iOS Development Rules

Xcode & Build

Clean build folder (Cmd+Shift+K) fixes most "impossible" build errors — derived data gets corrupted regularly
Simulator reset (Device > Erase All Content and Settings) clears cached app state that survives reinstalls
Archive builds use Release config — bugs that only appear in production often stem from optimization differences
xcodebuild -showsdks lists available SDKs — useful when builds fail with "SDK not found"
Parallel builds can cause race conditions in script phases — add input/output file lists to enforce ordering

"No signing certificate" usually means certificate is expired or revoked — check in Keychain Access, not just Xcode
Provisioning profiles embed device UDIDs — new test device requires profile regeneration and reinstall
Automatic signing fails in CI — always use manual signing with exported credentials for builds
Distribution certificates are limited to 3 per account — don't create new ones, export and share the existing one
After renewing a certificate, update ALL provisioning profiles that used the old one