Capacitor UIScene Migrator

Guides a Capacitor 8.4 → 8.5 iOS migration to the UIScene lifecycle. The CLI migrator (npx cap migrate) handles projects that still match the Capacitor templates; this skill exists for everything else. It audits before editing, asks the developer where judgement is required, merges into existing files rather than replacing them, and delegates the mechanical work to the CLI whenever the project shape allows.

The canonical migration reference is the 8.4 → 8.5 migration guide. Link it whenever a step is left for the developer to do manually.

When to Use This Skill

• Migrating a Capacitor 8.x iOS app to the UIScene lifecycle
• A project where npx cap migrate reported a partial state and skipped
• An app with a hand-rolled SceneDelegate.swift or a customized AppDelegate.swift (deep-link routing, third-party SDK forwarding)
• Auditing a Capacitor plugin repo for UIScene compatibility
• Diagnosing the Xcode "CLIENT OF UIKIT REQUIRES UPDATE: This process does not adopt UIScene lifecycle" warning in a Capacitor app

When NOT to Use This Skill

• Cordova-to-Capacitor plugin migration → cordova-plugin-migrator
• Generating a new Capacitor plugin → capacitor-plugin-generator
• Capacitor 9 or later migrations (this skill is 8.4 → 8.5 only)
• Android lifecycle work (UIScene is iOS only)
• General Capacitor debugging unrelated to the scene lifecycle

Prerequisites

• A Capacitor 8.x project (app or plugin) with an ios/ platform or iOS sources
• @capacitor/cli 8.5+ available for the npx cap migrate handoff
• Xcode installed if the developer wants build verification

What Changed in 8.5 (facts the audit relies on)

These determine what breaks and what does not. Do not soften them.

• Scene adoption is opt-in. An app with no UIApplicationSceneManifest keeps the AppDelegate path, which still works on the 8.5 core. iOS posts UIScene.* notifications even for legacy apps (compatibility scene), so the bridge's JS resume/pause events fire in both modes.
• Once the scene manifest exists, iOS stops calling application(_:open:options:), application(_:continue:), and the four foreground/background AppDelegate methods (applicationDidBecomeActive, applicationWillResignActive, applicationDidEnterBackground, applicationWillEnterForeground). Custom code in any of those silently stops running. The UIApplication notifications still fire; didFinishLaunching, applicationWillTerminate, push token registration, and the remote-notification callbacks stay on the AppDelegate.
• SceneDelegateProxy re-posts the legacy .capacitorOpenURL, .capacitorOpenUniversalLink, and CDVPluginHandleOpenURL notifications with the same payload shape, so existing observers keep working. Cold-start URLs are delivered after the bridge view appears, so both appUrlOpen and getLaunchUrl() work on cold launch.
• New .capacitorSceneWillConnect, .capacitorSceneOpenURL, and .capacitorSceneOpenUniversalLink notifications carry the UIScene as the object. They are only posted on 8.5+; plugins that also support 8.4 must keep using the legacy names.
• TmpViewController and CapacitorBridge.tmpWindow were removed. Any reference is a build error on 8.5.
• The 8.5 templates create the window in code in scene(_:willConnectTo:); Main.storyboard no longer provides the root view controller. Custom CAPBridgeViewController subclasses are instantiated in the SceneDelegate, not set in the storyboard.

Agent Behavior

• Audit first, report second, edit last. Never modify a file before the developer has seen the findings and confirmed.
• Never overwrite an existing SceneDelegate.swift, AppDelegate.swift, or Info.plist structure. Merge surgically per references/surgical-merges.md.
• Prefer the CLI. If the project classifies as eligible (Phase 3), run npx cap migrate instead of editing files by hand.
• Ask, do not assume, at the decision points in Phase 6. Use AskUserQuestion where available; otherwise ask in plain text and wait.
• Do not commit, stage, or push. Leave version control to the developer.
• On a plugin repo, never touch Info.plist, AppDelegate.swift, or project files. The plugin branch is audit and advice only.

Procedures

Phase 1: Detect Repo Type

Decide app vs. plugin before anything else.

• App: has ios/App/App.xcodeproj (or capacitor.config.* with an ios/ platform directory).
• Plugin: has a Package.swift or .podspec depending on Capacitor, CAPPlugin/CapacitorPlugin subclasses in ios/Sources or ios/Plugin, and no App/App.xcodeproj.

Plugin repo → skip to Phase 10 (references/plugin-repo-audit.md).

Phase 2: Detect Package Manager and Versions

• Pods vs. SPM: ios/App/Podfile → CocoaPods; Package.swift or an SPM reference inside the Xcode project → SPM. This affects how npx cap sync ios behaves, not the SceneDelegate content: the 8.5 templates ship one SceneDelegate for both.
• Check @capacitor/ios version in package.json. If below 8.5, the dependency update is part of the migration; the CLI migrator handles it, or update manually per the guide.

Phase 3: Classify the Project State

Read the same three signals the CLI migrator uses:

1. Info.plist contains UIApplicationSceneManifest
2. SceneDelegate.swift exists on disk in the app target directory (pbxproj registration is a separate concern, handled in Phase 7)
3. AppDelegate.swift contains UISceneConfiguration(name:

Every route audits before anything runs or changes; the routes differ only in who applies the changes.

