Resolve subconscious prompt placeholders in Mind

Lightweight resolver handles {{seen_current}}, {{seen_previous}}, and
{{input:KEY}} using the session_id and output_dir directly instead of
env vars. Runs in trigger_subconscious before creating AutoAgent.

Removes {{memory_ratio}} from surface-observe prompt — redundant with
existing budget mechanisms.

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

src/mind/mod.rs

@@ -72,6 +72,76 @@ impl SubconsciousAgent {
         conversation_bytes.saturating_sub(self.last_trigger_bytes) >= interval
     }
 }
+
+/// Resolve {{placeholder}} templates in subconscious agent prompts.
+/// Handles: seen_current, seen_previous, input:KEY.
+fn resolve_prompt(template: &str, session_id: &str, output_dir: &std::path::Path) -> String {
+    let mut result = String::with_capacity(template.len());
+    let mut rest = template;
+    while let Some(start) = rest.find("{{") {
+        result.push_str(&rest[..start]);
+        let after = &rest[start + 2..];
+        if let Some(end) = after.find("}}") {
+            let name = after[..end].trim();
+            let replacement = match name {
+                "seen_current" => resolve_seen_list(session_id, ""),
+                "seen_previous" => resolve_seen_list(session_id, "-prev"),
+                _ if name.starts_with("input:") => {
+                    let key = &name[6..];
+                    std::fs::read_to_string(output_dir.join(key))
+                        .unwrap_or_default()
+                }
+                _ => {
+                    // Unknown placeholder — leave as-is
+                    result.push_str("{{");
+                    result.push_str(&after[..end + 2]);
+                    rest = &after[end + 2..];
+                    continue;
+                }
+            };
+            result.push_str(&replacement);
+            rest = &after[end + 2..];
+        } else {
+            // Unclosed {{ — pass through
+            result.push_str("{{");
+            rest = after;
+        }
+    }
+    result.push_str(rest);
+    result
+}
+
+fn resolve_seen_list(session_id: &str, suffix: &str) -> String {
+    if session_id.is_empty() { return "(no session)".to_string(); }
+
+    let path = crate::store::memory_dir()
+        .join("sessions")
+        .join(format!("seen{}-{}", suffix, session_id));
+
+    let entries: Vec<(String, String)> = std::fs::read_to_string(&path).ok()
+        .map(|content| {
+            content.lines()
+                .filter(|s| !s.is_empty())
+                .filter_map(|line| {
+                    let (ts, key) = line.split_once('\t')?;
+                    Some((ts.to_string(), key.to_string()))
+                })
+                .collect()
+        })
+        .unwrap_or_default();
+
+    if entries.is_empty() { return "(none)".to_string(); }
+
+    let mut sorted = entries;
+    sorted.sort_by(|a, b| b.0.cmp(&a.0));
+    let mut seen = std::collections::HashSet::new();
+    sorted.into_iter()
+        .filter(|(_, key)| seen.insert(key.clone()))
+        .take(20)
+        .map(|(ts, key)| format!("- {} ({})", key, ts))
+        .collect::<Vec<_>>()
+        .join("\n")
+}
 /// Which pane streaming text should go to.
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]
 pub enum StreamTarget {
@@ -470,6 +540,12 @@ impl Mind {
                 .sum::<u64>()
         };
 
+        // Get session_id for placeholder resolution
+        let session_id = {
+            let ag = self.agent.lock().await;
+            ag.session_id.clone()
+        };
+
         // Collect which agents to trigger (can't hold lock across await)
         let to_trigger: Vec<(usize, Vec<AutoStep>, Vec<crate::agent::tools::Tool>, String, i32)> = {
             let mut subs = self.subconscious.lock().await;
@@ -481,9 +557,14 @@ impl Mind {
                 let sub = &mut subs[i];
                 sub.last_trigger_bytes = conversation_bytes;
 
+                // The output dir for this agent — used for input: placeholders
+                // and the output() tool at runtime
+                let output_dir = crate::store::memory_dir()
+                    .join("agent-output").join(&sub.name);
+
                 let steps: Vec<AutoStep> = sub.def.steps.iter().map(|s| {
-                    // TODO: resolve remaining placeholders (seen_current, input:walked, etc.)
-                    AutoStep { prompt: s.prompt.clone(), phase: s.phase.clone() }
+                    let prompt = resolve_prompt(&s.prompt, &session_id, &output_dir);
+                    AutoStep { prompt, phase: s.phase.clone() }
                 }).collect();
 
                 let all_tools = crate::agent::tools::memory_and_journal_tools();