feat(desktop): allow custom theme mapping for System theme mode

[github-actions]

Summary

• Adds systemLightThemeId and systemDarkThemeId fields to the theme store, allowing users to configure which installed theme to use for each OS mode when "System" is selected
• Updates resolveThemeId to use these custom mappings instead of hardcoded "dark"/"light" built-in IDs
• Enhances SystemThemeCard to show two dropdown selectors (filtered by theme type) when System is the active theme, letting users pick any matching-type theme for dark and light OS modes
• Resets system mapping to built-in defaults when a mapped custom theme is removed
• Backwards-compatible: defaults match current behavior ("dark" for dark mode, "light" for light mode)

Test plan

• Unit tests for store logic (store.test.ts) — 7 tests covering default mappings, resolution for dark/light OS modes, custom mapping, re-apply on mapping change, no-op when system not active, and reset on custom theme removal
• Manual: select System theme, verify dark/light dropdowns appear
• Manual: change dark mapping to Monokai, toggle OS dark mode — verify Monokai is applied
• Manual: import a custom dark theme, verify it appears in the dark dropdown
• Manual: remove a custom theme used as a system mapping, verify it resets to built-in

Closes #2547

---

Summary by cubic

Adds custom mapping for System theme mode so users can choose which theme applies in dark and light OS modes. Implements #2547; defaults to built-in dark/light and resets mappings if a chosen theme is removed.

• New Features
  • Added systemLightThemeId and systemDarkThemeId to the theme store and updated resolution logic to honor them.
  • Updated SystemThemeCard to show dark/light dropdowns (filtered by type) when System is selected, and re-apply instantly if System is active.
  • Persisted mappings and handled removal by falling back to built-in themes.

^{Written for commit a0725cc. Summary will update on new commits.}

[cubic-dev-ai]

1 issue found across 3 files

Prompt for AI agents (unresolved issues)

Check if these issues are valid — if so, understand the root cause of each and fix them. If appropriate, use sub-agents to investigate and fix each issue separately.


<file name="apps/desktop/src/renderer/stores/theme/store.ts">

<violation number="1" location="apps/desktop/src/renderer/stores/theme/store.ts:262">
P2: After removing a custom theme used by system mapping, the store resets mapping IDs but does not re-apply the active system theme. This can leave `activeTheme`/UI state on a deleted theme until a later theme change occurs.</violation>
</file>

_{Reply with feedback, questions, or to request a fix. Tag @cubic-dev-ai to re-run a review.}

[cubic-dev-ai]

P2: After removing a custom theme used by system mapping, the store resets mapping IDs but does not re-apply the active system theme. This can leave activeTheme/UI state on a deleted theme until a later theme change occurs.

Prompt for AI agents

Check if this issue is valid — if so, understand the root cause and fix it. At apps/desktop/src/renderer/stores/theme/store.ts, line 262:

<comment>After removing a custom theme used by system mapping, the store resets mapping IDs but does not re-apply the active system theme. This can leave `activeTheme`/UI state on a deleted theme until a later theme change occurs.</comment>

<file context>
@@ -210,6 +258,14 @@ export const useThemeStore = create<ThemeState>()(
 					}
 
+					// If removing a theme used in system mapping, reset to built-in
+					if (state.systemDarkThemeId === themeId) {
+						set({ systemDarkThemeId: "dark" });
+					}
</file context>

Suggested change

	if (state.systemDarkThemeId === themeId) {
	set({ systemDarkThemeId: "dark" });
	}
	if (state.systemLightThemeId === themeId) {
	set({ systemLightThemeId: "light" });
	}
	const removedMappedSystemTheme =
	state.systemDarkThemeId === themeId ||
	state.systemLightThemeId === themeId;
	if (state.systemDarkThemeId === themeId) {
	set({ systemDarkThemeId: "dark" });
	}
	if (state.systemLightThemeId === themeId) {
	set({ systemLightThemeId: "light" });
	}
	if (removedMappedSystemTheme && state.activeThemeId === SYSTEM_THEME_ID) {
	state.setTheme(SYSTEM_THEME_ID);
	}

[Kitenite]

Closing as stale: bot PR created 6+ weeks ago with no iteration since. Re-attempt from a fresh branch if a fix is still wanted. Bulk audit 2026-05-06.