docs(architecture): ADR-002 amendment — the key-algorithm position is ed25519-only
- ADR-002 decision 4 retitled and strengthened per review input: not
'rsa off, ed25519-first' but ed25519-only. Rationale recorded: one
key algorithm carries the family's identity — same ed25519 keys
behind alktls self-signed certs, iroh, and the downstream alknet
rewrite (ssh + ed25519, tcp + tls, quic + tls, iroh); legacy
schemes (rsa/dsa/ecdsa/sk) are issued, stored, or derived nowhere
in the family
- operational consequence: auth_publickey declines non-ed25519 keys
explicitly (ADR-004's explicit-over-inherited pattern), so the
posture survives pin bumps; registration is ed25519-only by family
posture, not assembler choice
- ADR-004: carries the matching dated amendment note; other
dispositions unchanged
- auth.md: disposition summary matches (ed25519-only)
- research/russh.md: pin-question list marked resolved by ADR-002
Verification: cargo test, cargo clippy --all-targets -- -D warnings,
cargo fmt --check — all pass
glm-5.3-flash
ff2d69c67b