feat: record and replay Gemini audio responses

Detects audio inlineData in both non-streaming JSON and streaming SSE
Gemini responses, producing AudioResponse fixtures with b64Json and
contentType. Widens recorder EndpointType to include audio-gen and
fal-audio. Adds Float32Array alignment guard for embeddings.

Author: jpr5

src/recorder.ts

@@ -168,23 +168,37 @@ export async function proxyAndRecord(
     if (collapsed.droppedChunks && collapsed.droppedChunks > 0) {
       defaults.logger.warn(`${collapsed.droppedChunks} chunk(s) dropped during stream collapse`);
     }
-    if (collapsed.content === "" && (!collapsed.toolCalls || collapsed.toolCalls.length === 0)) {
+    // Audio from streamed inlineData (e.g. Gemini SSE with audio parts)
+    if (collapsed.audioB64) {
+      fixtureResponse = {
+        audio: {
+          b64Json: collapsed.audioB64,
+          contentType: collapsed.audioMimeType ?? "audio/mpeg",
+        },
+      };
+    } else if (
+      collapsed.content === "" &&
+      (!collapsed.toolCalls || collapsed.toolCalls.length === 0)
+    ) {
       defaults.logger.warn("Stream collapse produced empty content — fixture may be incomplete");
-    }
-    const reasoningSpread = collapsed.reasoning ? { reasoning: collapsed.reasoning } : {};
-    if (collapsed.toolCalls && collapsed.toolCalls.length > 0) {
-      if (collapsed.content) {
-        // Both content and toolCalls present — save as ContentWithToolCallsResponse
-        fixtureResponse = {
-          content: collapsed.content,
-          toolCalls: collapsed.toolCalls,
-          ...reasoningSpread,
-        };
+      const reasoningSpread = collapsed.reasoning ? { reasoning: collapsed.reasoning } : {};
+      fixtureResponse = { content: collapsed.content ?? "", ...reasoningSpread };
+    } else {
+      const reasoningSpread = collapsed.reasoning ? { reasoning: collapsed.reasoning } : {};
+      if (collapsed.toolCalls && collapsed.toolCalls.length > 0) {
+        if (collapsed.content) {
+          // Both content and toolCalls present — save as ContentWithToolCallsResponse
+          fixtureResponse = {
+            content: collapsed.content,
+            toolCalls: collapsed.toolCalls,
+            ...reasoningSpread,
+          };
+        } else {
+          fixtureResponse = { toolCalls: collapsed.toolCalls, ...reasoningSpread };
+        }
       } else {
-        fixtureResponse = { toolCalls: collapsed.toolCalls, ...reasoningSpread };
+        fixtureResponse = { content: collapsed.content ?? "", ...reasoningSpread };
       }
-    } else {
-      fixtureResponse = { content: collapsed.content ?? "", ...reasoningSpread };
     }
   } else {
     // Non-streaming — try to parse as JSON
@@ -221,7 +235,10 @@ export async function proxyAndRecord(
   const fixtureMatch = buildFixtureMatch(matchRequest);
 
   // Build and save the fixture
-  const fixture: Fixture = { match: fixtureMatch, response: fixtureResponse };
+  const fixture: Fixture = {
+    match: fixtureMatch,
+    response: fixtureResponse,
+  };
 
   // Check if the match is empty (all undefined values) — warn but still save to disk
   const matchValues = Object.values(fixtureMatch);
@@ -451,6 +468,10 @@ function buildFixtureResponse(
     }
     if (typeof first.embedding === "string" && encodingFormat === "base64") {
       const buf = Buffer.from(first.embedding, "base64");
+      if (buf.byteLength % 4 !== 0) {
+        // Malformed embedding — return a zero-dimension embedding fixture
+        return { embedding: [] };
+      }
       const aligned = new Uint8Array(buf).buffer; // Always offset 0
       const floats = new Float32Array(aligned, 0, buf.byteLength / 4);
       return { embedding: Array.from(floats) };
@@ -626,6 +647,24 @@ function buildFixtureResponse(
     const content = candidate.content as Record<string, unknown> | undefined;
     if (content && Array.isArray(content.parts)) {
       const parts = content.parts as Array<Record<string, unknown>>;
+
+      // Audio inlineData parts take priority over text
+      const audioParts = parts.filter(
+        (p: Record<string, unknown>) =>
+          p.inlineData &&
+          typeof (p.inlineData as Record<string, unknown>).mimeType === "string" &&
+          ((p.inlineData as Record<string, unknown>).mimeType as string).startsWith("audio/"),
+      );
+      if (audioParts.length > 0) {
+        const inlineData = audioParts[0].inlineData as Record<string, unknown>;
+        return {
+          audio: {
+            b64Json: String(inlineData.data ?? ""),
+            contentType: String(inlineData.mimeType),
+          },
+        };
+      }
+
       const fnCallParts = parts.filter((p) => p.functionCall);
       const textParts = parts.filter((p) => typeof p.text === "string" && !p.thought);
       const thoughtParts = parts.filter((p) => p.thought === true && typeof p.text === "string");
@@ -833,7 +872,15 @@ function buildFixtureResponse(
 /**
  * Derive fixture match criteria from the original request.
  */
-type EndpointType = "chat" | "image" | "speech" | "transcription" | "video" | "embedding";
+type EndpointType =
+  | "chat"
+  | "image"
+  | "speech"
+  | "transcription"
+  | "video"
+  | "embedding"
+  | "audio-gen"
+  | "fal-audio";
 
 function buildFixtureMatch(request: ChatCompletionRequest): {
   userMessage?: string;