diff --git a/backend/app/services/ai_tree_builder.py b/backend/app/services/ai_tree_builder.py
index c9f44c4b..6cfb50d2 100644
--- a/backend/app/services/ai_tree_builder.py
+++ b/backend/app/services/ai_tree_builder.py
@@ -45,7 +45,19 @@ No prose, no markdown fences.
 """
 
 
+def _strip_meta(walked_path: list[dict]) -> list[dict]:
+    """Drop the hidden ``meta`` entry (category carrier) the intake endpoint seeds.
+
+    The first walked_path entry on an ai_build session may be a
+    ``{"node_type": "meta", "category": ...}`` marker used to persist the
+    classified category; it is not a real walk step and must be excluded from
+    both model context and tree normalization.
+    """
+    return [s for s in walked_path if s.get("node_type") != "meta"]
+
+
 def _build_context(problem_text: str, category: str, walked_path: list[dict]) -> str:
+    walked_path = _strip_meta(walked_path)
     lines = [f"PROBLEM: {problem_text}", f"CATEGORY: {category}", "STEPS SO FAR:"]
     if not walked_path:
         lines.append("(none yet — produce the first diagnostic question)")
@@ -116,6 +128,7 @@ def normalize_walked_path(walked_path: list[dict]) -> dict[str, Any]:
     Returns {id, nodes: {id: node}} — a dict with an id (passes the proposal
     approval guard).
     """
+    walked_path = _strip_meta(walked_path)
     nodes: dict[str, Any] = {}
     if not walked_path:
         root_id = "root"