provenance: new_relation takes explicit provenance parameter

Remove POC_PROVENANCE env var lookup from new_relation - callers
now pass provenance explicitly. This fixes tracking when the env
var wasn't set correctly.

Co-Authored-By: Proof of Concept <poc@bcachefs.org>

src/hippocampus/store/types.rs

@@ -201,7 +201,6 @@ pub fn new_node(key: &str, content: &str) -> Node {
 }
 
 /// Create a new relation.
-/// Provenance is set from POC_PROVENANCE env var if present, else "manual".
 pub fn new_relation(
     source_uuid: [u8; 16],
     target_uuid: [u8; 16],
@@ -209,10 +208,8 @@ pub fn new_relation(
     strength: f32,
     source_key: &str,
     target_key: &str,
+    provenance: &str,
 ) -> Relation {
-    // Use raw env var for provenance — agent names are dynamic
-    let provenance = std::env::var("POC_PROVENANCE")
-        .unwrap_or_else(|_| "manual".to_string());
     Relation {
         uuid: *Uuid::new_v4().as_bytes(),
         version: 1,
@@ -221,7 +218,7 @@ pub fn new_relation(
         target: target_uuid,
         rel_type,
         strength,
-        provenance,
+        provenance: provenance.to_string(),
         deleted: false,
         source_key: source_key.to_string(),
         target_key: target_key.to_string(),

src/subconscious/digest.rs

@@ -196,6 +196,7 @@ pub fn apply_digest_links(store: &mut Store, links: &[DigestLink]) -> (usize, us
             store::RelationType::Link,
             0.5,
             &source, &target,
+            "agent:digest",
         );
         if store.add_relation(rel).is_ok() {
             println!("  + {} → {}", source, target);