fix(offhost): judge the bucket's rules for database/ against this instance's folder

The dumps now live under database/<host of APP_URL>/, so the rule check reads
a sample key in that folder: a rule scoped to this instance's folder counts,
one scoped to another instance's does not.

src/lib/jobs/__tests__/offhost-lifecycle.test.ts

@@ -3,7 +3,7 @@
  * from the account copies: a rule scoped to another prefix, or to a tag, does
  * not touch them.
  */
-import { describe, expect, it } from "vitest";
+import { describe, expect, it, vi } from "vitest";
 import type { LifecycleRule } from "@aws-sdk/client-s3";
 
 import { lifecycleFromRules, ruleAppliesTo } from "../offhost-lifecycle";
@@ -29,6 +29,25 @@ describe("lifecycle rules and the database dumps", () => {
     ).toEqual({ state: "configured", expirationDays: 14 });
   });
 
+  it("reads the rules for this instance's own folder under database/", () => {
+    vi.stubEnv("APP_URL", "https://health.example.org");
+    try {
+      expect(
+        lifecycleFromRules([
+          rule(30, { Filter: { Prefix: "2026-" } }),
+          rule(9, { Filter: { Prefix: "database/health.example.org/" } }),
+        ]).database,
+      ).toEqual({ state: "configured", expirationDays: 9 });
+      expect(
+        lifecycleFromRules([
+          rule(9, { Filter: { Prefix: "database/staging.example.org/" } }),
+        ]).database,
+      ).toEqual({ state: "missing", expirationDays: null });
+    } finally {
+      vi.unstubAllEnvs();
+    }
+  });
+
   it("says database/ is not covered when the only rule is scoped elsewhere", () => {
     const result = lifecycleFromRules([
       rule(30, { Filter: { Prefix: "2026-" } }),

src/lib/jobs/offhost-lifecycle.ts

@@ -16,6 +16,10 @@
  * without `s3:GetLifecycleConfiguration`, a target that does not implement the
  * call, a network failure) and says nothing either way.
  */
+import {
+  instanceIdFromEnv,
+  offhostObjectKey,
+} from "@/lib/database-backup/dump-core.mjs";
 import type { LifecycleRule } from "@aws-sdk/client-s3";
 
 export interface LifecycleVerdict {
@@ -40,9 +44,17 @@ export const LIFECYCLE_MISSING: OffhostLifecycle = {
   database: { state: "missing", expirationDays: null },
 };
 
-/** A key a database dump is stored under, to test the rules against. */
-const DATABASE_SAMPLE_KEY =
-  "database/healthlog-20260101T013000Z-daily.dump.enc";
+/**
+ * A key this instance's database dumps are stored under, to test the rules
+ * against: inside its own folder (`database/<host of APP_URL>/`), so a rule
+ * scoped to that folder counts and one scoped to another instance's does not.
+ */
+function databaseSampleKey(): string {
+  return offhostObjectKey(
+    "healthlog-20260101T013000Z-daily.dump.enc",
+    instanceIdFromEnv(),
+  );
+}
 
 /**
  * Whether a rule's filter takes in `key`. Our objects carry no tags, so a
@@ -73,7 +85,7 @@ export function lifecycleFromRules(
   return {
     ...verdict(rules),
     database: verdict(
-      rules.filter((rule) => ruleAppliesTo(rule, DATABASE_SAMPLE_KEY)),
+      rules.filter((rule) => ruleAppliesTo(rule, databaseSampleKey())),
     ),
   };
 }