feat(learning): boundary filter — only dotted aspects reach domain_hints / primary_domain

Two sites enforce: a string is a valid domain key iff it contains '.'.

  - gnn_augment_tactics filters state.metadata["aspects"] before sending
    to /gnn/rank, so structural tags like "axiom"/"constructor" never
    pollute Julia's PROVER_DOMAIN_WEIGHTS key space.
  - primary_domain in meta_controller skips non-dotted aspects when
    selecting the canonical domain for outcome recording.

Adds two unit tests confirming primary_domain skips "axiom" and falls
through to "unspecified" when only structural tags are present. Parser
literals (8 sites listed in THEOREM-METADATA-MIGRATION.md) remain
unchanged and harmless under this filter.

https://claude.ai/code/session_01YPqu7gti4azBach6ZvpRFJ

Author: claude

src/rust/agent/meta_controller.rs

@@ -756,8 +756,11 @@ pub enum PlanOutcome {
 /// the first aspect (lexicographically? no — order-as-given so the user
 /// can prioritise).  Empty aspect list → "unspecified".
 fn primary_domain(goal: &AgenticGoal) -> String {
+    // Only dotted "category.aspect" strings are valid domain keys; structural
+    // meta-tags (e.g. "axiom", "constructor") do not reach the learning loop.
     goal.aspects
-        .first()
+        .iter()
+        .find(|s| s.contains('.'))
         .cloned()
         .unwrap_or_else(|| "unspecified".to_string())
 }
@@ -772,6 +775,18 @@ mod tests {
     use crate::core::{Goal, Term};
     use crate::verification::confidence::TrustLevel;
 
+    #[test]
+    fn test_primary_domain_skips_structural_tags() {
+        let goal = dummy_goal(vec!["axiom", "arithmetic.natural_numbers"]);
+        assert_eq!(primary_domain(&goal), "arithmetic.natural_numbers");
+    }
+
+    #[test]
+    fn test_primary_domain_all_structural_returns_unspecified() {
+        let goal = dummy_goal(vec!["axiom"]);
+        assert_eq!(primary_domain(&goal), "unspecified");
+    }
+
     fn dummy_goal(aspects: Vec<&str>) -> AgenticGoal {
         AgenticGoal {
             goal: Goal {

src/rust/provers/mod.rs

@@ -1540,6 +1540,10 @@ pub(crate) async fn gnn_augment_tactics(
         .get("aspects")
         .and_then(|v| serde_json::from_value(v.clone()).ok())
         .unwrap_or_default();
+    // Boundary filter: only dotted "category.aspect" strings reach the learning-loop
+    // key space. Structural meta-tags without a dot (e.g. "axiom", "constructor")
+    // are excluded here so they never pollute domain_hints or training records.
+    let aspects: Vec<String> = aspects.into_iter().filter(|s| s.contains('.')).collect();
     let result = gnn.rank_premises_with_aspects(&graph, &aspects).await;
     // Prepend apply tactics for top premises (in score order, before heuristic hints)
     let mut gnn_tactics: Vec<Tactic> = result