Fix four review findings: busy release, poison recovery, core.md errors, chat loop

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

crates/loopd/src/baseline.rs

@@ -47,12 +47,20 @@ impl Baseline {
         let mut system = system.trim_end().to_string();
 
         let core = cfg.paths.home.join("memory/core.md");
-        if let Ok(text) = std::fs::read_to_string(&core) {
-            let trimmed = text.trim();
-            if !trimmed.is_empty() {
-                system.push_str("\n\n");
-                system.push_str(trimmed);
+        match std::fs::read_to_string(&core) {
+            Ok(text) => {
+                let trimmed = text.trim();
+                if !trimmed.is_empty() {
+                    system.push_str("\n\n");
+                    system.push_str(trimmed);
+                }
             }
+            // A missing file is fine; an unreadable one is reported so the owner is not given a
+            // session without the memory they curated and no sign of it.
+            Err(e) if e.kind() != std::io::ErrorKind::NotFound => {
+                return Err(BaselineError::Read(core.clone(), e));
+            }
+            Err(_) => {}
         }
 
         Ok(Baseline {