fix: restore null-tolerance lost in strictNullChecks migration (#2060)

Two runtime regressions from the strict-mode migration (range 125db2e..c6be722) where a real runtime guard was replaced by a non-null assertion:

- services/cluster-fork.ts: findPluginDevice(...)!._id threw and aborted fork() when the plugin device was not found. Restored ?._id so options.id stays undefined (it is only a worker-affinity hint).
- plugin/plugin-host-api.ts: onDevicesChanged() coerced a missing optional 'devices' field to [], turning a fail-safe throw into mass (cascading) removal of all of a provider's devices. Restored fail-fast on missing devices.

Both compile under strictNullChecks.

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

server/src/plugin/plugin-host-api.ts

@@ -146,7 +146,9 @@ export class PluginHostAPI extends PluginAPIManagedListeners implements PluginAP
                 throw new Error(`providerId state not found for device ${p._id}`);
             return state.value === provider._id;
         });
-        const devices = deviceManifest.devices || [];
+        if (!deviceManifest.devices)
+            throw new Error(`onDevicesChanged called without devices for provider ${deviceManifest.providerNativeId}`);
+        const devices = deviceManifest.devices;
         const newIds = devices.map(device => device.nativeId);
         const toRemove = existing.filter(e => e.nativeId && !newIds.includes(e.nativeId));
 

server/src/services/cluster-fork.ts

@@ -82,7 +82,7 @@ export class ClusterForkService {
         const fork: ClusterForkParam = await worker.fork;
 
         const forkResultPromise = fork(options.runtime!, runtimeWorkerOptions, peerLiveness, getZip);
-        options.id! ||= this.runtime.findPluginDevice(runtimeWorkerOptions.packageJson.name)!._id;
+        options.id! ||= this.runtime.findPluginDevice(runtimeWorkerOptions.packageJson.name)?._id;
 
         // the server is responsible for killing the forked process when the requestor is killed.
         // minimizes lifecycle management duplication in python and node.