Docs: E2E instructions say `pnpm run build`, which strips the mock bridge and breaks all smoke specs

Start with the listed E2E guidance in AGENTS.md and desktop/src-tauri/src/managed_agents/screenshot_skill.md, then check the header comments in the four named desktop/tests/e2e/.perf.ts files. Compare the commands with the test:e2e scripts and main.tsx; done means every cited instruction uses the E2E build mode and warns about the plain production build stripping the mock bridge.

Problem

The E2E docs tell contributors to run a plain production build before re-running Playwright tests, which produces a bundle without the E2E Tauri mock bridge — so every smoke spec fails at boot.

Occurrences of the wrong instruction:

• AGENTS.md — "Writing E2E Screenshot Specs" → Stale server paragraph: "Kill port 4173 and pnpm run build before re-running tests after code changes."
• desktop/src-tauri/src/managed_agents/screenshot_skill.md — Gotcha 1 repeats the same pnpm run build advice.
• Header comments of the four perf specs in desktop/tests/e2e/ (typing-latency.perf.ts, scroll-smoothness.perf.ts, warm-switch-markdown.perf.ts, cold-switch-longtask.perf.ts) say to run pnpm build first — they all call installMockBridge, so the same failure applies.

Why it fails

desktop/src/main.tsx deliberately compiles the mock bridge only into dev and explicit E2E builds:

if (
  !(import.meta.env.DEV || import.meta.env.MODE === "e2e") ||
  !(window as E2eWindow).__BUZZ_E2E__
) {
  return;
}
const { maybeInstallE2eTauriMocks } = await import("@/testing/e2eBridge");

pnpm build (vite build) runs in production mode, so the bridge is stripped. The Playwright web server (python3 -m http.server 4173 -d dist) then serves a bridge-less bundle and every spec that calls installMockBridge dies at boot with:

Community connection failed / Cannot read properties of undefined (reading 'invoke')

The correct command is pnpm build:e2e (vite build --mode e2e) — it's what the test:e2e* package scripts already use.

Impact

Two independent agent sessions lost real debugging time to this on 2026-07-27, chasing what looked like an app regression but was just a doc-induced wrong build mode.

Fix

Update the docs (and perf-spec header comments) to say pnpm build:e2e, with a one-line warning that a plain pnpm build strips the mock bridge.