Fix sidebar accessibility children cycle

[austinywang]

A URL in a workspace description can crash cmux when an accessibility client walks the window or observes a row update (#14273). The row text's children getter both forwarded AppKit cell children and set attributedStringValue while its link state was still stale. That setter can synchronously re-enter the same getter through AppKit's table-cell notification path.

The text view now owns an accessible static-text element and only its purpose-built link children. AX queries return attributed text with link annotations without changing the rendered text or posting notifications. Content changes publish link descriptors before AppKit's text setter can call back, and link replacement publishes the new children before retiring old proxies.

The regression mounts the actual AppKit sidebar alongside a loaded Project panel, includes an https:// workspace description, and walks window children with a visited set and depth cap before and after changing that description. Additional cases preserve readable plain text, verify link parents/geometry, and reject display-text writes during AX queries. Existing link/pointer/truncation/retirement coverage is retained. All children/parent overrides under Sources/Sidebar/AppKitList and Sources/Panels/ProjectPanel* were audited: the text view is the only custom children override; ProjectPanel has no custom AX parent/children override.

Trade-offs:

• The text view replaces its inherited cell as the readable AX element. Returning only links while leaving the view ignored would remove plain workspace text; the new static-text role preserves it.
• AX-attributed text is assembled on request instead of being stored in display attributes. Link materialization remains demand-driven, preserving ordinary sidebar layout costs.
• The text view and its existing shared pointer/AX glyph geometry were split into files below 500 lines. Neither Swift budget TSV changed.
• No release-build experiment opt-out was added. It could offer a fallback, but it expands rollout/settings policy and would not repair the AX invariant; the crash fix remains the priority.

Validation:

• python3 scripts/verify-local.py --swift-changed origin/main --receipt artifacts/accessibility/preflight.json
• ./scripts/lint-pbxproj-test-wiring.sh
• python3 scripts/swift_file_length_budget.py
• git diff --check
• ./scripts/localize-changes --base origin/main: no changed user-facing keys; all nine catalogs passed.
• Original regression b9ab24fd857063eb0943cc7cf431a592610498c8: hosted run 36094335347, blocked twice by the pinned Iroh artifact checksum before test execution.
• Expanded regression 088d07ecf314d95c2f079d2ed8176a517f33b492: hosted run 36096815108, pending.
• Fix plus existing row/retirement suites: hosted run 36096886608, also blocked by the Iroh checksum. No executed-test or end-to-end pass is claimed yet.
• Isolated local AppKit diagnostic with an external AX observer reproduced getter re-entry: old setter-in-getter pattern reached the safety cap at depth 8; the read-only pattern stayed at depth 1. This uses a standalone Python/AppKit fixture, not a compiled cmux build.

Current head 209a48443759ee2020213bc7bf5963a28a9eaaf6 is submitted as controller job c87cab94011c151904ff2594 with tag issue-14273-accessibility-children-cycle. Submission receipt: artifacts/fleet/209a48443759ee2020213bc7bf5963a28a9eaaf6-submit.json. Controller doctor passes with one eligible worker. The job is queued.

Reproduction uses the reporter's stated recursive-AXChildren alternative and HQ's isolated-test/tagged-app safety instruction. The stable cmux app is never an AX-walk target. The earlier fleet job c3551eb73979f3c975611fb3 was cancelled while still unassigned because its source was superseded; it is not final-head evidence.

Fixes #14273

— MarbleWren pending
run: run_issue_14273_accessibility_20260925
session: cmux182-14273-20260925

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📝 Walkthrough

Walkthrough

Sidebar row text now uses a dedicated text view and shared glyph layout for HTTP(S) link rendering, pointer activation, and accessibility proxies. New tests inspect mounted accessibility trees and link attributes, and existing row tests query link attributes through the text view.

