Audit Swiftui Concurrency Safety

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name: audit-swiftui-concurrency-safety description: Audit macOS SwiftUI concurrency safety for correctness, current APIs, and production conventions. Use for that domain or as part of a full audit.

Bundled resource root

Let <swiftui-plugin-root> be the absolute plugin directory two levels above this SKILL.md. Resolve that path before running commands or opening shared references. When these instructions say swiftui-ctx, invoke <swiftui-plugin-root>/scripts/swiftui-ctx; do not assume the command is on PATH.

Audit SwiftUI Concurrency Safety

AUDIT-ONLY · macOS-only · SwiftUI-only. Run this on a finished or in-progress macOS SwiftUI project to detect — and where certain, fix — every way Swift concurrency goes wrong: non-Sendable types crossing actor boundaries, @Sendable closures touching main-actor state, the DispatchQueue.main.async cargo-cult, lifecycle-leaking Tasks, @MainActor spam, the Swift 6.2 opt-in misreads (@concurrent / nonisolated(nonsending) / NonisolatedNonsendingByDefault), and non-Sendable Transferable payloads. Findings are written in the toolkit's unified schema; the one mechanical defect (DispatchQueue.main.async) is fixed under the fix-safety protocol. This is never a from-scratch concurrency generator.

Concurrency is the toolkit's most version-sensitive domain — the rules changed twice in twelve months and most training data predates both changes. This is a CROSS-CUTTING SWEEP: it owns the isolation verdict wherever concurrency hazards appear, and routes the lifecycle / model / bridge fix to the owning sibling.

Two eras — keep them apart or every fix is wrong

• Swift 6 language mode (Sept 2024) = strict DATA-RACE-SAFETY CHECKING by default. Old warnings (non-Sendable crossing an actor, main-actor state in a @Sendable closure) are now hard errors. The default is checking, not isolation. Opt-in per target (SWIFT_VERSION = 6 / swiftLanguageMode(.v6)) — projects stay on their declared mode until bumped.
• Swift 6.2 (Sept 15 2025) = an OPT-IN "main actor by default" build mode (-default-isolation MainActor, surfaced as Approachable Concurrency + Default Actor Isolation = Main Actor). A setting you turn on, NOT the unconditional default. AI conflates the two → @MainActor spam OR code that assumes isolation it never enabled.

Record which mode the target is in (ORIENT, step 1) — half the findings depend on it. Toolchain facts (@concurrent, nonisolated(nonsending), -default-isolation MainActor, the NonisolatedNonsendingByDefault flag) are Swift 6.2+ and verified against swift.org / Swift Evolution, not swiftui-ctx.

Boundary / seam note (stay in lane)

This skill owns the isolation VERDICT; the fix shape often belongs to a sibling. Emit a cross_ref on every shared-seam finding (targets + primary-owner verdicts derive from <swiftui-plugin-root>/references/_shared/cross-ref-graph.md — do not restate them):

• Task in .onAppear / .onChange (conc-04, conc-10): async-data owns the lifecycle fix (.task / .task(id:)). THIS skill owns the verdict only when an isolation hazard is present (a non-Sendable capture, an off-actor mutation). cross_ref: audit-swiftui-async-data.
• SwiftData @Model mutation off-context (conc-11): swiftdata prescribes @ModelActor; this skill flags the race and routes. cross_ref: audit-swiftui-swiftdata.
• loadTransferable / Transferable Sendable race (conc-09): THIS skill owns Sendable correctness (primary); sandbox-files owns consent/bookmark. cross_ref: audit-swiftui-sandbox-files.
• AppKit Coordinator / NSViewRepresentable boundary: appkit-overuse owns whether the bridge exists, appkit-interop owns how. This skill flags only the Sendable/isolation hazard at the boundary. cross_ref: audit-swiftui-appkit-interop.
• @MainActor on an @Observable (conc-06): state-observation owns model-correctness; this skill owns the isolation angle. cross_ref: audit-swiftui-state-observation.

Defect index (conc-01 … conc-11)

id · tell · severity · fix · open reference. Severities: hard-fail (errors under the Swift 6 language mode / never-correct), warning (compiles but unsafe / non-native), advisory (judgment / toolchain-gated). auto = mechanical single-answer fix; flag = show the ✅, dev applies.

