hive-c0re: validate cascade agent names in meta_update_cascade_agents' fanout path too

extract validate_agent_names() and use it for both the parsed
agent-<name> inputs and run_meta_lock's pre-computed fanout list, so a
malformed name can't reach the new fast_forward_applied_main / lock_update
filesystem+git+forge-URL operations regardless of which of the two
sources it came from

hive-c0re/src/job_queue/exec.rs

@@ -545,7 +545,7 @@ async fn run_meta_lock(
     // Lock file changed — meta-inputs panel re-renders.
     crate::dashboard::emit_meta_inputs_snapshot(coord);
     let cascade = match fanout {
-        Some(list) => list,
+        Some(list) => validate_agent_names(list),
         None => meta_update_cascade_agents(inputs).await,
     };
     // Pull each cascade agent's own input too — an agent's config-repo main
@@ -891,15 +891,20 @@ async fn run_deploy_tail(
 /// `inputs` or any input under `hyperhive` → every container;
 /// otherwise just the agents named by `agent-<name>` inputs.
 /// Topology-sorted so parents rebuild before their children.
+///
+/// `inputs` is the caller-supplied flake-input-name list
+/// (`RequestUpdateMetaInputs`'s `inputs` field, operator-approved but not
+/// otherwise validated) — the `agent-<name>` branch parses agent names
+/// straight out of it, so each is validated through [`hive_types::Ident`]
+/// before it ever reaches a filesystem path or a forge URL built from a
+/// cascade agent's name. The `touched_hyperhive` branch's names need no
+/// such filter: they come from `lifecycle::list()`, already real
+/// container names by construction, not parsed out of caller input.
 pub async fn meta_update_cascade_agents(inputs: &[String]) -> Vec<String> {
     let touched_hyperhive = inputs
         .iter()
         .any(|i| i == "hyperhive" || i.starts_with("hyperhive/"));
-    let touched_agents: Vec<String> = inputs
-        .iter()
-        .filter_map(|i| i.strip_prefix("agent-"))
-        .map(|rest| rest.split('/').next().unwrap_or(rest).to_owned())
-        .collect();
+    let touched_agents = parse_agent_input_names(inputs);
     let mut names = if touched_hyperhive || inputs.is_empty() {
         crate::lifecycle::list()
             .await
@@ -917,3 +922,86 @@ pub async fn meta_update_cascade_agents(inputs: &[String]) -> Vec<String> {
     crate::auto_update::topology_sort(&mut names, &topo);
     names
 }
+
+/// Parse `agent-<name>` input strings into validated agent names. Pure and
+/// synchronous (no `lifecycle::list()` call) so the validation — the part
+/// that actually matters for safety, since these names end up in
+/// filesystem paths and forge URLs — is unit-testable without touching
+/// live container state. Delegates the actual filtering to
+/// [`validate_agent_names`] after stripping the `agent-` prefix.
+fn parse_agent_input_names(inputs: &[String]) -> Vec<String> {
+    let candidates = inputs
+        .iter()
+        .filter_map(|i| i.strip_prefix("agent-"))
+        .map(|rest| rest.split('/').next().unwrap_or(rest).to_owned());
+    validate_agent_names(candidates)
+}
+
+/// Drop any name that isn't a well-formed [`hive_types::Ident`] — the same
+/// validating parser every other agent-name wire field in this codebase
+/// goes through, so a name that reaches
+/// [`fast_forward_applied_main`](crate::forge::fast_forward_applied_main) or
+/// a `git+http://.../agent-configs/<name>.git` URL built off it has already
+/// passed the same bar as one that arrived over a socket. Not just a
+/// helper for [`parse_agent_input_names`]: `run_meta_lock`'s `fanout`
+/// parameter carries pre-computed agent names too, and while today's only
+/// caller of that branch (the boot sweep, `sweep = true`) returns before
+/// ever reaching the filesystem/git code below, nothing in the type
+/// enforces that pairing — so this same filter also guards the
+/// `Some(list)` arm, closing the gap for good rather than relying on it
+/// staying incidental.
+fn validate_agent_names(names: impl IntoIterator<Item = String>) -> Vec<String> {
+    names
+        .into_iter()
+        .filter(|name| {
+            let valid = hive_types::Ident::parse(name).is_ok();
+            if !valid {
+                tracing::warn!(%name, "meta-update cascade: dropping malformed agent name");
+            }
+            valid
+        })
+        .collect()
+}
+
+#[cfg(test)]
+mod cascade_agent_tests {
+    use super::{parse_agent_input_names, validate_agent_names};
+
+    #[test]
+    fn well_formed_agent_inputs_pass_through() {
+        let inputs = vec!["agent-iris".to_owned(), "agent-atlas".to_owned()];
+        assert_eq!(parse_agent_input_names(&inputs), vec!["iris", "atlas"]);
+    }
+
+    #[test]
+    fn path_traversal_in_an_agent_input_is_dropped() {
+        let inputs = vec!["agent-../../etc".to_owned(), "agent-iris".to_owned()];
+        assert_eq!(parse_agent_input_names(&inputs), vec!["iris"]);
+    }
+
+    #[test]
+    fn non_agent_inputs_are_ignored_not_misparsed() {
+        let inputs = vec!["hyperhive".to_owned(), "nixpkgs".to_owned()];
+        assert!(parse_agent_input_names(&inputs).is_empty());
+    }
+
+    #[test]
+    fn oversized_or_uppercase_names_are_dropped() {
+        let too_long = format!("agent-{}", "a".repeat(64));
+        let inputs = vec![too_long, "agent-Iris".to_owned(), "agent-iris".to_owned()];
+        assert_eq!(parse_agent_input_names(&inputs), vec!["iris"]);
+    }
+
+    #[test]
+    fn fanout_supplied_names_are_validated_too() {
+        // `run_meta_lock`'s `Some(list)` arm feeds `fanout` straight into
+        // this filter — pin that a bogus name in that pre-computed list
+        // gets dropped exactly like a parsed `agent-<name>` input would.
+        let names = vec![
+            "iris".to_owned(),
+            "../../etc".to_owned(),
+            "atlas".to_owned(),
+        ];
+        assert_eq!(validate_agent_names(names), vec!["iris", "atlas"]);
+    }
+}