Changes

Sidebar text links and accessibility

Layer / File(s)	Summary
Text layout and link rendering Sources/Sidebar/AppKitList/Cells/SidebarRowTextLinkLayout.swift, Sources/Sidebar/AppKitList/Cells/SidebarRowTextView.swift, Sources/Sidebar/AppKitList/Cells/SidebarWorkspaceRowSlotViews.swift, cmux.xcodeproj/project.pbxproj	The new layout calculates visible glyph hit locations and clipped link frames. The text view applies row styling and retains HTTP(S) links. The prior implementation is removed from the workspace row slot file, and the project registers the new source files.
Link activation and accessibility Sources/Sidebar/AppKitList/Cells/SidebarRowTextView.swift, Sources/Sidebar/AppKitList/Cells/SidebarRowTextAccessibilityLink.swift	Pointer activation requires the same link at mouse-down and mouse-up. Accessibility queries expose visible link proxies, and invalidation detaches proxies before optionally notifying accessibility clients.
Accessibility tree validation cmuxTests/SidebarAccessibilityTreeWalk.swift, cmuxTests/SidebarAccessibilityTreeTests.swift, cmuxTests/SidebarAppKitRowCellTests.swift, cmux.xcodeproj/project.pbxproj	The bounded tree walker detects cycles and records maximum depth. Tests cover mounted sidebar and project-panel trees, text accessibility, and link attributes. Existing row tests now query the text view.

Priority: ➖ Normal

Estimated code review effort: 3 (Moderate) | ~25 minutes

Change: Bug fix · Severity of issue fixed: Medium

Merge Risk: 🔵 Low · up to 209a4

A hide-and-show transition can leave sidebar link text empty, and the new regression test may miss the reported accessibility cycle. Both concerns are bounded but worth addressing before merge.

Security Architecture Review

Security architecture risk: 🔵 Low · up to 209a4

The change removes a path that could make accessibility clients recurse through the sidebar tree. Link activation remains limited to visible HTTP(S) links, and no new security exposure was established. The mounted regression has not yet been confirmed by a completed run.

Retained concerns
No architecture-level concerns identified.

Security review details

Security Blast Radius

• inferred — The affected exposure is the local sidebar accessibility tree and its link-activation path. Removing synthesized text-field children narrows what an accessibility client can traverse; no broader service or datastore reach is established.

Trust Boundaries and Controls

• observed — Workspace-description links cross into pointer or assistive-client activation only through the row view’s callback. The view retains HTTP(S) descriptors, checks pointer down/up consistency, and checks current range and visible geometry for accessibility presses.

Resilience and Maintainability Implications

• observed — Removed link proxies lose their owner and accessibility parent before destruction notification. A later press on an invalidated proxy cannot use its former owner; proxy materialization is gated by requested and stale state.

🚥 Pre-merge checks | ✅ 24 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 34.15% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 41 functions across 6 files. (1 skipped: …	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (24 passed)