id	One-line tell	Sev	Fix	Reference
conc-01	Task.detached { … } carrying a non-Sendable class / ModelContext / NSView across the boundary	warning	flag	strict-checking-and-sendable.md
conc-02	@Sendable closure body reads self. / a @MainActor property ("can not be referenced from a Sendable closure")	warning	flag	strict-checking-and-sendable.md
conc-03	DispatchQueue.main.async inside async / SwiftUI code (GCD cargo-cult)	warning	auto	main-actor-hops.md
conc-04	bare Task { } in .onAppear / .onChange — not lifecycle-bound, not cancelled	warning	flag	main-actor-hops.md
conc-05	@MainActor on a pure-value struct/enum/free func (isolation spam)	advisory	flag	isolation-modes-and-execution.md
conc-06	@Observable UI type with no @MainActor while assuming "6.2 does it"	advisory	flag	isolation-modes-and-execution.md
conc-07	@concurrent present — confirm the target is Swift 6.2+	advisory	flag	isolation-modes-and-execution.md
conc-08	plain nonisolated … func … async assumed to run in the caller's context "because 6.2"	advisory	flag	isolation-modes-and-execution.md
conc-09	Transferable / loadTransferable payload wraps a reference / non-Sendable type	warning	flag	strict-checking-and-sendable.md
conc-10	rapid post-await writes (selection/refresh) with no cancel + generation guard → stale overwrite	advisory	flag	main-actor-hops.md
conc-11	@Model / modelContext mutation inside Task.detached (off-context race)	warning	flag	strict-checking-and-sendable.md

UNVERIFIED / toolchain-gated — carry as advisory and never assert as Swift-6.0/6.1 fact (each becomes source: verify against Xcode 26 SDK): everything that needs Swift 6.2+ — @concurrent (conc-07), nonisolated(nonsending) and the NonisolatedNonsendingByDefault default flip (conc-08), the -default-isolation MainActor mode (conc-05/06). Whether the target is in either era is read in ORIENT, not assumed.

The real API, at a glance

Real & era-stable (back-deploy to macOS 10.15+): @MainActor, Sendable, MainActor.run, Task.detached, sending, @preconcurrency import. .task / .task(id:) is macOS 12.0+; its closure inherits the caller's isolation via @isolated(any). Swift 6.2+ only (verify the toolchain): @concurrent (ALWAYS the global executor), nonisolated(nonsending) (ALWAYS the caller's context, SE-0461), -default-isolation MainActor, the NonisolatedNonsendingByDefault upcoming-feature flag, Task(name:).

The trap that is NOT a default: a plain nonisolated async function still hops to the global executor (SE-0338) — it stays on the caller's context only when NonisolatedNonsendingByDefault is enabled. @concurrent and nonisolated(nonsending) behave the same with or without the flag.

Floor values are the reconciled truth in <swiftui-plugin-root>/references/_shared/floors-master.md (read, never restate). There is no hallucinated-API surface here — concurrency defects are isolation mistakes on real symbols, not invented names.

✅ Correct — the grounded lifecycle shape (the anchor every fix imitates)

The most common concurrency defect (conc-04) is a bare Task { } in .onAppear — unbound to view lifetime, never cancelled. The lifecycle-correct shape is .task / .task(id:) (macOS 12.0+, caller-isolation-inheriting via @isolated(any), auto-cancelled on disappear). This is the real consensus shape, not a hand-written snippet — verified live via swiftui-ctx lookup task (step 5): .task { } 70% · .task(id:) 29% across the corpus.

// ❌ leaks — never cancelled, re-runs on every re-appear, races a fast-toggling view
.onAppear { Task { activity = isActive ? begin(options, reason) : nil } }

// ✅ bound to view lifetime, auto-cancelled, re-keyed on input change
.task(id: Tuple3(isActive, options, reason)) {
    activity = isActive ? SSApp.beginActivity(options, reason: reason) : nil
}

• Real example (swiftui-ctx file ex_a1cff2419c --smart): sindresorhus/Gifski — https://github.com/sindresorhus/Gifski/blob/7f873856e2acd8b52e6681dee3aec31e6cab23e4/Gifski/Utilities.swift#L5590
• doc: https://sosumi.ai/documentation/swiftui/view/task(name:priority:file:line:_:) (.task floor macOS 12.0+)
• Note the seam: the lifecycle fix (.task) is async-data's to prescribe — this skill owns the isolation verdict only when the captured value is non-Sendable or main-actor state is mutated off-context. Every ✅ in a written finding is reproduced this way: the consensus shape in ## Correct, a permalinked swiftui-ctx file … --smart example + this doc: in ## Source (step 7 FIX).

