Flake: oracle corpus case fails once with "I/O error: No such file or directory" applying a rule in the subscription group engine #401

Seen once on 2026-10-06 in a local make unit-test run (devbox, lean debug build, branch fm/t-bundle-b on top of 2ed4a4a; the oracle changes on that branch add a corpus pack and an optional adapter, not this path):

iql_corpus_agrees_with_spec_and_reference panicked at tests/differential_oracle/corpus.rs:333:5:
1 divergences:
examples/iql/14_aggregations/16_empty_agg_edge_cases.iql.out: Outcome divergence in 'subscription[group]' vs 'recompute' at `+empty_avg(avg<V>) <- filtered(_, V)` (revision 5): Rejected("I/O error: No such file or directory (os error 2)"), baseline Applied

The subscription[group] adapter's engine (its own Handler on a private /dev/shm data directory, tests/differential_oracle/engine.rs) refused a persistent-rule insert with ENOENT, while the recompute engine applied it. Another oracle run (INPUTLAYER_ORACLE_VIEWS=maintained, which panics on startup) was running at the same time on the host, but no oracle path is shared between processes. Four reruns of the oracle and a full rerun of the suite passed.

An ENOENT on a rule commit points at a persistence write whose file or directory went missing under it (a temp file renamed twice, or a directory created lazily by another thread). Per the flake policy in TESTING.md: find the write that can see ENOENT, or mark the case Reproduction::Racy with this issue until it is fixed.