diff --git a/s13code/gateway.py b/s13code/gateway.py
index c073ae8..e55830e 100644
--- a/s13code/gateway.py
+++ b/s13code/gateway.py
@@ -1,6 +1,7 @@
 """The only S13Code → GLC seam: ordinary authenticated HTTP."""
 from __future__ import annotations
 
+import asyncio
 import os
 from typing import Any
 
@@ -27,9 +28,17 @@ async def complete(self, prompt: str, system: str, *, session: str | None = None
         # independently metered gemini_1..N key pool; S13Code never sees keys.
         if provider := os.getenv("S13_GATEWAY_PROVIDER"):
             payload["provider"] = provider
-        response = await self._client.post(f"{self.base_url}/v1/chat", json=payload)
-        if response.status_code >= 400:
-            raise RuntimeError(f"GLC /v1/chat returned {response.status_code}: {response.text[:500]}")
+            
+        max_retries = 5
+        for attempt in range(1, max_retries + 1):
+            response = await self._client.post(f"{self.base_url}/v1/chat", json=payload)
+            if response.status_code in (429, 503) and attempt < max_retries:
+                await asyncio.sleep(2 ** attempt)
+                continue
+            if response.status_code >= 400:
+                raise RuntimeError(f"GLC /v1/chat returned {response.status_code}: {response.text[:500]}")
+            break
+            
         body = response.json()
         return {"text": body.get("text", ""), "provider": body.get("provider"), "model": body.get("model")}
 
diff --git a/s13code/planner.py b/s13code/planner.py
index c167b2b..fe6cbd2 100644
--- a/s13code/planner.py
+++ b/s13code/planner.py
@@ -35,7 +35,7 @@ def __init__(self, llm: TextLLM, fallback: FallbackPlanner, *, goal: str, roles:
     async def plan(self, graph: GraphSnapshot, event: Event) -> GraphPatch:
         try:
             reply = await self.llm(self._prompt(graph, event), "Return only valid GraphPatch JSON.")
-            patch = self._parse(reply.get("text", ""))
+            patch = self._parse(reply.get("text", ""), graph)
             self.last_selection = {"mode": "llm", "provider": reply.get("provider"), "model": reply.get("model"),
                                    "event": event.sequence}
             return patch
@@ -44,29 +44,47 @@ async def plan(self, graph: GraphSnapshot, event: Event) -> GraphPatch:
                                    "reason": f"{type(error).__name__}: {error}"}
             return await self.fallback.plan(graph, event)
 
-    def _parse(self, text: str) -> GraphPatch:
-        data = json.loads(text)
+    def _parse(self, text: str, graph: GraphSnapshot) -> GraphPatch:
+        text = text.strip()
+        if text.startswith("```json"):
+            text = text[7:]
+        elif text.startswith("```"):
+            text = text[3:]
+        if text.endswith("```"):
+            text = text[:-3]
+        data = json.loads(text.strip())
         if not isinstance(data, dict) or set(data).difference({"add", "connect", "cancel", "wait", "resume", "finish", "reason"}):
             raise ValueError("invalid GraphPatch object")
         add: list[TaskSpec] = []
+        add_ids: set[str] = set()
         for raw in data.get("add", []):
             if not isinstance(raw, dict) or set(raw).difference({"id", "role", "input", "metadata"}):
                 raise ValueError("invalid task object")
             node_id, role = raw.get("id"), raw.get("role")
             if not isinstance(node_id, str) or not _ID.fullmatch(node_id) or role not in self.roles:
                 raise ValueError("invalid node id or unsupported role")
+            if node_id in graph.nodes or node_id in add_ids:
+                raise ValueError(f"duplicate node id: {node_id}")
+            add_ids.add(node_id)
             task_input, metadata = raw.get("input", {}), raw.get("metadata", {})
             if not isinstance(task_input, dict) or not isinstance(metadata, dict):
                 raise ValueError("task input/metadata must be objects")
             add.append(TaskSpec(node_id, role, task_input, {**metadata, "agent": role}))
+        all_ids = set(graph.nodes).union(add_ids)
         def id_list(name: str) -> tuple[str, ...]:
             value = data.get(name, [])
             if not isinstance(value, list) or not all(isinstance(x, str) and _ID.fullmatch(x) for x in value):
                 raise ValueError(f"invalid {name}")
+            if any(x not in all_ids for x in value):
+                raise ValueError(f"{name} references unknown task")
             return tuple(value)
         edges = data.get("connect", [])
         if not isinstance(edges, list) or not all(isinstance(e, list) and len(e) == 2 and all(isinstance(x, str) and _ID.fullmatch(x) for x in e) for e in edges):
             raise ValueError("invalid connect")
+        if any(e[0] == e[1] for e in edges):
+            raise ValueError("a task cannot depend on itself")
+        if any(e[0] not in all_ids or e[1] not in all_ids for e in edges):
+            raise ValueError("edge references unknown task")
         if not isinstance(data.get("finish", False), bool) or not isinstance(data.get("reason", ""), str):
             raise ValueError("invalid finish/reason")
         return GraphPatch(tuple(add), tuple((e[0], e[1]) for e in edges), id_list("cancel"), id_list("wait"),
@@ -78,4 +96,4 @@ def _prompt(self, graph: GraphSnapshot, event: Event) -> str:
             "allowed_roles": sorted(self.roles),
             "patch_schema": {"add": [{"id": "safe_id", "role": "allowed_role", "input": {}, "metadata": {"agent": "role"}}],
                 "connect": [["parent", "child"]], "cancel": [], "wait": [], "resume": [], "finish": False, "reason": "short"},
-            "rules": ["emit only next useful work", "roles never call tools directly", "return JSON only"]})
+            "rules": ["emit only next useful work", "roles never call tools directly", "return JSON only", "the final node must have id 'answer'"]})