memoryd: serve, three sockets and one lock over the files and the index

Implemented-By: OpenCode session (model recorded in docs/implementer-log.md)

crates/memoryd/src/index.rs

@@ -352,6 +352,25 @@ impl Index {
     }
 }
 
+/// The logs of one session: `(epoch, path)`, sorted. A session with no directory has none.
+pub fn session_logs(sessions: &Path, session: &str) -> Result<Vec<(i64, PathBuf)>, String> {
+    let dir = sessions.join(session);
+    let files = match std::fs::read_dir(&dir) {
+        Ok(files) => files,
+        Err(e) if e.kind() == std::io::ErrorKind::NotFound => return Ok(Vec::new()),
+        Err(e) => return Err(format!("{}: {e}", dir.display())),
+    };
+    let mut found = Vec::new();
+    for file in files.filter_map(|f| f.ok()) {
+        let name = file.file_name().to_string_lossy().into_owned();
+        if let Some(Ok(epoch)) = name.strip_suffix(".jsonl").map(str::parse::<i64>) {
+            found.push((epoch, file.path()));
+        }
+    }
+    found.sort();
+    Ok(found)
+}
+
 /// Every session log under `sessions`: `(session, epoch, path)`, sorted.
 pub fn logs(sessions: &Path) -> Result<Vec<(String, i64, PathBuf)>, String> {
     // Read the directory `sessions` (NotFound -> Ok(empty); another error -> Err naming it). For