Preserve iPhone viewport lease across output stream churn

[teamleaderleo]

Follow-up to #13498 / #13474.

The focused TerminalSurfaceMountOwnershipTests run exposed one remaining ownership mismatch after #13498: MobileShellComposite.unregisterTerminalOutput still cleared the viewport whenever the output stream ended. A transient UIKit detach therefore advanced the viewport generation and dropped the cached report even though the presentation still owned the terminal.

This patch separates those lifetimes:

• ownerless and release-gate output streams keep the existing clear-on-termination behavior;
• the mounted UI stream unregisters output delivery while preserving the presentation-owned viewport lease;
• explicit presentation teardown remains the generation-fenced viewport release point.

The existing mount ownership regression from #13498 now exercises the intended rule directly.

Verification

• Direct macOS/iPhone Simulator run: CmuxMobileShellUITests/TerminalSurfaceMountOwnershipTests — 3/3 tests passed in 15.204s, TEST SUCCEEDED.
• The previously failing transient-detach test now passes while the same suite also proves explicit presentation teardown releases the viewport lease.
• Temporary verification workflows were removed; the PR diff remains production code only.

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Summary by cubic

Fixes the iPhone terminal viewport being dropped when the output stream ends during a transient UIKit detach, losing the cached report while the presentation still owns the terminal.

• MobileShellComposite.terminalOutputStream now accepts a releaseViewportOnTermination flag; the mounted UI stream passes false so stream churn from UIKit detaches no longer clears the viewport.
• Ownerless and release-gate streams keep the existing clear-on-termination behavior, and explicit presentation teardown remains the generation-fenced release point.

^{Written for commit ebe3d6f. Summary will update on new commits.}

Summary by CodeRabbit

• Bug Fixes
  • Preserved terminal viewport state during temporary UI detachments and consumer restarts.
  • Prevented terminal output stream termination from unnecessarily clearing the active viewport.
  • Ensured viewport ownership is released explicitly during final teardown while retaining previous behavior for standard streams.

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ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Repository: manaflow-ai/cmux/.coderabbit.yaml

Review profile: ASSERTIVE

Plan: Advanced

Run ID: 7bc190fb-792f-4aec-ab67-87ef4c85c8a6

📥 Commits

Reviewing files that changed from the base of the PR and between 2c4282e and ebe3d6f.

📒 Files selected for processing (2)

• Packages/iOS/CmuxMobileShell/Sources/CmuxMobileShell/MobileShellComposite.swift
• Packages/iOS/CmuxMobileShellUI/Sources/CmuxMobileShellUI/GhosttySurfaceRepresentable.swift

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📝 Walkthrough

Walkthrough

The terminal output stream now separates stream cleanup from viewport lease cleanup. Mounted UIKit surfaces keep the viewport lease across stream termination and release it during explicit teardown. The default stream API retains viewport release behavior.

Changes

Viewport Lease Lifecycle

Layer / File(s)	Summary
Configurable stream cleanup Packages/iOS/CmuxMobileShell/Sources/CmuxMobileShell/MobileShellComposite.swift	unregisterTerminalOutput now accepts a release flag. The stream factory forwards this flag and clears the viewport only when enabled.
Presentation-owned viewport release Packages/iOS/CmuxMobileShellUI/Sources/CmuxMobileShellUI/GhosttySurfaceRepresentable.swift	Mounted surfaces request stream termination without releasing the viewport lease.

Priority: ⬇️ Low

Estimated code review effort: 3 (Moderate) | ~20 minutes

Change: Bug fix

Sequence Diagram(s)

sequenceDiagram
  participant GhosttySurfaceRepresentable
  participant CmuxMobileShell
  participant StreamTeardown
  participant Viewport
  GhosttySurfaceRepresentable->>CmuxMobileShell: request output stream with releaseViewportOnTermination false
  CmuxMobileShell->>StreamTeardown: retain release flag
  StreamTeardown->>CmuxMobileShell: unregister output with releaseViewport false
  CmuxMobileShell->>Viewport: preserve viewport lease
  GhosttySurfaceRepresentable->>Viewport: release lease during explicit teardown

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Merge Risk: ⚪ Minimal · up to ebe3d

The change preserves the viewport lease across transient stream detaches and releases it during presentation teardown; no actionable merge-blocking risk remains.

