docs: record transaction.rs decomposition status — StagingTxn deferred (I141)

[Xof]

Records the disposition of the 2026-06-22 review's transaction.rs god-module finding (SMELL) as ISSUES.md I141.

The decomposition was worked through four behavior-preserving unit extractions — SlotPacker (#77), FreemapRecycle (#78), CommitProtocol (#79), FaultInjector (#76) — and then deliberately stopped. The planned final StagingTxn extraction is deferred: the candidate-prepare/install staging vocabulary (handle_table_insert_candidate, membership_*_candidate, abort_allocate_prepare, inject_membership_failure, insert_into_data_page) is shared across allocate_inner (staging.rs) and update_inner/delete_inner (mutate.rs), so a context-based extraction can't be contained to staging.rs without dragging the most delicate mutation paths + packing through a mechanical wrapper change for little cohesion gain. staging.rs is already a focused concern file.

Future work: fold the shared vocabulary into a StagingTxn unit incrementally if/when those paths are touched for a real reason — not re-triggered from the SMELL alone.

Docs-only; no code change.

[github-actions]

🚦 Bench results: PR vs main

✅ No regressions detected

Scenario	Mode	Δ throughput	Worst Δ
document-store	chisel-mem	-0.3%	—
document-store	chisel-strict	-0.9%	—
document-store	redb-strict	-0.0%	—
document-store	sqlite-strict	-0.3%	—
mutation-log	chisel-mem	+0.6%	—
mutation-log	chisel-strict	+1.1%	—
mutation-log	redb-strict	+0.2%	—
mutation-log	sqlite-strict	+0.3%	—
ycsb-a	chisel-mem	+2.0%	—
ycsb-a	chisel-strict	+4.4%	—
ycsb-a	redb-strict	-0.0%	—
ycsb-a	sqlite-strict	+1.2%	—
ycsb-b	chisel-mem	+3.6%	—
ycsb-b	chisel-strict	+3.6%	—
ycsb-b	redb-strict	+0.4%	—
ycsb-b	sqlite-strict	+1.6%	—

Per-scenario detail (4 metrics × cells)

document-store

Mode	Throughput	p50	p95	p99
chisel-mem	19003 ops/s → 18942 ops/s (-0.3%)	14.7 µs → 14.7 µs (+0.3%)	136.2 µs → 135.6 µs (-0.4%)	650.0 µs → 658.2 µs (+1.3%)
chisel-strict	3047 ops/s → 3020 ops/s (-0.9%)	22.7 µs → 22.6 µs (-0.2%)	786.8 µs → 799.9 µs (+1.7%)	2.89 ms → 2.83 ms (-2.2%)
redb-strict	3997 ops/s → 3996 ops/s (-0.0%)	12.1 µs → 12.0 µs (-0.7%)	444.2 µs → 441.7 µs (-0.6%)	1.31 ms → 1.30 ms (-1.0%)
sqlite-strict	5147 ops/s → 5133 ops/s (-0.3%)	21.1 µs → 21.3 µs (+0.9%)	323.1 µs → 333.9 µs (+3.3%)	1.27 ms → 1.32 ms (+3.7%)

mutation-log

Mode	Throughput	p50	p95	p99
chisel-mem	53031 ops/s → 53355 ops/s (+0.6%)	22.7 µs → 22.5 µs (-0.9%)	26.2 µs → 26.2 µs (-0.2%)	35.1 µs → 34.9 µs (-0.5%)
chisel-strict	1792 ops/s → 1812 ops/s (+1.1%)	286.9 µs → 282.6 µs (-1.5%)	589.9 µs → 576.1 µs (-2.4%)	20.92 ms → 20.89 ms (-0.1%)
redb-strict	1805 ops/s → 1808 ops/s (+0.2%)	139.1 µs → 136.6 µs (-1.8%)	214.4 µs → 204.8 µs (-4.5%)	35.33 ms → 35.71 ms (+1.1%)
sqlite-strict	5068 ops/s → 5083 ops/s (+0.3%)	92.8 µs → 92.4 µs (-0.4%)	256.5 µs → 254.5 µs (-0.8%)	327.7 µs → 317.1 µs (-3.3%)

ycsb-a

Mode	Throughput	p50	p95	p99
chisel-mem	38054 ops/s → 38824 ops/s (+2.0%)	41.2 µs → 40.7 µs (-1.2%)	58.1 µs → 56.1 µs (-3.5%)	81.2 µs → 78.3 µs (-3.6%)
chisel-strict	2288 ops/s → 2389 ops/s (+4.4%)	250.1 µs → 247.4 µs (-1.1%)	676.4 µs → 623.0 µs (-7.9%)	993.9 µs → 768.9 µs (-22.6%)
redb-strict	2682 ops/s → 2682 ops/s (-0.0%)	113.7 µs → 113.6 µs (-0.1%)	184.1 µs → 186.9 µs (+1.5%)	275.3 µs → 279.2 µs (+1.4%)
sqlite-strict	131886 ops/s → 133524 ops/s (+1.2%)	7.7 µs → 7.7 µs (-0.9%)	10.2 µs → 10.1 µs (-0.8%)	11.8 µs → 11.7 µs (-1.3%)

ycsb-b

Mode	Throughput	p50	p95	p99
chisel-mem	164764 ops/s → 170719 ops/s (+3.6%)	4.6 µs → 4.5 µs (-2.8%)	42.9 µs → 41.1 µs (-4.2%)	48.5 µs → 46.1 µs (-4.9%)
chisel-strict	22128 ops/s → 22917 ops/s (+3.6%)	6.7 µs → 6.6 µs (-2.1%)	252.8 µs → 255.0 µs (+0.9%)	596.2 µs → 580.2 µs (-2.7%)
redb-strict	26793 ops/s → 26888 ops/s (+0.4%)	3.1 µs → 3.0 µs (-0.7%)	115.0 µs → 114.3 µs (-0.5%)	176.2 µs → 173.4 µs (-1.6%)
sqlite-strict	159611 ops/s → 162187 ops/s (+1.6%)	6.3 µs → 6.2 µs (-1.3%)	8.5 µs → 8.3 µs (-1.5%)	10.8 µs → 10.7 µs (-0.9%)

_{Generated by chisel-bench-diff at 2026-06-23T05:34:21Z. Compares PR HEAD against main. Never blocks merge — signal, not gate. Thresholds: throughput 5%, p50 5%, p95 10%, p99 10%.}