fix(db): stop documenting 0090 as a grandfathered migration duplicate

scripts/check-migrations.ts

@@ -23,12 +23,12 @@
 //   • 0074 — both 0074_ai_review_cache (#1462) and 0074_orb_self_enrollment_disabled (#1465, a bare ADD COLUMN)
 //     merged + deployed before the collision surfaced; the column already exists in prod, so a rename would
 //     re-run the ALTER and fail. Grandfathered for the same reason as 0015/0017.
-//   • 0090 — both 0090_contributor_cap_label (#2479) and 0090_pull_request_detail_sync_head_sha (#2527)
-//     merged with bare ADD COLUMN statements. Preserve both filenames so already-applied databases never
-//     replay either ALTER under a new migration name.
+//   • 0090 — NOT grandfathered: 0090_pull_request_detail_sync_head_sha (#2527) was renumbered to
+//     migrations/0092_* by #8897, so only 0090_contributor_cap_label (#2479) exists at 0090 today — a single
+//     file, no collision, and correctly absent from KNOWN_MIGRATION_DUPLICATES. Do not re-add it from git history.
 //   • 0156 — both 0156_draft_pr_close_policy and 0156_pull_request_screenshot_table_presence_satisfied
 //     merged independently from the same base and were both applied to production before the collision
-//     surfaced; bare ADD COLUMN statements, same grandfather reasoning as 0074/0090.
+//     surfaced; bare ADD COLUMN statements, same grandfather reasoning as 0074.
 import { readdirSync, readFileSync } from "node:fs";
 import { detectMigrationCollisions, extractMigrationNumber, KNOWN_MIGRATION_DUPLICATES, MIGRATION_FILENAME_PATTERN } from "../src/db/migration-collisions";
 import { detectColumnCollisions } from "../src/db/migration-column-extraction";

test/unit/migration-collisions.test.ts

@@ -1,3 +1,4 @@
+import { readdirSync } from "node:fs";
 import { describe, expect, it } from "vitest";
 import { detectMigrationCollisions, extractMigrationNumber, KNOWN_MIGRATION_DUPLICATES, MIGRATION_FILENAME_PATTERN } from "../../src/db/migration-collisions";
 
@@ -90,4 +91,32 @@ describe("KNOWN_MIGRATION_DUPLICATES (#2550)", () => {
     // And the renumbered file at its new number is likewise a lone, non-colliding entry.
     expect(detectMigrationCollisions(["0092_pull_request_detail_sync_head_sha.sql"], KNOWN_MIGRATION_DUPLICATES)).toEqual([]);
   });
+
+  describe("stays bidirectionally in step with the real migrations/ directory (#9653)", () => {
+    const realMigrationFiles = readdirSync("migrations").filter((f) => MIGRATION_FILENAME_PATTERN.test(f));
+
+    it("every filename in KNOWN_MIGRATION_DUPLICATES exists on disk (no dead grandfather entries)", () => {
+      // A re-added 0090 entry (or any stale filename) fails here — the file no longer exists, so the list would
+      // point at a migration that isn't there.
+      const onDisk = new Set(realMigrationFiles);
+      const missing: string[] = [];
+      for (const files of KNOWN_MIGRATION_DUPLICATES.values()) {
+        for (const file of files) if (!onDisk.has(file)) missing.push(file);
+      }
+      expect(missing).toEqual([]);
+    });
+
+    it("every migration number with more than one file on disk is a KNOWN_MIGRATION_DUPLICATES key", () => {
+      // The reverse direction: a genuine on-disk collision that isn't grandfathered would surface here rather
+      // than only at premerge, keeping the two sources in step in both directions.
+      const filesByNumber = new Map<number, string[]>();
+      for (const file of realMigrationFiles) {
+        const number = extractMigrationNumber(file);
+        if (number == null) continue;
+        filesByNumber.set(number, [...(filesByNumber.get(number) ?? []), file]);
+      }
+      const collidingNumbers = [...filesByNumber.entries()].filter(([, files]) => files.length > 1).map(([number]) => number);
+      for (const number of collidingNumbers) expect(KNOWN_MIGRATION_DUPLICATES.has(number)).toBe(true);
+    });
+  });
 });