fix: improve state detection accuracy and notification UX

- Hook reads JSON from stdin (not env vars) matching Claude Code protocol
- end_turn = Idle (not NeedsInput); real questions come from hooks
- Permission prompt (stale tool_use) never becomes Idle
- Notifications auto-expire after 10s (--expire-time)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

state_test.go

@@ -8,6 +8,8 @@ import (
 var testNow = time.Date(2026, 3, 23, 12, 0, 30, 0, time.UTC)
 
 func TestDetectState_EndTurnText(t *testing.T) {
+	// end_turn = Claude finished, prompt waiting. This is Idle, not NeedsInput.
+	// Real NeedsInput comes from hooks (Stop, Notification) or AskUserQuestion.
 	msgs := []JSONLMessage{{
 		Type:      "assistant",
 		Timestamp: "2026-03-23T12:00:00Z",
@@ -19,8 +21,8 @@ func TestDetectState_EndTurnText(t *testing.T) {
 	}}
 
 	state := DetectState(msgs, testNow)
-	if state != NeedsInput {
-		t.Errorf("expected NeedsInput, got %v", state)
+	if state != Idle {
+		t.Errorf("expected Idle for end_turn, got %v", state)
 	}
 }
 
@@ -84,6 +86,24 @@ func TestDetectState_ToolUseStale(t *testing.T) {
 	}
 }
 
+func TestDetectState_ToolUseStaleNeverIdle(t *testing.T) {
+	// A tool_use older than IdleThreshold should still be NeedsInput, not Idle
+	msgs := []JSONLMessage{{
+		Type:      "assistant",
+		Timestamp: "2026-03-23T11:58:00Z", // 2min30s before testNow (> IdleThreshold)
+		Message: &MessagePayload{
+			Role:       "assistant",
+			Content:    []ContentBlock{{Type: "tool_use", Name: "Bash"}},
+			StopReason: "tool_use",
+		},
+	}}
+
+	state := DetectState(msgs, testNow)
+	if state != NeedsInput {
+		t.Errorf("expected NeedsInput for very old tool_use (permission), got %v", state)
+	}
+}
+
 func TestDetectState_Progress(t *testing.T) {
 	msgs := []JSONLMessage{{
 		Type:      "progress",