session: --session flag, journal agent cycle, conversation bytes config

- memory-search: add --session flag for multi-session support
- config: add surface_conversation_bytes option
- journal_agent_cycle: trigger journal agent every 10KB of conversation
- Session::from_id() constructor

Co-Authored-By: ProofOfConcept <poc@bcachefs.org>

src/hippocampus/memory_search.rs

@@ -231,6 +231,60 @@ fn surface_agent_cycle(session: &Session, out: &mut String, log_f: &mut File) {
     }
 }
 
+const JOURNAL_INTERVAL_BYTES: u64 = 10_000;
+
+fn journal_agent_cycle(session: &Session, log_f: &mut File) {
+    let offset_path = session.path("journal-offset");
+    let pid_path = session.path("journal-pid");
+
+    // Check if a previous run is still going
+    if let Ok(content) = fs::read_to_string(&pid_path) {
+        let pid: u32 = content.split('\t').next()
+            .and_then(|s| s.trim().parse().ok()).unwrap_or(0);
+        if pid != 0 && unsafe { libc::kill(pid as i32, 0) == 0 } {
+            let _ = writeln!(log_f, "journal: still running (pid {})", pid);
+            return;
+        }
+    }
+    fs::remove_file(&pid_path).ok();
+
+    // Check transcript size vs last run
+    let transcript_size = fs::metadata(&session.transcript_path)
+        .map(|m| m.len()).unwrap_or(0);
+    let last_offset: u64 = fs::read_to_string(&offset_path).ok()
+        .and_then(|s| s.trim().parse().ok()).unwrap_or(0);
+
+    if transcript_size.saturating_sub(last_offset) < JOURNAL_INTERVAL_BYTES {
+        return;
+    }
+
+    let _ = writeln!(log_f, "journal: spawning (transcript {}, last {})",
+                     transcript_size, last_offset);
+
+    // Save current offset
+    fs::write(&offset_path, transcript_size.to_string()).ok();
+
+    // Spawn journal agent — it writes directly to the store via memory tools
+    let log_dir = crate::store::memory_dir().join("logs");
+    fs::create_dir_all(&log_dir).ok();
+    let journal_log = fs::File::create(log_dir.join("journal-agent.log"))
+        .unwrap_or_else(|_| fs::File::create("/dev/null").unwrap());
+
+    if let Ok(child) = Command::new("poc-memory")
+        .args(["agent", "run", "journal", "--count", "1", "--local"])
+        .env("POC_SESSION_ID", &session.session_id)
+        .stdout(journal_log.try_clone().unwrap_or_else(|_| fs::File::create("/dev/null").unwrap()))
+        .stderr(journal_log)
+        .spawn()
+    {
+        let pid = child.id();
+        let ts = now_secs();
+        if let Ok(mut f) = fs::File::create(&pid_path) {
+            write!(f, "{}\t{}", pid, ts).ok();
+        }
+    }
+}
+
 fn cleanup_stale_files(dir: &Path, max_age: Duration) {
     let entries = match fs::read_dir(dir) {
         Ok(e) => e,
@@ -308,6 +362,7 @@ fn hook(session: &Session) -> String {
         let cfg = crate::config::get();
         if cfg.surface_hooks.iter().any(|h| h == &session.hook_event) {
             surface_agent_cycle(session, &mut out, &mut log_f);
+            journal_agent_cycle(session, &mut log_f);
         }
     }