Fix Github Issue

Load agent-device skill. DO NOT SKIP

Fix a GitHub Issue

Constraints

These are hard rules. Violating any of them is a failure.

1. NO mobile MCP — Never call any mcp__mobile-mcp__* tool. No exceptions. 2. Device interaction = `agent-device` only — All simulator/emulator interaction (screenshots, taps, typing, scrolling, app launch/kill) MUST go through agent-device CLI commands. Read the agent-device skill for allowed commands. Exception: adb is allowed for Android emulator setup (devices, install, reverse, shell getprop, screenrecord). 3. Reproduce first, code later — Always reproduce the issue on the simulator before exploring code. The bug might already be fixed. Do not explore the codebase until you have confirmed the bug exists. Exception: Feature requests and new example screens have nothing to reproduce — go straight to implementation. 4. If you can't repro — When running interactively, stop and prompt the user with suggestions. When running on CI (no user), attempt to diagnose from code and issue description.

Steps

1. Understand the issue and reproduce the problem using agent-device skill before exploring the code because the bug might not be there now. It will be good to initially add sample to the top of examples screen to avoid scrolling. 2. Diagnose root cause 3. Implement the fix 4. Review your code for any obvious problems 5. Verify the fix using agent-device skill 6. Kill background processes — before raising a PR, kill any Metro bundler or other background processes you started (see Cleanup section below). 7. Raise a PR using the raise-pr skill. When running interactively, confirm with dev first. On CI, raise directly.

Running Metro

Start from fixture/react-native/:

cd fixture/react-native && yarn start

Verify: curl -s http://localhost:8081/status

Building & Installing the Fixture App

Only build the native app if it's not already installed. Check first:

xcrun simctl get_app_container booted org.reactjs.native.example.FlatListPro 2>/dev/null

• If it succeeds: app is installed. Just yarn build (TS) and relaunch.
• If it fails: app is not installed. Build and install:

cd fixture/react-native && yarn react-native run-ios

E2E Tests

Run E2E tests before raising a PR if any of these changed:

• E2E test files (*.e2e.*)
• Example/sample screens in fixture/react-native/src/
• New example screens added

yarn e2e:ios

This runs detox build -c ios.sim.release followed by detox test -c ios.sim.release. E2E test files live in fixture/react-native/e2e/tests/.

Warning: E2E builds a release app that replaces the debug app on the simulator. After running E2E, rebuild debug to continue interactive testing:

cd fixture/react-native && yarn react-native run-ios

Cleanup (MANDATORY on CI)

Before raising a PR or finishing, kill all background processes you started. On CI, leftover processes (especially Metro) prevent the GitHub Actions job from exiting, causing it to run until the timeout.

# Kill Metro bundler
lsof -ti:8081 | xargs kill -9 2>/dev/null || true
# Kill any other background processes you started
kill %1 2>/dev/null || true

Always do this before the raise-pr step.

Common Pitfalls

• `estimatedItemSize` does not exist in this FlashList — it is not a prop. Do not add it to repro screens.
• Repro only triggers after scroll — add onEndReached or prepend items to force the scroll path
• Android and iOS behave differently — always test both; Android uses a native RecyclerView bridge
• Stale layout cache — if sizes look wrong after a fix, call ref.current?.clearLayoutCacheOnUpdate()
• Prop not forwarded — check FlashListProps.ts and RecyclerView.tsx to confirm the prop reaches the layout manager
• Grid row detection with spans — never use Math.floor(index / numColumns) to determine which row an item is in when overrideItemLayout spans are possible. Instead, compare layout.y values from the layout manager — items in the same row always share the same y.
• Metro port conflict — kill anything on port 8081, then restart Metro from fixture/react-native/. See the Metro section above.
• App can't connect to Metro — if the app shows a red/yellow error about connecting to the bundler, configure the port: iOS simulator Cmd+D → "Configure Bundler" → set host localhost and port 8081. Then reload.
• React Native version mismatch — the native build (0.84.x) must connect to the fixture's own Metro, not another project's bundler running a different RN version.

• `dist/` is NOT rebuilt on branch switch — you MUST yarn build after every git checkout. Verify with grep in dist/ that the expected code change is present. Without this, you test stale code and get false results.
• Always reproduce the bug on `main` BEFORE testing the fix — without confirming the bug exists on the base branch, you can't prove the fix works. See review-and-test skill → "Review Methodology".
• Code-only diagnosis is acceptable on CI — layout/scroll bugs, Android-only issues (no emulator on macOS CI), and web/SSR issues (no browser on CI) can be diagnosed from code analysis + unit tests when simulator reproduction isn't feasible.

For more testing/debugging pitfalls (console.log, RTL setup, agent-device swipe, observable callbacks), see the `review-and-test` skill.

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Self-Evolving Instructions

When running interactively (not on CI), update this file AND the review-and-test skill after each fix session:

1. Add any new pitfalls discovered to the appropriate skill 2. Add affected edge cases to review-and-test edge case checklists

On CI, only update skill files if the learning is critical (e.g., a new pitfall that would cause repeated failures). Minor improvements should wait for interactive sessions.