feat(tui): workflow-start intent input box wired to StartSession.input

apps/tui-go/internal/protocol/protocol.go

@@ -213,9 +213,14 @@ func ChatInput(sessionID, text, mode string) []byte {
 	return encode("ChatInput", map[string]any{"sessionId": sessionID, "text": text, "mode": mode})
 }
 
-// StartSession launches a workflow-backed session.
-func StartSession(workflowID string) []byte {
-	return encode("StartSession", map[string]any{"workflowId": workflowID, "config": nil})
+// StartSession launches a workflow-backed session. input is the optional freeform request
+// seeded into the decision journal; pass "" for fixed-task workflows (e.g. healthcheck).
+func StartSession(workflowID, input string) []byte {
+	msg := map[string]any{"workflowId": workflowID, "config": nil}
+	if input != "" {
+		msg["input"] = input
+	}
+	return encode("StartSession", msg)
 }
 
 // CancelSession cancels a running session.

apps/tui-go/internal/protocol/start_session_test.go

@@ -0,0 +1,32 @@
+package protocol
+
+import (
+	"encoding/json"
+	"testing"
+)
+
+func decodeFrame(t *testing.T, b []byte) map[string]any {
+	t.Helper()
+	var m map[string]any
+	if err := json.Unmarshal(b, &m); err != nil {
+		t.Fatalf("unmarshal: %v", err)
+	}
+	return m
+}
+
+func TestStartSessionOmitsEmptyInput(t *testing.T) {
+	m := decodeFrame(t, StartSession("healthcheck", ""))
+	if m["workflowId"] != "healthcheck" {
+		t.Fatalf("unexpected frame: %+v", m)
+	}
+	if _, present := m["input"]; present {
+		t.Fatalf("empty input must be omitted, got: %+v", m)
+	}
+}
+
+func TestStartSessionCarriesIntent(t *testing.T) {
+	m := decodeFrame(t, StartSession("role_pipeline", "add an auth layer to the account service"))
+	if m["input"] != "add an auth layer to the account service" {
+		t.Fatalf("intent not carried: %+v", m)
+	}
+}