fix(theme): make graphite the explicit default across startup modes

[elucid]

Summary

Make graphite the single built-in fallback theme across startup modes, removing implicit renderer-mode-based fallback selection for unspecified themes.

This is intentionally scoped on top of elucid/tty-mouse-pager-fixes, where stdin-backed patch - / pager sessions need split terminal plumbing to preserve mouse scrolling.

Why this change

On main, piped patch/pager sessions happened to come up dark under the old all-/dev/tty renderer wiring.

On elucid/tty-mouse-pager-fixes, fixing mouse scrolling required keeping interactive input on /dev/tty while rendering through process.stdout. That change is necessary for the branch goal, but it also changes the effective renderer theme-mode signal in stdin-backed startup paths. As a result, an unspecified theme can resolve to light there even though other startup modes still resolve to graphite.

We tested the obvious alternative: reverting the stdout-side plumbing change. That does make the piped patch/pager theme dark again, but it also regresses the mouse-scroll fix that motivated the branch. So reverting the transport change is not a viable fix.

Given that constraint, the pragmatic choice is to stop treating an unspecified theme as an implicit auto-detect mode and instead make the built-in fallback explicit: graphite.

What this changes

• Config/bootstrap resolution now defaults unspecified themes to graphite.
• Theme fallback resolution now also defaults to graphite regardless of renderer-reported light/dark mode.
• Explicit user and config overrides still work (--theme, theme = "paper", etc.).

In other words, Hunk no longer treats an omitted theme as an implicit terminal-following mode.

Why this is pragmatic

• Preserves the branch's mouse-scroll behavior.
• Removes startup-path-dependent theme drift.
• Keeps behavior deterministic across diff, file-backed patch, stdin-backed patch -, and pager.
• Avoids depending on a renderer-mode signal that changes under the tty plumbing required for stdin-backed interactivity.
• Still allows explicit overrides via CLI or config.

This chooses a stable product fallback over transport-sensitive autodetect behavior.

Tradeoff

This intentionally changes the old behavior where an unspecified or unrecognized theme could fall back through renderer light/dark detection (paper on light terminals, graphite on dark terminals). After this change, Hunk always falls back to graphite unless a specific theme is requested via config or CLI.

That tradeoff is intentional. If terminal-following theme selection is something we want to preserve as a product feature, the cleaner long-term design is to make that explicit (for example with a future theme = auto / --theme auto) rather than relying on renderer startup details.

Tests

• bun test src/core/config.test.ts src/ui/lib/ui-lib.test.ts
• bun test test/pty/ui-integration.test.ts -t "(stdin patch mode enables mouse wheel scrolling in pager UI|general pager mode enables mouse wheel scrolling for diff-like stdin)"
• bun run typecheck

[greptile-apps]

Greptile Summary

Makes graphite the single explicit built-in theme fallback by defaulting theme to "graphite" in resolveConfiguredCliInput and removing the renderer-mode-sensitive paper branch from resolveTheme. User and config-file overrides continue to work correctly via the existing ??-based mergeOptions chain. All findings are P2.

Confidence Score: 5/5

Safe to merge; all remaining findings are non-blocking style suggestions.

The logic change is correct and well-scoped. Override precedence is preserved by the ??-based merge chain. Tests cover the new default path. Only P2 style findings remain.

No files require special attention.

Important Files Changed

Filename	Overview
src/core/config.ts	Sets theme: "graphite" as the explicit base default in resolveConfiguredCliInput; user/config/CLI overrides still propagate correctly via mergeOptions.
src/ui/themes.ts	Removes the paper light-mode fallback branch from resolveTheme; _themeMode parameter is kept but unused — callers in App.tsx still pass it silently.
src/core/config.test.ts	Adds graphite-default assertion to an existing test and a new loadAppBootstrap test; no coverage for explicit user-config override winning over the graphite default.
src/ui/lib/ui-lib.test.ts	Updates resolveTheme fallback test to expect graphite instead of paper for a light-mode renderer; straightforward and correct.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A[resolveConfiguredCliInput] --> B[base: theme = graphite]
    B --> C{user config file\nspecifies theme?}
    C -- yes --> D[mergeOptions: use config theme]
    C -- no --> E[keep graphite]
    D --> F{CLI --theme flag?}
    E --> F
    F -- yes --> G[mergeOptions: use CLI theme]
    F -- no --> H[keep resolved theme]
    G --> I[bootstrap.initialTheme]
    H --> I
    I --> J[resolveTheme called in App.tsx]
    J --> K{exact match\nin THEMES list?}
    K -- yes --> L[return matched theme]
    K -- no --> M[return graphite fallback\n_themeMode ignored]

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[elucid]

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