fix: address argus review on ensure_claude_dir — narrow to EPERM, fix doc comment

hive-agent-user-migrate chowns the bind-mounted claude dir to the agent
user on every container boot. After that, hive-core (a different user)
cannot chmod it — set_permissions fails with EPERM, which was propagated
as an error and caused the rebuild to fail entirely.

Fix: make the chmod best-effort. Newly created dirs (owned by hive-core)
get the 0755 mode set immediately; after the agent-migration chown the
mode is preserved so claude_has_session works correctly. Subsequent calls
that hit the EPERM path just log at DEBUG and continue.

hive-c0re/src/lifecycle.rs

@@ -767,12 +767,15 @@ pub async fn setup_applied(
     Ok(())
 }
 
-/// Create the per-agent Claude credentials dir if missing. Mode 0700 — only
-/// root inside the container reads/writes it. Idempotent: existing dirs are
-/// left untouched (an agent's OAuth tokens survive `destroy`/recreate).
+/// Create the per-agent Claude credentials dir if missing. Mode 0755 — hive-core
+/// needs read+execute to list the directory so `claude_has_session` can detect a
+/// valid session; credential files inside (`.credentials.json` etc.) are 0600 so
+/// secrets stay private regardless of the directory mode. Idempotent: existing
+/// dirs are left untouched (an agent's OAuth tokens survive `destroy`/recreate).
 /// Public for the `InitConfig` approval path in `actions.rs` which seeds
 /// dirs without calling the full `spawn`.
 pub fn ensure_claude_dir(claude_dir: &Path) -> Result<()> {
+    use std::io;
     if !claude_dir.exists() {
         std::fs::create_dir_all(claude_dir)
             .with_context(|| format!("create {}", claude_dir.display()))?;
@@ -781,11 +784,27 @@ pub fn ensure_claude_dir(claude_dir: &Path) -> Result<()> {
     // list the directory so `claude_has_session` can detect a valid session.
     // The credential files inside (`.credentials.json` etc.) are 0600 so the
     // secrets themselves stay private regardless of the directory mode.
+    //
+    // Best-effort: on the first container boot, `hive-agent-user-migrate`
+    // chowns this dir to the agent user. After that, hive-core (a different
+    // user) cannot chmod it (EPERM) — that's fine because the mode set during
+    // initial creation (0755) is preserved through the chown.  Any other error
+    // (ENOENT, I/O error) is unexpected and propagated.
     #[cfg(unix)]
     {
         use std::os::unix::fs::PermissionsExt;
-        std::fs::set_permissions(claude_dir, std::fs::Permissions::from_mode(0o755))
-            .with_context(|| format!("chmod 755 {}", claude_dir.display()))?;
+        match std::fs::set_permissions(claude_dir, std::fs::Permissions::from_mode(0o755)) {
+            Ok(()) => {}
+            Err(e) if e.kind() == io::ErrorKind::PermissionDenied => {
+                tracing::debug!(
+                    path = %claude_dir.display(),
+                    "ensure_claude_dir: chmod 755 skipped (dir likely owned by agent user after migration)"
+                );
+            }
+            Err(e) => {
+                return Err(e).with_context(|| format!("chmod 755 {}", claude_dir.display()));
+            }
+        }
     }
     Ok(())
 }