[bug] EXPath File: file:append doesn't persist content (1 QT4 test)

[joewiz]

Surfaced while running the EXPath File 4.0 QT4 suite against PR #6257 (174/190 passing). One test fails with a clean repro.

Failing test

• `EXPath-file-append2-001` — After `file:append`, the file is expected to end with `"a b c 10"` but ends up empty.

Spec reference

EXPath File 4.0 §4.3 `file:append`: https://qt4cg.org/specifications/expath-file-40/Overview.html#append

Diagnostic

Possibly the append-write isn't flushing the stream before the test reads it back, or the file wasn't created by the test's setup. Worth a focused look at `FileManipulation.append` for buffer / close semantics.

Disposition

Doesn't block PR #6257 from landing. Follow-up.