feat(protocol): add interactive prompt resolution tombstone

prompt.go

@@ -0,0 +1,16 @@
+package protocol
+
+// MsgInteractivePromptResolved is the daemon->PWA tombstone broadcast after
+// an interactive prompt answer is accepted by the daemon-side agent adapter.
+const MsgInteractivePromptResolved = "interactive_prompt_resolved"
+
+// InteractivePromptResolvedPayload is carried by MsgInteractivePromptResolved.
+// The PWA records QuestionID as resolved for SessionID and clears only matching
+// pending/in-flight prompt UI state. Reason is a stable, human-readable machine
+// string such as "answered".
+type InteractivePromptResolvedPayload struct {
+	QuestionID string `json:"question_id"`
+	SessionID  string `json:"session_id"`
+	Reason     string `json:"reason"`
+	ResolvedAt int64  `json:"resolved_at"`
+}

prompt_test.go

@@ -0,0 +1,45 @@
+package protocol
+
+import (
+	"encoding/json"
+	"strings"
+	"testing"
+)
+
+func TestMsgInteractivePromptResolvedConstant(t *testing.T) {
+	t.Parallel()
+
+	if MsgInteractivePromptResolved != "interactive_prompt_resolved" {
+		t.Fatalf("MsgInteractivePromptResolved = %q, want %q", MsgInteractivePromptResolved, "interactive_prompt_resolved")
+	}
+}
+
+func TestInteractivePromptResolvedPayloadRoundtrip(t *testing.T) {
+	t.Parallel()
+
+	original := InteractivePromptResolvedPayload{
+		QuestionID: "q-123",
+		SessionID:  "s-123",
+		Reason:     "answered",
+		ResolvedAt: 1778915600123,
+	}
+
+	raw, err := json.Marshal(original)
+	if err != nil {
+		t.Fatalf("marshal: %v", err)
+	}
+	rawStr := string(raw)
+	for _, want := range []string{`"question_id"`, `"session_id"`, `"reason"`, `"resolved_at"`} {
+		if !strings.Contains(rawStr, want) {
+			t.Fatalf("marshaled JSON missing %s: %s", want, rawStr)
+		}
+	}
+
+	var decoded InteractivePromptResolvedPayload
+	if err := json.Unmarshal(raw, &decoded); err != nil {
+		t.Fatalf("unmarshal: %v", err)
+	}
+	if decoded != original {
+		t.Fatalf("roundtrip mismatch:\n  got:  %+v\n  want: %+v", decoded, original)
+	}
+}