fix(tui): exclude buffered bursts from the output rate at turn start

packages/tui/src/tui/controller/projection/turn-output-rate.ts

@@ -29,6 +29,14 @@ export class TuiTurnOutputRate {
     const decodeDurationMs = event.message.usage?.decodeDurationMs;
     // Missing timing is not a zero-duration sample and must not use the full request duration.
     if (!nonnegativeFinite(outputTokens) || !nonnegativeFinite(decodeDurationMs)) return this.value;
+    if (
+      bufferedBurst(
+        outputTokens,
+        decodeDurationMs,
+        event.message.usage?.requestDurationMs,
+      )
+    )
+      return this.value;
     this.samples.set(event.message.id, { outputTokens, decodeDurationMs });
     let tokens = 0;
     let duration = 0;
@@ -60,6 +68,20 @@ export class TuiTurnOutputRate {
   }
 }
 
+/** Buffered upstream output arrives in one burst; its decode window says nothing about model speed. */
+const BURST_MIN_TOKENS_PER_SECOND = 1_000;
+const BURST_MAX_DECODE_SHARE = 0.1;
+
+function bufferedBurst(
+  tokens: number,
+  decodeMs: number,
+  requestMs: number | undefined,
+): boolean {
+  if (!nonnegativeFinite(requestMs) || decodeMs >= requestMs * BURST_MAX_DECODE_SHARE)
+    return false;
+  return tokens > (decodeMs / 1_000) * BURST_MIN_TOKENS_PER_SECOND;
+}
+
 function nonnegativeFinite(value: number | undefined): value is number {
   return typeof value === 'number' && Number.isFinite(value) && value >= 0;
 }

packages/tui/test/unit/tui/controller/projection/turn-output-rate.test.ts

@@ -209,6 +209,29 @@ describe("TuiTurnOutputRate", () => {
     expect(rate.finalize()).toBeUndefined();
   });
 
+  it("drops a buffered burst at turn start instead of reporting an inflated rate", () => {
+    const rate = new TuiTurnOutputRate();
+    rate.beginTurn("turn-1");
+    const apply = (
+      id: string,
+      outputTokens: number,
+      decodeDurationMs: number,
+      requestDurationMs: number,
+    ) =>
+      rate.apply("turn-1", {
+        type: "message",
+        message: {
+          id,
+          role: "assistant",
+          usage: { outputTokens, decodeDurationMs, requestDurationMs },
+        },
+      });
+    expect(apply("burst", 107, 2, 2_221)).toBeUndefined();
+    expect(apply("instant-burst", 100, 0, 3_000)).toBeUndefined();
+    expect(apply("normal", 400, 2_000, 4_000)).toBe(200);
+    expect(apply("fast-provider", 1_500, 1_000, 1_200)).toBe(1_900 / 3);
+  });
+
   it("ignores late events from an older turn after reset", () => {
     const rate = new TuiTurnOutputRate();
     rate.beginTurn("turn-old");