diff --git a/plugins/warp/scripts/on-post-tool-use.sh b/plugins/warp/scripts/on-post-tool-use.sh
index 568e5b3..6a386b6 100755
--- a/plugins/warp/scripts/on-post-tool-use.sh
+++ b/plugins/warp/scripts/on-post-tool-use.sh
@@ -3,22 +3,26 @@
 # Sends a structured Warp notification after a tool call completes,
 # transitioning the session status from Blocked back to Running.
 
+[ -z "${WARP_CLI_AGENT_PROTOCOL_VERSION:-}" ] && exit 0
+
 SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
 source "$SCRIPT_DIR/should-use-structured.sh"
 
-# No legacy equivalent for this hook
 if ! should_use_structured; then
     exit 0
 fi
 
-source "$SCRIPT_DIR/build-payload.sh"
-
-# Read hook input from stdin
-INPUT=$(cat)
+PROTOCOL_VERSION="${WARP_CLI_AGENT_PROTOCOL_VERSION:-1}"
+[[ "$PROTOCOL_VERSION" =~ ^[0-9]+$ ]] || PROTOCOL_VERSION=1
+[ "$PROTOCOL_VERSION" -gt 1 ] && PROTOCOL_VERSION=1
 
-TOOL_NAME=$(echo "$INPUT" | jq -r '.tool_name // empty' 2>/dev/null)
+BODY=$(jq -nc \
+    --argjson v "$PROTOCOL_VERSION" \
+    --arg agent "claude" \
+    --arg event "tool_complete" \
+    '{v:$v, agent:$agent, event:$event}
+     + (input | {session_id: (.session_id // ""), cwd: (.cwd // ""), project: ((.cwd // "") | sub("/+$"; "") | sub(".*/"; "")), tool_name: (.tool_name // "")})' 2>/dev/null) || exit 0
 
-BODY=$(build_payload "$INPUT" "tool_complete" \
-    --arg tool_name "$TOOL_NAME")
+[ -z "$BODY" ] && exit 0
 
-"$SCRIPT_DIR/warp-notify.sh" "warp://cli-agent" "$BODY"
+printf '\033]777;notify;%s;%s\007' "warp://cli-agent" "$BODY" > /dev/tty 2>/dev/null &
diff --git a/plugins/warp/tests/test-hooks.sh b/plugins/warp/tests/test-hooks.sh
index 754bdd0..55006c9 100755
--- a/plugins/warp/tests/test-hooks.sh
+++ b/plugins/warp/tests/test-hooks.sh
@@ -287,6 +287,87 @@ for HOOK in on-permission-request.sh on-prompt-submit.sh on-post-tool-use.sh; do
     assert_eq "$HOOK exits 0 without protocol version" "0" "$?"
 done
 
