docs(service-cluster-redis): record the measured ioredis 5-vs-6 gap in the contract test header, and drop a live-Redis path that never existed

packages/services/service-cluster-redis/src/redis.contract.test.ts

@@ -3,12 +3,87 @@
 /**
  * Driver contract tests for the Redis cluster driver, run against
  * `ioredis-mock` so they execute without a real Redis instance in CI.
+ * There is no live-Redis path in this file: every suite below runs on the
+ * mock. (An earlier version of this header promised `RUN_REAL_REDIS=1` +
+ * `REDIS_URL` and "conditional `describe.skipIf` blocks at the bottom" —
+ * no such blocks were ever here. Scanning the whole package, not just
+ * `src/`: `RUN_REAL_REDIS` and `skipIf` occur nowhere outside that
+ * sentence, so the escape hatch never existed. `REDIS_URL` does occur, at
+ * `README.md:42` — but as the env var a caller feeds to
+ * `createRedisClient()`, which is unrelated to any test path.)
  *
- * The same suites can be invoked against a live Redis by setting
- * `RUN_REAL_REDIS=1` and providing `REDIS_URL` — see the conditional
- * `describe.skipIf` blocks at the bottom.
+ * ## The double is one major version behind the client it doubles
+ *
+ * This package depends on `ioredis@^6`, while `ioredis-mock@8.13.1`
+ * declares `peerDependencies: { ioredis: "^5" }` — so a resolving
+ * `pnpm install` prints an unmet-peer warning for it (a frozen re-link
+ * prints nothing). That gap is real, and it is
+ * declared here rather than closed, because it was measured to be inert
+ * on the surface these suites actually drive. Measured against ioredis
+ * 5.11.1 (newest release satisfying the mock's `^5` peer) and 6.0.0 (the
+ * version resolved in this workspace):
+ *
+ *   - Every Redis command issued by this package's `src/*.ts` — get, set,
+ *     del, incr, incrby, pttl, watch, unwatch, exec, publish, subscribe,
+ *     unsubscribe, quit, eval — carries all of its v5 overloads verbatim
+ *     into v6's `RedisCommander.d.ts`. `set` is a strict superset there
+ *     (v6 adds the IFEQ/IFNE/IFDEQ/IFDNE tokens); nothing used here was
+ *     removed or re-shaped.
+ *   - `multi()` is deliberately not in that list: it is declared on
+ *     `Transaction` (`transaction.d.ts`) and appears in
+ *     `RedisCommander.d.ts` in neither version. Measured separately, it
+ *     DID change — all four overloads went from returning
+ *     `ChainableCommander` to `ChainableCommander` parameterised by a
+ *     mapping. It is inert here because the parameter defaults to "resp2"
+ *     and a client built without `replyMapping` reaches it as such: the
+ *     class defaults to "legacy" and extends `Transaction` at "resp2".
+ *     So this package's `multi()` resolves to the non-RESP3 instantiation,
+ *     and `exec()`'s own declaration is byte-identical across the pair.
+ *   - v6's one substantive change reachable from the surface these suites
+ *     drive is RESP3 reply mapping, and it is opt-in: the class is
+ *     declared with a `ReplyMapping` parameter defaulting to "legacy",
+ *     `ChainableCommander` defaults to "resp2", and `duplicate()` with no
+ *     override inherits the caller's mapping. This package never passes
+ *     `replyMapping`, so every reply shape these suites see is the v5 one.
+ *     ⚠️ Scoped deliberately: v6 also changes connection defaults that are
+ *     NOT opt-in — `protocol: 3` (no such option in v5) and `keepAlive`
+ *     0 -> 30000. Those are reached in production through
+ *     `createRedisClient()`, which no suite here calls (see below), so
+ *     they are changed-but-unexercised rather than absent.
+ *   - The three `RedisOptions` keys client.ts sets — lazyConnect,
+ *     maxRetriesPerRequest, enableAutoPipelining — are declared
+ *     identically in both versions.
+ *
+ * That named set is the whole basis for the claim; it is not a statement
+ * about ioredis 5 vs 6 in general. 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.
+ *
+ * ## What these suites therefore do NOT certify
+ *
+ * They reach the mock only through the injected `client` and the
+ * `client.duplicate()` the pub/sub adapter makes. They never call
+ * `createRedisClient()`, so `new Redis(url, options)` — this package's
+ * only contact with ioredis's constructor and connection surface, and the
+ * area v6 changed most — is exercised by nothing in this file. That is
+ * why the version gap is inert here, and it is not a reason to trust the
+ * double: the mock is simply never asked to stand in for the surface on
+ * which the two majors differ.
  */
 
+// `ioredis-mock` publishes no type declarations of its own — no `types`
+// field in its manifest and no `.d.ts` in the tarball — so this import
+// raises TS7016 ("could not find a declaration file ... implicitly has an
+// 'any' type") and the directive below is what silences it. Note the
+// second cost, beyond the missing types: with the module untyped
+// `RedisMock` is `any`, so every `client:` argument constructed from it
+// satisfies ioredis's `Redis` type without ever being checked against it.
+// That is the other reason a v5-vs-v6 divergence could not surface here.
+// `@types/ioredis-mock` exists and would type this seam, but it only
+// *asserts* `new(): ioredis.Redis` rather than describing the mock, so
+// adopting it would trade an honest `any` for an unearned certainty —
+// that trade has not been made, deliberately.
 // @ts-expect-error — ioredis-mock has no published types
 import RedisMock from 'ioredis-mock';
 import { describe, expect, it, vi } from 'vitest';