The 8-step audit workflow (execute verbatim)

1. ORIENT. tree / find the SwiftUI sources. Read (a) the Swift language mode (SWIFT_VERSION in project.pbxproj, or swiftLanguageMode / swift-tools-version in Package.swift) and (b) whether the opt-in mode is on (SWIFT_DEFAULT_ACTOR_ISOLATION = MainActor / -default-isolation MainActor / Approachable Concurrency). Both are load-bearing: conc-01/02/09/11 are errors only under the Swift 6 language mode; conc-05/06 flip meaning under the opt-in mode; conc-07/08 require Swift 6.2+. Record the swift_era.
2. LOCATE. Run the shared hybrid lint runner: bash <swiftui-plugin-root>/scripts/swiftui-lint.sh --skill audit-swiftui-concurrency-safety --dir <sources> --json /tmp/conc.json --sarif /tmp/conc.sarif. It runs this skill's tier-1 grep tells (lint/grep-tells.tsv) + tier-2 structural ast-grep rules (lint/ast-grep/*.yml — the Task-in-onAppear and off-context-@Model containment rules grep can't express), plus a per-file parse probe, emitting unified JSON + SARIF. Read its parse_warnings — a flagged file did not fully parse, so a structural miss can't masquerade as clean; READ those by hand. The runner only LOCATES. Engine + rule-file format + degradation: <swiftui-plugin-root>/references/_shared/lint-architecture.md.
3. READ. Open every located file in full — actor isolation, closure capture lists, gate scope, and the @Sendable-vs-@MainActor interplay are invisible to grep. Build a per-file inventory: each crossing site + what type crosses + the receiving actor + which era's rule applies.
4. DETECT. Apply the index. Assign each candidate a confidence; report a finding only at 100% certainty (a non-Sendable class in Task.detached, a DispatchQueue.main.async in async code, an @Observable UI type with no isolation under an OFF opt-in mode). Tag isolation_kind + swift_era.
5. VERIFY. For anything ≤ ~70% confidence (a symbol's existence/floor, "does this run on the caller or the pool", whether a type is Sendable), run both evidence sources. (a) Practice — bash <swiftui-plugin-root>/scripts/swiftui-ctx lookup <api> --json (and swiftui-ctx deprecated <api> for a currency rule): read its consensus (the canonical shape), recommended permalink, introduced_macos, and co_occurs_with; an exit-3 corroborates an invented spelling. (b) Spec — for an API floor / signature confirm via Sosumi (curl -sSL https://sosumi.ai/<apple-path> using references/source-directory.md for the path + <swiftui-plugin-root>/references/_shared/sosumi-reference.md for the protocol; never WebFetch developer.apple.com); for a toolchain / isolation-semantics fact (@concurrent, nonisolated(nonsending), the flag, the language-mode default) the spec source is swift.org / Swift Evolution (SE-0338, SE-0461) in references/source-directory.md, NOT swiftui-ctx. Cross-check introduced_macos against floors-master.md. Promote with the citation or discard; carry toolchain-gated items as advisory with source: verify against Xcode 26 SDK.
6. REPORT. Write each confirmed finding (output contract below). One finding per file, zero-padded, ordered. Write the run's _index.md.
7. FIX. Apply corrections under the fix-safety protocol (<swiftui-plugin-root>/references/_shared/fix-safety-protocol.md): clean-tree gate, findings-first, only fix_mode: auto (conc-03 DispatchQueue.main.async → await MainActor.run / @MainActor), one conventional commit per finding citing its rule_id, never weaken a check. The ✅ "Correct" is not a hand-written snippet — it is the swiftui-ctx consensus shape put in ## Correct, backed by a real macOS-26 example fetched with bash <swiftui-plugin-root>/scripts/swiftui-ctx file <recommended.id> --smart whose GitHub permalink (plus the swift.org / Sosumi doc:) goes in ## Source. Leave flag-only findings open with that ✅ in ## Correct.
8. DOUBLE-CHECK. Re-grep each fixed file to confirm the tell no longer matches; record the evidence in ## Fix applied?. Re-confirm every citation still resolves. If a fix introduced a new tell (a MainActor.run you added now needs an await, or a removed Task.detached leaves a non-Sendable capture), loop that file back to DETECT.

Confidence gating (load-bearing)

Report a finding only at 100% certainty. Anything ≤ ~70% goes to VERIFY (step 5). Whether the target is in the Swift 6 language mode / opt-in mode is read in ORIENT, never assumed — an era-dependent finding without a confirmed era is at best advisory. Auto-fix only conc-03; everything else is fix_mode: flag-only.

Output contract

Inherits the toolkit's unified contract (full schema + body sections + frontmatter keys: <swiftui-plugin-root>/references/_shared/finding-schema.md — do not restate it). Specialized for this domain:

• Findings: swiftui-audits/concurrency-safety/<context>/NN-slug.md (one finding per file, zero-padded, ordered). Per-run index: swiftui-audits/concurrency-safety/_index.md.
• domain: concurrency-safety. fix_mode is auto only for conc-03, else flag-only. Additive fields (per finding-schema.md §4 — concurrency-safety owns these): swift_era: (swift6-checking | swift6.2-optin | era-independent) and isolation_kind: (boundary-crossing | sendable-closure | gcd-cargo-cult | lifecycle-task | mainactor-spam | nonisolated-misread | transferable-sendable | modelactor-race). MUST use swift_era, never era (that is api-currency's). source is a swift.org / Swift-Evolution / Apple URL + access date, or verify against Xcode 26 SDK.

