fix(js/ts/python): preserve JS/TS generic unit arguments and Python unit continuations

[dbrattli]

Why

The JavaScript and TypeScript compiler drops unit arguments when calling local generic functions, generating fromValue() instead of fromValue(undefined). Call-site types are specialized to unit, so using them to erase arguments loses the function's declared generic parameter. This affects the shared JS/TS code generator and causes TypeScript compilation to fail with TS2554. Generic functions must receive their unit value while ordinary unit -> unit callbacks retain their zero-argument convention.

Python has two related unit continuation failures. Async.FromContinuations(fun (ok, _, _) -> ok ()) invokes a runtime success continuation without its required value. A unit continuation inside a tail-recursive function can also put a captured callback in its first default parameter, which the runtime's None argument overwrites. Both failures reproduce by executing generated Python.

How

• Retain declaration types for local bindings, recursive bindings, and function parameters in the shared JavaScript/TypeScript Babel transform.
• Preserve unit arguments when a curried call's declared parameter requires a value, including generic aliases whose parameter type is erased to any. Generate fromValue(undefined) for a generic factory and keep callback() for an ordinary unit callback.
• Add a dedicated Python unit FromContinuations runtime adapter and select it at the replacement boundary, preserving the existing generic API and ordinary unit call semantics.
• Reserve a real unit argument before Python captured tail-call defaults so runtime arguments cannot overwrite captures. Give it a unique name, including when a captured F# variable is named __unit.
• Add generated JS/TypeScript/Python/BEAM regressions for unit and non-unit computations, generic and explicitly unit-typed callbacks, recursive generic factories and aliases, and a Python capture-name collision.

Validation

• Published compiler/library 5.19.0: both Python unit tests failed (on_success missing value, and a callback overwritten with None). They pass with the compiler/runtime fixes.
• Before the JS/TS compiler fix: ./build.sh test typescript reproduces TS2554 at AsyncTests.ts(134,34) for fromValue(). After: ./build.sh test typescript --force-fable-library passes TypeScript compilation and all 2,884 generated tests using TypeScript 7.0.2. Generated code passes undefined to the factory and alias, and invokes ordinary unit callbacks without arguments.
• Exact PR branch: ./build.sh test javascript --force-fable-library passes 2,937 .NET, 3,107 JS, 3,132 Temporal JS, React 26 tests/19 snapshots, and Adaptive 1 test.
• Exact PR branch: ./build.sh test python --type-check --skip-fable-library-core passes 2,399 .NET and 2,489 Python tests. Generated Pyright matches the existing baseline of 34 errors/45 warnings; the async regression module and changed Python adapter have 0 errors/0 warnings. Existing abandoned-event-loop warnings remain observable with the published runtime as well.
• ./build.sh test beam passes 2,712 .NET and 2,746 BEAM tests, plus entry-point checks. Repository-wide Fantomas and git diff --check pass.
• This requires an updated compiler and Python runtime together; Fable.Actor adapters remain until publication and a passing four-target Actor suite without them.

[github-actions]

Python Type Checking Results (Pyright)

Metric	Value
Total errors	34
Files with errors	4
Excluded files	4
New errors	✅ No

Excluded files with errors (4 files)

These files have known type errors and are excluded from CI. Remove from pyrightconfig.ci.json as errors are fixed.

File	Errors	Status
temp/tests/Python/test_hash_set.py	18	Excluded
temp/tests/Python/test_applicative.py	12	Excluded
temp/tests/Python/test_nested_and_recursive_pattern.py	2	Excluded
temp/tests/Python/fable_modules/thoth_json_python/encode.py	2	Excluded