agents: bail script support, pid file simplification, cleanup

- Bail command moved from hardcoded closure to external script
  specified in agent JSON header ("bail": "bail-no-competing.sh")
- Runner executes script between steps with pid file path as $1,
  cwd = state dir. Non-zero exit stops the pipeline.
- PID files simplified to just the phase name (no JSON) for easy
  bash inspection (cat pid-*)
- scan_pid_files helper deduplicates pid scanning logic
- Timeout check uses file mtime instead of embedded timestamp
- PID file cleaned up on bail/error (not just success)
- output() tool validates key names (rejects pid-*, /, ..)
- Agent log files append instead of truncate
- Fixed orphaned derive and doc comment on AgentStep/AgentDef
- Phase written after bail check passes, not before

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

src/subconscious/defs.rs

@@ -24,8 +24,6 @@ use serde::Deserialize;
 
 use std::path::PathBuf;
 
-/// Agent definition: config (from JSON header) + prompt (raw markdown body).
-#[derive(Clone, Debug)]
 /// A single step in a multi-step agent.
 pub struct AgentStep {
     pub prompt: String,
@@ -34,6 +32,7 @@ pub struct AgentStep {
     pub phase: String,
 }
 
+/// Agent definition: config (from JSON header) + prompt steps.
 pub struct AgentDef {
     pub agent: String,
     pub query: String,
@@ -47,6 +46,9 @@ pub struct AgentDef {
     pub chunk_size: Option<usize>,
     pub chunk_overlap: Option<usize>,
     pub temperature: Option<f32>,
+    /// Bail check command — run between steps with pid file path as $1,
+    /// cwd = state dir. Non-zero exit = stop the pipeline.
+    pub bail: Option<String>,
 }
 
 /// The JSON header portion (first line of the file).
@@ -73,6 +75,10 @@ struct AgentHeader {
     /// LLM temperature override
     #[serde(default)]
     temperature: Option<f32>,
+    /// Bail check command — run between steps with pid file path as $1,
+    /// cwd = state dir. Non-zero exit = stop the pipeline.
+    #[serde(default)]
+    bail: Option<String>,
 }
 
 fn default_model() -> String { "sonnet".into() }
@@ -143,10 +149,11 @@ fn parse_agent_file(content: &str) -> Option<AgentDef> {
         chunk_size: header.chunk_size,
         chunk_overlap: header.chunk_overlap,
         temperature: header.temperature,
+        bail: header.bail,
     })
 }
 
-fn agents_dir() -> PathBuf {
+pub fn agents_dir() -> PathBuf {
     let repo = PathBuf::from(env!("CARGO_MANIFEST_DIR")).join("src/subconscious/agents");
     if repo.is_dir() { return repo; }
     crate::store::memory_dir().join("agents")