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/audit.rs

@@ -2,11 +2,12 @@
 //
 // Each batch of links gets reviewed by Sonnet, which returns per-link actions:
 // KEEP, DELETE, RETARGET, WEAKEN, STRENGTHEN. Batches run in parallel via rayon.
+//
+// TODO: Redesign to use tool-based agent instead of text parsing.
 
-use crate::store::{self, Store, new_relation};
-
-use std::collections::HashSet;
+use crate::store::Store;
 
+#[allow(dead_code)]
 struct LinkInfo {
     rel_idx: usize,
     source_key: String,
@@ -26,6 +27,7 @@ pub struct AuditStats {
     pub errors: usize,
 }
 
+#[allow(dead_code)]
 fn build_audit_prompt(batch: &[LinkInfo], batch_num: usize, total_batches: usize) -> String {
     let mut prompt = format!(
         "You are auditing memory graph links for quality (batch {}/{}).\n\n\
@@ -63,6 +65,7 @@ fn build_audit_prompt(batch: &[LinkInfo], batch_num: usize, total_batches: usize
     prompt
 }
 
+#[allow(dead_code)]
 fn parse_audit_response(response: &str, batch_size: usize) -> Vec<(usize, AuditAction)> {
     let mut actions = Vec::new();
 
@@ -109,6 +112,7 @@ fn parse_audit_response(response: &str, batch_size: usize) -> Vec<(usize, AuditA
     actions
 }
 
+#[allow(dead_code)]
 enum AuditAction {
     Keep,
     Delete,
@@ -118,7 +122,11 @@ enum AuditAction {
 }
 
 /// Run a full link audit: walk every link, batch to Sonnet, apply results.
-pub fn link_audit(store: &mut Store, apply: bool) -> Result<AuditStats, String> {
+pub fn link_audit(_store: &mut Store, _apply: bool) -> Result<AuditStats, String> {
+    // TODO: Reimplement to use tool-based agent instead of text parsing
+    Err("link_audit disabled: needs redesign to use tool-based agent".to_string())
+
+    /*
     // Collect all non-deleted relations with their info
     let mut links: Vec<LinkInfo> = Vec::new();
 
@@ -330,4 +338,5 @@ pub fn link_audit(store: &mut Store, apply: bool) -> Result<AuditStats, String>
     }
 
     Ok(stats)
+    */
 }