fix: propagate resolved port to build when default port is unavailable

[janicduplessis]

Summary

When the default Metro port (8081) is unavailable, the resolved port is not properly propagated to the native build, causing the app to fail to connect to Metro.

There are two issues fixed:

1. handlePortUnavailable returns wrong port when packager is already running elsewhere

When port 8081 is busy and getNextPort discovers a packager already running on a different port (e.g. 8082) for the same project, handlePortUnavailable logs the correct port but returns the original unavailable port. This is the main bug — it affects both the interactive prompt flow and the "already running" flow.

Fix: Set port = nextPort in the !start branch of handlePortUnavailable.

2. createRun (iOS) and runAndroid don't propagate the resolved port to the build

When findDevServerPort returns a different port than requested (after the user accepts a port change prompt), the new port is only used to start Metro but never written back to args.port. This causes:

• iOS: RCT_METRO_PORT env var passed to xcodebuild still contains the original port
• Android: -PreactNativeDevServerPort gradle arg and adb reverse still use the original port

Fix: Update args.port = newPort when the port changes in both createRun.ts and runAndroid/index.ts.

Test plan

• Start a process on port 8081 (e.g. nc -l 8081)
• Run npx react-native start — accept port 8082
• In another terminal, run npx react-native run-ios (or run-android)
• Verify the app connects to Metro on 8082
• Also test: with Metro already running on 8082, run npx react-native run-android without Metro prompt
• Verify gradle receives -PreactNativeDevServerPort=8082 and adb reverse uses port 8082

[thymikee]

Thank you!

[thymikee]

Released in 20.1.3