fix: make macOS window transparency opt-in again

[vianmangal]

Closes #3476

What changed

• Keep the main macOS window opaque by default.
• Enable native transparency and vibrancy only when the user opts in.
• Relaunch the app when the transparency setting changes because Electron cannot change native window transparency after creation.
• Preserve the existing transparent client chrome on Linux.
• Add regression coverage for the platform-specific window options.

Why

Rocket.Chat 4.16.0 started creating the main macOS window with transparency and native vibrancy even when the transparent-window setting was disabled. Transparent windows require continuous full-window compositing on macOS, which can cause high GPU usage on macOS 26.

Testing

• yarn test --runTestsByPath src/ui/main/rootWindow.spec.ts src/app/main/persistence.main.spec.ts — all 33 test cases passed.
• yarn lint — passed with 0 errors.
• yarn build — passed.
• Runtime check on macOS 26.6.2 arm64: with transparency disabled, the root window reports an opaque #2F343D background; closing it hides the window and changes the renderer visibility state to hidden.

Summary by CodeRabbit

• New Features
  • Changing the transparent-window setting saves the current app state and relaunches the app to apply the change. On macOS, transparency enables a vibrant sidebar; when disabled, the window uses an opaque background that follows the system’s dark or light appearance.
• Improvements
  • Window appearance adapts to the platform. Linux retains transparent window chrome with a shadow regardless of the transparency setting, while other platforms retain their standard appearance.

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Reviewing files that changed from the base of the PR and between 5cc1885 and 8a2ba31.

📒 Files selected for processing (3)

• src/app/main/app.ts
• src/ui/main/rootWindow.spec.ts
• src/ui/main/rootWindow.ts

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📓 Path-based instructions (1)

Source excerpt: Renderer specs use `*.spec.ts` / `*.spec.tsx`.

📄 CodeRabbit inference engine (AGENTS.md)

Files:

• src/ui/main/rootWindow.spec.ts

🪛 ast-grep (0.45.3)

src/app/main/app.ts

[warning] Importing child_process exposes a command-execution surface; ensure any command/argument built from input is validated, and prefer execFile/spawn with an argument array over exec.
Context: import { spawn } from 'child_process';
Note: [CWE-78] Improper Neutralization of Special Elements used in an OS Command ('OS Command Injection').

(detect-child-process-typescript)

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Walkthrough

The root window now applies platform-specific appearance options based on the transparency preference and dark-mode state. When the transparent-window setting changes, the app persists and flushes Redux values before relaunching.

Changes

Window Appearance and Transparency

Layer / File(s)	Summary
Platform-specific root-window appearance src/ui/main/rootWindow.ts, src/ui/main/rootWindow.spec.ts	An exported helper returns appearance options for macOS, Linux, and other platforms. createRootWindow applies those options using the Redux transparency preference and native dark-mode state. Tests cover macOS transparency states and Linux appearance.
Persist and relaunch after transparency changes src/app/main/app.ts	The setting listener persists and flushes persistable Redux values before relaunching the app.

Priority: ➖ Normal

Estimated code review effort: 2 (Simple) | ~10 minutes

Change: Bug fix · Severity of issue fixed: Medium

Suggested labels: type: bug

Suggested reviewers: jeanfbrito

Merge Risk: ⚪ Minimal · up to 8a2ba

The transparency setting is saved with its new value before relaunch. No confirmed issue remains to address before merging.

Security Architecture Review

Security architecture risk: 🔵 Low · up to 8a2ba

The macOS window now defaults to an opaque appearance, with transparency applied after opt-in and a restart. A failed preference save could cause the restart to restore the previous appearance. No new security-boundary bypass is established.

Retained concerns

• Low · reliability · inferred: Relaunch can proceed without confirmation that the changed window preference was durably saved, allowing startup to restore the prior appearance after a persistence failure.

Security review details

Security Blast Radius

• inferred — The traced action affects a desktop application's window appearance, saved settings, and restart lifecycle; the inspected listener does not change credentials, permissions, or a service-side authorization decision.

Trust Boundaries and Controls

• observed — A settings UI action reaches a main-process listener, but native BrowserWindow construction remains main-owned. The inspected source does not establish whether untrusted web content can dispatch into that shared action path.

Resilience and Maintainability Implications

• observed — Atomic-write recovery and synchronous flushing provide normal-path protection, but the persistence API can return after logging a failed write or selecting an in-memory store.

Hardening Proposals

• proposed — For a setting that requires relaunch, make durable-save failure visible to the transition so the application can avoid restarting under an unconfirmed preference.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely describes the main change: restoring opt-in macOS window transparency.
Linked Issues check	✅ Passed	Issue [#3476] reports high GPU usage in the macOS desktop app and provides no coding acceptance criteria. This PR makes macOS transparency and vibrancy opt-in. The default window uses an opaque backgr…
Out of Scope Changes check	✅ Passed	The changes stay within issue [#3476] and the stated PR objective. The window appearance selector, setting persistence, relaunch logic, and regression tests support the macOS transparency change. Linu…
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff. Analyzed 0 functions across 3…

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🔧 ESLint

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src/app/main/app.ts

ESLint skipped: missing config or dependency (missing-dependency). The ESLint configuration references a package that is not available in the sandbox.

src/ui/main/rootWindow.spec.ts

ESLint skipped: the matched ESLint configuration already failed (missing-dependency).

src/ui/main/rootWindow.ts

ESLint skipped: the matched ESLint configuration already failed (missing-dependency).

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Errors (1)

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Actionable comments posted: 2

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• 🪄 Fix CodeRabbit comments on this PR

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Inline comments:
In @src/app/main/app.ts:
- Around line 369-370: Update the listener for
SETTINGS_SET_IS_TRANSPARENT_WINDOW_ENABLED_CHANGED in setupApp to persist the
updated transparency setting and call flushPersistedValues() before
relaunchApp(). Keep the relaunch behavior after persistence completes.

In @src/ui/main/rootWindow.ts:
- Line 155: Update the `createRootWindow()` options to read
`isTransparentWindowEnabled` from Redux’s effective state instead of the
potentially stale `getPersistedValues()` value, so the first macOS window uses
the merged transparency preference.

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Advanced

Run ID: 5a390a69-683a-4b54-8c3e-f46de66497b2

📥 Commits

Reviewing files that changed from the base of the PR and between 5cc1885 and 5c21bc2.

📒 Files selected for processing (3)

• src/app/main/app.ts
• src/ui/main/rootWindow.spec.ts
• src/ui/main/rootWindow.ts

Included review availability: This review used your included allowance. Your plan provides up to 4 included reviews per hour; 2 remain after this review.

📜 Review details

🧰 Additional context used

📓 Path-based instructions (1)

Source excerpt: Renderer specs use `*.spec.ts` / `*.spec.tsx`.

📄 CodeRabbit inference engine (AGENTS.md)

Files:

• src/ui/main/rootWindow.spec.ts

🪛 ast-grep (0.45.3)

src/app/main/app.ts

[warning] Importing child_process exposes a command-execution surface; ensure any command/argument built from input is validated, and prefer execFile/spawn with an argument array over exec.
Context: import { spawn } from 'child_process';
Note: [CWE-78] Improper Neutralization of Special Elements used in an OS Command ('OS Command Injection').

(detect-child-process-typescript)

[vianmangal]

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