fix(coverage): exempt .d.ts files from diff coverage gate

Ambient declaration files have no runtime code so v8 coverage
never generates DA records for them. Without an allowlist entry,
coverage:diff reports no-coverage-data for every .d.ts in the
diff. Add /\.d\.ts$/ to ALLOWED_GLOBS with a companion test.

Also configure @vitest/coverage-v8 for core-shared and add
targeted vitest exclusions for infrastructure files that are not
unit-testable (DI symbols, interface files, tRPC context, Sentry
SDK init) — bringing core-shared into the L2 aggregate and making
the L1 diff gate enforce coverage on new executable code.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

coverage/summary.json

@@ -1,18 +1,18 @@
 {
-  "generatedAt": "2026-05-18T18:22:54.558Z",
-  "commit": "c298f39",
+  "generatedAt": "2026-05-18T18:25:58.074Z",
+  "commit": "a94e803",
   "repo": {
     "statements": 96.34,
-    "branches": 91.4,
-    "functions": 96.75,
+    "branches": 91.41,
+    "functions": 96.76,
     "lines": 96.34,
     "counts": {
       "lf": 4100,
       "lh": 3950,
-      "brf": 767,
-      "brh": 701,
-      "fnf": 246,
-      "fnh": 238
+      "brf": 768,
+      "brh": 702,
+      "fnf": 247,
+      "fnh": 239
     }
   },
   "byPackage": {
@@ -60,16 +60,16 @@
     },
     "@repo/core-shared": {
       "statements": 97.75,
-      "branches": 95.52,
-      "functions": 91.49,
+      "branches": 95.54,
+      "functions": 91.58,
       "lines": 97.75,
       "counts": {
         "lf": 935,
         "lh": 914,
-        "brf": 268,
-        "brh": 256,
-        "fnf": 94,
-        "fnh": 86
+        "brf": 269,
+        "brh": 257,
+        "fnf": 95,
+        "fnh": 87
       }
     },
     "@repo/marketing-pages": {

packages/core-shared/vitest.config.ts

@@ -16,8 +16,6 @@ export default mergeConfig(nodeVitestConfig, {
         "src/trpc/context.ts",
         // Sentry client init — browser/node SDK init, tested in apps
         "src/instrumentation/sentry/**",
-        // Pure type-alias file — no executable code
-        "src/payload/retention-types.ts",
       ],
     },
   },

scripts/coverage/diff.mjs

@@ -62,6 +62,7 @@ const ALLOWED_GLOBS = [
   /\/integrations\/cms\//,
   /\/ui\//,
   // Pure type-alias / interface files (no executable code)
+  /\.d\.ts$/, // ambient declaration files — no runtime code by definition
   /\.interface\.ts$/,
   /\/index\.ts$/, // barrel re-exports — no executable code
   // Build artifacts

scripts/coverage/diff.test.mjs

@@ -154,6 +154,23 @@ describe("computeDiffCoverage", () => {
     assert.equal(result.summary.filesChanged, 4);
   });
 
+  test("skips TypeScript ambient declaration files (.d.ts)", () => {
+    const lcov = parseLcov(lcovText);
+    const diff = new Map([
+      // Ambient declaration files have no runtime code — v8 coverage never
+      // sees them, so they must be exempted from the no-coverage-data gate.
+      [
+        "packages/core-shared/src/payload/payload-custom-ambient.d.ts",
+        new Set([1, 2, 3, 4, 5, 6, 7, 8, 9, 10]),
+      ],
+      ["packages/foo/src/bar/some-types.d.ts", new Set([1, 2])],
+    ]);
+    const result = computeDiffCoverage(diff, lcov);
+    assert.equal(result.status, "pass");
+    assert.equal(result.summary.filesGated, 0);
+    assert.equal(result.summary.filesChanged, 2);
+  });
+
   test("skips .env template files (.env, .env.example, .env.local)", () => {
     const lcov = parseLcov(lcovText);
     const diff = new Map([