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_work_duplicate_gate.py

@@ -1,3 +1,7 @@
+import sys as _sys
+from pathlib import Path as _Path
+_sys.path.insert(0, str(_Path(__file__).resolve().parent))
+from mutation_profile_fixture import shared_mutation_env  # noqa: E402
 """Tests for early duplicate-work detection (#400)."""
 import os
 import sys
@@ -144,10 +148,12 @@ class TestInjectableDuplicateFetcher(unittest.TestCase):
             },
         ):
             with tempfile.TemporaryDirectory() as lock_dir:
-                with patch.dict(os.environ, {
-                    "GITEA_ALLOWED_OPERATIONS": "gitea.issue.comment",
-                    "GITEA_ISSUE_LOCK_DIR": lock_dir,
-                }, clear=True):
+                env = shared_mutation_env(
+                    "test-author-prgs",
+                    include_example_repo=True,
+                    GITEA_ISSUE_LOCK_DIR=lock_dir,
+                )
+                with patch.dict(os.environ, env, clear=True):
                     mcp_server.gitea_lock_issue(
                         issue_number=400,
                         branch_name="feat/issue-400-duplicate-work-preflight",
@@ -161,7 +167,11 @@ class TestMcpDuplicateRecheck(unittest.TestCase):
         self._dir = tempfile.TemporaryDirectory()
         self._env_patch = patch.dict(
             os.environ,
-            {"GITEA_ISSUE_LOCK_DIR": self._dir.name},
+            shared_mutation_env(
+                "test-author-prgs",
+                include_example_repo=True,
+                GITEA_ISSUE_LOCK_DIR=self._dir.name,
+            ),
             clear=False,
         )
         self._env_patch.start()
@@ -171,6 +181,11 @@ class TestMcpDuplicateRecheck(unittest.TestCase):
         })
         self._remotes.start()
         mcp_server._IDENTITY_CACHE.clear()
+        try:
+            import session_context_binding as _sc
+            _sc._reset_session_context_for_testing()
+        except Exception:
+            pass
 
     def tearDown(self):
         patch.stopall()
@@ -205,6 +220,8 @@ class TestMcpDuplicateRecheck(unittest.TestCase):
         "allowed_operations": ["gitea.read", "gitea.repo.commit"],
         "forbidden_operations": [],
         "audit_label": "test-author",
+        "allowed_repositories": ["Example-Org/Example-Repo"],
+        "base_url": "https://gitea.example.com",
     })
     @patch("mcp_server.get_auth_header", return_value="token x")
     def test_commit_files_blocked_on_recheck(self, _auth, _profile, mock_gate):
@@ -239,6 +256,8 @@ class TestMcpDuplicateRecheck(unittest.TestCase):
         "allowed_operations": ["gitea.read", "gitea.pr.create"],
         "forbidden_operations": [],
         "audit_label": "test-author",
+        "allowed_repositories": ["Example-Org/Example-Repo"],
+        "base_url": "https://gitea.example.com",
     })
     @patch("mcp_server.get_auth_header", return_value="token x")
     def test_create_pr_returns_handoff_on_duplicate(self, _auth, _profile, mock_gate):