TurnResult: remove text field, simplify oneshot loop

- Remove TurnResult.text (was dead code - Agent::turn handles text internally)
- Simplify run_with_backend to just iterate over steps (Agent::turn loops
  for tool calls and handles empty responses internally)
- Change run/run_shared/run_forked_shared to return Result<(), String>
- Remove AgentResult.output field (no callers used it)
- Stub out legacy text-parsing code (audit, compare) that needs redesign
- Update digest.rs to not depend on text return
- Add level parameter to journal_new/journal_update for digest support

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

src/subconscious/digest.rs

@@ -284,14 +284,13 @@ fn generate_digest(
             .filter(|t| def.tools.iter().any(|w| w == &t.name))
             .collect()
     };
-    let digest = crate::agent::oneshot::call_api_with_tools_sync(
+    // Agent writes digest via memory_write tool - we just run it
+    crate::agent::oneshot::call_api_with_tools_sync(
         &def.agent, &prompts, &phases, def.temperature, def.priority,
         &tools, None)?;
 
-    let key = digest_node_key(level.name, label);
-    store.upsert_provenance(&key, &digest, "digest:write")?;
-
     // Structural links: connect all source entries to this digest
+    let key = digest_node_key(level.name, label);
     let mut linked = 0;
     for source_key in source_keys {
         // Skip if link already exists
@@ -299,10 +298,17 @@ fn generate_digest(
             !r.deleted && r.source_key == *source_key && r.target_key == key);
         if exists { continue; }
 
+        // Reload store to pick up agent's writes
+        *store = Store::load().map_err(|e| format!("reload: {}", e))?;
+
         let source_uuid = store.nodes.get(source_key)
             .map(|n| n.uuid).unwrap_or([0u8; 16]);
         let target_uuid = store.nodes.get(&key)
             .map(|n| n.uuid).unwrap_or([0u8; 16]);
+        if target_uuid == [0u8; 16] {
+            println!("  Warning: digest key {} not found after agent run", key);
+            continue;
+        }
         let mut rel = new_relation(
             source_uuid, target_uuid,
             store::RelationType::Link, 0.8,
@@ -314,12 +320,10 @@ fn generate_digest(
     }
     if linked > 0 {
         println!("  Linked {} source entries → {}", linked, key);
+        store.save()?;
     }
 
-    store.save()?;
-    println!("  Stored: {}", key);
-
-    println!("  Done: {} lines", digest.lines().count());
+    println!("  Done");
     Ok(())
 }