fix(reset): default-deny destructive reset against prod target

/admin/reset and reset_environment.reset() act on os.environ['SUPABASE_URL'].
A platform-admin call on a prod-deployed API would wipe prod data + exam
corpus + storage. Refuse when the target matches a known prod marker
(.156 / supabase.classroomcopilot) unless RESET_ALLOW_PROD=1 is set.

Addresses overwatch review finding #1 on feature/exam-seeding-overhaul.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

run/initialization/reset_environment.py

@@ -129,6 +129,28 @@ def _sb_headers():
     }
 
 
+# Markers that identify a production Supabase target. Destructive reset against any of these is
+# refused by default (project rule: ".94 only; .156 human-gated") — set RESET_ALLOW_PROD=1 to override.
+PROD_TARGET_MARKERS = ("192.168.0.156", "supabase.classroomcopilot")
+
+
+def _assert_reset_allowed(url: str, scope: str) -> None:
+    """Default-deny destructive reset against a production-looking Supabase target.
+
+    The /admin/reset route and this module both act on os.environ['SUPABASE_URL']; without this guard
+    a platform-admin call on a prod-deployed API would wipe prod data + exam corpus + storage. We refuse
+    when the target matches a known prod marker unless an explicit RESET_ALLOW_PROD opt-in is set.
+    """
+    target = (url or "").lower()
+    looks_prod = any(m in target for m in PROD_TARGET_MARKERS)
+    override = os.environ.get("RESET_ALLOW_PROD", "").strip().lower() in ("1", "true", "yes")
+    if looks_prod and not override:
+        raise RuntimeError(
+            f"refusing destructive reset (scope={scope}) against production-looking target {target!r}; "
+            f"this is human-gated — set RESET_ALLOW_PROD=1 to override."
+        )
+
+
 # ─── Neo4j helpers ────────────────────────────────────────────────────────────
 
 def _neo4j_drop_all_non_system() -> Dict[str, List[str]]:
@@ -243,6 +265,7 @@ def reset(scope: str = "all") -> Dict[str, Any]:
     if scope not in ("all", "exam-corpus", "timetable"):
         raise ValueError(f"invalid scope {scope!r} (want all|exam-corpus|timetable)")
     url, headers = _sb_headers()
+    _assert_reset_allowed(url, scope)
 
     if scope == "exam-corpus":
         logger.info("RESET (scope=exam-corpus) — exam tables + cc.examboards storage")