Fix theme source not resetting when using system theme

[fmartingr]

Summary

• Fixed an inverted condition in ThemeManager where isUsingSystemTheme was negated, preventing resetThemeSource() from being called when the user switches to the system theme
• Now correctly resets the theme source when the system theme is active and applies the custom theme source only when the system theme is not in use

Test plan

• Set a server theme, then switch to "Use system theme" — verify the desktop app follows the OS dark/light mode
• Switch from system theme to a custom theme — verify the desktop app applies the correct light/dark mode based on the center channel background color
• Toggle between system and custom themes multiple times to ensure no stale state

Change Impact: 🟡 Medium

Regression Risk: The change corrects an inverted conditional in updateMainViews(), flipping when resetThemeSource() is called based on the isUsingSystemTheme flag. While the code modification is minimal and isolated to a single method, it addresses a logic bug that affects user-facing theme behavior. Potential risks include: (1) if existing workarounds or dependencies exist around the broken behavior, this fix could surface unexpected issues; (2) theme state transitions between system and custom themes need to work correctly across both main and popout views; (3) the fix changes the path through which nativeTheme.themeSource gets updated, which could have side effects with Electron's native theme handling if there are edge cases not covered by tests.

QA Recommendation: Manual QA is essential. Verify both code paths thoroughly following the test plan provided in the PR: confirm system theme correctly follows OS dark/light mode changes, verify custom theme application uses proper light/dark modes based on server colors, and stress-test repeated toggling between system and custom themes. A test file exists (src/main/themeManager.test.js), but coverage verification is recommended to ensure both conditional branches are tested. Pay particular attention to theme persistence and visual consistency when switching between themes.

[mm-cloud-bot]

@fmartingr: Adding the "do-not-merge/release-note-label-needed" label because no release-note block was detected, please follow our release note process to remove it.

Details

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No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Repository UI

Review profile: CHILL

Plan: Pro

Run ID: dd2cf129-d559-4414-93d4-01d64927cd77

📥 Commits

Reviewing files that changed from the base of the PR and between 85e7929 and a37d0b0.

📒 Files selected for processing (1)

• src/main/themeManager.ts

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📝 Walkthrough

Walkthrough

The ThemeManager.updateMainViews method's theme source update logic is modified to conditionally reset the native theme source to 'system' when the server uses system theme, versus deriving the theme from server colors when not using system theme.

Changes

Cohort / File(s)	Summary
Theme Source Update Logic src/main/themeManager.ts	Modified updateMainViews method to flip the conditional: when isUsingSystemTheme is true, calls resetThemeSource() to set nativeTheme.themeSource to 'system'; when false, derives theme from centerChannelBg and updates nativeTheme.themeSource if changed.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~12 minutes

🚥 Pre-merge checks | ✅ 3

✅ Passed checks (3 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately describes the main fix in the changeset: correcting the inverted condition so that resetThemeSource() is called when using system theme, which was the primary bug being addressed.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

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✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/reset-theme-source-on-system-theme

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