fix(shard-manager): Correctly parse when time is zero

service/sharddistributor/store/etcd/etcdtypes/state_test.go

@@ -223,6 +223,29 @@ func TestAssignedState_JSONMarshalling(t *testing.T) {
 	}
 }
 
+func TestAssignedState_JSONUnmarshalWithZeroLastUpdated(t *testing.T) {
+	tests := map[string]struct {
+		jsonStr string
+	}{
+		"last_updated is string zero": {
+			jsonStr: `{"assigned_shards":{"1":{"status":"AssignmentStatusREADY"}},"last_updated":"0"}`,
+		},
+		"last_updated is numeric zero": {
+			jsonStr: `{"assigned_shards":{"1":{"status":"AssignmentStatusREADY"}},"last_updated":0}`,
+		},
+	}
+
+	for name, tc := range tests {
+		t.Run(name, func(t *testing.T) {
+			var unmarshalled AssignedState
+			err := json.Unmarshal([]byte(tc.jsonStr), &unmarshalled)
+			require.NoError(t, err)
+			require.Equal(t, types.AssignmentStatusREADY, unmarshalled.AssignedShards["1"].Status)
+			require.True(t, time.Time(unmarshalled.LastUpdated).IsZero())
+		})
+	}
+}
+
 func TestShardStatistics_FieldNumberMatched(t *testing.T) {
 	require.Equal(t,
 		reflect.TypeOf(ShardStatistics{}).NumField(),

service/sharddistributor/store/etcd/etcdtypes/time.go

@@ -39,11 +39,17 @@ func (t Time) MarshalJSON() ([]byte, error) {
 
 // UnmarshalJSON implements the json.Unmarshaler interface.
 // It decodes the time from time.RFC3339Nano format.
+// It also handles the special case where the value is "0" or 0 (zero),
+// which is treated as the zero value of time.Time.
 func (t *Time) UnmarshalJSON(data []byte) error {
 	str := string(data)
 	if len(str) >= 2 && str[0] == '"' && str[len(str)-1] == '"' {
 		str = str[1 : len(str)-1]
 	}
+	if str == "0" {
+		*t = Time(time.Time{})
+		return nil
+	}
 	parsed, err := ParseTime(str)
 	if err != nil {
 		return err

service/sharddistributor/store/etcd/etcdtypes/time_test.go

@@ -89,6 +89,16 @@ func TestTimeUnmarshalJSON(t *testing.T) {
 			expectTime: Time(time.Date(2025, 11, 17, 23, 2, 3, 456789012, time.UTC)),
 			expectErr:  "",
 		},
+		"zero string": {
+			input:      []byte(`"0"`),
+			expectTime: Time(time.Time{}),
+			expectErr:  "",
+		},
+		"zero number": {
+			input:      []byte(`0`),
+			expectTime: Time(time.Time{}),
+			expectErr:  "",
+		},
 		"invalid format": {
 			input:      []byte(`"not-a-time"`),
 			expectTime: Time{},