teach ts type gen how to handle nullable return types

[hahn-kev]

now methods with a return type of eg Task<string?> get converted into Promise<string | undefined>

I opted to use undefined instead of null as that fits best with svelte params which are declared as param?: type or $state<type>() which defaults to type | undefined.

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📝 Walkthrough

Walkthrough

The PR adds nullable async return handling to TypeScript generation, removes explicit TsFunction annotations, updates backend method contracts, and aligns generated frontend interfaces with nullable results.

Changes

Nullable API contracts

Layer / File(s)	Summary
Nullable return type generation backend/FwLite/FwLiteShared/TypeGen/ReinforcedFwLiteTypingConfig.cs	The generator preserves nullable return types for asynchronous methods and emits Promise<T | null> when required.
Backend invocation contracts backend/FwLite/FwLiteShared/Events/JsEventListener.cs, backend/FwLite/FwLiteShared/Services/*.cs	Explicit TsFunction annotations are removed. GetFileStream becomes non-nullable, and TryGetCrdtProjectName returns string? synchronously.
Generated frontend interfaces frontend/viewer/src/lib/dotnet-types/generated-types/FwLiteShared/**/*.ts	Generated interfaces now allow nullable results for event, project, history, and sync methods. Type imports are consolidated and reordered.
Estimated code review effort: 3 (Moderate)	~20 minutes

Possibly related PRs

• sillsdev/languageforge-lexbox#2358: Updates the same TypeScript nullability generation and generated service contracts.

Suggested reviewers: myieye

Poem

I’m a rabbit with types in my den,
Nulls now hop through the code again.
Promises speak true,
Interfaces do too,
And annotations rest in their pen.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Description check	✅ Passed	The description directly addresses nullable return type generation and the rationale for the chosen TypeScript representation.
Title check	✅ Passed	The title clearly and concisely identifies the main change: adding nullable return type support to TypeScript generation.

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch generated-types-respect-nullability

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Build	Status	Details	Updated (UTC)
default (Inspect)	✅ No changes detected	-	Aug 6, 2026, 8:04 AM
e2e (Inspect)	✅ No changes detected	-	Aug 6, 2026, 8:11 AM