Fix iOS composer compile break (nonisolated image helpers)

[lawrencecchen]

main's iOS build is currently broken. TerminalComposerView: View is implicitly @MainActor, so its static boundedSendPayload / downsampledImageData are main-actor-isolated, but the nonisolated prepare(url:) calls them synchronously off-actor inside a background TaskGroup. ios-simulator fails to compile:

TerminalComposerView.swift:516: error: main actor-isolated static method 'boundedSendPayload(from:)' cannot be called from outside of the actor
TerminalComposerView.swift:520: error: expression is 'async' but is not marked with 'await'

These are pure ImageIO functions with no main-actor state (the doc comment already says the decode must not run on the main actor), so both are marked nonisolated. The size constants they read are static let Sendable Ints, already nonisolated-accessible; PreparedAttachment is a Sendable nested struct (no inherited isolation).

Landed on main via #6102 because ios-simulator is not a required check (iOS CI false-green). Unblocks the in-flight iOS PRs (#6038, #6044, #6096, #6119) which all merged main and inherited the break.

🤖 Generated with Claude Code

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Note

Low Risk
Isolation annotations only; image encode logic and store caps are unchanged.

Overview
Fixes the iOS simulator compile failure where background image staging called main-actor-isolated static helpers on TerminalComposerView.

prepare(url:) already runs ImageIO in a background TaskGroup; boundedSendPayload and downsampledImageData are now nonisolated so they can be invoked from that path without crossing the main actor. Related size constants (maxImageBytes, sendMaxPixelSize, thumbnailMaxPixelSize) and CMUXMobileShellStore.maxPendingAttachmentImageBytes are also marked nonisolated so the off-main encode path can read the same caps. No change to attachment limits or encoding behavior.

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Summary by cubic

Fix iOS build by marking TerminalComposerView image helpers and size-cap constants as nonisolated so background calls from prepare(url:) compile under Swift 6. Keeps ImageIO work off the main thread and removes the main-actor isolation error in the iOS simulator.

• Bug Fixes
  • Marked boundedSendPayload and downsampledImageData in TerminalComposerView as nonisolated.
  • Marked maxImageBytes, thumbnailMaxPixelSize, sendMaxPixelSize, and the store’s maxPendingAttachmentImageBytes as nonisolated for off-actor reads.
  • No behavioral changes; isolation-only update.

^{Written for commit ffadba7. Summary will update on new commits.}

Summary by CodeRabbit

• Chores
  • Updated terminal composer image-encoding helpers to use nonisolated static declarations, improving correctness/performance in off-main encoding paths.
  • Marked the exported pending-attachment image size limit as nonisolated for safe reads from the composer image-encoding workflow.
  • No changes to image size limits, encoding results, or other user-facing behavior.

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Project	Deployment	Actions	Updated (UTC)
cmux	Ready	Preview, Comment	Jun 16, 2026 12:59am
cmux-staging	Building	Preview, Comment	Jun 16, 2026 12:59am

[coderabbitai]

📝 Walkthrough

Walkthrough

Image-encoding helpers and size constants across two modules are marked nonisolated static to enable safe concurrent access from off-main composer paths. A shared public byte-capacity constant in MobileShellComposite is exported as nonisolated static so that TerminalComposerView can read it safely from nonisolated contexts. Private encoding constants and methods in TerminalComposerView are similarly annotated. No implementation or call-site logic changes.

Image-encoding concurrency isolation

Layer / File(s)	Summary
Authorize external nonisolated access to image cap Packages/CmuxMobileShell/Sources/CmuxMobileShell/MobileShellComposite.swift	maxPendingAttachmentImageBytes is marked public nonisolated static with a comment noting its use in composer off-main image-encoding paths.
Mark private encoding constants and methods nonisolated Packages/CmuxMobileShellUI/Sources/CmuxMobileShellUI/TerminalComposerView.swift	Encoding size constants maxImageBytes and sendMaxPixelSize, and helper methods boundedSendPayload(from:) and downsampledImageData(...), are marked private nonisolated static.

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~3 minutes

Possibly related PRs

• manaflow-ai/cmux#6102: Concurrency annotations on image-encoding helpers directly support the image-attachment composer send path added in that PR.

