Persist memory scores, use them for eviction in trim_entries

Scores are saved to memory-scores.json alongside the conversation log
after each scoring run, and loaded on startup — no more re-scoring
on restart.

trim_entries now evicts lowest-scored memories first (instead of
oldest-first) when memories exceed 50% of context. The 50% threshold
stays as a heuristic for memory-vs-conversation balance until we have
a scoring signal for conversation entries too. Unscored memories get
0.0, so they're evicted before scored ones.

save_memory_scores rebuilds from current entries, so evicted memories
are automatically expired from the scores file.

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

src/mind/mod.rs

@@ -28,6 +28,49 @@ use crate::subconscious::learn;
 
 pub use dmn::{SubconsciousSnapshot, Subconscious};
 
+use crate::agent::context::ConversationEntry;
+
+/// Load persisted memory scores from disk and apply to Memory entries.
+fn load_memory_scores(entries: &mut [ConversationEntry], path: &std::path::Path) {
+    let data = match std::fs::read_to_string(path) {
+        Ok(d) => d,
+        Err(_) => return,
+    };
+    let scores: std::collections::BTreeMap<String, f64> = match serde_json::from_str(&data) {
+        Ok(s) => s,
+        Err(_) => return,
+    };
+    let mut applied = 0;
+    for entry in entries.iter_mut() {
+        if let ConversationEntry::Memory { key, score, .. } = entry {
+            if let Some(&s) = scores.get(key.as_str()) {
+                *score = Some(s);
+                applied += 1;
+            }
+        }
+    }
+    if applied > 0 {
+        dbglog!("[scoring] loaded {} scores from {}", applied, path.display());
+    }
+}
+
+/// Save all memory scores to disk.
+fn save_memory_scores(entries: &[ConversationEntry], path: &std::path::Path) {
+    let scores: std::collections::BTreeMap<String, f64> = entries.iter()
+        .filter_map(|e| {
+            if let ConversationEntry::Memory { key, score: Some(s), .. } = e {
+                Some((key.clone(), *s))
+            } else {
+                None
+            }
+        })
+        .collect();
+    if let Ok(json) = serde_json::to_string_pretty(&scores) {
+        let _ = std::fs::write(path, json);
+        dbglog!("[scoring] saved {} scores to {}", scores.len(), path.display());
+    }
+}
+
 /// Which pane streaming text should go to.
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]
 pub enum StreamTarget {
@@ -267,6 +310,11 @@ impl Mind {
         // Restore conversation
         let mut ag = self.agent.lock().await;
         ag.restore_from_log();
+
+        // Restore persisted memory scores
+        let scores_path = self.config.session_dir.join("memory-scores.json");
+        load_memory_scores(&mut ag.context.entries, &scores_path);
+
         ag.changed.notify_one();
         drop(ag);
 
@@ -335,6 +383,7 @@ impl Mind {
     pub fn start_memory_scoring(&self) {
         let agent = self.agent.clone();
         let bg_tx = self.bg_tx.clone();
+        let scores_path = self.config.session_dir.join("memory-scores.json");
         let cfg = crate::config::get();
         let max_age = cfg.scoring_interval_secs;
         let response_window = cfg.scoring_response_window;
@@ -362,6 +411,8 @@ impl Mind {
                             }
                         }
                     }
+                    // Persist all scores to disk
+                    save_memory_scores(&ag.context.entries, &scores_path);
                 }
             }
             let _ = bg_tx.send(BgEvent::ScoringDone);