present and future — re-bases onto the skin atomically, exactly like the background. No skin background ⇒ both defaults restore to the terminal's own; a skinless session never touches the terminal.

• terminalModes: the OSC-11 background slot generalizes to defaultColorSlot(10 | 11) — one paint/clear/exit-restore contract, painted-state tracked per slot, exit reset appends only what was actually painted.
• reapplyTheme repaints the fg too: polarity flips swap paired palettes, moving the text tone while the skin's background stays put.
• #69616's explicit input theming stays on top — the composer is first-class themed, not merely default-correct.

Tests

• terminalModes — the slot contract runs table-driven over both OSC codes: paint from hex, ignore junk/non-TTY, exit-reset restores only-if-painted, dropping the color releases the default
• createGatewayEventHandler — the invariant: a skin owning the background paints both defaults, fg == theme.color.text; dropping the background releases both (OSC-110 + OSC-111)
• full ui-tui suite 125 files / 1344✓; typecheck, lint, prettier clean

[github-actions]

૮ >ﻌ< ა ci review

_{running on 1f65221}

CI timings

CI timings · View job

Wall time 7m28s vs 8m10s (-8.6%). 3 job(s) slower, 3 faster, 1 unchanged.

• Build&Test Docker image / build (amd64, ubuntu-latest, linux/amd64, type=gha,scope=docker-amd64, type=gha,mode=max,scope=do...: -25.0s
• Build&Test Docker image / build (arm64, ubuntu-24.04-arm, linux/arm64, type=gha,scope=docker-arm64, type=gha,mode=max,scope...: +14.0s
• OSV scan / Scan lockfiles / osv-scan: -11.0s
• Detect affected areas: +2.0s
• OSV scan / Emit review status: -1.0s