fix(mcp): invalidate review session state on cross-profile activation (Closes #690)

A mid-run profile switch (reviewer -> author -> reviewer) left workflow-load
proof, reviewer lease binding, the review decision lock, live namespace
health, and preflight identity/capability stamps intact, so a formal verdict
could be recorded under contaminated session state.

- gitea_activate_profile now invalidates all review-critical session state
  on a cross-profile switch, in memory and in durable state keyed by either
  profile identity, and reports the invalidation + re-preflight requirement.
- Full reviewer preflight (whoami, load_review_workflow,
  resolve_task_capability(review_pr), head re-pin, lease re-acquire) is
  required before any formal verdict after a switch; switching back cannot
  resurrect the stale run.
- Namespace provenance: optional launcher-declared GITEA_MCP_NAMESPACE is
  reported by whoami/runtime context/capability resolution, and a declared
  namespace that disagrees with a task's required namespace fails closed.
- Docs: supported pattern is separate session/namespace per role, not
  in-process profile hopping mid-review.

mcp_namespace_health.py

@@ -16,6 +16,7 @@ Probe sources
 
 from __future__ import annotations
 
+import os
 from typing import Any
 
 
@@ -57,8 +58,56 @@ SAFE_ENV_KEYS = (
     "GITEA_SERVICE",
     "GITEA_EXECUTION_ROLE",
     "GITEA_MCP_CONFIG",
+    "GITEA_MCP_NAMESPACE",
 )
 
+# Optional launcher-provided env declaring the client-managed MCP namespace
+# this process is registered under (e.g. ``gitea-reviewer``). The server
+# cannot derive its own IDE namespace name, so the launcher declares it; when
+# declared, reviewers/mergers can fail closed on a namespace/task mismatch
+# (#690 AC4). Absence means "unknown" — reported, never guessed.
+NAMESPACE_ENV = "GITEA_MCP_NAMESPACE"
+
+
+def configured_client_namespace(env: dict[str, str] | None = None) -> str | None:
+    """Return the launcher-declared client namespace, or None when unknown."""
+    source = os.environ if env is None else env
+    value = (source.get(NAMESPACE_ENV) or "").strip()
+    return value or None
+
+
+def namespace_provenance(
+    task: str | None = None,
+    *,
+    active_profile: str | None = None,
+    env: dict[str, str] | None = None,
+) -> dict[str, Any]:
+    """Report configured client namespace vs active execution profile (#690).
+
+    When *task* carries a required namespace (``TASK_REQUIRED_NAMESPACES``)
+    and the launcher declared a different one, ``mismatch`` is True and the
+    caller must fail closed for that task. An undeclared namespace is
+    reported as unknown — never treated as proof either way.
+    """
+    configured = configured_client_namespace(env)
+    required = TASK_REQUIRED_NAMESPACES.get(task or "")
+    mismatch = bool(configured and required and configured != required)
+    reasons: list[str] = []
+    if mismatch:
+        reasons.append(
+            f"configured client namespace '{configured}' does not match "
+            f"required namespace '{required}' for task '{task}' (fail closed)"
+        )
+    return {
+        "configured_namespace": configured,
+        "namespace_source": NAMESPACE_ENV if configured else "unknown",
+        "active_profile": active_profile,
+        "requested_task": task,
+        "required_namespace": required,
+        "mismatch": mismatch,
+        "reasons": reasons,
+    }
+
 
 def _as_list(value: Any) -> list[str] | None:
     if value is None: