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/bin/memory-search.rs

@@ -18,6 +18,10 @@ struct Args {
     #[arg(long)]
     hook: bool,
 
+    /// Session ID (overrides stash file; for multiple concurrent sessions)
+    #[arg(long)]
+    session: Option<String>,
+
     #[command(subcommand)]
     command: Option<Cmd>,
 }
@@ -30,13 +34,19 @@ enum Cmd {
     Reflect,
 }
 
-fn show_seen() {
-    let input = match fs::read_to_string(STASH_PATH) {
-        Ok(s) => s,
-        Err(_) => { eprintln!("No session state available"); return; }
-    };
-    let Some(session) = poc_memory::memory_search::Session::from_json(&input) else {
-        eprintln!("No session state available");
+fn resolve_session(session_arg: &Option<String>) -> Option<poc_memory::memory_search::Session> {
+    use poc_memory::memory_search::Session;
+
+    if let Some(id) = session_arg {
+        return Session::from_id(id.clone());
+    }
+    let input = fs::read_to_string(STASH_PATH).ok()?;
+    Session::from_json(&input)
+}
+
+fn show_seen(session_arg: &Option<String>) {
+    let Some(session) = resolve_session(session_arg) else {
+        eprintln!("No session state available (use --session ID)");
         return;
     };
 
@@ -75,18 +85,18 @@ fn show_seen() {
     }
 }
 
-fn run_agent_and_parse(agent: &str) {
-    let session_id = std::env::var("CLAUDE_SESSION_ID")
-        .or_else(|_| {
+fn run_agent_and_parse(agent: &str, session_arg: &Option<String>) {
+    let session_id = session_arg.clone()
+        .or_else(|| std::env::var("CLAUDE_SESSION_ID").ok())
+        .or_else(|| {
             fs::read_to_string(STASH_PATH).ok()
                 .and_then(|s| poc_memory::memory_search::Session::from_json(&s))
                 .map(|s| s.session_id)
-                .ok_or(std::env::VarError::NotPresent)
         })
         .unwrap_or_default();
 
     if session_id.is_empty() {
-        eprintln!("No session ID available (set CLAUDE_SESSION_ID or run --hook first)");
+        eprintln!("No session ID available (use --session ID, set CLAUDE_SESSION_ID, or run --hook first)");
         std::process::exit(1);
     }
 
@@ -180,8 +190,8 @@ fn main() {
 
     if let Some(cmd) = args.command {
         match cmd {
-            Cmd::Surface => run_agent_and_parse("surface"),
-            Cmd::Reflect => run_agent_and_parse("reflect"),
+            Cmd::Surface => run_agent_and_parse("surface", &args.session),
+            Cmd::Reflect => run_agent_and_parse("reflect", &args.session),
         }
         return;
     }
@@ -203,6 +213,6 @@ fn main() {
         let output = poc_memory::memory_search::run_hook(&input);
         print!("{}", output);
     } else {
-        show_seen()
+        show_seen(&args.session)
     }
 }