nanoda fails on Lean 4.28 export stream with invalid digit

Description

On a minimal Lake package pinned to leanprover/lean4:v4.28.0, leanprover/lean-action@v1.5.0 reaches nanoda successfully but nanoda rejects the generated export stream with:

Detected module name: LogicZigOracle
Exporting LogicZigOracle...
Running nanoda type checker...
Error: invalid digit found in string

The same package builds successfully and passes the bundled leanchecker. It contains no sorry, admit, custom axioms, or unsafe declarations.

Reproduction

- uses: leanprover/lean-action@v1.5.0
  with:
    lake-package-directory: lean
    build: true
    test: false
    nanoda: true
    nanoda-allow-sorry: false

with lean/lean-toolchain:

leanprover/lean4:v4.28.0

Notes

The current nanoda_lib debug branch head predates Lean 4.28. The exporter builds against 4.28 and emits the file, so this appears to be an export-format/parser compatibility problem rather than module discovery or a Lean elaboration failure.

A useful short-term outcome would be either a supported-version guard with a clear diagnostic or a compatible nanoda/exporter pin. The current generic parse error makes the gate difficult to diagnose.

Start by reproducing the failure with leanprover/lean-action@v1.5.0, Lean 4.28.0, nanoda enabled, and the minimal Lake package described in the issue. Inspect the nanoda_lib debug branch and the generated export stream to determine whether a supported-version guard or compatible exporter/nanoda pin is feasible. Done means a compatible run or a clear diagnostic instead of the generic invalid-digit error.