Fix mobile feature flag isolation warning

[lawrencecchen]

Summary

• mark the immutable feature-flag definition as nonisolated and Sendable
• expose the mobile workspace flag definition and fallback as immutable off-main values
• keep the mutable feature-flag store MainActor-isolated

Unblocks the speculative merge gate for #8850.

Testing

• tagged cloud build: https://github.com/manaflow-ai/cmux/actions/runs/30301889950
• verified the build log contains no mobileWorkspaceChangesFlag actor-isolation warning
• no behavior-level regression test added because this is a compiler-warning regression and source-shape tests are prohibited

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Summary by cubic

Fixes the Swift concurrency actor-isolation warning for the mobile workspace feature flag. Removes the mobileWorkspaceChangesFlag warning and unblocks the merge for #8850.

• Bug Fixes
  • Marked CmuxFeatureFlagDefinition as nonisolated and Sendable.
  • Made mobileWorkspaceChangesFlag and its defaults nonisolated static let.
  • Kept the mutable feature-flag store MainActor-isolated; no behavior changes.

^{Written for commit 355bb3f. Summary will update on new commits.}

Summary by CodeRabbit

• Refactor
  • Improved feature-flag access across execution contexts without changing available flags or their values.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

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Plan: Pro Plus

Run ID: 05f3b98b-a876-4c33-94c9-fc6ca9d2a18e

📥 Commits

Reviewing files that changed from the base of the PR and between 45a4ddf and 355bb3f.

📒 Files selected for processing (1)

• Sources/FeatureFlags.swift

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📝 Walkthrough

Walkthrough

Swift actor-isolation annotations are updated for feature-flag definitions and the mobile workspace changes cached default and flag, enabling non-main-actor access without changing flag values or semantics.

Changes

Feature flag isolation

Layer / File(s)	Summary
Update feature flag isolation annotations Sources/FeatureFlags.swift	CmuxFeatureFlagDefinition, mobileWorkspaceChangesDefault, and mobileWorkspaceChangesFlag are marked nonisolated.

Estimated code review effort: 1 (Trivial) | ~2 minutes

Possibly related PRs

• manaflow-ai/cmux#8937: Modifies the same feature-flag definitions with remote-gated behavior.

Suggested reviewers: azooz2003-bit

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Important

Pre-merge checks failed

Please resolve all errors before merging. Addressing warnings is optional.

❌ Failed checks (1 error)

Check name	Status	Explanation	Resolution
Cmux Swift @Concurrent	❌ Error	loadPostHogControlPlaneFlags is a nonisolated async network helper awaited inside a @MainActor task in refreshRemoteFlags(), so it lacks the required @concurrent boundary.	Mark the network loader (and any async callee chain it depends on) @concurrent, or move the fetch onto a detached/background actor before awaiting it.

✅ Passed checks (24 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately summarizes the main change: fixing the mobile feature flag isolation warning.
Description check	✅ Passed	The description covers the required Summary and Testing sections and is detailed enough, though some template-only sections are omitted.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Cmux Swift Actor Isolation	✅ Passed	The PR only marks immutable Sendable feature-flag values nonisolated; it doesn’t add shared mutable Sendable state or loosen any UI-bound store isolation.
Cmux Swift Blocking Runtime	✅ Passed	Diff only adds nonisolated/Sendable annotations in FeatureFlags.swift; it introduces no waits, sleeps, sync dispatch, polling, or locks.
Cmux Browser Automation Off-Main	✅ Passed	Only Sources/FeatureFlags.swift changed; no browser.* routing, WebKit waits, socket-worker policy, or browser automation tests were touched.
Cmux Expensive Synchronous Load	✅ Passed	PASS: The only change is actor-isolation annotations in Sources/FeatureFlags.swift; no synchronous agent-history loads, scans, or close-path parsing were added or moved.
Cmux Cache Substitution Correctness	✅ Passed	The patch only marks immutable feature-flag definitions/defaults nonisolated; it doesn’t replace any fresh persistence/history/snapshot read with cache-backed data.
Cmux No Hacky Sleeps	✅ Passed	Only Sources/FeatureFlags.swift changed, and it adds Swift actor-isolation annotations; the no-hacky-sleeps rule targets non-Swift runtime scripts.
Cmux Algorithmic Complexity	✅ Passed	Diff only tweaks actor-isolation on feature-flag constants/definitions; no new scans, sorts, joins, or scalable-data algorithm changes. allFlags is a fixed 9-item registry.
Cmux Swift Concurrency	✅ Passed	The diff only adds nonisolated annotations to feature-flag declarations; it does not introduce DispatchQueue, Combine, completion-handler, or new fire-and-forget Task patterns.
Cmux Swift Package Boundaries	✅ Passed	The diff only adjusts actor isolation/Sendable on existing feature-flag declarations; it doesn’t introduce or expand independently testable domain logic in the app target.
Cmux Swiftpm Lockfiles	✅ Passed	Diff only changes Sources/FeatureFlags.swift; no Package.swift, Package.resolved, .gitignore, or Xcode project paths were modified.
Cmux Swift Logging	✅ Passed	Diff only changes actor isolation in FeatureFlags.swift; no print/debugPrint/dump/NSLog/Logger additions or changes appear.
Cmux User-Facing Error Privacy	✅ Passed	The diff only changes actor-isolation annotations in FeatureFlags.swift; it adds no user-facing errors, alerts, or recovery copy.
Cmux Full Internationalization	✅ Passed	Diff only changes Swift actor-isolation annotations; no user-facing text, catalogs, or locale files were added or changed.
Cmux Swiftui State Layout	✅ Passed	Diff only changes feature-flag isolation in Sources/FeatureFlags.swift; it introduces no SwiftUI state/layout patterns covered by the rule.
Cmux Architecture Rethink	✅ Passed	Diff only relaxes actor isolation for immutable feature-flag values; it adds no timing, locking, observer, or split-ownership workaround.
Cmux Swift Auxiliary Window Close Shortcuts	✅ Passed	Diff only changes Sources/FeatureFlags.swift; no NSWindow/NSPanel/WindowGroup or cmux window-identifier code is introduced or modified.
Cmux Source Artifacts	✅ Passed	Only Sources/FeatureFlags.swift changed, and it’s a normal hand-written source edit; no logs, caches, build output, or other artifacts were added.
Cmux No Test Or Debug Seam In Production Source	✅ Passed	The DEBUG-gated values are production feature-flag defaults used by the flag itself, and no test/debug accessor or seam was added in Sources/.
Cmux No Ambient Global State	✅ Passed	Patch only adds nonisolated/Sendable to existing flag definitions and static lets; no new free funcs, mutable globals, namespaces, or singletons.

✨ 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-main-mobile-flag-warning

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[lawrencecchen]

Superseded by the equivalent isolation fix now on main via #8699, specifically bbcbf81. Closing this duplicate; the feature PR will be re-gated against current main.