Redesign Serengeti theme — fix washed-out warm-earth light surfaces

[gregpriday]

Summary

The Serengeti light theme is inspired by the East African savanna — warm golden earth, amber grasses, and acacia silhouettes. The warm-tone direction is stronger than Atacama's neutrality, but the theme still reads as washed out: surfaces don't have enough contrast between layers, and the activity/status palette uses defaults from dark themes that look out of place on warm ochre backgrounds.

Problem Statement

Serengeti uses #F4EDE0 (canvas) and #EBE1D0 (sidebar) — warm sandy cream. The palette has potential but several choices pull it toward mediocrity:

• The difference between surface-canvas: #F4EDE0 and surface-sidebar: #EBE1D0 is small. The sidebar and canvas blend together, especially when the panels are #FAF7F2 (barely whiter than canvas). The panel grid #E4D9CA is only slightly darker — these four surfaces are all within a narrow warm-tan band.
• border-default: #D5C8B8 disappears against surface-panel: #FAF7F2 — they're both warm near-white. Component boundaries are invisible.
• activity-active: #22c55e and activity-working: #22c55e are the dark-theme neon greens. Against a warm golden canvas, they're extremely jarring — they read like wrong-colored pixels rather than UI elements.
• activity-idle: #8b95a1 and activity-waiting: #d97706 are borrowed from Daintree defaults. The amber for waiting (#d97706) clashes with the warm surface tones — they're the same color family, making waiting states nearly invisible.
• terminal-black: #4A3F35 and terminal-white: #9B8D7A are custom-set — good — but terminal-bright-black: #A89A8A and terminal-bright-white: #4A3F35 invert the black/white relationship in a way that may produce confusing output.
• text-muted: #9B8D7A has very low contrast against surface-panel: #FAF7F2 (approximately 2.5:1) — below WCAG AA for normal text.

Relevant code:

• shared/theme/themes.ts#L812-L877 — current Serengeti token definitions
• e2e/core/core-light-theme-smoke.spec.ts — smoke test
• Issue Improve theme token coverage to fix washed-out light themes #3346 — token coverage improvements (foundation)

Desired Behavior

Serengeti should feel like the savanna at golden hour: warm amber and cream surfaces with richer mid-tone contrast. There should be clear differentiation between the canvas, sidebar, panels, and grid. Activity colors should feel like they belong in a warm-earth palette — earth greens and deep ambers rather than neon. Specifically:

• Surface layers should have clear stepped contrast: canvas brighter than sidebar, panels floating above canvas.
• Borders should visibly separate UI regions.
• Agent state colors should be adapted to the warm palette — muted earthy greens and ambers instead of neons.
• text-muted should meet a minimum contrast ratio for readability.

Verification Workflow

1. Apply: await setAppTheme(window, "serengeti").
2. Run getThemeChromeMetrics — verify smoke test checks pass.
3. Screenshot: full page plus sidebar, worktree cards, and a panel with activity indicators.
4. Measure text-muted contrast against surface-panel.
5. AI evaluation: does the theme evoke warm savanna? Are surfaces differentiated? Are the agent state colors coherent?
6. Iterate; npm run check.

Acceptance Criteria

• E2E smoke test passes for Serengeti.
• text-muted has ≥ 3:1 contrast against surface-panel.
• Surface layers are clearly stepped — canvas, sidebar, panel, and grid are visually distinct.
• Agent state indicators are adapted for the warm palette and don't appear as jarring neon intrusions.
• The theme reads as warm savanna — distinct from Bondi (coastal) and Atacama (mineral desert) in screenshot evaluation.
• All E2E tests pass.

Dependencies

Depends on #3346 for improved border token overridability.

Edge Cases & Risks

• The terminal-black/terminal-bright-black/terminal-white/terminal-bright-white custom override creates an unusual inverted relationship — review this carefully, as terminal output depending on semantic ANSI black/white may render unexpectedly.
• Terminal scheme pairing from PR feat(terminal): match terminal color scheme to app theme automatically #3345 — verify after changes.

[gregpriday]

Terminal color scheme — review as part of redesign

The APP_THEME_TERMINAL_SCHEME_MAP currently maps serengeti → solarized-light (Solarized Light). As part of this theme redesign, review whether the terminal color scheme still pairs well with the updated app surfaces:

1. Evaluate the current pairing — after updating the surface/accent tokens, check whether Solarized Light still feels cohesive. If the surface palette shifts significantly, the terminal may look disconnected.
2. Research alternatives — search for well-known open-source terminal color schemes whose character matches the redesigned theme. Evaluate candidates for ANSI color legibility against the new surface background, not just aesthetic similarity.
3. Consider a bespoke scheme — if no existing scheme is a tight fit, create a dedicated one derived from the redesigned app tokens (like we did for Daintree via getTerminalThemeFromAppScheme). This gives the tightest visual integration.
4. Adapt rather than copy — if borrowing an open-source palette, adjust selection background, cursor, and bright variants so they harmonize with the app's surface/accent tokens.

Update APP_THEME_TERMINAL_SCHEME_MAP in src/config/terminalColorSchemes.ts and add any new scheme to the BUILT_IN_SCHEMES array. Update the test count in src/config/__tests__/terminalColorSchemes.test.ts if adding a new scheme.