diff --git a/packages/services/service-cluster-redis/src/ioredis-pair.pin.test.ts b/packages/services/service-cluster-redis/src/ioredis-pair.pin.test.ts
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+// Copyright (c) 2026 ObjectStack. Licensed under the Apache-2.0 license.
+
+/**
+ * **The tripwire on the ioredis / ioredis-mock version pair** that the
+ * inertness declaration at the top of `redis.contract.test.ts` was measured
+ * against (#15467 / PR #15985).
+ *
+ * ## What that declaration claims, and why prose alone was not enough
+ *
+ * This package depends on `ioredis@^6`, while the double its contract suites
+ * run on declares `peerDependencies: { ioredis: "^5" }`. That one-major gap
+ * was not closed — it was measured, command by command, and declared INERT on
+ * the surface those suites actually drive. The entire deliverable of that
+ * work is a paragraph of prose.
+ *
+ * And that paragraph states its own expiry condition:
+ *
+ * > If the `ioredis` or `ioredis-mock` range in package.json moves — OR if the
+ * > version either one RESOLVES to moves under an unchanged caret range, which
+ * > a lockfile bump alone will do — this paragraph expires and the diff has to
+ * > be re-taken.
+ *
+ * Nothing checked that. A bump six months out silently invalidates a header
+ * that still reads as authoritative — prose that was correct when written and
+ * rotted without a signal. This file is that signal.
+ *
+ * ## Why it keys on the RESOLVED versions, not only on the declared ranges
+ *
+ * A pin asserting only that the two ranges still read `^6.0.0` and `^8.13.1`
+ * would stay green through a **lockfile-only bump** — a resolution moving
+ * under an unchanged caret — which is one of the two moves the expiry clause
+ * names, and the one no manifest read can see. So the resolved versions are
+ * read off the **installed tree**, out of the very manifests
+ * `import RedisMock from 'ioredis-mock'` and ioredis's own types resolve to.
+ * That is the honest source: a lockfile records what pnpm WOULD install, the
+ * installed tree is what this test process is loading right now. The declared
+ * ranges are pinned as well, because the expiry clause names them too and a
+ * range can move without moving the resolution.
+ *
+ * ## Why the last assertion reads the declaration's own text
+ *
+ * The failure mode this design is most afraid of is the one the card asking
+ * for it named: *a pin that fires on routine maintenance trains people to
+ * edit the pin rather than re-do the measurement, which would be worse than
+ * no pin.* ⇒ Editing the constants below is deliberately NOT enough to get
+ * back to green — the pinned pair must also still appear in the declaration's
+ * own text, so a bump that updates this file and leaves the header stale
+ * stays red. Green costs a re-measure, which is the only outcome worth having.
+ *
+ * ## What it deliberately does NOT check
+ *
+ * The declaration's v5 leg — "5.11.1, newest release satisfying the mock's
+ * `^5` peer" — is a REGISTRY fact, not a workspace one: no ioredis 5.x is
+ * installed here (the mock's peer resolves onto the 6.x copy). A newer 5.x
+ * release ages that leg with no local signal, and no offline pin can see it.
+ * Recorded rather than pretended.
+ *
+ * ⛔ Nor does it re-litigate the inertness measurement, and ⛔ nor should the
+ * untyped `ioredis-mock` import be "fixed" by adopting `@types/ioredis-mock`:
+ * measured and rejected, because those types declare the mock constructor as
+ * returning a real ioredis `Redis` — asserting conformance instead of
+ * verifying it, which is this whole family's failure mode one layer up.
+ *
+ * Both reads stay inside this package (`src/` to the package root, and a
+ * sibling source file), so neither is a `check:cross-package-test-inputs`
+ * escape and neither needs a declaration.
+ */
+
+import { readFileSync } from 'node:fs';
+import { createRequire } from 'node:module';
+import { resolve } from 'node:path';
+import { fileURLToPath } from 'node:url';
+
+import { describe, expect, it } from 'vitest';
+
+const HERE = resolve(fileURLToPath(import.meta.url), '..');
+
+// One `resolve(HERE, …)` per line on purpose — `check:cross-package-test-inputs`
+// reconstructs a test's reads by scanning source text, and a path assembled
+// across statements is a spelling it does not know.
+const MANIFEST = resolve(HERE, '../package.json');
+const DECLARATION = resolve(HERE, './redis.contract.test.ts');
+
+/** Repo-relative, for the failure message — an absolute temp path helps nobody. */
+const DECLARATION_PATH =
+    'packages/services/service-cluster-redis/src/redis.contract.test.ts';
+const DECLARATION_SECTION =
+    '## The double is one major version behind the client it doubles';
+
+/**
+ * The pair the declaration was measured against, and the ranges that resolved
+ * to it.
+ *
+ * ⛔ These are not configuration. Editing them to match a new install is the
+ * one move this file exists to prevent; the failure message explains why and
+ * the last assertion makes it insufficient anyway.
