phase: 07_canvas_client_and_hud

**Final report — phase 07 final verification pass**

- **Verified:** all 5 tasks present in `complete/`; app boots (`/healthz` 200, `/` 200, static + atlas + `/api/levels` served); `docs/CLIENT.md` module map matches the on-disk `app/static/` tree; no code defects found.
- **Tests/lint/coverage:** `bash .agents/validate.sh` → ruff clean, pyright 0 errors, `undercooked-levels validate` pass, **full pytest 1838 passed, 97.21% coverage (floor 90%)**, slow sim stage 2 passed, repo hygiene clean. `uv run pytest tests/e2e -q` → **53 passed** (all 8 suites added this phase).
- **Criteria:** (1) two tabs create→join→ready→start→serve one dish, keyboard only — green via `test_us01/02/03/04` ✔; (2) e2e green ✔; (3) canvas non-blank, pixels change after a move — `test_us04_render_smoke` ✔; (4) HUD score within 200 ms of the `served` event — asserted, green ✔; (5) zero console errors + zero off-origin requests — `test_atlas_loads` / `test_us01_landing_surface` ✔; (6) `docs/CLIENT.md` matches layout ✔; (7) 100% suite + 97.21% ✔; (8) docs pass below ✔; (9) no regression in completed phases (all prior suites green) ✔.
- **README.md fixed:** status still said "next pending phase is 07" → now 07 complete, 08 pending; the phase-07 client text buried in the phase-05 bullet → its own "canvas client, art, HUD (phase 07)" bullet; stale "What does not exist yet" (claimed movement/controls missing) → rewritten to phases 08–14; "once the room flow ships" → "live in the browser today"; Layout `app/static/` "renderer arrives with the rest of phase 07" → full shipped-client map; Layout `docs/` "CLIENT lands with phase 07" → `CLIENT.md` listed; added `gen_art_index.py` Layout entry.
- **AGENTS.md fixed:** "the eight screens" (7 listed) → "the seven screens" (+ `dom.js` is the shared builder, not a screen); e2e naming line → notes the non-story guard `test_atlas_loads.py`.
- **Decisions:** no code changes were needed; only the two doc fixes above. Docs re-verified by `test_docs_commands`/`test_docs_index` (44 passed) plus the final full gate.
- **Next pending phase:** `08_client_prediction_and_touch`.

app/static/js/screens/error.js

@@ -0,0 +1,87 @@
+// Undercooked — the error screen (phase 07 task 02).
+//
+// Friendly copy per failure (the `err` codes of docs/PROTOCOL.md and
+// the close codes the connection classifies), with the *right* retry
+// affordance for each: a `4400` protocol mismatch must not auto-retry
+// (the client is out of date), a `4401` room-gone must not retry the
+// dead code, a `4402` full room points at another room — and the room
+// code is shown for support.
+
+import { el } from "./dom.js";
+
+/** code → { title, detail, retry } (retry = "a retry is offered"). */
+const COPY = {
+  room_gone: {
+    title: "That kitchen is gone",
+    detail: "It may have closed, or the code was mistyped.",
+    retry: false,
+  },
+  room_full: {
+    title: "That kitchen is full",
+    detail: "Every seat is taken. Start your own room, or try another code.",
+    retry: false,
+  },
+  protocol_mismatch: {
+    title: "Protocol mismatch",
+    detail:
+      "This server speaks a protocol version this client does not. Retrying will not help — the client needs an update.",
+    retry: false,
+  },
+  evicted: {
+    title: "You are on another tab",
+    detail: "A second tab took this seat. Use the other tab, or come back later.",
+    retry: false,
+  },
+  internal: {
+    title: "The kitchen hit an internal error",
+    detail: "The round was aborted for everyone. Start a new room.",
+    retry: false,
+  },
+  closed: {
+    title: "The connection closed",
+    detail: "The server closed the socket. You can try the same room again.",
+    retry: true,
+  },
+  unreachable: {
+    title: "Cannot reach the server",
+    detail: "The socket could not be opened. Check the address and try again.",
+    retry: true,
+  },
+};
+
+export function mount(target, data, app) {
+  const code = data.code ?? "closed";
+  const copy = COPY[code] ?? COPY.closed;
+  const buttonRow = el(
+    "div",
+    { class: "error-actions" },
+    el("button", {
+      id: "error-back",
+      class: "btn btn-primary",
+      type: "button",
+      onClick: () => app.backToLanding(),
+    }, "Back to landing"),
+  );
+  if (copy.retry && app.roomCode !== "") {
+    buttonRow.prepend(
+      el("button", {
+        id: "error-retry",
+        class: "btn",
+        type: "button",
+        onClick: () => app.retryJoin(),
+      }, "Try again"),
+    );
+  }
+  const children = [
+    el("h2", { id: "error-title" }, copy.title),
+    el("p", { id: "error-detail" }, copy.detail),
+  ];
+  if (app.roomCode !== "") {
+    children.push(el("p", { id: "error-code" }, `Room code: ${app.roomCode}`));
+  }
+  target.append(el("div", { class: "panel error" }, el("div", { role: "alert" }, ...children), buttonRow));
+}
+
+export function unmount() {
+  /* static */
+}