From fbdbe9c162c32f223688f304ab95df80be5995a2 Mon Sep 17 00:00:00 2001
From: Peter Steinberger <steipete@gmail.com>
Date: Sat, 8 Aug 2026 18:59:23 -0700
Subject: [PATCH] fix(mistral): reset transcription state after reconnect
 (#120813)

---
 .../realtime-transcription-provider.test.ts   | 61 ++++++++++++++++++-
 .../realtime-transcription-provider.ts        |  2 +
 2 files changed, 62 insertions(+), 1 deletion(-)

diff --git a/extensions/mistral/realtime-transcription-provider.test.ts b/extensions/mistral/realtime-transcription-provider.test.ts
index 56c0abf87e7d..aa6a7a12f91c 100644
--- a/extensions/mistral/realtime-transcription-provider.test.ts
+++ b/extensions/mistral/realtime-transcription-provider.test.ts
@@ -12,13 +12,16 @@ let cleanup: (() => Promise<void>) | undefined;
 async function createRealtimeServer(
   onRequest: (url: URL) => void,
   transcriptionEvents: readonly Record<string, unknown>[] = [],
+  eventsByConnection?: readonly (readonly Record<string, unknown>[])[],
 ) {
   const server = createServer();
   const wss = new WebSocketServer({ noServer: true, maxPayload: 1024 * 1024 });
   const clients = new Set<WebSocket>();
+  let connectionCount = 0;
   server.on("upgrade", (request, socket, head) => {
     onRequest(new URL(request.url ?? "/", "http://127.0.0.1"));
     wss.handleUpgrade(request, socket, head, (ws) => {
+      const connectionIndex = connectionCount++;
       clients.add(ws);
       ws.on("close", () => {
         clients.delete(ws);
@@ -31,9 +34,12 @@ async function createRealtimeServer(
             : Buffer.from(data);
         const message = JSON.parse(bytes.toString("utf8")) as { type?: unknown };
         if (message.type === "session.update") {
-          for (const event of transcriptionEvents) {
+          for (const event of eventsByConnection?.[connectionIndex] ?? transcriptionEvents) {
             ws.send(JSON.stringify(event));
           }
+          if (eventsByConnection && connectionIndex === 0) {
+            setTimeout(() => ws.terminate(), 10);
+          }
         }
       });
       ws.send(JSON.stringify({ type: "session.created" }));
@@ -338,6 +344,59 @@ describe("buildMistralRealtimeTranscriptionProvider", () => {
     expect(onPartial.mock.calls.map(([text]) => text)).toEqual(partials);
   });
 
+  it.each([
+    {
+      name: "preserves the replacement session's terminal-only speech",
+      firstEvents: [{ type: "transcription.segment", text: "earlier turn" }],
+      secondEvents: [{ type: "transcription.done", text: "replacement final" }],
+      partials: [],
+    },
+    {
+      name: "does not mix the interrupted session's partial text into replacement speech",
+      firstEvents: [
+        { type: "transcription.segment", text: "earlier turn" },
+        { type: "transcription.text.delta", text: "old fragment " },
+      ],
+      secondEvents: [
+        { type: "transcription.text.delta", text: "new fragment" },
+        { type: "transcription.done", text: "replacement final" },
+      ],
+      partials: ["old fragment ", "new fragment"],
+    },
+  ])("$name after a real provider reconnect", async ({ firstEvents, secondEvents, partials }) => {
+    const requests: URL[] = [];
+    const baseUrl = await createRealtimeServer(
+      (url) => requests.push(url),
+      [],
+      [firstEvents, secondEvents],
+    );
+    const onPartial = vi.fn();
+    const onTranscript = vi.fn();
+    const onError = vi.fn();
+    const session = buildMistralRealtimeTranscriptionProvider().createSession({
+      providerConfig: { apiKey: "fixture-value", baseUrl },
+      onPartial,
+      onTranscript,
+      onError,
+    });
+
+    await session.connect();
+    await vi.waitFor(
+      () => {
+        expect(requests).toHaveLength(2);
+        expect(session.isConnected()).toBe(false);
+      },
+      { timeout: 3_000 },
+    );
+
+    expect(onTranscript.mock.calls.map(([text]) => text)).toEqual([
+      "earlier turn",
+      "replacement final",
+    ]);
+    expect(onPartial.mock.calls.map(([text]) => text)).toEqual(partials);
+    expect(onError).not.toHaveBeenCalled();
+  });
+
   it("tracks the in-progress transcript limit as aggregate UTF-8 bytes", async () => {
     const exactUtf8Limit = "🙂".repeat((256 * 1024) / 4);
     const splitSurrogatePrefix = "x".repeat(256 * 1024 - 4);
diff --git a/extensions/mistral/realtime-transcription-provider.ts b/extensions/mistral/realtime-transcription-provider.ts
index 8fc7b5175e64..7bbbed102dc2 100644
--- a/extensions/mistral/realtime-transcription-provider.ts
+++ b/extensions/mistral/realtime-transcription-provider.ts
@@ -222,6 +222,8 @@ function createMistralRealtimeTranscriptionSession(
       return;
     }
     if (event.type === "session.created") {
+      clearPartial();
+      hasFinalSegment = false;
       transport.sendJson({
         type: "session.update",
         session: {