feat(hooks): ring terminal on turn end via Stop hook

Notification matcher covers input-needed events only; end of turn had no
signal but idle_prompt, ~60s late. Wire notify-attention.sh on Stop too,
branching on hook_event_name for the message. Signal only: returns
terminalSequence + suppressOutput, never blocks (guard vs BDR-083).

Header documents both client-side prerequisites found in BLK-020.

hooks/notify-attention.sh

@@ -1,21 +1,35 @@
 #!/usr/bin/env bash
-# Notification hook — signal the user through the terminal when Claude
-# needs input (permission prompt, question, idle wait).
+# Notification + Stop hook — signal the user through the terminal when
+# Claude needs input (permission prompt, question, idle wait) or has
+# finished responding.
 #
 # Runs on the remote (Linux); the only channel that crosses SSH into the
 # VS Code client is the terminal stream. Hooks have no controlling TTY,
 # so the sequence goes through the supported `terminalSequence` JSON
 # output field and Claude Code writes it to the terminal:
 #   - BEL x2 (double beep) -> sound, needs VS Code setting
-#     accessibility.signals.terminalBell { "sound": "on" }
+#     accessibility.signals.terminalBell { "sound": "on" } AND a non-zero
+#     volume for Code in the Windows volume mixer (BLK-020).
 #   - OSC 777 notify -> Windows toast via the client-side extension
-#     "Terminal Notification" (wenbopan.vscode-terminal-osc-notifier)
+#     "Terminal Notification" (wenbopan.vscode-terminal-osc-notifier).
+#     The extension only instruments terminals created AFTER it is
+#     active: install it first, then start or re-attach the session.
 # Both are invisible no-ops in terminals that ignore them.
 set -u
 
-msg=$(jq -r '.message // .notification_type // empty' 2>/dev/null \
-  | tr -d '\000-\037' | cut -c1-200)
-[ -n "$msg" ] || msg="Claude Code needs your input"
+payload=$(cat 2>/dev/null)
+read_field() {
+  printf '%s' "$payload" | jq -r "$1 // empty" 2>/dev/null \
+    | tr -d '\000-\037' | cut -c1-200
+}
+
+msg=$(read_field '.message // .notification_type')
+if [ -z "$msg" ]; then
+  case "$(read_field '.hook_event_name')" in
+    Stop) msg="Claude has finished responding" ;;
+    *) msg="Claude Code needs your input" ;;
+  esac
+fi
 
 bell=$(printf '\a')
 esc=$(printf '\033')

settings.json

@@ -286,6 +286,18 @@
         ]
       }
     ],
+    "Stop": [
+      {
+        "hooks": [
+          {
+            "type": "command",
+            "command": "bash ~/.claude/hooks/notify-attention.sh",
+            "timeout": 5,
+            "statusMessage": "Ringing terminal bell..."
+          }
+        ]
+      }
+    ],
     "UserPromptSubmit": [
       {
         "hooks": [