diff --git a/src/kernel_ci_cloud_labs/pull_labs_poller.py b/src/kernel_ci_cloud_labs/pull_labs_poller.py
index 121bd5e..3538fa8 100644
--- a/src/kernel_ci_cloud_labs/pull_labs_poller.py
+++ b/src/kernel_ci_cloud_labs/pull_labs_poller.py
@@ -79,6 +79,26 @@
 ENV_BASE_CONFIG = "PULLAB_BASE_CONFIG"
 
 
+# System and read-only database-managed fields on node objects.
+# These fields are omitted when updating a node (PUT /node/<id>) to prevent
+# FastAPI/Pydantic validation errors (HTTP 400 Bad Request / 422 Unprocessable Entity)
+# since they are read-only and not accepted in the update schema.
+NODE_READ_ONLY_FIELDS = {
+    "id",
+    "_id",
+    "created",
+    "updated",
+    "user",
+    "user_groups",
+    "owner",
+    "submitter",
+    "treeid",
+    "processed_by_kcidb_bridge",
+    "retry_counter",
+    "timeout",
+}
+
+
 def _parse_kcidb_rest(env_value: str) -> Tuple[Optional[str], Optional[str]]:
     """Parse a KCIDB_REST URL of the form https://<token>@<host>[/path].
 
@@ -115,9 +135,17 @@ def _http_get_json(url: str, token: Optional[str] = None, timeout: float = 30.0)
     if token:
         headers["Authorization"] = f"Bearer {token}"
     req = urllib.request.Request(url, method="GET", headers=headers)
-    with urllib.request.urlopen(req, timeout=timeout) as resp:
-        body = resp.read().decode("utf-8", errors="replace")
-        return json.loads(body) if body else None
+    try:
+        with urllib.request.urlopen(req, timeout=timeout) as resp:
+            body = resp.read().decode("utf-8", errors="replace")
+            return json.loads(body) if body else None
+    except urllib.error.HTTPError as e:
+        try:
+            err_body = e.read().decode("utf-8", errors="replace")
+            logger.error("HTTP GET to %s failed (HTTP %s): %s. Response body: %s", url, e.code, e.reason, err_body)
+        except Exception:
+            pass
+        raise
 
 
 def _http_put_json(
@@ -136,9 +164,17 @@ def _http_put_json(
         headers["Authorization"] = f"Bearer {token}"
     body = json.dumps(payload).encode("utf-8")
     req = urllib.request.Request(url, data=body, method="PUT", headers=headers)
-    with urllib.request.urlopen(req, timeout=timeout) as resp:
-        resp_body = resp.read().decode("utf-8", errors="replace")
-        return json.loads(resp_body) if resp_body else None
+    try:
+        with urllib.request.urlopen(req, timeout=timeout) as resp:
+            resp_body = resp.read().decode("utf-8", errors="replace")
+            return json.loads(resp_body) if resp_body else None
+    except urllib.error.HTTPError as e:
+        try:
+            err_body = e.read().decode("utf-8", errors="replace")
+            logger.error("HTTP PUT to %s failed (HTTP %s): %s. Response body: %s", url, e.code, e.reason, err_body)
+        except Exception:
+            pass
+        raise
 
 
 def _validate_api_token(
@@ -615,8 +651,9 @@ def _claim_node(self, node: Dict[str, Any]) -> bool:
             logger.info("Skipping node %s: already claimed (state=%s)", node_id, state)
             return False
         current["state"] = "running"
+        payload = {k: v for k, v in current.items() if k not in NODE_READ_ONLY_FIELDS}
         try:
-            _http_put_json(url, current, token=self.api_token)
+            _http_put_json(url, payload, token=self.api_token)
         except (urllib.error.URLError, json.JSONDecodeError) as e:
             logger.error("Failed to claim node %s (PUT state=running): %s", node_id, e)
             return False
@@ -647,8 +684,9 @@ def _finish_node(self, node_id: str, outcome: NodeOutcome) -> bool:
             data["error_code"] = outcome.error_code
             data["error_msg"] = outcome.error_msg
             current["data"] = data
+        payload = {k: v for k, v in current.items() if k not in NODE_READ_ONLY_FIELDS}
         try:
-            _http_put_json(url, current, token=self.api_token)
+            _http_put_json(url, payload, token=self.api_token)
         except (urllib.error.URLError, json.JSONDecodeError) as e:
             logger.error(
                 "Failed to finish node %s (PUT state=done result=%s): %s",