No silent data drop

The ASH 2026-06-04 cluster: user and model content silently vanishing from delivered reports through render gates, model-assigned routing keys, and JSON parse failures — discovered by the recipient, never by the pipeline. Layer: norm + playbook — the one-line norm in the global CLAUDE.md is the everyday trigger; this file is the depth.

The rule

Wherever code can discard data — a filter, a gate, a continue, a catch, a ?? fallback — ask: what happens to the non-matching data? A gate may hide an empty section; it must never drop content. Anything holding content still renders somewhere, and a safe default bucket always beats a drop.

How to apply

• Gates hide empty things only. A property-flag render gate once dropped mis-classified photos from delivered reports for weeks; the fix routes non-matching content to a visible default section instead.
• A parse failure never discards content. A truncated model JSON threw in JSON.parse and five report sections vanished silently. Salvage what can be salvaged, log the stop reason, surface the failure.
• Model-emitted enums, keys, and ids used for routing are untrusted input. Clamp to the canonical vocabulary where the value enters AND again at render (stored rows may hold unclamped values), defaulting unknowns to a visible bucket.
• Two renderers share the grouping function. Hand-synced twins drift, and the divergence masks the loss — one representation kept all photos while the other dropped them, so the audit trail looked complete.
• Verify the delivered artifact (count sections, count photos), and be suspicious of any test that asserts content IS dropped — a passing test once encoded the bug.

What this skill does not do

It does not govern how failures are messaged to the user — that is honest-failure-surfacing. It does not apply to filters over data the user never receives (internal telemetry, debug output).

Why

Dropped content is the worst failure class in a document pipeline because the artifact still ships: everything looks successful, and only the recipient can notice the hole. Evidence: ASH LESSONS_LEARNED 2026-06-04 (all entries) and the CLAUDE.md max_tokens truncation lesson; ICC L-008.

Additions from the misses-log sweep (2026-10-22)

• An ignore rule is a filter too. Before the first commit of new files, compare git status with the files written and run git check-ignore -v on any that is missing; a broad ignore pattern can hide a file meant to ship. (ICC L-101.)