fix(compression): bump vendored GCF with numeric-domain and surplus fixes

[blackwell-systems]

Summary

• Bring the vendored GCF (Headroom codec) current with two correctness fixes it has lacked since the v3.2 vendoring (feat(compression): replace headroom tabular encoder with vendored GCF #4167, feat(compression): update vendored GCF (Headroom) codec to spec v3.2 — nested flattening #6838). Both are losslessness-safety fixes at the codec boundary; behavior is unchanged for every payload except the two edge cases below, which previously round-tripped incorrectly.
  • Numeric domain (encode). scalar.ts formatNumber emitted plain-decimal up to 1e21, so an integer-valued double in [2^53, 1e21) was written as a bare integer that is ambiguous with an int64 and beyond the JS safe-integer range. Gate the plain form at 2^53 and use exponent form above it (SPEC 2.3.1). Shorter than the bare integer, so no budget regression.
  • Root-array count (decode). decode_generic.ts discarded parseArrayFromHeader's consumed count, so a wire declaring fewer rows than it carried silently dropped the surplus. Verify the consumed lines cover the document and throw count_mismatch otherwise (SPEC §13).

Related Issues

• Related to feat(compression): replace headroom tabular encoder with vendored GCF #4167 (original GCF vendoring) and feat(compression): update vendored GCF (Headroom) codec to spec v3.2 — nested flattening #6838 (v3.2 nested-flattening update)

Validation

• Change type: other (compression codec, open-sse/services/compression/engines/headroom/gcf)
• Focused tests and category gates: the two new compression tests plus the existing gcf-inline-array-quote test pass locally
• [~] npm run lint: prettier is clean on the touched files; the full check:compression-budget and typecheck:core gates could not run in my environment (missing optional omniglyph dependency) and are left to CI (docs: official 'golden path' contribution guide by change type #8329)
• Reconciled with the current active release base (release/v3.8.50, 0 commits behind at push)
• Production-code changes include new automated tests in this PR

Tests Added Or Updated

• tests/unit/compression/gcf-numeric-domain.test.ts (new) — integer-valued double at/above 2^53 renders in exponent form, not a bare integer
• tests/unit/compression/gcf-count-mismatch.test.ts (new) — a root array carrying more rows than its declared count throws count_mismatch; an exact count decodes normally

Coverage Notes

• Touches open-sse/services/compression/engines/headroom/gcf/{scalar.ts, decode_generic.ts}. The two new tests cover both changed branches (the numeric formatting boundary and the root-array surplus guard). No touched file loses coverage.

Reviewer Notes

• Surgical by design: the encode change is boundary-only (values < 2^53 are byte-for-byte identical), and the decode change adds a guard that turns a previously silent truncation into an explicit error. generic.ts is intentionally left untouched to avoid a lint-staged prettier reformat of its pre-existing long lines. The vendored file headers note both fixes and the README credits entry is refreshed to match.