api: retry transient connection errors, misc fixes

- Retry up to 5 times with exponential backoff (2s, 4s, 8s, 16s)
  on transient errors: IncompleteMessage, connection closed/reset/
  refused, timeouts. Non-transient errors fail immediately.
- tail command: print to stdout instead of stderr
- state_dir rename: output_dir → state_dir throughout knowledge.rs

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

src/subconscious/knowledge.rs

@@ -264,9 +264,8 @@ pub fn spawn_agent(
 
     let log_dir = store::memory_dir().join("logs");
     fs::create_dir_all(&log_dir).ok();
-    let agent_log = fs::OpenOptions::new()
-        .create(true).append(true)
-        .open(log_dir.join(format!("{}.log", agent_name)))
+    let agent_log = fs::File::create(
+        log_dir.join(format!("{}-{}.log", agent_name, store::compact_timestamp())))
         .unwrap_or_else(|_| fs::File::create("/dev/null").unwrap());
 
     let child = std::process::Command::new("poc-memory")