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_issue_714_session_context_immutability.py

@@ -55,6 +55,7 @@ CONFIG_714 = {
                 "gitea.pr.merge",
                 "gitea.pr.request_changes",
             ],
+            "allowed_repositories": ["Scaled-Tech-Consulting/Gitea-Tools"],
             "execution_profile": "prgs-author",
         },
         "mdcps-reviewer": {
@@ -78,6 +79,7 @@ CONFIG_714 = {
                 "gitea.pr.merge",
                 "gitea.repo.commit",
             ],
+            "allowed_repositories": ["913443/eAgenda"],
             "execution_profile": "mdcps-reviewer",
         },
         "mdcps-author": {
@@ -102,6 +104,7 @@ CONFIG_714 = {
                 "gitea.pr.merge",
                 "gitea.pr.request_changes",
             ],
+            "allowed_repositories": ["913443/eAgenda"],
             "execution_profile": "mdcps-author",
         },
     },
@@ -131,6 +134,14 @@ class TestIssue714SessionContextImmutability(unittest.TestCase):
             clear=False,
         )
         self._remotes.start()
+        def _url(name):
+            if name == "dadeschools":
+                return "https://gitea.dadeschools.net/913443/eAgenda.git"
+            if name == "prgs":
+                return "https://gitea.prgs.cc/Scaled-Tech-Consulting/Gitea-Tools.git"
+            return None
+        self._url_patch = patch.object(mcp_server, "_local_git_remote_url", side_effect=_url)
+        self._url_patch.start()
         mcp_server._IDENTITY_CACHE.clear()
         gitea_config._active_profile_override = None
         mcp_server._MUTATION_AUTHORITY = None
@@ -143,6 +154,7 @@ class TestIssue714SessionContextImmutability(unittest.TestCase):
         }
 
     def tearDown(self):
+        self._url_patch.stop()
         self._remotes.stop()
         mcp_server._IDENTITY_CACHE.clear()
         gitea_config._active_profile_override = None