feat(#141): export FileCoveredByDocMap helper in review/docmap.go

Adds FileCoveredByDocMap(cfg *DocMapConfig, file string) bool — a thin wrapper
over the existing unexported mappingMatches that lets cmd/ check per-file docmap
coverage without duplicating glob logic.

Also adds unit tests covering matched globs, non-matching paths, empty file,
and empty config.

review/docmap.go

@@ -66,6 +66,18 @@ func ParseDocMapConfig(localPath string) (*DocMapConfig, error) {
 	return &cfg, nil
 }
 
+// FileCoveredByDocMap reports whether at least one paths: glob in any mapping
+// of cfg matches the given file path. It is used by static validation tooling
+// (e.g. the validate-docmap subcommand) to check per-file docmap coverage.
+func FileCoveredByDocMap(cfg *DocMapConfig, file string) bool {
+	for _, mapping := range cfg.Mappings {
+		if mappingMatches(mapping.Paths, []string{file}) {
+			return true
+		}
+	}
+	return false
+}
+
 // MatchDocs returns deduplicated doc paths for the given changed file paths.
 // A mapping matches if any of its path globs matches any of the changed files.
 func MatchDocs(cfg *DocMapConfig, changedFiles []string) []string {

review/docmap_test.go

@@ -436,3 +436,52 @@ func writeTempYAML(t *testing.T, content string) string {
 	}
 	return filepath.Clean(f.Name())
 }
+
+// ============================================================
+// FileCoveredByDocMap
+// ============================================================
+
+func TestFileCoveredByDocMap(t *testing.T) {
+	cfg := &DocMapConfig{
+		Mappings: []DocMapping{
+			{
+				Paths: []string{"lib/foo/**", "lib/bar/*.go"},
+				Docs:  []string{"docs/foo.md"},
+			},
+			{
+				Paths: []string{"cmd/**"},
+				Docs:  []string{"docs/cmd.md"},
+			},
+		},
+	}
+
+	cases := []struct {
+		file    string
+		covered bool
+	}{
+		{"lib/foo/baz.ex", true},
+		{"lib/foo/sub/deep.ex", true},
+		{"lib/bar/util.go", true},
+		{"lib/bar/sub/util.go", false}, // *.go only matches one level
+		{"cmd/main.go", true},
+		{"cmd/sub/main.go", true},
+		{"internal/secret.go", false},
+		{"", false},
+	}
+
+	for _, tc := range cases {
+		t.Run(tc.file, func(t *testing.T) {
+			got := FileCoveredByDocMap(cfg, tc.file)
+			if got != tc.covered {
+				t.Errorf("FileCoveredByDocMap(%q) = %v, want %v", tc.file, got, tc.covered)
+			}
+		})
+	}
+}
+
+func TestFileCoveredByDocMap_EmptyConfig(t *testing.T) {
+	cfg := &DocMapConfig{}
+	if FileCoveredByDocMap(cfg, "lib/foo/bar.go") {
+		t.Error("expected false for empty config, got true")
+	}
+}