Poem

🐇 Hop, hop — constants set free,
No actor to bind them, just pure concurrency.
nonisolated stamped from core to the view,
The image encoders have work they can do.
Safe off the main thread—the bunny's delight! 🌿

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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 File And Package Boundaries	❌ Error	PR adds new MobileShellComposite.swift (5553 lines), far exceeding 800-line threshold, mixing connection state, terminal management, workspace actions, event streaming, and attachment logic—violati...	Extract domain logic from MobileShellComposite into separate focused packages (e.g., MobileConnection, MobileTerminalSession, MobileWorkspaceActions) to keep individual files under 800 lines with single clear responsibility.

✅ Passed checks (20 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and concisely describes the main change: fixing an iOS compiler issue by marking image helpers as nonisolated.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.
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	PR marks pure ImageIO methods and immutable Sendable constants as nonisolated—correctly restores off-MainActor calls in background TaskGroup, fixing a Swift 6 compilation error without introducing...
Cmux Swift Blocking Runtime	✅ Passed	PR introduces no blocking/timing-based synchronization: only adds 'nonisolated' annotations to pure image-processing functions and immutable constants for Swift 6 actor-isolation compliance.
Cmux Expensive Synchronous Load	✅ Passed	PR marks expensive ImageIO image-encoding functions as nonisolated to move them OFF the main actor, enabling background task execution; does not add expensive sync loads to main actor or interactiv...
Cmux Cache Substitution Correctness	✅ Passed	PR contains only Swift concurrency isolation annotations (nonisolated) with no logic changes. No cache substitution or persistence paths involved—check not applicable.
Cmux No Hacky Sleeps	✅ Passed	Custom check "cmux no hacky sleeps" explicitly scopes out Swift files (deferred to swift-blocking-runtime.md). This PR modifies only Swift files with concurrency annotations and no timing/delay l...
Cmux Algorithmic Complexity	✅ Passed	Changes are purely Swift concurrency isolation annotations (adding nonisolated keyword). No algorithmic changes: function bodies unchanged, no new loops/sorting/filtering, constants values unchan...
Cmux Swift Concurrency	✅ Passed	PR only adds nonisolated isolation annotations to existing code; no legacy async patterns (DispatchQueue, Combine, completion handlers, fire-and-forget Tasks) are introduced or expanded.
Cmux Swift @Concurrent	✅ Passed	All changes correctly apply nonisolated to synchronous pure helper functions and immutable static constants, with no invalid @concurrent annotations. Changes comply with swift-concurrent-annotati...
Cmux Swift Logging	✅ Passed	PR contains no new logging statements or log modifications. Changes are isolation-only (adding nonisolated to static methods/constants), with no violations of swift-logging.md rules.
Cmux User-Facing Error Privacy	✅ Passed	Changes are pure Swift concurrency isolation fixes with no user-facing error messages, exposed credentials, vendor/provider names, or sensitive implementation details.
Cmux Full Internationalization	✅ Passed	PR contains only Swift concurrency annotations (nonisolated keywords) with no user-facing text, string catalog, or localization changes. Qualifies as allowed developer-only code per i18n rules.
Cmux Swiftui State Layout	✅ Passed	This PR contains only actor isolation annotations (adding nonisolated keywords to static functions and constants). There are no new SwiftUI state patterns, GeometryReader uses, lazy list row store...
Cmux Architecture Rethink	✅ Passed	Pure concurrency/isolation annotation fix (nonisolated keyword additions) for Swift 6 compilation. No logic changes, no timing constructs, no state additions, no architectural debt introduced—match...
Cmux Swift Auxiliary Window Close Shortcuts	✅ Passed	PR makes no window-related changes; only adds 'nonisolated' isolation annotations to image encoding helpers and constants. No NSWindow, NSPanel, NSWindowController, SwiftUI Window, or WindowGroup c...
Cmux Source Artifacts	✅ Passed	PR modifies only hand-written Swift source files in standard Packages/*/Sources/ directories with concurrency isolation annotations; no artifacts, generated code, logs, build output, or problematic...
Description check	✅ Passed	The pull request description provides a clear summary of what changed (marking methods/constants as nonisolated), why (fixing iOS build compilation errors due to actor isolation), and includes detailed context about the root cause, affected code, and unblocked PRs.

