v0.27.0

Added

• Diagnostics: ReadOptions.OnDiagnostic reports parse anomalies — a value shorter than its length field, a header cut off mid-element, a sequence item header past the end of the file, a deferred value whose source has gone away — each carrying its tag, VR, byte offset, and enclosing sequences. Diagnostic is itself an error, so returning it from the hook rejects the file while returning nil keeps the tolerant default
• Setters: dictionary-VR setters SetString / SetInt / SetFloat / SetBytes / SetSequence, the plural SetStrings / SetInts / SetFloats, and SetDA / SetTM / SetDT / SetPN / SetDS / SetIS. Each resolves the VR from the data dictionary and rejects value kinds that VR cannot hold. Tags outside the dictionary still need Set(NewDataElement(tag, vr, value))

Changed

• BREAKING: transfer syntax parameters and returns are uid.UID, not string: EncodeDataset, WriteDataset, Dataset.Encode, DecodeDataset, DecodeDatasetContext, CompressPixelData, CompressPixelDataContext, FileDataset.TransferSyntaxUID, and pixels.FileSource. String literals still compile at call sites; string variables need an explicit uid.UID(...)
• Read hands a reader that already offers io.ReaderAt plus Size() int64 (*bytes.Reader, *strings.Reader, *io.SectionReader) to the parser as-is instead of wrapping it in Seek+Read, so neither the parse nor a later deferred load moves the caller's offset
• Internal: one shared data element header decoder for the streaming and in-memory readers; the sequence readers return errors instead of latching them on the read context

Fixed

• Deferred values were permanently unreachable after Read from a seekable reader that is not an *os.File (bytes.Reader, io.SectionReader, range-request adapters): the tag stayed listed while Get / GetBytes reported it absent
• Deferred values in a Deflated dataset read through ReadBytes / Read loaded from the still-compressed buffer, failing with a tag or VR mismatch. ReadFile was unaffected
• The streaming reader silently dropped a defined-length sequence whose length ran past the end of the file, complete items included. It now parses the items that are present and reports a truncated item, matching ReadBytes and pydicom's read_sequence_item
• A diagnostic raised inside a sequence — and a hook error rejecting it — now reaches the caller instead of being swallowed by the sequence readers
• AT elements were encoded as a single 32-bit value instead of the group / element pair of 16-bit values required by PS3.5 7.1.1. The two coincide under big endian and differ under little endian, so godicom wrote AT values that it and every other implementation read back swapped: (0018,1063) came back as (1063,0018). encodeAT also accepts []Tag, []int and *MultiValue[int] now, so SetInts on an AT tag encodes rather than silently producing an empty value