Salvage round on the Phase 1 skeleton (three findings from review):
1. The DELETE leg was silently upgraded to WAL on healthy SQLite:
pre-seeding the file via PRAGMA was undone by SessionDB.__init__'s
apply_wal_with_fallback(), which upgrades any non-WAL file whenever
the configured mode (default wal) says so — only WAL-reset-vulnerable
interpreters preserved DELETE, i.e. the leg tested the advertised
mode only where CI wasn't running. Each matrix leg now pins
database.journal_mode in an isolated HERMES_HOME for the child and
audits the ON-DISK mode after the run (effective_mode_or_skip):
a leg that ran in a different mode skips instead of double-counting.
2. Cell 2 exit-code conflation: a claimant crashing with an unhandled
exception exits 1 — indistinguishable from the clean "lost the
claim" exit(1), so one winner + seven crashes passed as consume-once
proof. Codes are now disjoint (0=won, 10=lost, anything else=crash).
3. Crashed-writer diagnostics: wait_for now fails immediately with the
child's stderr when the writer dies before reaching the kill window
(was: 60s opaque deadline, stderr discarded). spawn_child prepends
to an inherited PYTHONPATH instead of clobbering it.
Plus: dead `if False` scaffolding removed from cell 1's writer; README
matrix section corrected (cell 2 is default-mode-only by design — the
consume-once property rests on a single predicated UPDATE).
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