🚥 Pre-merge checks | ✅ 24 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 1 functions across 1 files. (1 skipped: 1 …	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (24 passed)

Check name	Status	Explanation
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 Cloud Persistent Session And Early Input	✅ Passed	PASS. The authoritative diff changes only iOS output-stream and viewport-lease lifetime handling in two files. It does not change Cloud terminal creation, cmux-tui clients, physical transports, manual…
Cmux Swift Actor Isolation	✅ Passed	PASS. The production diff only adds a Bool parameter and conditional cleanup inside the existing @MainActor MobileShellComposite, plus passes that value from the existing UI coordinator task. `G…
Cmux Swift Blocking Runtime	✅ Passed	PASS. The PR changes two production Swift files, but the authoritative diff adds no semaphore waits, sleeps, delayed dispatch, polling, main-queue sync, or manual locks. It only adds a Boolean lease f…
Cmux Browser Automation Off-Main	✅ Passed	PASS. The pull request changes only iOS terminal viewport/output-stream lifecycle code in two files. The authoritative diff adds no browser socket command, WebKit wait, worker-router change, main-acto…
Cmux Expensive Synchronous Load	✅ Passed	PASS. The authoritative diff changes only terminal output-stream teardown semantics in two Swift files. It adds no agent-history loader, file scan, JSON/JSONL parsing, transcript or trajectory read, o…
Cmux Cache Substitution Correctness	✅ Passed	The diff changes terminal output teardown and viewport lease ownership only. It does not replace a fresh authoritative read with a cached or opportunistic value, and it does not alter persistence, his…
Cmux No Hacky Sleeps	✅ Passed	PASS. The pull request changes only Swift files: MobileShellComposite.swift and GhosttySurfaceRepresentable.swift. The custom check applies to TypeScript, JavaScript, shell, and non-Swift build/ru…
Cmux Algorithmic Complexity	✅ Passed	The pull request does not introduce an algorithmic-complexity violation. The Swift changes add a Boolean parameter, conditional viewport release, and an overload delegation. The existing output loop r…
Cmux Swift Concurrency	✅ Passed	PASS. The diff changes viewport-release state and adds an overload; it does not introduce a new legacy async pattern. The existing Task { @mainactor in ... } termination hop and stored output task r…
Cmux Swift @Concurrent	✅ Passed	The PR introduces no @concurrent or nonisolated async code. The new terminalOutputStream(...releaseViewportOnTermination:) overload is synchronous and belongs to @MainActor `MobileShellComposi…
Cmux Swift Package Boundaries	✅ Passed	The diff changes only existing SwiftPM targets: CmuxMobileShell and CmuxMobileShellUI. It adds viewport-release semantics to an existing terminal stream and passes that option from `GhosttySurface…
Cmux Swiftpm Lockfiles	✅ Passed	The pull request changes only two Swift source files. It does not change Package.swift, Package.resolved, .gitignore, workflow files, or Xcode project package references. Therefore, no SwiftPM lockfil…
Cmux Swift Logging	✅ Passed	The PR diff changes stream and viewport-lifetime handling only. It adds no print, debugPrint, dump, NSLog, ad hoc file/stdout logging, or sensitive-data logging. The existing mobileShellLog …
Cmux User-Facing Error Privacy	✅ Passed	The authoritative diff changes only terminal stream teardown behavior and internal Swift comments. It adds releaseViewport handling and passes releaseViewportOnTermination: false from the mounted …
Cmux Full Internationalization	✅ Passed	PASS: The pull request changes only Swift stream and viewport-lease lifecycle behavior. Added and modified text is limited to developer comments and API documentation; no user-facing Swift text, local…
Cmux Swiftui State Layout	✅ Passed	The PR changes only terminal stream teardown and viewport-lease handling. The added Swift code contains no new ObservableObject, @Published, @StateObject, @EnvironmentObject, GeometryReader,…
Cmux Architecture Rethink	✅ Passed	The PR is a small correctness fix with a clear invariant. The diff adds no sleeps, delayed dispatch, polling, locks, observers, caches, or new mutable state. It separates output-stream lifetime from t…
Cmux Swift Auxiliary Window Close Shortcuts	✅ Passed	PASS: The authoritative PR diff changes only terminal output-stream and viewport-lease behavior in MobileShellComposite.swift and GhosttySurfaceRepresentable.swift. It adds no NSWindow, `NSPanel…
Cmux Source Artifacts	✅ Passed	The PR changes only two tracked Swift source files under Packages/iOS/.... The diff adds and updates hand-written stream and viewport-lease logic. It adds no logs, screenshots, recordings, temporary…
Cmux No Test Or Debug Seam In Production Source	✅ Passed	PASS. The PR changes only two production Swift files and adds no #if DEBUG test-observation block, debug/test-named member, or wrapper accessor for private state. The new `terminalOutputStream(..., …
Title check	✅ Passed	The title clearly and concisely describes the main change: preserving the iPhone viewport lease during output stream churn.
Description check	✅ Passed	The description clearly explains the problem, behavior change, ownership rules, and verification results. It omits the template's Demo Video, review trigger, and checklist confirmations, but the core …

Full details: Docstring Coverage

Explanation

Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 1 functions across 1 files. (1 skipped: 1 too large.)

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[teamleaderleo]

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