✨ 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-ios-composer-actor

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[greptile-apps]

Greptile Summary

This PR fixes an iOS simulator compile break introduced by PR #6102, where boundedSendPayload and downsampledImageData inherited implicit @MainActor isolation from TerminalComposerView: View but were called synchronously from the already-nonisolated background prepare(url:) child task.

• Marks boundedSendPayload, downsampledImageData, and the three static let size constants they read (maxImageBytes, thumbnailMaxPixelSize, sendMaxPixelSize) as nonisolated in TerminalComposerView.
• Marks MobileShellComposite.maxPendingAttachmentImageBytes (aliased as CMUXMobileShellStore) as nonisolated so the initializer of maxImageBytes can reference it from a nonisolated context — completing the isolation-safe call chain.
• Runtime behavior is entirely unchanged; only the Swift concurrency isolation annotations are affected.

Confidence Score: 5/5

Safe to merge — purely additive isolation annotations on immutable constants and pure ImageIO functions with no observable behavior change.

All changed symbols are either static let integer literals or pure ImageIO encode/downsample functions. Marking them nonisolated cannot introduce data races because there is no shared mutable state involved. The nonisolated call chain from prepare(url:) through boundedSendPayload and downsampledImageData is now complete and consistent, and the sibling constants that remain main-actor-bound are untouched. No logic, data flow, or error handling was modified.

No files require special attention.

Important Files Changed

Filename	Overview
Packages/CmuxMobileShellUI/Sources/CmuxMobileShellUI/TerminalComposerView.swift	Adds nonisolated to five static members (3 let constants, 2 pure ImageIO functions) that are called from the already-nonisolated prepare(url:) background task; no logic changes.
Packages/CmuxMobileShell/Sources/CmuxMobileShell/MobileShellComposite.swift	Marks maxPendingAttachmentImageBytes as nonisolated static let so the TerminalComposerView.maxImageBytes initializer can safely reference it from a nonisolated context; sibling constants that remain main-actor-bound are unchanged.

Sequence Diagram

%%{init: {'theme': 'neutral'}}%%
sequenceDiagram
    participant ST as Staging Task (MainActor)
    participant P as prepare(url:) nonisolated static
    participant BG as TaskGroup child (background priority)
    participant BS as boundedSendPayload nonisolated static
    participant DD as downsampledImageData nonisolated static

    ST->>P: await prepare(url:)
    P->>BG: group.addTask(priority: .background)
    BG->>BS: boundedSendPayload(from: source)
    BS->>DD: downsampledImageData(PNG at sendMaxPixelSize)
    DD-->>BS: Data?
    BS->>DD: downsampledImageData(JPEG fallbacks...)
    DD-->>BS: Data?
    BS-->>BG: (data, format)?
    BG->>DD: downsampledImageData(thumbnail at thumbnailMaxPixelSize)
    DD-->>BG: Data?
    BG-->>P: PreparedAttachment?
    P-->>ST: PreparedAttachment?

Loading

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sequenceDiagram
    participant ST as Staging Task (MainActor)
    participant P as prepare(url:) nonisolated static
    participant BG as TaskGroup child (background priority)
    participant BS as boundedSendPayload nonisolated static
    participant DD as downsampledImageData nonisolated static

    ST->>P: await prepare(url:)
    P->>BG: group.addTask(priority: .background)
    BG->>BS: boundedSendPayload(from: source)
    BS->>DD: downsampledImageData(PNG at sendMaxPixelSize)
    DD-->>BS: Data?
    BS->>DD: downsampledImageData(JPEG fallbacks...)
    DD-->>BS: Data?
    BS-->>BG: (data, format)?
    BG->>DD: downsampledImageData(thumbnail at thumbnailMaxPixelSize)
    DD-->>BG: Data?
    BG-->>P: PreparedAttachment?
    P-->>ST: PreparedAttachment?

Loading

_{Reviews (2): Last reviewed commit: "Composer fix: also mark the size-cap con..." | Re-trigger Greptile}

[lawrencecchen]

Superseded by #6199 (723329f), which landed the identical fix (mark the composer image-encode helpers + size-cap constants + the store's maxPendingAttachmentImageBytes nonisolated) and is already on main. Closing as redundant.