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Architecture Decision Records

Issue: #1197

Records of significant architectural decisions and the reasoning behind them — not a design spec (see Technical design for that) but the why, so a later reader doesn't have to re-derive a decision from scratch or accidentally re-litigate one that was already made deliberately. New ADRs are required for future architectural changes — see blueprint.md for when a change needs a blueprint/plan before code, which is a related but distinct requirement.

Use template.md for new entries. Number sequentially; never edit a published ADR's decision after the fact — if a decision changes, write a new ADR and mark the old one "Superseded by ADR-NNNN."

ADR Decision
0001 Cedar as the policy engine
0002 SQLite as the default storage backend (Postgres at scale)
0003 aegis-jcs-1 canonicalization scheme for action_hash
0004 Ed25519 for optional receipt signing
0005 Fail-closed defaults for unknown/ambiguous state