feat(plugin): add SubagentStop hook to auto-check inbox after subagent runs

Delivers peer messages that arrive during a long-running subagent into the
parent context the moment the Task tool returns, instead of waiting until
the next user prompt. Reuses the existing `claude-mailbox check --hook` so
the mailbox identity stays consistent with UserPromptSubmit.

Plugin 1.2.0 → 1.3.0.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

plugin/.claude-plugin/plugin.json

@@ -1,7 +1,7 @@
 {
   "name": "claude-mailbox",
-  "version": "1.2.0",
-  "description": "Auto-checks the local Claude-Mailbox daemon before every prompt and injects pending messages into the conversation context.",
+  "version": "1.3.0",
+  "description": "Auto-checks the local Claude-Mailbox daemon before every prompt and after each subagent run, and injects pending messages into the conversation context.",
   "author": {
     "name": "Mika Kuns"
   },

plugin/README.md

@@ -39,8 +39,9 @@ The `SessionStart` hook announces the current session's mailbox name in the conv
 |---|---|---|
 | `SessionStart` | `claude-mailbox session-announce` | Registers the session with the daemon, then prints (a) this session's mailbox name, (b) the exact `from` / `name` args to pass to MCP tools, and (c) a list of other mailboxes active in the last hour — so Claude knows who's around without needing to call `list_mailboxes` first. |
 | `UserPromptSubmit` | `claude-mailbox check --hook` | Pulls unread messages for the session's mailbox and injects them as context. Silent on empty inbox; emits a one-line setup hint when the daemon is unreachable. |
+| `SubagentStop` | `claude-mailbox check --hook` | Same as `UserPromptSubmit`, but fires when a subagent finishes (Task tool). Lets the parent see peer messages that arrived during a long-running subagent run, instead of waiting until the next user prompt. |
 
-Cost: one local HTTP round-trip per prompt + Node coldstart (~100ms on Windows).
+Cost: one local HTTP round-trip per prompt and per subagent stop + Node coldstart (~100ms on Windows).
 
 ## MCP tools
 

plugin/hooks/hooks.json

@@ -19,6 +19,16 @@
           }
         ]
       }
+    ],
+    "SubagentStop": [
+      {
+        "hooks": [
+          {
+            "type": "command",
+            "command": "claude-mailbox check --hook"
+          }
+        ]
+      }
     ]
   }
 }