Check name	Status	Explanation
Linked Issues check	✅ Passed	Issue [#14273] requires an acyclic accessibility tree that completes a full children walk without a crash. SidebarRowTextView now exposes only its owned SidebarRowTextAccessibilityLink descendants…
Out of Scope Changes check	✅ Passed	The changes stay within issue [#14273]. The shared text-link layout supports consistent visible-link geometry for accessibility and pointer behavior. Proxy invalidation, link-preservation tests, proje…
Cmux Cloud Persistent Session And Early Input	✅ Passed	PASS: The custom check applies to Cloud terminal creation and persistent transport changes. The authoritative PR diff changes only sidebar accessibility code, sidebar text/link layout, project wiring,…
Cmux Swift Actor Isolation	✅ Passed	The production changes do not introduce the checked actor-isolation mistakes. SidebarRowTextView and SidebarRowTextAccessibilityLink were already @MainActor in the base revision. The new `Sideba…
Cmux Swift Blocking Runtime	✅ Passed	The production Swift diff adds no semaphore, blocking wait, sleep, delayed dispatch, polling loop, main-queue sync, or manual lock. The only timing-related additions are in `cmuxTests/SidebarAccessibi…
Cmux Browser Automation Off-Main	✅ Passed	The check is not triggered. The PR changes only sidebar accessibility/layout code, project wiring, and tests. Sources/TerminalController.swift and `Packages/macOS/CmuxControlSocket/Sources/CmuxContr…
Cmux Expensive Synchronous Load	✅ Passed	PASS: The production diff only changes sidebar accessibility, link geometry, and TextKit layout. It adds no agent-history loader, transcript/trajectory/workstream JSON or JSONL parsing, directory scan…
Cmux Cache Substitution Correctness	✅ Passed	PASS — The production diff adds only transient AppKit accessibility/link state and a cached TextKit geometry layout. cachedLinkHitLayout is invalidated when text or layout changes and is keyed by te…
Cmux No Hacky Sleeps	✅ Passed	PASS: The PR changes Swift source/tests and cmux.xcodeproj/project.pbxproj only. It introduces no TypeScript, JavaScript, shell, or non-Swift build/runtime script changes, and the patch contains no …
Cmux Algorithmic Complexity	✅ Passed	No algorithmic-complexity failure is introduced. The production change removes the prior nested accessibilityChildren scan (children.contains for each link). New link materialization uses linear p…
Cmux Swift Concurrency	✅ Passed	The changed production Swift code adds no background Dispatch queues, DispatchGroup, Combine state, completion-handler API, or fire-and-forget Task. The new @MainActor AppKit types use synchronous U…
Cmux Swift @Concurrent	✅ Passed	PASS. The PR adds no @concurrent annotations and no new nonisolated async functions. The only new async test is isolated by @MainActor and performs AppKit tree setup; its awaits call the existin…
Cmux Swift Package Boundaries	✅ Passed	PASS: The changed production code is AppKit-bound UI glue. SidebarRowTextView subclasses NSTextField and overrides AppKit accessibility, layout, hit-testing, and mouse APIs. `SidebarRowTextAccessi…
Cmux Swiftpm Lockfiles	✅ Passed	The PR changes only Swift source files, tests, and Xcode file/build wiring. The cmux.xcodeproj/project.pbxproj diff adds file references and source entries, not SwiftPM package references or depende…
Cmux Swift Logging	✅ Passed	The changed production Swift files add no print, debugPrint, dump, NSLog, Logger, stdout/stderr, or ad hoc diagnostic file logging. The only new file write creates a project fixture in `cmux…
Cmux User-Facing Error Privacy	✅ Passed	PASS. The production diff changes AppKit accessibility ownership, link geometry, and proxy notifications. It adds no user-facing error, alert, command output, API error body, or recovery copy. The onl…
Cmux Full Internationalization	✅ Passed	PASS. The production diff adds no user-facing copy. SidebarRowTextView is moved from SidebarWorkspaceRowSlotViews.swift; its only added quoted values are the existing coder initializer diagnostic,…
Cmux Swiftui State Layout	✅ Passed	PASS: The PR adds AppKit code, not SwiftUI state or layout code. SidebarRowTextView subclasses NSTextField, and the new layout helper is an AppKit text layout struct. The only new import SwiftUI…
Cmux Architecture Rethink	✅ Passed	The diff is a local AppKit accessibility ownership fix. SidebarRowTextView becomes the explicit static-text owner, returns only its owned link proxies, and each proxy points back to that owner; inva…
Cmux Swift Auxiliary Window Close Shortcuts	✅ Passed	The PR does not add or materially change a standalone cmux-owned window. The changed production types are SidebarRowTextView: NSTextField, SidebarRowTextAccessibilityLink: NSAccessibilityElement, …
Cmux Source Artifacts	✅ Passed	All changed paths are intentional Swift source, Swift tests, or Xcode project wiring. The diff adds no local output, logs, screenshots, recordings, caches, build output, dependency checkout, temporary…
Cmux No Test Or Debug Seam In Production Source	✅ Passed	No test/debug seam was added to production Sources/ Swift. The changed production files contain no #if DEBUG, XCTest/test-build guard, or seam-named member. SidebarRowTextView members are normal…
Title check	✅ Passed	The title clearly identifies the main change: fixing a cycle in sidebar accessibility children.
Description check	✅ Passed	The description clearly explains the crash, implementation changes, trade-offs, regression coverage, and validation status. It omits the template headings, demo attachment, and checklist, but the core…

Full details: Docstring Coverage

Explanation

Docstring coverage is 34.15% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 41 functions across 6 files. (1 skipped: 1 unsupported.)

