feat(voice): harden Gemini Live provider integration

server/providers/gemini/config.js

@@ -0,0 +1,54 @@
+import { realtimeInstructions } from '../openai/instructions.js';
+import { GEV_REALTIME_TOOLS } from '../openai/tools.js';
+
+export const GEMINI_LIVE_MODEL_DEFAULT = 'gemini-3.8-live';
+export const GEMINI_TOKEN_ENDPOINT =
+  'https://generativelanguage.googleapis.com/v1beta/auth_tokens';
+export const GEMINI_LIVE_WEBSOCKET_URL =
+  'wss://generativelanguage.googleapis.com/ws/google.ai.generativelanguage.v1beta.GenerativeService.BidiGenerateContentConstrained';
+
+export function normalizeGeminiModel(value) {
+  const model = String(value ?? GEMINI_LIVE_MODEL_DEFAULT)
+    .trim()
+    .replace(/^models\//, '');
+  return /^gemini-[a-z0-9][a-z0-9.-]{0,119}$/.test(model) ? model : null;
+}
+
+/** REST BidiGenerateContentSetup fields, excluding its model resource name. */
+export function createGeminiLiveConfig(
+  annotationGuidance,
+  inputMode = 'open-mic',
+  tools = GEV_REALTIME_TOOLS,
+  capabilities,
+) {
+  if (!['open-mic', 'push-to-talk'].includes(inputMode))
+    throw new Error('Invalid Gemini input mode');
+  const config = {
+    generationConfig: { responseModalities: ['AUDIO'] },
+    systemInstruction: {
+      parts: [{ text: realtimeInstructions(annotationGuidance, capabilities) }],
+    },
+    tools: [
+      {
+        functionDeclarations: tools.map(
+          ({ name, description, parameters }) => ({
+            name,
+            description,
+            // GEV's canonical schemas are JSON Schema, not Google's Schema.
+            parametersJsonSchema: structuredClone(parameters),
+            // App actions must finish before the model confirms their result.
+            behavior: 'BLOCKING',
+          }),
+        ),
+      },
+    ],
+    inputAudioTranscription: {},
+    outputAudioTranscription: {},
+    contextWindowCompression: { slidingWindow: {} },
+  };
+  if (inputMode === 'push-to-talk')
+    config.realtimeInputConfig = {
+      automaticActivityDetection: { disabled: true },
+    };
+  return config;
+}