fix: improve text contrast on light terminal backgrounds

[altimate-harness-bot]

Summary

Fixes #704 (follow-up to #617). Code output was rendering as white/light text on light terminal backgrounds, making it unreadable.

Three fixes:

• COLORFGBG env var fallback (app.tsx): When OSC 11 terminal background detection times out (common in many terminal setups), fall back to checking the COLORFGBG environment variable before defaulting to "dark" mode. Many terminals (iTerm2, xterm, etc.) set this to indicate their color scheme.

• Light-mode foreground fallback (theme.tsx): When defaultForeground is unavailable and mode is "light", use #1a1a1a (near-black) instead of ANSI palette index 7 (#c0c0c0 — light gray), which is invisible on white backgrounds.

• Inline code background (theme.tsx): Use backgroundElement instead of background for markup.raw.inline scope. background can be transparent (especially in the system theme), leaving inline code with no contrast protection. This is consistent with the Asking the model to do a suggestion for rewrite of code during review returns white lines of code while terminal background is white #617 fix already applied to markup.raw.block.

Test plan

• Run CLI on a light-background terminal (e.g. Terminal.app with default white theme)
• Verify code suggestions and rewrites are readable
• Verify inline code blocks have visible background contrast
• Test on a terminal that sets COLORFGBG env var
• Test on a terminal that responds to OSC 11 (should still work as before)
• Verify dark terminal themes are unaffected

Requested by @saravmajestic via harness

---

Summary by cubic

Fixes unreadable code on light terminal backgrounds with better detection and safer color fallbacks. Also removes the 1s startup delay on terminals without OSC 11; inline code now always has a solid background. Closes #704.

• Bug Fixes
  • Use COLORFGBG via detectModeFromCOLORFGBG (util/terminal-detection.ts); only bg 7/15 count as light; reject invalid values; run this check before OSC 11 to avoid delays.
  • In light mode, fallback foreground uses palette[0] or #1a1a1a instead of palette[7]; dark mode unchanged.
  • Inline code (markup.raw.inline) now uses backgroundElement to ensure contrast on transparent themes.
  • Tests updated to import the real helper, add edge cases, and cover contrast and cross-mode regressions.

^{Written for commit 8f747a1. Summary will update on new commits.}

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[claude]

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[cubic-dev-ai]

No issues found across 4 files

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[anandgupta42]

Ran multi-model consensus review (9 participants: Claude + GPT 5.4, Gemini 3.1 Pro, Kimi K2.5, DeepSeek V3.2, MiniMax M2.7, GLM-5, MiMo-V2-Pro, Qwen 3.5 Plus). One convergence round. Summary below, followed by the fixes just pushed (commit 8f747a1).

---

Review findings

Major blocker (unanimous): Tests duplicated production logic (generateSystem, getSyntaxRules, the COLORFGBG parser). Reverting the production fix left all 55 tests green — living documentation of the bug, not regression protection.

Minor — COLORFGBG threshold: bg >= 8 was semantically wrong at the palette boundary.

• Index 7 (#c0c0c0, light-gray) is a light bg but 7 >= 8 is false → classified dark.
• Index 8 (#808080, dark-gray) is dark but 8 >= 8 is true → classified light.
• Naive fix (bg === 7 || bg >= 9) would mis-classify indices 9/12/13 (bright red/blue/magenta, luminance 28-76/255 = dark).

Minor — #1a1a1a foreground fallback: Hardcoded, ignored the user palette. Dark mode respects colors.palette[7]; light mode should at least consider colors.palette[0].

Minor — 1000ms startup delay: COLORFGBG was only consulted after the OSC 11 timeout. Terminals without OSC 11 (urxvt, older gnome-terminal) paid 1s on every launch.

Minor — Missing dark-mode regression for markup.raw.inline: The backgroundElement change affects both modes; only light-mode tests existed.

---

Fixes applied in commit 8f747a1

packages/opencode/src/cli/cmd/tui/util/terminal-detection.ts (new)

• Extracted detectModeFromCOLORFGBG as a pure-TypeScript helper. Tests now import the real function; reverting it fails the 18 COLORFGBG tests.
• Narrowed threshold to bg === 7 || bg === 15 (conservative: only canonically light indices).
• Rejects out-of-range (< 0, > 15), non-numeric (default), and empty values explicitly.
• Tolerates surrounding whitespace; parseInt(..., 10) with explicit radix.

packages/opencode/src/cli/cmd/tui/app.tsx

• Imports the new helper.
• Checks COLORFGBG eagerly before the OSC 11 query — light terminals without OSC 11 support skip the 1s timeout.

packages/opencode/src/cli/cmd/tui/context/theme.tsx

• Light-mode foreground fallback: colors.palette[0] ?? "#1a1a1a". Respects the user palette when present; keeps #1a1a1a as a safety net for empty-palette edge cases.

packages/opencode/test/cli/tui/theme-light-mode-704.test.ts

• Imports real detectModeFromCOLORFGBG.
• Added coverage: 0;7 (light-gray bg → light), 15;8 (dark-gray bg → dark), 0;9/0;12/0;13 (bright colors → dark), default;default, out-of-range, negatives, empty, whitespace, undefined.
• Added regression: fallback prefers palette[0] when present; defaultForeground always honored.

packages/opencode/test/cli/tui/theme-light-mode.test.ts

• Added dark-mode markup.raw.inline regression test.
• Removed duplicate COLORFGBG tests (consolidated in the 704 file).

Full test suite: 59 pass, 0 fail. altimate_change markers validated. TypeScript clean.

---

Test architecture note: the theme-level tests still use local helpers because theme.tsx can't be imported from bun:test (the @opentui/solid JSX runtime types don't resolve in the test loader). Leaving that extraction as a follow-up — the highest-value test architectural fix was the COLORFGBG helper, which was where the actual semantic bug lived. The system-theme tests reproduce only the specific fgFallback expression under test, not the full generateSystem, so the duplication surface is much smaller.

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