The CLI warns and skips on partial states by design. Partial is exactly where this skill does its own editing.

Phase 4: Audit the Codebase

Run the scans in references/audit-patterns.md across the app's iOS sources and installed plugins (node_modules/@capacitor*, plus any local plugin paths). Collect findings for:

• UIApplication.shared.applicationState usage
• Custom application(_:open:) / application(_:continue:) bodies beyond the ApplicationDelegateProxy forwarder
• Custom code in AppDelegate lifecycle methods
• Existing SceneDelegate.swift implementations and what they contain
• References to tmpWindow / TmpViewController (build errors on 8.5)
• Existing or partial UIApplicationSceneManifest entries
• .capacitorOpenURL / .capacitorOpenUniversalLink observers (informational: they keep working)

Phase 5: Present Findings and Confirm

Report every finding with file and line before touching anything. Group as: blocks the build (tmpWindow/TmpViewController), needs a decision (custom delegate bodies, existing SceneDelegate), informational (observers, applicationState in plugins the developer does not own). Ask the developer to confirm proceeding.

Phase 6: Decision Points

Ask, at minimum:

1. Legacy URL handlers: keep or remove application(_:open:options:) / application(_:continue:) in AppDelegate.swift? They become dead code under scenes. Keeping them is harmless; removing them is cleaner. If the body contains custom logic, it must move to the SceneDelegate either way. On the eligible route, apply the answer after the CLI has run.
2. Custom application(_:open:) body: migrate it manually (the developer moves the logic) or have the skill move it into scene(_:openURLContexts:) alongside the proxy forwarder? Show the body before asking. Skip this question when the body is forwarder-only per the audit test.
3. Existing SceneDelegate: confirm each proposed insertion (missing forwarders, window setup) as a diff before applying.

Phase 7a: Eligible → CLI Handoff

Verify the resolved CLI first: run npm install if node_modules is missing, then npx cap --version; the UIScene migrator needs 8.5 or newer. Then run npx cap migrate and interpret its output. It writes SceneDelegate.swift, patches Info.plist and AppDelegate.swift, registers the file in project.pbxproj, warns on the scan patterns from Phase 4, and links the migration guide. Confirm each step's log line; if the CLI skipped a step (file existed, partial state raced in), fall through to Phase 7b for that step only.

Phase 7b: Partial or Hand-Rolled → Surgical Merges

Apply only the missing pieces, per references/surgical-merges.md:

• Missing manifest → merge UIApplicationSceneManifest into Info.plist, preserving existing keys
• Missing configurationForConnecting → insert into the existing AppDelegate.swift before the class's closing brace, displacing nothing
• Missing or incomplete SceneDelegate.swift → create from references/scene-delegate-template.md, or add the missing SceneDelegateProxy.shared forwarders to the existing one, preserving all custom logic
• New file → register in project.pbxproj (Xcode does this when the file is added through the IDE; otherwise follow the reference)

Phase 8: Sync and Build

Run npx cap sync ios. If Xcode is available, build the app target and surface any errors (most commonly leftover tmpWindow references).

Phase 9: Verification Checklist

Walk the developer through, linking the guide for detail:

• App launches to the web view
• Background and foreground the app: JS resume/pause fire (they are scoped to the app's scene now)
• Custom URL scheme: cold launch and warm open both deliver the URL (appUrlOpen listener and App.getLaunchUrl())
• Universal link, if the app uses them (requires an associated domain)

Phase 10: Plugin Repo Branch

No app-level files to patch. Audit the plugin's Swift per references/plugin-repo-audit.md and report: lifecycle assumptions that break under scenes, APIs removed in 8.5, and the compatibility rules for supporting 8.4 and 8.5 with one plugin version. Apply code changes only if the developer asks, and only in the plugin's own sources.

Best Practices

DO

• Show diffs before applying them
• Keep every finding tied to a file and line
• Re-run the Phase 3 classification after edits to confirm the project reads as fully migrated
• Tell plugin authors to keep the legacy notification names while they support 8.4

DON'T

• Overwrite user code, ever
• Rewrite third-party plugin code under node_modules (report it; the fix belongs upstream)
• Duplicate the CLI's work by hand-editing an eligible project
• Promise universal-link behavior without an associated domain to test

Error Handling

• npx cap migrate warns "partial state" → expected; this skill's Phase 7b exists for that. Do not reset the project without asking.
• project.pbxproj edits fail or the project no longer opens → revert the pbxproj change and register the file through Xcode instead.
• Build fails on tmpWindow / TmpViewController → the references must be deleted; there is no 8.5 replacement (the bridge's viewController is the presentation anchor).
• SceneDelegate exists but the app shows a black screen → the delegate neither creates a window nor lets a storyboard do it; add the window setup from the template.

Related Skills

• cordova-plugin-migrator: Cordova plugin to Capacitor migration
• capacitor-plugin-generator: new Capacitor plugin scaffolds

References