feat: add msglib display entity extraction

internal/msglib/sidecar_client_test.go

@@ -55,6 +55,44 @@ func TestDisplaySourcesPassesConfiguredPathsAndDecodesMetadata(t *testing.T) {
 	}
 }
 
+func TestDisplayEntitiesPassesBoundedArgsAndDecodesMetadata(t *testing.T) {
+	cfg := Config{
+		SQLiteDLLPath: `C:\fixture\System.Data.SQLite.dll`,
+		DBPath:        `C:\fixture\MsgLib.db`,
+		Password:      "123",
+	}
+	client := newFakeClient(t, "display_entities_ok", cfg)
+
+	got, err := client.DisplayEntities(context.Background(), DisplayEntitiesOptions{EntityType: "contacts", Query: "alice", Limit: 2})
+	if err != nil {
+		t.Fatalf("DisplayEntities returned error: %v", err)
+	}
+	if len(got) != 2 {
+		t.Fatalf("len(DisplayEntities) = %d, want 2", len(got))
+	}
+	if got[0].EntityType != "contacts" || got[0].SourceTable != "TD_Roster" || got[0].JID != "alice@example" || got[0].DisplayName != "Alice" {
+		t.Fatalf("unexpected first entity: %+v", got[0])
+	}
+	if got[0].Confidence <= 0 || strings.Join(got[0].MatchedColumns, ",") != "JId,Nick" {
+		t.Fatalf("unexpected first entity metadata: %+v", got[0])
+	}
+	if got[1].SourceTable != "tblRecent" || got[1].JID != "recent@example" || got[1].DisplayName != "Recent Alice" {
+		t.Fatalf("unexpected second entity: %+v", got[1])
+	}
+}
+
+func TestDisplayEntitiesRejectsUnsupportedEntityType(t *testing.T) {
+	client := newFakeClient(t, "display_entities_ok", Config{})
+
+	_, err := client.DisplayEntities(context.Background(), DisplayEntitiesOptions{EntityType: "messages", Limit: 5})
+	if err == nil {
+		t.Fatal("DisplayEntities returned nil error, want unsupported entity_type error")
+	}
+	if !strings.Contains(err.Error(), "entity_type") {
+		t.Fatalf("DisplayEntities error = %v, want entity_type context", err)
+	}
+}
+
 func TestClientReturnsStructuredSidecarError(t *testing.T) {
 	client := newFakeClient(t, "sidecar_error", Config{})
 
@@ -202,6 +240,31 @@ func fakeSidecarMain() int {
 			"error":    nil,
 			"warnings": []any{},
 		})
+	case "display_entities":
+		args, _ := req["args"].(map[string]any)
+		if args["sqlite_dll_path"] != `C:\fixture\System.Data.SQLite.dll` || args["db_path"] != `C:\fixture\MsgLib.db` || args["password"] != "123" || args["entity_type"] != "contacts" || args["query"] != "alice" || args["limit"] != float64(2) {
+			fmt.Fprintf(os.Stderr, "bad display_entities args: %#v\n", args)
+			return 2
+		}
+		return writeFakeResponse(map[string]any{
+			"protocol":   Protocol,
+			"request_id": requestID,
+			"op":         op,
+			"ok":         true,
+			"data": map[string]any{
+				"metadata_only": true,
+				"read_only":     true,
+				"entity_type":   "contacts",
+				"limit":         2,
+				"result_count":  2,
+				"entities": []any{
+					map[string]any{"entity_type": "contacts", "source_table": "TD_Roster", "jid": "alice@example", "display_name": "Alice", "confidence": 0.95, "matched_columns": []any{"JId", "Nick"}},
+					map[string]any{"entity_type": "contacts", "source_table": "tblRecent", "jid": "recent@example", "display_name": "Recent Alice", "confidence": 0.70, "matched_columns": []any{"PersonId", "PersonName"}},
+				},
+			},
+			"error":    nil,
+			"warnings": []any{},
+		})
 	default:
 		fmt.Fprintf(os.Stderr, "unexpected op: %s\n", op)
 		return 2