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Actionable comments posted: 2

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• 🪄 Fix CodeRabbit comments on this PR

🤖 Prompt to fix review comments

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Inline comments:
In `@cmuxTests/SidebarAccessibilityTreeTests.swift`:
- Line 95: Update the mounted accessibility traversal test around
`SidebarAccessibilityTreeWalk` to assert reachability by identity instead of
relying on `walk.visited.count`. Require the row’s
`SidebarRowTextAccessibilityLink` from `textView.accessibilityChildren()`, then
separately assert that the walk visits `textView`, that link, and `projectView`.

In `@Sources/Sidebar/AppKitList/Cells/SidebarRowTextView.swift`:
- Around line 21-29: Update the isHidden observer in SidebarRowTextView to
release accessibility proxies and clear the pending URL when the view becomes
hidden, without calling invalidateLinkAccessibility(), which also clears the
text and link descriptors. Preserve those values so unhiding restores the
existing content and links.

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ℹ️ Review info

⚙️ Run configuration

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

Review profile: ASSERTIVE

Plan: Advanced

Run ID: 781b1b5a-6103-4779-b6d2-c2c41511cced

📥 Commits

Reviewing files that changed from the base of the PR and between 85a3655 and 209a484.

📒 Files selected for processing (8)

• Sources/Sidebar/AppKitList/Cells/SidebarRowTextAccessibilityLink.swift
• Sources/Sidebar/AppKitList/Cells/SidebarRowTextLinkLayout.swift
• Sources/Sidebar/AppKitList/Cells/SidebarRowTextView.swift
• Sources/Sidebar/AppKitList/Cells/SidebarWorkspaceRowSlotViews.swift
• cmux.xcodeproj/project.pbxproj
• cmuxTests/SidebarAccessibilityTreeTests.swift
• cmuxTests/SidebarAccessibilityTreeWalk.swift
• cmuxTests/SidebarAppKitRowCellTests.swift

💤 Files with no reviewable changes (1)

• Sources/Sidebar/AppKitList/Cells/SidebarWorkspaceRowSlotViews.swift

Included review availability: Your plan provides up to 10 included reviews per hour; 0 remain after this review.

[teamleaderleo]

SidebarAccessibilityTreeTests/mountedSidebarAndProjectPanelAccessibilityWalkIsAcyclic() fails in the numbered app-host shard.

It failed on all three attempts of shard 5/7 in run 36099432041, which is PR #14379 on a merge with main after this PR landed:

✘ Test mountedSidebarAndProjectPanelAccessibilityWalkIsAcyclic() recorded an issue at SidebarAccessibilityTreeTests.swift:99:9: Expectation failed: walk.textValues.contains { $0.contains("Context.swift") }
RATCHET_NEW_FAILURE SidebarAccessibilityTreeTests/mountedSidebarAndProjectPanelAccessibilityWalkIsAcyclic()

Jobs: 107961430004 (attempt 1), 107967261552 (attempt 2), 107969348604 (attempt 3).

The walk finds no Context.swift row, so the project panel's file list is either not loaded yet or not mounted. The load wait (waitUntil(timeout: .seconds(5)) near line 36) may pass on a condition that doesn't imply the tree rows exist yet. Or the panel may depend on state that an earlier suite in the same host changes; the changed-suites lane runs this suite alone.

The failing PR only touches test infrastructure (it restores AppDelegate.shared after each XCTest case), and this suite is Swift Testing, which that change does not observe.

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