fix(session): require config-backed mutation authority and workspace-bound targets (#714)

Close the #714 remediation gap left at 943d402 where env-only mutation
profiles, REMOTES Timesheet defaults treated as explicit caller input, and
machine-dependent Git remotes produced false greens.

- Fail closed when mutations lack a config-backed profile with non-empty
  allowed_repositories; env ops cannot invent mutation authority.
- Preserve omitted-vs-explicit org/repo provenance through the mutation
  gate; omitted targets bind to the verified workspace repository.
- Prefer workspace-aligned Git remotes over historical Timesheet defaults
  in MCP _resolve and CLI resolve_remote.
- Centralize deterministic config-backed mutation fixtures; migrate
  mutation tests off env-only authority without weakening security
  assertions.

Full suite: 2744 passed, 6 skipped.

tests/test_create_pr.py

@@ -1,3 +1,4 @@
+import os
 """Tests for create_pr.py.
 
 Every test mocks `get_credentials` and `urllib.request.urlopen` so no real
@@ -8,7 +9,7 @@ import json
 import sys
 import unittest
 import contextlib
-from unittest.mock import MagicMock, patch
+from unittest.mock import patch, MagicMock, patch
 
 sys.path.insert(0, str(__import__("pathlib").Path(__file__).resolve().parent.parent))
 import create_pr  # noqa: E402
@@ -74,6 +75,26 @@ class TestRemoteResolution(unittest.TestCase):
 # API payload
 # ---------------------------------------------------------------------------
 class TestAPIPayload(unittest.TestCase):
+    """#714: omitted --org/--repo uses workspace-bound repo (Gitea-Tools),
+    not the historical REMOTES Timesheet default. Intentional security-policy
+    migration of legacy omitted-target assertions.
+    """
+
+    def setUp(self):
+        self._ws_env = patch.dict(
+            os.environ,
+            {
+                "GITEA_TEST_WORKSPACE_REMOTE_URL": (
+                    "https://gitea.prgs.cc/Scaled-Tech-Consulting/Gitea-Tools.git"
+                )
+            },
+            clear=False,
+        )
+        self._ws_env.start()
+
+    def tearDown(self):
+        self._ws_env.stop()
+
 
     @patch("create_pr.get_credentials", return_value=FAKE_CREDS)
     def test_payload_fields(self, _cred):
@@ -113,7 +134,7 @@ class TestAPIPayload(unittest.TestCase):
             url = MockReq.call_args[0][0]
             self.assertEqual(
                 url,
-                "https://gitea.prgs.cc/api/v1/repos/Scaled-Tech-Consulting/Timesheet/pulls",
+                "https://gitea.prgs.cc/api/v1/repos/Scaled-Tech-Consulting/Gitea-Tools/pulls",
             )