Add agent instructions for managing worktrees

[markmur]

What changes are you making?

Makes a fresh git worktree usable without manual setup by auto-seeding it from the main checkout during dev up.

A fresh worktree is a clean checkout without the gitignored root .env, so sample-app setup can't regenerate its nested config. This wires that copy into dev up so it just happens.

• scripts/copy_worktree_env + dev copy-env — copies the repo-root .env (and any other root-level machine-local config) from the main checkout into the current worktree, so dev up's setup_storefront_env can regenerate all nested sample config (Android .env, Swift Storefront.xcconfig, RN sample .env) from it. It locates the main checkout via git rev-parse --git-common-dir, so it works regardless of where the worktree lives — sibling, nested, ~/.ae/worktrees, etc. No-ops from the main checkout, and prints paths/status only — never config values.
• dev.yml — dev up now auto-detects a worktree and runs the copy before workspace setup, via a met?/meet step. copy_worktree_env --check reports whether a copy is needed without performing it; the copy itself is idempotent, so it only does work on a fresh worktree.

How to test

dev up from a fresh worktree now seeds .env automatically — no separate step, wherever the worktree lives:

git worktree add ../ck-feature -b area/topic   # sibling, ~/.ae/worktrees, anywhere
cd ../ck-feature
dev up   # detects the worktree, copies root .env, then regenerates nested sample config

The copy is also available standalone and is a friendly no-op from the main checkout:

dev copy-env
# from main checkout => Already in the main checkout (...); nothing to copy.

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Before you merge

Important

• I've added tests to support my implementation
• I have read and agree with the Contribution Guidelines
• I have read and agree with the Code of Conduct
• I've updated the relevant platform README (platforms/swift/README.md and/or platforms/android/README.md)

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Releasing a new Swift version?

• I have bumped the version in ShopifyCheckoutKit.podspec
• I have bumped the version in platforms/swift/Sources/ShopifyCheckoutKit/ShopifyCheckoutKit.swift
• I have updated the SwiftPM/CocoaPods version snippets in platforms/swift/README.md (major version only)

Releasing a new Embedded Checkout Protocol version?

• I have bumped embeddedCheckoutProtocolAndroid in platforms/android/gradle/libs.versions.toml
• I have updated protocol/languages/kotlin/embedded-checkout-protocol/api/embedded-checkout-protocol.api if the public API changed

Releasing a new Android version?

• I have bumped checkoutKitAndroid in platforms/android/gradle/libs.versions.toml
• I have updated the Gradle/Maven version snippets in platforms/android/README.md

Tip

See the Contributing documentation for the full release process per platform.