adr-backfill

Retroactively records a past architectural decision that was made but never documented. Surfaces typically come from /doc-audit BACKFILL-ADR rows or from a user who realises a past change should have been an ADR. Operates with relaxed gates relative to adr-drafting (the decider may be unrecoverable, alternatives may not be reconstructible) but enforces stricter honesty: a backfill ADR must visibly mark itself as a backfill so future readers do not mistake it for a contemporaneous record.

When to use this skill

• /doc-audit surfaced a BACKFILL-ADR candidate row and the user wants to record it.
• The user describes a decision in past tense — "we decided years ago," "back when," "before my time," "we never wrote it down" — about a change whose effects are visible in the codebase today.
• A code-archaeology session uncovered a migration, vendor removal, or subsystem retirement with no corresponding decision record.

When NOT to use this skill

• The decision is current or in-flight — use adr-drafting instead.
• The decision is already recorded in any form — use adr-critique to tighten the existing record.
• reconstruction-confidence is low (only the what is recoverable, not the why) — refuse to draft and route to open-questions.md.
• The change is not architecturally significant — see _shared/adr-is-backfillable.md § 2. Route via the alternatives catalog in doc-diagnostic.

Inputs