Phase 4 — Custom RainMaker fabric init

Layer: Native MTR

After Apple commissioning succeeds, the host app commissions the device onto the RainMaker fabric.

Call chain

initializeMatterControllerWithFabric

1. Loads user NOC from Keychain (loadUserNOCFromKeychain).
2. Starts MTRDeviceControllerFactory with ESPMatterStorage (UserDefaults-backed).
3. Creates MTRCSRKeys(groupId:) for operational keypair + IPK.
4. Builds MTRDeviceControllerStartupParams (IPK, user NOC, root CA, vendor ID from Info.plist).
5. Sets operationalCertificateIssuer = self (for device node NOC in Phase 6).
6. Creates controller via createController(onExistingFabric:) or createController(onNewFabric:).
7. Sets MTRDeviceControllerDelegate + attestation delegate.

What could go wrong

User NOC not in Keychain → throws before session starts. Certificate PEM→DER conversion fails → controller init error. Factory already running from prior session → handled by shutdownMatterController() first.