fix: stop parsing email domains as maintainer handles

packages/darnit/src/darnit/context/sieve.py

@@ -518,25 +518,23 @@ def _detect_governance_deterministic(self, local_path: str) -> list[ContextSigna
     # =========================================================================
 
     def _parse_maintainers_file(self, content: str) -> list[str]:
-        """Parse maintainers from MAINTAINERS.md content.
+        """Parse maintainer handles from MAINTAINERS.md content.
 
-        Looks for:
-        - @username mentions
-        - GitHub usernames in lists
-        - Email addresses with names
+        Returns only ``@username`` handles. Email addresses are stripped
+        before matching so a domain (``realcorp`` in ``alice@realcorp.io``)
+        is never read as a handle, and display names are left out: a bare
+        name is not a GitHub handle, and GitHub rejects it as a code owner.
         """
-        maintainers = []
-
-        # Pattern for @username
-        at_mentions = re.findall(r"@([a-zA-Z0-9][-a-zA-Z0-9]*)", content)
-        maintainers.extend([f"@{m}" for m in at_mentions])
-
-        # Pattern for "Name (email)" or "Name <email>"
-        name_email = re.findall(
-            r"[-*]\s*([A-Z][a-zA-Z]+(?:\s+[A-Z][a-zA-Z]+)*)\s*[(<]",
-            content,
+        # Strip email addresses first: the @ in alice@example.com is never a
+        # handle, and without this its domain would match the handle pattern.
+        no_emails = re.sub(
+            r"[A-Za-z0-9._%+-]+@[A-Za-z0-9.-]+\.[A-Za-z]{2,}", "", content
         )
-        maintainers.extend(name_email)
+
+        # Pattern for @username. The lookbehind keeps the @ of any surviving
+        # address-like text (e.g. user@localhost) from matching as a handle.
+        at_mentions = re.findall(r"(?<![\w.])@([a-zA-Z0-9][-a-zA-Z0-9]*)", no_emails)
+        maintainers = [f"@{m}" for m in at_mentions]
 
         # Dedupe while preserving order
         seen = set()

tests/darnit/context/test_context_sieve.py

@@ -168,6 +168,58 @@ def test_detect_maintainers_from_file(self, temp_repo):
         # High confidence from explicit file
         assert result.confidence >= 0.8
 
+    @pytest.mark.unit
+    def test_detect_maintainers_from_file_ignores_email_domain(self, temp_repo):
+        """An email domain must not become a maintainer handle (issue #464)."""
+        (Path(temp_repo) / "MAINTAINERS.md").write_text(
+            "# Maintainers\n\n- Alice Example <alice@realcorp.io> @alice\n"
+        )
+
+        sieve = ContextSieve()
+        result = sieve.detect("maintainers", temp_repo, "owner", "repo")
+
+        assert result.key == "maintainers"
+        assert "@alice" in result.value
+        assert not any("realcorp" in str(v).lower() for v in result.value)
+
+    @pytest.mark.unit
+    def test_parse_maintainers_file_email_domain_not_a_handle(self):
+        """The issue's exact example: only the real handle is returned."""
+        sieve = ContextSieve()
+        assert (
+            sieve._parse_maintainers_file("- Alice Example <alice@realcorp.io> @alice\n")
+            == ["@alice"]
+        )
+
+    @pytest.mark.unit
+    def test_parse_maintainers_file_name_and_email_without_handle(self):
+        """A display name plus email, with no @handle, yields no maintainers."""
+        sieve = ContextSieve()
+        assert sieve._parse_maintainers_file("- Alice Example <alice@realcorp.io>\n") == []
+
+    @pytest.mark.unit
+    def test_parse_maintainers_file_plain_email_yields_nothing(self):
+        """A bare email address contributes no handle."""
+        sieve = ContextSieve()
+        assert sieve._parse_maintainers_file("Contact: bob@example.com\n") == []
+
+    @pytest.mark.unit
+    def test_parse_maintainers_file_keeps_plain_handles(self):
+        """Ordinary @mentions still parse as before."""
+        sieve = ContextSieve()
+        assert sieve._parse_maintainers_file(
+            "- @alice - Lead maintainer\n- @bob - Core contributor\n"
+        ) == ["@alice", "@bob"]
+
+    @pytest.mark.unit
+    def test_parse_maintainers_file_handle_glued_to_email(self):
+        """A handle written directly after an email still parses."""
+        sieve = ContextSieve()
+        assert (
+            sieve._parse_maintainers_file("- Alice Example <alice@realcorp.io>@alice\n")
+            == ["@alice"]
+        )
+
     @pytest.mark.unit
     def test_detect_maintainers_from_codeowners(self, temp_repo):
         """Detects maintainers from CODEOWNERS file."""