Build Run Debug Skill for Codex

Build / Run / Debug

Quick Start

Use this skill to set up one project-local script/build_and_run.sh entrypoint,

wire .codex/environments/environment.toml so the Codex app shows a Run button,

then use that script as the default build/run path.

Prefer shell-first workflows:

• ./script/build_and_run.sh as the single kill + build + run entrypoint once it exists
• xcodebuild for Xcode workspaces or projects
• swift build plus raw executable launch inside that script for true SwiftPM command-line tools
• swift build plus project-local .app bundle staging and /usr/bin/open -n launch for SwiftPM AppKit/SwiftUI GUI apps
• optional script flags for lldb, log stream, telemetry verification, or post-launch process checks

Do not assume simulators, touch interaction, or mobile-specific tooling.

If an Xcode-aware MCP surface is already available and the user explicitly wants

it, use it only where it fits. Keep that usage narrow and honest: prefer it for

Xcode-oriented discovery, logging, or debugging support, and do not force

simulator-specific workflows onto pure macOS tasks.

Workflow

• Discover the project shape.
• Check whether the workspace is already inside a git repo with git rev-parse --is-inside-work-tree.
• If no git repo is present, run git init at the project/workspace root before building so Codex app git-backed features are available. Never run git init inside a nested subdirectory when the current workspace already belongs to a parent repo.
• Look for .xcworkspace, .xcodeproj, and Package.swift.
• If more than one candidate exists, explain the default choice and the ambiguity.

• Resolve the runnable target and process name.
• For Xcode, list schemes and prefer the app-producing scheme unless the user names another one.
• For SwiftPM, identify executable products when possible.
• Split SwiftPM launch handling by product type:
• use raw executable launch only for true command-line tools,
• use a generated project-local .app bundle for AppKit/SwiftUI GUI apps.
• Determine the app/process name to kill before relaunching.

• Create or update script/build_and_run.sh.
• Make the script project-specific and executable.
• It should always:
• stop the existing running app/process if present,
• build the macOS target,
• launch the freshly built app or executable.
• Add optional flags for debugging/log inspection:
• --debug to launch under lldb or attach the debugger
• --logs to stream process logs after launch
• --telemetry to stream unified logs filtered to the app subsystem/category
• --verify to launch the app and confirm the process exists with pgrep -x <AppName>
• Keep the default no-flag path simple: kill, build, run.
• Prefer writing one script that owns this workflow instead of repeatedly asking the agent to manually run swift build, locate the artifact, then invoke an ad hoc run command.
• For SwiftPM GUI apps, make the script build the product, create dist/<AppName>.app, copy the binary to Contents/MacOS/<AppName>, generate a minimal Contents/Info.plist with CFBundlePackageType=APPL, CFBundleExecutable, CFBundleIdentifier, CFBundleName, LSMinimumSystemVersion, and NSPrincipalClass=NSApplication, then launch with /usr/bin/open -n <bundle>.
• For SwiftPM GUI --logs and --telemetry, launch the bundle with /usr/bin/open -n first, then stream unified logs with /usr/bin/log stream --info ....
• Do not recommend direct SwiftPM executable launch for AppKit/SwiftUI GUI apps.
• Use references/run-button-bootstrap.md as the canonical source for the

script shape and exact environment file format. Do not fork a second

authoritative snippet in another skill or command.

• Keep the run script outside app source. It belongs in script/build_and_run.sh, not in App/, Views/, Models/, Stores/, Services/, or Support/.

• Write .codex/environments/environment.toml at the project root once the script exists.
• Use this exact placement: .codex/environments/environment.toml.
• Use the exact action shape in references/run-button-bootstrap.md.
• This file is what gives the user a Codex app Run button wired to the script.
• If the project already has this file, update the Run action command to point at ./script/build_and_run.sh instead of creating a duplicate action.
• Keep this Codex environment config separate from Swift app source files.

• Build and run through the script.
• Default to ./script/build_and_run.sh.
• Use ./script/build_and_run.sh --debug, --logs, --telemetry, or --verify when the user asks for debugger/log/telemetry/process verification support.

• Summarize failures correctly.
• Classify the blocker as compiler, linker, signing, build settings, missing SDK/toolchain, script bug, or runtime launch.
• Quote the smallest useful error snippet and explain what it means.

• Debug the right way.
• Use the script's --logs or --telemetry mode for config, entitlement, sandbox, and action-event verification.
• For SwiftPM GUI apps, if the app bundle launches but its window still does not come forward, check whether the entrypoint needs NSApp.setActivationPolicy(.regular) and NSApp.activate(ignoringOtherApps: true).
• Use the script's --debug mode or direct lldb if symbolized crash debugging is needed.
• If the user needs to instrument and verify specific window, sidebar, menu, or menu bar actions, switch to telemetry.
• Keep evidence tight and user-facing.

• Use Xcode-aware MCP tooling only when it helps.
• If the user explicitly asks for XcodeBuildMCP and it is already available, prefer it over ad hoc setup.
• Use the MCP for Xcode-aware discovery or debug/logging workflows when the available tool surface clearly matches the task.
• Fall back to shell commands immediately when the MCP does not provide a clean macOS path.

Preferred Commands

• Project discovery:
• find . -name '*.xcworkspace' -o -name '*.xcodeproj' -o -name 'Package.swift'
• Scheme discovery:
• xcodebuild -list -workspace <workspace>
• xcodebuild -list -project <project>
• Build/run:
• ./script/build_and_run.sh
• ./script/build_and_run.sh --debug
• ./script/build_and_run.sh --logs
• ./script/build_and_run.sh --telemetry
• ./script/build_and_run.sh --verify

References

• references/run-button-bootstrap.md: canonical build_and_run.sh and .codex/environments/environment.toml contract.

Guardrails

• Prefer the narrowest command that proves or disproves the current theory.
• Do not leave the user with a one-off manual command chain once a stable build_and_run.sh script can own the workflow.
• Do not write .codex/environments/environment.toml before the run script exists, and do not point the Run action at a stale script path.
• Do not launch a SwiftUI/AppKit SwiftPM GUI app as a raw executable unless the user explicitly wants to diagnose that failure mode: it can produce no Dock icon, no foreground activation, and missing bundle identifier warnings. Keep raw executable launch only for true command-line tools.
• Do not claim UI state you cannot inspect directly.
• Do not describe mobile or simulator workflows as if they apply to macOS.
• If build output is huge, summarize the first real blocker and point to follow-up commands.

Output Expectations

Provide:

• the detected project type
• the script path and Codex environment action you configured, if applicable
• the command you ran
• whether build and launch succeeded
• the top blocker if they failed
• the smallest sensible next action