agents: phase tracking, pid files, pipelining, unified cycle

- AgentStep with phase labels (=== PROMPT phase:name ===)
- PID files in state dir (pid-{PID} with JSON phase/timestamp)
- Built-in bail check: between steps, bail if other pid files exist
- surface_observe_cycle replaces surface_agent_cycle + journal_agent_cycle
- Reads surface output from state dir instead of parsing stdout
- Pipelining: starts new agent if running one is past surface phase
- link_set upserts (creates link if missing)
- Better error message for context window overflow

Co-Authored-By: Kent Overstreet <kent.overstreet@linux.dev>

src/subconscious/api.rs

@@ -35,6 +35,7 @@ pub async fn call_api_with_tools(
     agent: &str,
     prompts: &[String],
     temperature: Option<f32>,
+    bail_fn: Option<&(dyn Fn(usize) -> Result<(), String> + Sync)>,
     log: &dyn Fn(&str),
 ) -> Result<String, String> {
     let client = get_client()?;
@@ -178,8 +179,12 @@ pub async fn call_api_with_tools(
 
         log(&format!("\n=== RESPONSE ===\n\n{}", text));
 
-        // If there are more prompts, inject the next one and continue
+        // If there are more prompts, check bail condition and inject the next one
         if next_prompt_idx < prompts.len() {
+            // Run bail check before continuing to next step
+            if let Some(ref check) = bail_fn {
+                check(next_prompt_idx)?;
+            }
             messages.push(Message::assistant(&text));
             let next = &prompts[next_prompt_idx];
             next_prompt_idx += 1;
@@ -200,6 +205,7 @@ pub fn call_api_with_tools_sync(
     agent: &str,
     prompts: &[String],
     temperature: Option<f32>,
+    bail_fn: Option<&(dyn Fn(usize) -> Result<(), String> + Sync)>,
     log: &(dyn Fn(&str) + Sync),
 ) -> Result<String, String> {
     std::thread::scope(|s| {
@@ -211,7 +217,7 @@ pub fn call_api_with_tools_sync(
             let prov = format!("agent:{}", agent);
             rt.block_on(
                 crate::store::TASK_PROVENANCE.scope(prov,
-                    call_api_with_tools(agent, prompts, temperature, log))
+                    call_api_with_tools(agent, prompts, temperature, bail_fn, log))
             )
         }).join().unwrap()
     })