+ */
+const PINNED = {
+    resolved: { ioredis: '6.0.0', 'ioredis-mock': '8.13.1' },
+    ranges: { ioredis: '^6.0.0', 'ioredis-mock': '^8.13.1' },
+} as const;
+
+const requireFromHere = createRequire(import.meta.url);
+
+/** The version actually installed for `name`, read from its own manifest. */
+function resolvedVersion(name: string): string {
+    const path = requireFromHere.resolve(`${name}/package.json`);
+    return (JSON.parse(readFileSync(path, 'utf8')) as { version: string }).version;
+}
+
+const manifest = JSON.parse(readFileSync(MANIFEST, 'utf8')) as {
+    dependencies: Record<string, string>;
+    devDependencies: Record<string, string>;
+};
+
+const declarationText = readFileSync(DECLARATION, 'utf8');
+
+/** `6.0.0` as a standalone token, so `16.0.0` and `6.0.0-rc.1` do not match. */
+function namesVersion(text: string, version: string): boolean {
+    const escaped = version.replace(/\./g, '\\.');
+    return new RegExp(`(?<![\\w.])${escaped}(?![\\w.])`).test(text);
+}
+
+/**
+ * The message a reader gets mid-bump, having never heard of the measurement.
+ * It has to answer three questions before they reach for the constants above:
+ * what just expired, where it is written, and what the remedy is.
+ */
+function expired(fact: string, pinned: string, found: string): string {
+    return [
+        '',
+        "The ioredis / ioredis-mock pair this package's inertness declaration was",
+        'measured against has moved:',
+        '',
+        `    ${fact}: pinned ${pinned}, found ${found}`,
+        '',
+        `That declaration is the section "${DECLARATION_SECTION}"`,
+        `at the top of ${DECLARATION_PATH}. It states, in its own words, that it`,
+        'expires when either range moves OR either resolved version moves — which',
+        'is what just happened. Every "inert" conclusion in it now describes a',
+        'pair that is no longer what this package installs.',
+        '',
+        '⛔ Do NOT edit the pinned constants to match. This file is not the claim,',
+        'it is the tripwire on the claim, and editing it green re-asserts a',
+        'measurement nobody has taken. It would not even work: the last assertion',
+        "in this file requires the declaration's own text to name the same pair.",
+        '',
+        'Re-do the measurement instead:',
+        '  1. Re-take the diff that section describes, for the NEW pair — the type',
+        '     declarations of every command `src/*.ts` issues, of `multi()` and',
+        '     `exec()`, and of the `RedisOptions` keys `client.ts` sets.',
+        '  2. Rewrite the section with the new pair and whatever it now reads.',
+        '  3. Only then update the constants here, in the same commit.',
+        '',
+        'If the re-measure finds the gap is no longer inert, the fix is upstream —',
+        'the dependency or the double — not this pin and not the declaration.',
+        '',
+    ].join('\n');
+}
+
+describe('ioredis / ioredis-mock version pair pin', () => {
+    it('still resolves the ioredis version the declaration was measured against', () => {
+        const found = resolvedVersion('ioredis');
+        const pinned = PINNED.resolved.ioredis;
+        expect(found, expired('ioredis, resolved on disk', pinned, found)).toBe(pinned);
+    });
+
+    it('still resolves the ioredis-mock version the declaration was measured against', () => {
+        const found = resolvedVersion('ioredis-mock');
+        const pinned = PINNED.resolved['ioredis-mock'];
+        expect(found, expired('ioredis-mock, resolved on disk', pinned, found)).toBe(
+            pinned,
+        );
+    });
+
+    it('still declares the two ranges that resolved to that pair', () => {
+        // Pinned per dependency block, not looked up across both: moving the
+        // double into `dependencies` would ship a test-only package to every
+        // consumer, and that move should be seen here too.
+        const foundClient = manifest.dependencies['ioredis'];
+        expect(
+            foundClient,
+            expired('ioredis, declared range', PINNED.ranges.ioredis, String(foundClient)),
+        ).toBe(PINNED.ranges.ioredis);
+
+        const foundDouble = manifest.devDependencies['ioredis-mock'];
+        expect(
+            foundDouble,
+            expired(
+                'ioredis-mock, declared devDependency range',
+                PINNED.ranges['ioredis-mock'],
+                String(foundDouble),
+            ),
+        ).toBe(PINNED.ranges['ioredis-mock']);
+    });
+
+    it('keeps the declaration itself present and naming the pinned pair', () => {
+        // Without this, the cheapest way back to green after a bump is to edit
+        // the constants above and leave the header describing a pair nobody
+        // installs any more — a pin that has been trained to lie. With it, the
+        // header and the pin can only move together.
+        const remedy = [
+            '',
+            `${DECLARATION_PATH} no longer carries the claim this file defends,`,
+            'or no longer names the pair pinned here.',
+            '',
+            `Expected that file to contain the section "${DECLARATION_SECTION}"`,
+            `naming ioredis-mock ${PINNED.resolved['ioredis-mock']} and ioredis ${PINNED.resolved.ioredis}.`,
+            '',
+            'If the measurement was re-taken, update the constants in this file in',
+            'the same commit. If the declaration was deleted on purpose, delete',
+            'this pin with it — a tripwire on a claim that no longer exists is the',
+            'same rot one level up. ⛔ What is not an option is silencing this',
+            'assertion and leaving the header in place.',
+            '',
+        ].join('\n');
+
+        expect(declarationText.includes(DECLARATION_SECTION), remedy).toBe(true);
+        expect(
+            declarationText.includes(`ioredis-mock@${PINNED.resolved['ioredis-mock']}`),
+            remedy,
+        ).toBe(true);
+        expect(namesVersion(declarationText, PINNED.resolved.ioredis), remedy).toBe(true);
+    });
+});