fix(credentials): guard optional auth/provider when resolving credentials

- oauth-login-service.start: require definition.auth to be present and
  oauth kind before dispatching; captures oauthId in a local so the rest
  of the flow does not re-assert the nullable chain
- ipc-credentials-handlers save: reject connectors without an auth
  schema instead of crashing on property access
- ipc-credentials-handlers test: require provider and defaultModel to be
  set before calling into pi-ai, returning a diagnostic result otherwise

src/main/credentials/oauth-login-service.ts

@@ -31,12 +31,13 @@ export class OAuthLoginService {
 
   async start(connectorId: string): Promise<void> {
     const definition = getConnectorDefinition(connectorId);
-    if (definition.auth.type !== "oauth") {
+    if (!definition.auth || definition.auth.type !== "oauth" || !definition.auth.oauthId) {
       throw new Error(`Connector ${connectorId} does not use OAuth.`);
     }
-    const provider = getOAuthProvider(definition.auth.oauthId);
+    const oauthId = definition.auth.oauthId;
+    const provider = getOAuthProvider(oauthId);
     if (!provider) {
-      throw new Error(`Unknown OAuth provider: ${definition.auth.oauthId}`);
+      throw new Error(`Unknown OAuth provider: ${oauthId}`);
     }
 
     if (this.active.has(connectorId)) {

src/main/ipc-credentials-handlers.ts

@@ -89,6 +89,9 @@ export function registerCredentialIpcHandlers(deps: CredentialHandlerDeps): () =
     if (typeof definition === "string") return deps.fail("UNKNOWN_CONNECTOR", definition);
 
     const payload = parsed.data.payload;
+    if (!definition.auth) {
+      return deps.fail("UNSUPPORTED_PAYLOAD", `Connector ${parsed.data.connectorId} has no auth schema.`);
+    }
     if (definition.auth.type === "oauth") {
       return deps.fail("UNSUPPORTED_PAYLOAD", "Use OAuth login flow for OAuth connectors.");
     }
@@ -141,9 +144,17 @@ export function registerCredentialIpcHandlers(deps: CredentialHandlerDeps): () =
 
     const runTest = async (): Promise<DesktopResult<{ ok: boolean; message: string }>> => {
       try {
-        const model = resolveModel(definition.provider, definition.defaultModel);
-        if (!model) return ok({ ok: false, message: `Unknown model ${definition.defaultModel} for provider ${definition.provider}` });
-        const extraHeaders = resolveExtraStreamHeaders(definition.provider, resolved.apiKey);
+        if (!definition.provider) {
+          return ok({ ok: false, message: `Connector ${parsed.data.connectorId} has no pi-ai provider id configured.` });
+        }
+        if (!definition.defaultModel) {
+          return ok({ ok: false, message: `Connector ${parsed.data.connectorId} has no default model configured.` });
+        }
+        const provider = definition.provider;
+        const defaultModel = definition.defaultModel;
+        const model = resolveModel(provider, defaultModel);
+        if (!model) return ok({ ok: false, message: `Unknown model ${defaultModel} for provider ${provider}` });
+        const extraHeaders = resolveExtraStreamHeaders(provider, resolved.apiKey);
         const options: SimpleStreamOptions = {
           apiKey: resolved.apiKey,
           maxTokens: 1,