🐛 fix(manifest): reject duplicate fields in command example entries

- Track seen keys during manifest parsing to detect duplicate keys
- Return explicit error instead of silently overwriting earlier values
- Add test coverage for duplicate field rejection

Author: cocosip

docs/go/maintainer/development-tracker.md

@@ -151,6 +151,13 @@ Immediate next tasks:
 
 ### 2026-03-18 Session Update
 
+- Completed: Tightened command-example manifest parsing to reject duplicate fields inside one entry instead of silently letting a later value overwrite an earlier one. Parser tests now cover duplicate-key rejection alongside missing metadata and malformed tag lists, which makes hand-edited catalog drift easier to catch before it reaches the embedded binary.
+- In progress: none.
+- Blockers: none.
+- Next step: keep chipping away at ambiguous or silent-fallback cases in the operator catalog path rather than adding more surface area.
+
+### 2026-03-18 Session Update
+
 - Completed: Tightened command-example manifest parsing so each entry must now carry non-empty `tags` and `summary` metadata, not just the required command/name/format/path fields. Parser coverage now explicitly rejects missing metadata alongside malformed or empty tag lists, so the embedded example catalog contract is enforced at parse time instead of only by higher-level tests.
 - In progress: none.
 - Blockers: none.

internal/app/command_example_manifest.go

@@ -167,11 +167,16 @@ func parseCommandExampleManifestEntry(line string) (commandExampleManifestEntry,
 		return commandExampleManifestEntry{}, err
 	}
 	entry := commandExampleManifestEntry{}
+	seenKeys := make(map[string]struct{}, len(fields))
 	for _, field := range fields {
 		key, value, ok := strings.Cut(field, "=")
 		if !ok {
 			return commandExampleManifestEntry{}, fmt.Errorf("invalid command example manifest field %q", field)
 		}
+		if _, exists := seenKeys[key]; exists {
+			return commandExampleManifestEntry{}, fmt.Errorf("duplicate command example manifest field %q in %q", key, line)
+		}
+		seenKeys[key] = struct{}{}
 		if strings.HasPrefix(value, `"`) {
 			unquoted, err := strconv.Unquote(value)
 			if err != nil {

internal/app/command_example_manifest_test.go

@@ -58,6 +58,20 @@ func TestParseCommandExampleManifestEntryRejectsEmptyTag(t *testing.T) {
 	}
 }
 
+func TestParseCommandExampleManifestEntryRejectsDuplicateField(t *testing.T) {
+	line := `command=follow-imports example=audit-only-single-text format=text tags="audit-only,single-input" summary="First summary." summary="Second summary." path=testdata/follow-imports-audit-only-single.txt`
+
+	_, err := parseCommandExampleManifestEntry(line)
+	if err == nil {
+		t.Fatal("expected duplicate field error")
+	}
+	for _, fragment := range []string{`duplicate command example manifest field "summary"`, "audit-only-single-text"} {
+		if !strings.Contains(err.Error(), fragment) {
+			t.Fatalf("error %q missing fragment %q", err.Error(), fragment)
+		}
+	}
+}
+
 func TestParseCommandExampleManifestEntryRejectsMissingTags(t *testing.T) {
 	line := `command=follow-imports example=audit-only-single-text format=text summary="Audit-only follow report." path=testdata/follow-imports-audit-only-single.txt`