Shared persistent state across all subconscious agents

Moved persistent_state from per-agent to a single shared BTreeMap on
Subconscious. All agents read/write the same state — surface's walked
keys are visible to observe and reflect, etc.

- Subconscious.state: shared BTreeMap<String, String>
- walked() derives from state["walked"] instead of separate Vec
- subconscious-state.json is now a flat key-value map
- All agent outputs merge into the shared state on completion
- Loaded on startup, saved after any agent completes

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

src/agent/oneshot.rs

@@ -102,7 +102,11 @@ impl Backend {
 }
 
 /// Resolve {{placeholder}} templates in subconscious agent prompts.
-fn resolve_prompt(template: &str, memory_keys: &[String], walked: &[String]) -> String {
+fn resolve_prompt(
+    template: &str,
+    memory_keys: &[String],
+    state: &std::collections::BTreeMap<String, String>,
+) -> String {
     let cfg = crate::config::get();
     let template = template.replace("{assistant_name}", &cfg.assistant_name);
     let mut result = String::with_capacity(template.len());
@@ -112,14 +116,17 @@ fn resolve_prompt(template: &str, memory_keys: &[String], walked: &[String]) ->
         let after = &rest[start + 2..];
         if let Some(end) = after.find("}}") {
             let name = after[..end].trim();
-            let replacement = match name {
-                "seen_current" => format_key_list(memory_keys),
-                "walked" => format_key_list(walked),
-                _ => {
-                    result.push_str("{{");
-                    result.push_str(&after[..end + 2]);
-                    rest = &after[end + 2..];
-                    continue;
+            let replacement = if let Some(key) = name.strip_prefix("state:") {
+                state.get(key).cloned().unwrap_or_else(|| "(not set)".to_string())
+            } else {
+                match name {
+                    "seen_current" => format_key_list(memory_keys),
+                    _ => {
+                        result.push_str("{{");
+                        result.push_str(&after[..end + 2]);
+                        rest = &after[end + 2..];
+                        continue;
+                    }
                 }
             };
             result.push_str(&replacement);
@@ -133,6 +140,8 @@ fn resolve_prompt(template: &str, memory_keys: &[String], walked: &[String]) ->
     result
 }
 
+
+
 fn format_key_list(keys: &[String]) -> String {
     if keys.is_empty() { "(none)".to_string() }
     else { keys.iter().map(|k| format!("- {}", k)).collect::<Vec<_>>().join("\n") }
@@ -177,10 +186,10 @@ impl AutoAgent {
         &mut self,
         agent: &std::sync::Arc<tokio::sync::Mutex<Agent>>,
         memory_keys: &[String],
-        walked: &[String],
+        state: &std::collections::BTreeMap<String, String>,
     ) -> Result<String, String> {
         let resolved_steps: Vec<AutoStep> = self.steps.iter().map(|s| AutoStep {
-            prompt: resolve_prompt(&s.prompt, memory_keys, walked),
+            prompt: resolve_prompt(&s.prompt, memory_keys, state),
             phase: s.phase.clone(),
         }).collect();
         let orig_steps = std::mem::replace(&mut self.steps, resolved_steps);