Merge feat/longform-pipeline: VAD long-form pipeline, opt-in (spec 001 workstream 3)

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

# Conflicts:
#	docs/Architecture.md
#	docs/Decisions.md
#	src/App.tsx
#	src/index.css
#	src/lib/engine.ts
#	src/worker/inference.worker.ts
#	src/worker/protocol.ts
#	tests/engine.test.ts
#	tests/live-real-model.test.ts
#	tests/offline.md
#	tests/protocol.test.ts

tests/protocol.test.ts

@@ -4,6 +4,7 @@ import {
   deviceAttempts,
   dtypeRequiresF16,
   initialLoadProgress,
+  choosePipeline,
   isUiToWorkerMessage,
   isWorkerToUiMessage,
   TranscribeProgressTracker,
@@ -36,7 +37,9 @@ describe("isUiToWorkerMessage", () => {
       { type: "transcribe", audio: new Float32Array(8), requestId: "engine-1-1", stream: true },
       { type: "transcribe", audio: new Float32Array(8), stream: false },
       { type: "transcribe", audio: new Float32Array(8), prompt: "Maxwell, Voices of the Void" },
+      { type: "transcribe", audio: new Float32Array(8), stream: true, longForm: true },
     ];
+    loads.push({ type: "load", modelId: "onnx-community/whisper-base", device: "auto", vad: true });
     for (const message of [...loads, ...transcribes]) {
       expect(isUiToWorkerMessage(message)).toBe(true);
     }
@@ -69,10 +72,26 @@ describe("isUiToWorkerMessage", () => {
     expect(
       isUiToWorkerMessage({ type: "transcribe", audio: new Float32Array(4), prompt: 5 }),
     ).toBe(false);
+    expect(
+      isUiToWorkerMessage({ type: "transcribe", audio: new Float32Array(4), longForm: 1 }),
+    ).toBe(false);
+    expect(isUiToWorkerMessage({ type: "load", modelId: "x", device: "auto", vad: "yes" })).toBe(
+      false,
+    );
     expect(isUiToWorkerMessage({ type: "result", text: "", chunks: [] })).toBe(false);
   });
 });
 
+describe("choosePipeline (D-WS3a/D-WS3b)", () => {
+  test("long-form only when asked for and the VAD model loaded", () => {
+    expect(choosePipeline({ longForm: true, vadReady: true })).toBe("longform");
+    // Offline / never downloaded: the old path, never an error (Review Focus 3).
+    expect(choosePipeline({ longForm: true, vadReady: false })).toBe("chunked");
+    expect(choosePipeline({ longForm: false, vadReady: true })).toBe("chunked");
+    expect(choosePipeline({ longForm: undefined, vadReady: true })).toBe("chunked");
+  });
+});
+
 describe("isWorkerToUiMessage", () => {
   test("accepts every worker → UI message shape", () => {
     const messages: WorkerToUiMessage[] = [
@@ -278,6 +297,37 @@ describe("TranscribeProgressTracker", () => {
     expect(tracker.timestamp(8)).toBe(8);
     expect(tracker.finalizeWindow()).toBeNull(); // 20 clamps to 8, not an advance
   });
+
+  describe("forWindows (variable-length VAD chunks, D-WS3a)", () => {
+    // Two speech chunks with a skipped 15 s silence between them: [0–20 s]
+    // and [35–60 s] of a 70 s file.
+    const windows = [
+      { toAbsolute: (t: number) => t, endSeconds: 20, nextStartSeconds: 35 },
+      { toAbsolute: (t: number) => 35 + t, endSeconds: 60, nextStartSeconds: 70 },
+    ];
+
+    test("maps chunk-relative times through each window", () => {
+      const tracker = TranscribeProgressTracker.forWindows(70, windows);
+      expect(tracker.timestamp(5)).toBe(5);
+      // Finishing a chunk counts the skipped silence up to the next one.
+      expect(tracker.finalizeWindow()).toBe(35);
+      expect(tracker.timestamp(10)).toBe(45);
+      expect(tracker.timestamp(2)).toBeNull(); // 37 < 45: no regression
+      expect(tracker.finalizeWindow()).toBe(70);
+      expect(tracker.finalizeWindow()).toBeNull(); // past the last window
+    });
+
+    test("clamps a stray timestamp to the window's end", () => {
+      const tracker = TranscribeProgressTracker.forWindows(70, windows);
+      expect(tracker.timestamp(400)).toBe(20);
+    });
+
+    test("no windows (no speech) → nothing to report but the end", () => {
+      const tracker = TranscribeProgressTracker.forWindows(70, []);
+      expect(tracker.timestamp(3)).toBeNull();
+      expect(tracker.finalizeWindow()).toBe(70);
+    });
+  });
 });
 
 describe("applyLoadProgress", () => {