fix(client): deliver exactly one terminal SSE callback (#1170) - #1173

[RequireExplicitNullMarking] [RequireExplicitNullMarking] Top-level classes must either be directly annotated with @NullMarked/@NullUnmarked, be in a package that is explicitly @NullMarked/@NullUnmarked, or be in a module that is explicitly @NullMarked.

[RequireExplicitNullMarking] [RequireExplicitNullMarking] Top-level classes must either be directly annotated with @NullMarked/@NullUnmarked, be in a package that is explicitly @NullMarked/@NullUnmarked, or be in a module that is explicitly @NullMarked.

[RequireExplicitNullMarking] [RequireExplicitNullMarking] Top-level classes must either be directly annotated with @NullMarked/@NullUnmarked, be in a package that is explicitly @NullMarked/@NullUnmarked, or be in a module that is explicitly @NullMarked.

[RequireExplicitNullMarking] [RequireExplicitNullMarking] Top-level classes must either be directly annotated with @NullMarked/@NullUnmarked, be in a package that is explicitly @NullMarked/@NullUnmarked, or be in a module that is explicitly @NullMarked.

[RequireExplicitNullMarking] [RequireExplicitNullMarking] Top-level classes must either be directly annotated with @NullMarked/@NullUnmarked, be in a package that is explicitly @NullMarked/@NullUnmarked, or be in a module that is explicitly @NullMarked.

[RequireExplicitNullMarking] [RequireExplicitNullMarking] Top-level classes must either be directly annotated with @NullMarked/@NullUnmarked, be in a package that is explicitly @NullMarked/@NullUnmarked, or be in a module that is explicitly @NullMarked.

[RequireExplicitNullMarking] [RequireExplicitNullMarking] Top-level classes must either be directly annotated with @NullMarked/@NullUnmarked, be in a package that is explicitly @NullMarked/@NullUnmarked, or be in a module that is explicitly @NullMarked.

[RequireExplicitNullMarking] [RequireExplicitNullMarking] Top-level classes must either be directly annotated with @NullMarked/@NullUnmarked, be in a package that is explicitly @NullMarked/@NullUnmarked, or be in a module that is explicitly @NullMarked.

[RequireExplicitNullMarking] [RequireExplicitNullMarking] Top-level classes must either be directly annotated with @NullMarked/@NullUnmarked, be in a package that is explicitly @NullMarked/@NullUnmarked, or be in a module that is explicitly @NullMarked.

[RequireExplicitNullMarking] [RequireExplicitNullMarking] Top-level classes must either be directly annotated with @NullMarked/@NullUnmarked, be in a package that is explicitly @NullMarked/@NullUnmarked, or be in a module that is explicitly @NullMarked.