# Develop Swift > Develop and review production Swift 6 code with strict concurrency, Swift Package Manager boundaries, typed APIs, and Swift Testing. Use for changes to .swift files, Package.swift, Swift modules, actors or Sendable code, Codable contracts, subprocess/runtime adapters, tests, refactors, and code-quality reviews in this repository. - **Type:** Skill - **Install:** `agentstack add skill-juju-w-safa-mac-develop-swift` - **Verified:** Yes — security-reviewed for prompt injection and unsafe behavior - **Seller:** [juju-w](https://agentstack.voostack.com/s/juju-w) - **Installs:** 0 - **Category:** [Cloud & Infrastructure](https://agentstack.voostack.com/c/cloud-infrastructure) - **Latest version:** 0.1.0 - **License:** MIT - **Upstream author:** [juju-w](https://github.com/juju-w) - **Source:** https://github.com/juju-w/safa-runtime/tree/main/.agents/skills/develop-swift ## Install ```sh agentstack add skill-juju-w-safa-mac-develop-swift ``` Requires the [AgentStack CLI](https://agentstack.voostack.com/docs/cli). Works with Claude Code, Cursor, and any MCP-compatible agent. ## About # Develop Swift Produce small, readable Swift changes that preserve SAFA's trust boundaries. Treat compilation as the first check, not the definition of correctness. ## Establish context Before editing: 1. Read `AGENTS.md`, `ARCHITECTURE.md`, and the relevant feature spec. 2. Inspect `Package.swift` and the touched target's dependency direction. 3. Read the complete type and its tests; do not infer behavior from one call site. 4. Check the working tree and preserve unrelated changes. 5. State which module owns the behavior before adding a type or dependency. If the requested behavior conflicts with a trust boundary, stop that implementation path and explain the conflict. Do not weaken an invariant to make a test or demo pass. ## Design the change - Prefer a value type and pure function for validation, classification, canonicalization, and state transitions. - Put I/O behind a narrow protocol and inject the implementation, clock, or process runner. - Keep parsing, domain decisions, platform adapters, and presentation separate. - Use one primary type per file. Split a file near 300 lines unless its cohesion is explicit. - Add a target dependency only when the architecture permits that direction. - Use explicit versioned request and response DTOs at CLI/XPC boundaries. Define `CodingKeys`; do not expose persistence models or add dynamic `[String: JSONValue]` payloads. - Model expected failures with precise error types and stable boundary error codes. Avoid `fatalError`, force unwraps, `try!`, and catch-all success fallbacks. - Prefer direct, unsurprising names. Avoid `Manager`, `Helper`, `Utils`, and generic dictionaries when a domain name or type exists. ## Apply Swift 6 concurrency rules - Preserve Swift 6 language mode and strict concurrency. - Make immutable value types `Sendable` when they cross tasks or actors. - Isolate shared mutable state in an actor or a visibly synchronized adapter. - Use `@unchecked Sendable` only for a small Foundation, Security, XPC, or process bridge whose synchronization is reviewable in the same file. - Prefer structured concurrency. Use `Task.detached` only when actor inheritance would be wrong and document ownership, cancellation, and lifetime. - Propagate cancellation and deadlines through subprocess and XPC boundaries. - Never block an actor executor with process waits, pipe reads, semaphores, or file I/O. - Ensure continuations resume exactly once on success, failure, cancellation, and invalidation. ## Test before implementation For security-sensitive behavior, add the failing test first. - Put pure invariants and policy cases in `Tests/Unit`. - Put stable CLI/XPC encoding and exit behavior in `Tests/Contract`. - Put composition and adapter journeys in `Tests/Integration`. - Put trust-boundary, tamper, secret-exposure, and fail-closed cases in `Tests/Security`. - Use synthetic resources only. Tests must not contact real infrastructure or read real Keychain items. - Test invalid inputs and cancellation, not only the happy path. - Prefer deterministic fakes over sleeps. When time is the subject, inject a clock where practical. ## Keep APIs readable - Prefer labeled initializers and small methods with one reason to change. - Keep public surface area minimal; default to internal visibility. - Use extensions only to group a real conformance or cohesive capability. - Keep comments focused on invariants, platform quirks, and security rationale. Do not narrate the syntax. - Do not hide side effects behind computed properties or innocent names. - Make resource ownership explicit for file handles, pipes, tasks, XPC connections, and temporary files; close or invalidate them on every path. ## Validate the slice Run the narrow test while iterating, then the repository gates: ```bash xcrun swift-format lint --recursive --strict Sources Tests Apps/SAFA/Targets Package.swift swift test --parallel swift build -c release xcodebuild -quiet -project Apps/SAFA/SAFA.xcodeproj -scheme "SAFA Runtime" \ -configuration Debug CODE_SIGNING_ALLOWED=NO build ``` Inspect the final diff for accidental public API, new dependencies, dynamic wire payloads, real infrastructure data, and unbounded output. Follow the repository PR workflow and never publish a tag, Release, signed artifact, or Skill package while the publication hold is active. ## Source & license This open-source skill is cataloged on AgentStack and links to its original source — we do not rehost the code. - **Author:** [juju-w](https://github.com/juju-w) - **Source:** [juju-w/safa-runtime](https://github.com/juju-w/safa-runtime) - **License:** MIT Install and usage instructions live in the source repository linked above. ## Pricing - **Free** — Free ## Security capabilities Automated source analysis of v0.1.0 — what this tool can access: - **Network access:** no - **Filesystem access:** no - **Shell / process execution:** yes - **Environment & secrets:** no - **Dynamic code execution:** no *"Yes" means the capability is present in the source — more access means more to trust, not that it is unsafe.* ## Versions - **0.1.0** — security scan: passed — Imported from the upstream source. ## Links - Listing page: https://agentstack.voostack.com/l/skill-juju-w-safa-mac-develop-swift - Seller: https://agentstack.voostack.com/s/juju-w - Browse the marketplace: https://agentstack.voostack.com/browse --- Listed on AgentStack — the marketplace for AI agent skills and MCP servers. Every listing is security-reviewed. Creators keep 70%.