hive-c0re: fail on a malformed agent name and on an unreadable container list

An agent name that is not a valid Ident made `Coordinator::agent_paths`
panic. Job payloads carry names as plain strings (the swarm's published
wanted state is one source), and a panic inside a job-queue node never
reaches `complete_growing`, so the node's resources (the deploy
window included) were held until hive-c0re restarted. `agent_paths` now
returns an error; the job-queue nodes, the admin-socket spawn and
set-limits paths, the root-agent spawn and the dashboard set-limits
handler propagate it.

`lifecycle::list().await.unwrap_or_default()` turned a failed container
list into "no agents":
- meta-update cascade: the lock bump committed and zero rebuilds fanned
  out, reported as success. The cascade is now resolved before the lock
  bump and a list failure fails the node.
- dashboard update-all: queued nothing and returned 200 "ok". Now 500
  with the error.
- container rescan: every row was emitted as removed and the cache
  emptied. Now the last snapshot stands; `hivectl status` gets an error.
- dashboard journal: answered 404 "no managed container". Now 500.
- spawn/rebuild port-collision check: silently skipped. Now fails.
- startup migration: the per-agent phases ran over nothing, and phase 3
  handed an empty agent list to `meta::sync_agents`, which renders the
  meta flake with exactly the agents it is given. Both now log the list
  failure and skip.

The hive-jobq scheduler still leaks a node's resources on any executor
panic; that root is not addressed here.

Refs #4723

hive-c0re/src/server.rs

@@ -293,7 +293,7 @@ async fn handle_spawn(coord: &Arc<Coordinator>, name: &str) -> Result<HostRespon
     tracing::info!(%name, "spawn");
     let agent_dir = crate::paths::agent_runtime_dir(name);
     let hive = coord.hive_env();
-    let paths = Coordinator::agent_paths(name, agent_dir);
+    let paths = Coordinator::agent_paths(name, agent_dir)?;
     // lifecycle::spawn creates the runtime dir internally before start.
     // MCP listener registration is event-driven: bind immediately on
     // success so the harness can connect on its first turn without
@@ -375,12 +375,15 @@ async fn handle_set_paused(
 
 /// Collect per-agent status rows for `hivectl status` and the dashboard.
 async fn handle_agent_status(coord: &Arc<Coordinator>) -> HostResponse {
-    let rows = crate::container_view::build_all(&coord.hive_env())
-        .await
-        .into_iter()
-        .map(hive_sh4re::container::AgentStatusRow::from)
-        .collect();
-    HostResponse::agent_statuses(rows)
+    match crate::container_view::build_all(&coord.hive_env()).await {
+        Ok(views) => HostResponse::agent_statuses(
+            views
+                .into_iter()
+                .map(hive_sh4re::container::AgentStatusRow::from)
+                .collect(),
+        ),
+        Err(e) => HostResponse::error(format!("listing containers: {e:#}")),
+    }
 }
 
 /// `SubscribeAgentStatus` — ack once, then push one single-row
@@ -502,7 +505,7 @@ async fn handle_set_resource_limits(
     // in the JSON until the agent's next spawn or rebuild.
     let agent_dir = crate::paths::agent_runtime_dir(name.as_str());
     let hive = coord.hive_env();
-    let paths = Coordinator::agent_paths(name.as_str(), agent_dir);
+    let paths = Coordinator::agent_paths(name.as_str(), agent_dir)?;
     crate::lifecycle::write_dropins(name.as_str(), &hive, &paths).await?;
 
     let (cpu, mem) = crate::resource_limits::effective(