fix: guard quantiseAndSend against zero-length sequence and hidden dim

[Copilot]

quantiseAndSend() had no input validation before calling into the WASM kernel. With seqLen=0, the kernel computes lastTokenPos = seqLen - 1 = -1, which wraps to a large address in WASM linear memory — an invalid read.

Changes

• src/worker.ts — Added early-return guards at the top of quantiseAndSend() for both seqLen < 1 and hiddenDim < 1, logging a warning and skipping the kernel call:

if (seqLen < 1) {
  workerLog('warn', 'quantiseAndSend: seqLen < 1; skipping Q² quantisation', { seqLen });
  return;
}
if (hiddenDim < 1) {
  workerLog('warn', 'quantiseAndSend: hiddenDim < 1; skipping Q² quantisation', { hiddenDim });
  return;
}

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[Copilot]

Pull request overview

Adds input validation to quantiseAndSend() in the worker to avoid unsafe/invalid WASM kernel calls when the embedding shape is degenerate (e.g., zero-length sequences).

Changes:

• Add early-return guard for seqLen < 1 with a warning log.
• Add early-return guard for hiddenDim < 1 with a warning log.

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[Copilot]

The new guards prevent the seqLen=0/hiddenDim=0 trap, but quantiseAndSend still doesn’t validate other documented kernel preconditions (e.g., n must be a power of 2 and ≤ 16,384, and the buffer must contain at least the last-token row). Without these checks it’s still possible to call into the WASM kernel with unsupported dimensions or an undersized buffer, which can lead to traps or incorrect fingerprints. Consider extending the early validation to enforce the kernel’s n constraints (and, if applicable, the expected byteLength for the given dtype) before copying/calling into WASM.

[Copilot]

This change introduces new early-return behavior for invalid seqLen/hiddenDim, but there’s no unit test asserting that the Q² kernel is not invoked in these cases. Since the repo already has worker unit tests, consider adding a test that triggers the embedding extraction path with seqLen=0 and/or hiddenDim=0 and verifies getKernel/quantise are not called (and that the worker continues without error).