Bastian Wagner ef9ca9eeca fix: harden FIT patcher error boundary and verify patched metadata ...

Final-review fixes for Plan 2 (fit-rewriter). Every failure mode below now
surfaces as FitFormatError so Plan 3 can classify invalid FIT input as a
non-retryable activity error (spec 10.4).

- Range-check numeric values against the field's declared size before
  struct.pack, so an oversized serial number or a 1-byte product field
  raises FitFormatError instead of leaking a raw struct.error.
- Reject zero-size field definitions during parsing. A zero-size
  device_info field 0 read back as device_index == 0 via
  int.from_bytes(b"", ...), which could have let a paired sensor be
  rewritten as an Edge 1030 Plus (spec 10.2).
- Add DeviceFieldValue.is_creator so callers can tell the creator
  device_info record from sensor records instead of silently keeping
  whichever record appeared last.
- Implement the missing spec 10.4 post-patch step: read the patched
  buffer back and verify file_id 1/2/8 and creator device_info 2/4/27
  hold the target values. A field that could not be written (e.g. a
  product_name field too small for the target string) now fails the whole
  conversion rather than producing a silent partial patch. Verification
  runs before the output is written, so a half-rewritten file never lands
  on disk.
- Use the field's actual endianness in _read_field_value's fallback path.
- Add curated re-exports in app/fit/__init__.py for Plan 3.
- Document _iter_data_fields' caller invariant (validate the container
  first; end_offset is not clamped).
- Extend the preservation fixture with a product_name string field so the
  zero-filling string write path is covered by the byte-preservation
  proof, and test convert_fit_device against a 12-byte header.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

2026-08-15 14:29:40 +02:00

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