fix: validate gitea_edit_pr no-fields before authentication (#43)

gitea_edit_pr called _auth() (and resolved the remote) before checking whether
any editable field was provided, so a pure validation error (no fields) surfaced
as a RuntimeError "no credentials" in environments without Gitea auth — making
test_edit_pr_no_fields_raises depend on credentials/network/env.

Move the payload build + no-fields ValueError ahead of _resolve/_auth/URL setup.
Behavior is unchanged when fields are provided (same _resolve → _auth → audited
PATCH path). No change to auth, retry/backoff, audit, config profiles, or
worktree helpers.

Tests: add test_edit_pr_no_fields_validates_before_auth asserting the no-fields
path raises ValueError and calls neither get_auth_header nor api_request (even
with auth mocked to None). Existing edit-PR tests unchanged.

Full suite passes with no Gitea credentials (287 passed, 0 failures) — the
no-fields test no longer depends on the environment.

Closes #43.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

tests/test_mcp_server.py

@@ -737,6 +737,17 @@ class TestEditPR(unittest.TestCase):
         with self.assertRaises(ValueError):
             gitea_edit_pr(pr_number=1)
 
+    @patch("mcp_server.api_request")
+    @patch("mcp_server.get_auth_header")
+    def test_edit_pr_no_fields_validates_before_auth(self, mock_auth, mock_api):
+        # No-fields validation must not depend on credentials/network: it raises
+        # ValueError before touching auth or the API, even with no creds.
+        mock_auth.return_value = None  # simulate an unauthenticated environment
+        with self.assertRaises(ValueError):
+            gitea_edit_pr(pr_number=1)
+        mock_auth.assert_not_called()
+        mock_api.assert_not_called()
+
 
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