[Kshot3000]

Summary

SByte was the only signed primitive without a serialize-time range check. Every other signed writer throws a RangeError for out-of-range values — writeI16, writeI32, writeI64 and writeI256 in SigmaByteWriter, plus the VLQ writers — but the data serializer wrote byte constants through the raw write() method:

case descriptors.byte.code:
  return writer.write(data as number);

A plain number has no byte range in JS, and the underlying Uint8Array assignment silently wraps, so an out-of-range SByte constant did not round-trip:

• SByte(200) serialized to the byte 0xc8, which readI8 parses back as -56
• SByte(128) parsed back as -128
• SByte(256) serialized to 0x00 and parsed back as 0
• SByte(511) became -1, SByte(-129) became 127, non-integers were truncated

In Scala the Byte type itself makes these values unrepresentable, so this gap only exists in the JS port.

Fix

• Add SigmaByteWriter.writeI8, mirroring writeI16: it throws RangeError ("out of range for an 8-bit integer") outside MIN_I8..MAX_I8 and writes negative values as their two's complement byte, which is exactly the conversion readI8 applies when reading.
• The data serializer's byte case now calls writeI8. In-range encodings are byte-identical to before (the existing byteVectors, including -128 → 0280 and 127 → 027f, pass unchanged).

Deliberate non-change: SColl[Byte] is unaffected — its elements are carried as a Uint8Array of raw bytes and serialized with writeBytes, not through the per-element signed-byte path.

Tests

Tests-first: on pristine master, SByte(200) parses back as -56 and SByte(256) as 0 (probe spec, both assertions failed), and the new specs fail with the fix stashed (3 failures) while passing with it.

• sigmaByteWriter.spec: new "Should put Byte" vectors (0, 1, 76, MAX_I8, -1, MIN_I8) and byte cases added to the existing out-of-range test
• sigmaConstant.spec: serializing 128, 200, 255, 256, -129 and -256 as SByte now throws

Full monorepo suite: 1134/1134 tests pass (66 files); serializer package 375/375. Biome check clean on the changed files.

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Submitted by @Kshot9000 — Ergo ecosystem work. If this is useful, tips in ERG are welcome: 9fcM5RWnAjmP4vx5bnW6yohB6H9bLq8sJbaPLHtwZLtQPB32Pvy

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Latest commit: c0cdbcc

The changes in this PR will be included in the next version bump.

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Name	Type
@fleet-sdk/serializer	Patch

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