presence: fix stale peer selections after delete, select-all lag, ghost-peer removal (findings group Y)

- wasm core: CORE::onDocChanged() from both collab listeners (local commit AND
  remote apply) repaints peers' shapes from the live document + re-checks the
  local selection post-settle; PresenceStart registers the bridge listener
- wasm core: cursors on their own overlay trio; shapes repaint only when the
  non-cursor snapshot changes; new kicadCollabSetRemoteCursors (cursor-only
  update, PEER.id) in both TUs + merged editor + JSPI mutator allowlist
- presence.ts: size-aware trailing throttle for cursor/viewport publishes
  (128 KB/s budget) + parsed-peers memo; presence-kicad.ts: cursor-only push
  when the shape signature is unchanged
- gateway.ts: honor the `gone` control (removeAwarenessStates)
- specs: kicad stale-after-delete gate, web ghost-peer timing (+diag), unit
  select-all budget (pcbjam-shared → 4573a7c)

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01AScTR39aqyrY5i3ZFHmnMn

tests/web/presence-ghost-diag.spec.ts

@@ -0,0 +1,100 @@
+import { test, expect, type Page, type BrowserContext } from '@playwright/test';
+import { openOverlayMenu } from './overlay-menu';
+
+/** Diagnostic companion of presence-ghost-peer.spec.ts: records bob's inbound
+ *  awareness entries (clientId/clock) after alice's socket is cut, so we can
+ *  tell "alice keeps getting re-published" from "bob never times her out". */
+
+const SCOPE = 'default';
+const ROUTE = 'demo.kicad_wks';
+const TITLE = /demo — Drawing Sheet Editor/i;
+
+const HOOK = `
+  (() => {
+    const Orig = window.WebSocket;
+    const list = [];
+    window.__wsList = list;
+    window.__cutAll = false;
+    window.__awLog = [];
+    const rv = (b, p) => { let r = 0, m = 1; for (;;) { const x = b[p++]; r += (x & 127) * m; if (x < 128) return [r, p]; m *= 128; } };
+    const decode = (u8) => {
+      try {
+        let p = 0, v;
+        [v, p] = rv(u8, p); const ch = v;
+        [v, p] = rv(u8, p); const type = v;
+        if (type !== 1) return { ch, type };
+        [v, p] = rv(u8, p);
+        [v, p] = rv(u8, p); const n = v;
+        const ents = [];
+        for (let i = 0; i < n; i++) {
+          let cid, clk, len;
+          [cid, p] = rv(u8, p); [clk, p] = rv(u8, p); [len, p] = rv(u8, p);
+          const s = new TextDecoder().decode(u8.subarray(p, p + len)); p += len;
+          let user = null; try { user = JSON.parse(s)?.user?.id ?? (s === 'null' ? 'REMOVED' : '?'); } catch {}
+          ents.push({ cid, clk, user });
+        }
+        return { ch, type, ents };
+      } catch (e) { return { err: String(e) }; }
+    };
+    window.WebSocket = new Proxy(Orig, {
+      construct(target, args) {
+        const ws = new target(...args);
+        list.push({ ws, url: String(args[0]), t: Date.now() });
+        ws.addEventListener('message', async (ev) => {
+          let d = ev.data;
+          if (d instanceof Blob) d = await d.arrayBuffer();
+          if (d instanceof ArrayBuffer) window.__awLog.push({ t: Date.now(), ...decode(new Uint8Array(d)) });
+        });
+        if (window.__cutAll) { ws.send = () => {}; setTimeout(() => ws.close(), 0); }
+        return ws;
+      },
+    });
+    window.__wsCut = (close) => {
+      window.__cutAll = true;
+      let n = 0;
+      for (const { ws } of list) {
+        if (ws.readyState !== 1) continue;
+        ws.send = () => {}; n++;
+        if (close) ws.close();
+      }
+      return n;
+    };
+  })();
+`;
+
+async function bootAs(context: BrowserContext, user: string): Promise<Page> {
+  const page = await context.newPage();
+  await page.addInitScript(HOOK);
+  await page.goto(`/${SCOPE}/projects/demo/${ROUTE}?user=${user}`);
+  await expect(page.locator('#canvas')).toBeVisible({ timeout: 120000 });
+  await expect.poll(() => page.title(), { timeout: 120000, intervals: [1000] }).toMatch(TITLE);
+  return page;
+}
+
+test.skip(!process.env.PRESENCE_DIAG, 'diagnostic only — PRESENCE_DIAG=1 to run');
+for (const close of [true, false]) test(`diag: what bob receives after alice ${close ? 'closes uncleanly' : 'goes half-open'}`, async ({ browser }) => {
+  test.setTimeout(400000);
+  const ctxA = await browser.newContext();
+  const ctxB = await browser.newContext();
+  const alice = await bootAs(ctxA, 'alice');
+  const bob = await bootAs(ctxB, 'bob');
+  await openOverlayMenu(bob);
+  await expect(bob.locator('[data-presence-user="alice"]')).toBeVisible({ timeout: 30000 });
+
+  const tCut = Date.now();
+  const n = await alice.evaluate((c) => (window as any).__wsCut(c), close);
+  console.log(`[diag] cut ${n} alice sockets at ${tCut}`);
+
+  const before = await bob.evaluate((since) => (window as any).__awLog.filter((e: any) => e.type === 1 && e.t < since).flatMap((e: any) => e.ents.map((x: any) => `${new Date(e.t).toISOString().slice(14, 19)} ch${e.ch} cid=${x.cid} clk=${x.clk} ${x.user}`)), tCut);
+  console.log(`[diag] bob inbound awareness BEFORE cut (last 12):\n  ${before.slice(-12).join('\n  ')}`);
+  for (let i = 1; i <= 4; i++) {
+    await bob.waitForTimeout(10000);
+    const present = await bob.locator('[data-presence-user="alice"]').count();
+    const aliceWs = await alice.evaluate(() => (window as any).__wsList.map((w: any) => ({ url: w.url.slice(0, 60), state: w.ws.readyState, t: w.t })));
+    const log = await bob.evaluate((since) => (window as any).__awLog.filter((e: any) => e.t >= since), tCut);
+    const aw = log.filter((e: any) => e.type === 1).flatMap((e: any) => e.ents.map((x: any) => `${new Date(e.t).toISOString().slice(14, 19)} ch${e.ch} cid=${x.cid} clk=${x.clk} ${x.user}`));
+    console.log(`[diag] +${i * 10}s alice-in-roster=${present} aliceSockets=${JSON.stringify(aliceWs)} bobInboundAwareness(since cut)=\n  ${aw.join('\n  ')}`);
+  }
+  await ctxA.close();
+  await ctxB.close();
+});