Starter <context> folders (file here when…):

<context>	File a finding here when…
sendable-crossing/	a non-Sendable type crosses an actor (conc-01), or a @Model mutates off-context (conc-11)
sendable-closures/	a @Sendable closure touches main-actor state (conc-02)
main-actor-hops/	a DispatchQueue.main.async cargo-cult or un-batched post-async write (conc-03)
task-lifecycle/	a bare Task in .onAppear/.onChange, or a stale-result race (conc-04, conc-10)
isolation-modes/	@MainActor spam, a missing-isolation @Observable, or an opt-in-mode misread (conc-05, conc-06)
execution-semantics/	@concurrent / nonisolated(nonsending) / nonisolated async caller-context confusion (conc-07, conc-08)
transferable-sendable/	a Transferable / loadTransferable payload isn't Sendable-correct (conc-09)

New-folder rule: if a finding does not fit any existing context folder, create a new one under swiftui-audits/concurrency-safety/ with a lowercase-hyphen slug, and note it in the run's _index.md. Prefer an existing folder when the fit is reasonable; consistency across runs is a hard requirement. Two runs over the same code produce structurally identical trees.

Reference routing

File	Open when
references/strict-checking-and-sendable.md	a Sendable-crossing, @Sendable-closure, Transferable, or off-context-@Model question — the Swift 6 strict-checking era (conc-01/02/09/11)
references/main-actor-hops.md	a GCD cargo-cult, the .task-vs-Task lifecycle, MainActor.run batching, or a stale-result generation guard (conc-03/04/10)
references/isolation-modes-and-execution.md	the Swift 6.2 opt-in confusion, @MainActor spam, @concurrent, and the nonisolated(nonsending) / NonisolatedNonsendingByDefault execution-context trap (conc-05/06/07/08)
references/source-directory.md	step VERIFY — the swift.org / Swift-Evolution / Apple source map fetched via Sosumi
lint/grep-tells.tsv + lint/ast-grep/*.yml	step LOCATE — this skill's declarative lint rule set fed to the shared runner (tier-1 grep tells + tier-2 structural ast-grep); edit here to tune detection

Shared toolkit references (point in, never restate):

Shared file	For
<swiftui-plugin-root>/references/_shared/floors-master.md	every floor/availability value (the reconciled truth)
<swiftui-plugin-root>/references/_shared/hallucination-blacklist.md	the canonical invented-name list
<swiftui-plugin-root>/references/_shared/finding-schema.md	the unified finding schema + the swift_era/isolation_kind additive fields
<swiftui-plugin-root>/references/_shared/fix-safety-protocol.md	the fix-safety protocol (step 7)
<swiftui-plugin-root>/references/_shared/sosumi-reference.md	the Apple-doc spec fetch protocol (step 5 VERIFY)
<swiftui-plugin-root>/references/_shared/swiftui-ctx-reference.md	the practice-corpus CLI contract — lookup/deprecated/file --smart for the consensus shape + permalinked example (steps 5 VERIFY · 7 FIX)
<swiftui-plugin-root>/references/_shared/cross-ref-graph.md	seam ownership + cross_ref targets (async-data · swiftdata · sandbox-files · appkit-interop · state-observation)
<swiftui-plugin-root>/references/_shared/macos-arm-gating.md	the macOS-arm gating rule (for any availability gate on a 6.2 API)

Detection accelerator

bash <swiftui-plugin-root>/scripts/swiftui-lint.sh --skill audit-swiftui-concurrency-safety --dir <files-or-dir> [--json out.json] [--sarif out.sarif] — the toolkit's one shared hybrid lint engine, fed this skill's declarative rules: tier-1 grep tells (lint/grep-tells.tsv, conc-01/02/03/04/05/06/07/08/09) + tier-2 ast-grep structural rules (lint/ast-grep/*.yml — conc-04 Task-in-onAppear containment, conc-11 @Model-mutation-in-Task.detached co-occurrence) that grep cannot express. conc-10 (a missing generation guard) is intentionally read-only — no lint tell can prove an absence; READ rapid-trigger sites by hand. It runs a per-file parse probe, emits unified JSON + SARIF, and degrades to grep-only with a notice if ast-grep is unreachable (npx --package @ast-grep/cli ast-grep; faster: brew install ast-grep). It only LOCATES — always READ each hit in full before reporting (step 3). The legacy scripts/conc-lint.sh is a thin pointer to this runner. Engine + rule-file format + JSON/SARIF shape: <swiftui-plugin-root>/references/_shared/lint-architecture.md.