diff --git a/hive-subagent-mcp/src/session.rs b/hive-subagent-mcp/src/session.rs
index 8d116c3d..0699dc36 100644
--- a/hive-subagent-mcp/src/session.rs
+++ b/hive-subagent-mcp/src/session.rs
@@ -45,6 +45,14 @@ use hive_claude::{Attach, Cancel, Claude, Config, NoopSink, SessionStore};
 /// reviewer caught in the original check-then-insert version: checking "is
 /// `name` free" and committing to it are two different lock acquisitions
 /// unless the check *is* the reservation — see `reserve`.
+///
+/// ⚠️ This concurrency guard is keyed by `name` alone — a `start`/`continue`
+/// for `name` with a *different* `dir` than one already in flight under
+/// that name is refused as "already running," even though the two would
+/// resolve to entirely separate on-disk sessions. Deliberate: `name` is the
+/// caller's one chosen identity for a subagent, not `(name, dir)` — reuse a
+/// name across directories at your own risk, the tool doesn't disambiguate
+/// it (flagged in review when `dir` was added).
 pub struct State {
     running: Mutex<HashMap<String, Option<Cancel>>>,
     dirs: Mutex<HashMap<String, String>>,