+# --- PostToolUse payload tests ---
+# The optimized on-post-tool-use.sh inlines payload construction and writes
+# to /dev/tty. We use `script` to capture pty output and extract the JSON.
+
+run_hook_capture() {
+    local hook="$1"
+    local input="$2"
+    local tmpfile inputfile
+    tmpfile=$(mktemp)
+    inputfile=$(mktemp)
+    printf '%s' "$input" > "$inputfile"
+    script -q "$tmpfile" bash -c "bash \"$HOOK_DIR/$hook\" < \"$inputfile\"; wait; sleep 0.2" >/dev/null 2>&1
+    local payload
+    payload=$(tr -d '\r' < "$tmpfile" | grep -o '{[^}]*}' | tail -1)
+    rm -f "$tmpfile" "$inputfile"
+    echo "$payload"
+}
+
+echo ""
+echo "=== on-post-tool-use.sh (payload) ==="
+
+echo ""
+echo "--- Basic payload construction ---"
+export WARP_CLI_AGENT_PROTOCOL_VERSION=1
+export WARP_CLIENT_VERSION="v0.2026.04.29.08.57.preview_01"
+
+PAYLOAD=$(run_hook_capture "on-post-tool-use.sh" '{"tool_name":"Read","session_id":"sess-456","cwd":"/Users/alice/my-project"}')
+assert_json_field "v is 1" "$PAYLOAD" ".v" "1"
+assert_json_field "agent is claude" "$PAYLOAD" ".agent" "claude"
+assert_json_field "event is tool_complete" "$PAYLOAD" ".event" "tool_complete"
+assert_json_field "session_id extracted" "$PAYLOAD" ".session_id" "sess-456"
+assert_json_field "cwd extracted" "$PAYLOAD" ".cwd" "/Users/alice/my-project"
+assert_json_field "project is basename of cwd" "$PAYLOAD" ".project" "my-project"
+assert_json_field "tool_name extracted" "$PAYLOAD" ".tool_name" "Read"
+
+echo ""
+echo "--- Trailing slash in cwd ---"
+PAYLOAD=$(run_hook_capture "on-post-tool-use.sh" '{"tool_name":"Read","session_id":"s1","cwd":"/Users/alice/project/"}')
+assert_json_field "trailing slash stripped for project" "$PAYLOAD" ".project" "project"
+
+echo ""
+echo "--- Missing fields produce empty strings ---"
+PAYLOAD=$(run_hook_capture "on-post-tool-use.sh" '{"tool_name":"Bash"}')
+assert_json_field "missing session_id is empty" "$PAYLOAD" ".session_id" ""
+assert_json_field "missing cwd is empty" "$PAYLOAD" ".cwd" ""
+assert_json_field "missing cwd gives empty project" "$PAYLOAD" ".project" ""
+assert_json_field "tool_name still works" "$PAYLOAD" ".tool_name" "Bash"
+
+echo ""
+echo "--- Protocol version negotiation (inline) ---"
+export WARP_CLI_AGENT_PROTOCOL_VERSION=99
+PAYLOAD=$(run_hook_capture "on-post-tool-use.sh" '{"tool_name":"Edit","session_id":"s1","cwd":"/tmp"}')
+assert_json_field "protocol capped to 1 when warp declares 99" "$PAYLOAD" ".v" "1"
+
+export WARP_CLI_AGENT_PROTOCOL_VERSION=1
+PAYLOAD=$(run_hook_capture "on-post-tool-use.sh" '{"tool_name":"Edit","session_id":"s1","cwd":"/tmp"}')
+assert_json_field "protocol is 1 when warp declares 1" "$PAYLOAD" ".v" "1"
+
+echo ""
+echo "--- Non-numeric protocol version falls back to 1 ---"
+export WARP_CLI_AGENT_PROTOCOL_VERSION="garbage"
+PAYLOAD=$(run_hook_capture "on-post-tool-use.sh" '{"tool_name":"Edit","session_id":"s1","cwd":"/tmp"}')
+assert_json_field "non-numeric protocol falls back to 1" "$PAYLOAD" ".v" "1"
+
+echo ""
+echo "--- Early exit without protocol version ---"
+unset WARP_CLI_AGENT_PROTOCOL_VERSION
+PAYLOAD=$(run_hook_capture "on-post-tool-use.sh" '{"tool_name":"Read","session_id":"s1","cwd":"/tmp"}')
+assert_eq "no output when WARP_CLI_AGENT_PROTOCOL_VERSION unset" "" "$PAYLOAD"
+
+echo ""
+echo "--- Early exit for broken Warp version ---"
+export WARP_CLI_AGENT_PROTOCOL_VERSION=1
+export WARP_CLIENT_VERSION="v0.2026.03.25.08.24.stable_05"
+PAYLOAD=$(run_hook_capture "on-post-tool-use.sh" '{"tool_name":"Read","session_id":"s1","cwd":"/tmp"}')
+assert_eq "no output for broken stable version" "" "$PAYLOAD"
+
+# Clean up
+unset WARP_CLI_AGENT_PROTOCOL_VERSION
+unset WARP_CLIENT_VERSION
+
 # --- Summary ---
 
 echo ""