JS-048: bin/lib write-side — wtlog appender + `refs` writer

Now: DONE

The pure-JS WRITE substrate for the reflog verbs. wtlog and reflog are BOTH ULOGs, so the write side lives IN ulog.js (beside its each/drain readers) — no new file — and the ref-store semantics live in the store lib. Generalises the ULOG-write code inlined in bin/get.js (writeWtlog/appendWtlog) + ingest.js::writeUlog. Pure JS over the abc ULOG container + io. Blocks the write verbs. Part of JS-046. Method: Issues. (Review: no multiplying files — fold, don't add.)

Input

Context

wtlog.js/keeper.js are READ-only today. Native wt row format is <ron60-ms>\t<verb>\t<uri> (sniff/AT.md); refs rows are set ?<br>#<sha> with a bare-40hex val, verbs post/delete (keeper/REFS.h).
ulog._feed(buf,off,verb,uri,ts) accepts an explicit ts → monotonic rows are expressible; get.js::writeWtlog is the existing (non-crash-safe) precedent.

Goals

bin/lib/ulog.js gains the WRITE side beside its each/drain readers: append(bePath, rows) (port SNIFFAtNow monotonic ts, CLOCKBAD guard, crash- safe temp+rename) + write/_stage/nowAfter. No separate wtwrite.js.
bin/lib/store.js (renamed from keeper.js) gains the ref WRITES: set(shard,key,sha)/tombstone(shard,key)/createShard, beside resolveRef.

Constraints

libabc+libdog ONLY (abc ULOG + io). Crash-safe: write a temp then io.rename (NOT get.js's resize-in-place). No keeper binding — append the ULOG file in JS.

WIP

Design decisions

No multiplying files (review): wtlog+reflog are both ULOGs → ONE writer in ulog.js; the ref semantics fold into store.js (was keeper.js). Repoint get.js + all keeper.js consumers; no output change.
CAS stays the caller's job (POST does resolve-then-conditional-append); PUT/DELETE append unconstrained — the reflog escape hatch (PUT.h).

TODOs

Repro-first test/js/*: append rows → re-drain, assert order + ts strict- increase; set/tombstone a ref → keeper.resolveRef round-trips; a mid-write crash (kill before rename) leaves the OLD file intact. (be/test/ulog.js + be/test/store.js, ctest JABCulogLib/JABCstore.)
Implement wtwrite.js + refs.js; repoint get.js; re-run be-js-get (no change). (Folded per review: writers in ulog.js + store.js, no new files; 3ce8aee5.)

Blockers and bummers

File-disjoint from JS-047 → parallel. Blocks JS-049/JS-050/JS-051.

Outcome

LANDED 3ce8aee5 (jab-fork lineage 05e81ec): ULOG write side folded into ulog.js (crash-safe _stage temp+rename, monotonic nowAfter, write/ append) + ref writers (createShard/set/tombstone) folded into store.js (was keeper.js). Today at be/shared/{ulog,store}.js; the appender later moved onto the native C ULOG family (abc._ulog_open/_append/_close, an in-place booked append — see the ulog.js header). Unblocked JS-049..051.

JS-048: bin/lib write-side — wtlog appender + refs writer