chore(portal): wave-4 follow-up hygiene (FinalizedHead stubs, doc drift)

Promised in the PR #45 merge comment:
- portal-realtime.test.ts: two bare-number `finalizedHead: async () => 673`
  stubs → object form `async () => ({ number: 673 })`. FinalizedHead is
  object-only since #45 (the bare-number variant was dropped); these two
  test-only stubs were the last holdouts.
- pr-quality-gate/SKILL.md: drop `realtime.ts` from the source↔test pair
  list and `statediffs.json` from the fixture list — both deleted in #45.
- harness/euler-multichain/probe.mjs: rewrite the stale header comment; the
  mirrored `portal/realtime.ts` module was deleted in #45. The comment now
  describes what the probe does with no dead cross-reference.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: dzhelezov

.agents/skills/pr-quality-gate/SKILL.md

@@ -23,7 +23,7 @@ by `scripts/sync-upstream.sh`. Keep that in mind for Step 2.
 3. If tests are missing, **write them** (Step 3 conventions) before proceeding, or flag it explicitly
    in the PR body under a `## Missing tests` section.
 
-The current source ↔ test pairs are `portal.ts`, `portal-transform.ts`, `realtime.ts`,
+The current source ↔ test pairs are `portal.ts`, `portal-transform.ts`,
 `portal-realtime.ts`, `portal-realtime-wire.ts` — each with a matching `*.test.ts`.
 
 ## Step 2: Run the Portal tests (they must be green)
@@ -59,8 +59,8 @@ fixtures. Match the existing style rather than inventing utilities:
 - **Mock the Portal per test:** stand up a local `http` server or pass a `fetchImpl` stub that replays
   canned batches (see `mockPortal(...)` in `portal-realtime-wire.test.ts`). Model realistic Portal
   responses — `204`/`409`/`503`, finalized-head advances, chunk boundaries.
-- **Fixtures** live in `portal/__fixtures__/*.json` (`receipts.json`, `statediffs.json`,
-  `traces.json`), loaded with `readFileSync(join(__dirname, "__fixtures__"), ...)`.
+- **Fixtures** live in `portal/__fixtures__/*.json` (`receipts.json`, `traces.json`),
+  loaded with `readFileSync(join(__dirname, "__fixtures__"), ...)`.
 - **Matchers:** `toBe` / `toEqual` for values, `toMatch` for hex-shape checks, `toMatchInlineSnapshot`
   for large structured output. Assert against the **RPC shape** the Portal transform must reproduce
   (hex normalization, accessList shape, receipt/status fields) — that byte-for-byte parity vs RPC is

harness/euler-multichain/probe.mjs

@@ -1,7 +1,8 @@
 #!/usr/bin/env node
-// Endpoint health probe for the realtime soak — evaluates each endpoint's latency / tip-freshness /
-// responsiveness. Standalone (no imports beyond node) so it survives an overnight run alongside ponder.
-// Mirrors portal/realtime.ts (unit-tested). Writes PROBE_METRICS_FILE (rolling JSON) + a .log trail.
+// Endpoint health probe for the realtime soak — polls each configured endpoint and records its
+// latency, tip-freshness (how far behind chain head it reports), and responsiveness. Standalone (no
+// imports beyond node) so it survives an overnight run alongside ponder. Writes PROBE_METRICS_FILE
+// (rolling JSON) + a .log trail.
 //
 //   REALTIME_RPC_KEY=... [SQD_RPC_KEY=...] [PROBE_INTERVAL_MS=15000] node probe.mjs
 import fs from 'node:fs';

portal/portal-realtime.test.ts

@@ -438,7 +438,7 @@ test('portalRealtimeEvents: a 1-block orphan at tip heals via 409 fork negotiati
     anchor,
     fetchImpl: mockForkFetch(conns, bodies, () => ac.abort()),
     signal: ac.signal,
-    finalizedHead: async () => 673, // floor stays at the anchor; nothing new finalizes
+    finalizedHead: async () => ({ number: 673 }), // floor stays at the anchor; nothing new finalizes
     finalizePollMs: 999999,
   })) {
     events.push(e);
@@ -884,7 +884,7 @@ test('portalRealtimeEvents: the unknown-parent gap fatal MESSAGE carries the win
     anchor,
     fetchImpl: mockFetch(batches, () => ac.abort()),
     signal: ac.signal,
-    finalizedHead: async () => 673,
+    finalizedHead: async () => ({ number: 673 }),
     finalizePollMs: 999999,
   });
   let msg = '';