chore(lint): detect fully-fixed files in ratchet advisory (#3962)

Add a second pass in compare() that scans baseline entries missing from
the current lint output (file became fully clean). Without this pass,
advisory messages only fire when a file still has *some* violation but
fewer than baseline — completely-fixed files were silently ignored.

Also add a Vitest unit test covering the fully-fixed-file advisory case.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01AphLfgUJWaFNAgU5UXdJ4n

Author: Yeraze

scripts/lint-ratchet.mjs

@@ -90,6 +90,15 @@ export function compare(counts, base, lines = {}) {
       }
     }
   }
+  // Detect baseline files/rules that have dropped to zero entirely
+  // (file no longer appears in counts, but baseline had violations).
+  for (const [file, rules] of Object.entries(base)) {
+    for (const [rule, prev] of Object.entries(rules)) {
+      if (prev > 0 && (counts[file]?.[rule] ?? 0) === 0) {
+        advisories.push(`${file}: ${rule} ${prev}→0`);
+      }
+    }
+  }
   return { failures, advisories };
 }
 

scripts/lint-ratchet.test.mjs

@@ -45,6 +45,15 @@ describe('compare()', () => {
     expect(advisories[0]).toMatch(/3→1/);
   });
 
+  it('generates advisory when a file is entirely absent from current counts (fully fixed)', () => {
+    const counts = {}; // file completely clean now
+    const base = { 'src/clean.ts': { 'no-unused-vars': 2 } };
+    const { failures, advisories } = compare(counts, base, {});
+    expect(failures).toHaveLength(0);
+    expect(advisories).toHaveLength(1);
+    expect(advisories[0]).toMatch(/2→0/);
+  });
+
   it('handles multiple files and rules independently', () => {
     const counts = {
       'a.ts': { 'no-unused-vars': 2, '@typescript-eslint/no-explicit-any': 1 },