fix(telemetry): attribute studio renders to the browser user (joinable funnel) (#1492)

Studio-triggered renders emit render_complete / render_error from the CLI
preview-server process, which stamps every event with the install's
anonymousId (client.ts drainQueueToPayload). The browser, meanwhile, fires
studio_session_start / studio_render_start under its own getAnonymousId(). So
the render outcome and the render start never share a person_id — verified in
data: of 15,125 users who started a studio render in 30d, ZERO have any
render_complete under any source, and the 898 studio-tagged completers are
disjoint server UUIDs. The studio render funnel — the product's core value
moment and strongest retention signal — is therefore unmeasurable.

Thread the browser's telemetry id through to the render-outcome events:

- client.ts: trackEvent takes an optional distinctId; drainQueueToPayload uses
  `event.distinctId ?? config.anonymousId`. CLI renders unchanged.
- events.ts: trackRenderComplete/trackRenderError forward an optional distinctId.
- studioRenderTelemetry.ts: emitStudioRender* pass opts.distinctId through.
- core studio-api (types.ts + routes/render.ts): the render route reads
  `telemetryDistinctId` from the request body (validated string) and passes it
  to the adapter's startRender, which already forwards opts to the emitters.
- studio (useRenderQueue.ts): include getAnonymousId() as telemetryDistinctId
  in the render POST — the same id studio_* events already use.

Result: studio render_complete/error now carry the browser user's id and join
studio_session_start / studio_render_start. Older clients that don't send the
field fall back to anonymousId (no regression). No new tracking surface — it's
the existing anonymous studio id.

Tests: per-event override forwarding (events), studio render distinctId
threading + older-client fallback (studioRenderTelemetry), and route body →
adapter forwarding incl. non-string rejection (core render route).

packages/cli/src/server/studioRenderTelemetry.test.ts

@@ -132,6 +132,16 @@ describe("studioRenderTelemetry", () => {
       expect(payload.gpu).toBe(false);
     });
 
+    it("forwards the browser user's distinctId so the render funnel is joinable", () => {
+      emitStudioRenderComplete({ ...opts, distinctId: "browser-user-123" }, 5000, fullPerf);
+      expect(trackRenderComplete.mock.calls[0]![0].distinctId).toBe("browser-user-123");
+    });
+
+    it("leaves distinctId undefined for older clients that don't send one", () => {
+      emitStudioRenderComplete(opts, 5000, fullPerf);
+      expect(trackRenderComplete.mock.calls[0]![0].distinctId).toBeUndefined();
+    });
+
     it("maps every RenderPerfSummary field to the expected payload key", () => {
       emitStudioRenderComplete(opts, 5000, fullPerf);
       const p = trackRenderComplete.mock.calls[0]![0];

packages/cli/src/server/studioRenderTelemetry.ts

@@ -20,6 +20,10 @@ import { bytesToMb } from "../telemetry/system.js";
 export interface StudioRenderOpts {
   fps: Fps;
   quality: string;
+  // Telemetry id of the browser user who triggered the render, so the render
+  // outcome joins their studio_session_start / studio_render_start events.
+  // Undefined for older studio clients → falls back to the install anonymousId.
+  distinctId?: string;
 }
 
 type RenderCompleteProps = Parameters<typeof trackRenderComplete>[0];
@@ -105,6 +109,7 @@ export function emitStudioRenderError(
     failedStage,
     errorMessage: err instanceof Error ? err.message : String(err),
     elapsedMs,
+    distinctId: opts.distinctId,
     ...renderJobObservabilityTelemetryPayload(job),
     ...memSnapshot(),
   });
@@ -122,6 +127,7 @@ export function emitStudioRenderComplete(
     docker: false,
     gpu: false,
     source: "studio",
+    distinctId: opts.distinctId,
     ...perfPayload(perf, elapsedMs),
     ...memSnapshot(),
   });