Compaction re-injects the todo list verbatim (TODO_INJECTION_HEADER +
TodoStore.format_for_injection) while skill instructions are pruned down
to [SKILL_PRUNED: ...] markers — the imperative crosses the boundary
without the policy that governed it, and the agent keeps executing
preserved tasks with the guidance deleted (#84718's T6 pattern).
Close the retention asymmetry at the injection site: when the compressed
transcript carries [SKILL_PRUNED: ...] markers AND a todo snapshot is
being re-injected, append a bounded reload notice to the snapshot naming
each pruned skill with its exact skill_view() reload call, plus a
one-line instruction to re-check that preserved tasks are still
justified. Skill guidance recovery now travels in the SAME boundary
artifact as the imperative — same message, same stale-snapshot strip
lifecycle, so repeated compactions refresh rather than accumulate.
Properties:
- deterministic: derived only from the compressed transcript (same input,
same bytes) — no per-turn nondeterminism in the rebuilt prompt
- zero recurring cost when nothing was pruned (clean sessions unchanged)
- bounded: shares _MAX_PRUNED_SKILL_MARKERS with the summary re-injection
cap; the notice text never contains the canonical marker prefix, so it
can never feed the marker extractor at the next boundary
- rides after TODO_INJECTION_HEADER, so _strip_stale_todo_snapshot
removes snapshot + notice together and the synthetic-row classifier
(_is_synthetic_compression_user_turn) is unaffected
Tests: tests/agent/test_skill_todo_retention_parity.py — unit contract of
the notice builder (naming, dedup/order, cap, determinism, no marker
self-feed) and behavioral compaction runs through the real
_compress_context path (notice travels with the snapshot, absent when
nothing pruned, synthetic-row classification unbroken, strip lifecycle
across repeated boundaries). Sabotage-verified: disabling the append
flips the 3 behavioral tests red.
Part of #84718
7a16840add