docs(architecture): add ADR-025 — vault local-only dispatch, drop irpc

Drops irpc from alknet-vault entirely. The vault's dispatch is now direct
method calls on VaultServiceHandle — no VaultProtocol enum, no
VaultMessage, no VaultServiceActor, no mpsc channel, no Service trait, no
RemoteService trait, no postcard serialization. The vault is local-only by
construction.

The core security argument: irpc made the vault remote-capable by default
(RemoteService generated unless no_rpc is passed). The IrohProtocol handler
forwards all messages without auth. The docs framed 'register an ALPN' as a
server-setup change. This is the default-insecure anti-pattern — security
should be opt-in, not opt-out. ADR-025 inverts the default: local-only is
the only mode, and remote access requires building a separate vault-server
crate (a visible architectural act, not a flag flip).

The actor path was already dead code — service.md said 'prefer
VaultServiceHandle directly — no channel, no serialization.' The actor
existed only to make irpc's Service trait work, which existed only to make
RemoteService work, which was the footgun. VaultServiceHandle's
Arc<RwLock> provides concurrent reads and exclusive writes — better
throughput than the actor's sequential processing.

DerivedKey serialization simplifies: always redact on serialize (for
logging safety), reject '[REDACTED]' on deserialize with an error. No
'postcard preserves bytes' path. This resolves review #002 W8 (silent
corruption on JSON-deserialized DerivedKey).

Resolves:
- OQ-21: remote vault access — resolved (not deferred). Not a vault crate
  feature; if needed, a separate vault-server crate with its own ADR.
- C7: vault-server-crate question decided — not created now, not precluded.
- C8: operation access policy table dissolved — all operations local-only
  by default; if a vault-server crate exposes some remotely, that crate
  defines the policy.
- W8: DerivedKey JSON deserialization — resolved (reject redacted payloads).

Amends ADR-005 (irpc remains for alknet-call, not for alknet-vault),
ADR-018 (vault is even more standalone — zero RPC framework deps),
ADR-019 (vault is the only layer, not just the only direct-caller layer),
ADR-008 (vault integration point unchanged, but now local-only by
construction).

docs/architecture/decisions/008-secret-service-integration.md

@@ -6,11 +6,11 @@ Accepted
 
 ## Context
 
-alknet-vault (formerly alknet-secret) is a standalone crate with zero alknet crate dependencies. It provides BIP39 mnemonic generation, SLIP-0010 Ed25519 HD key derivation, AES-256-GCM encryption, and an irpc-based `VaultProtocol` for message dispatch. It is already implemented and stable.
+alknet-vault (formerly alknet-secret) is a standalone crate with zero alknet crate dependencies and zero RPC framework dependencies (ADR-025). It provides BIP39 mnemonic generation, SLIP-0010 Ed25519 HD key derivation, AES-256-GCM encryption, and a direct-method-call API (`VaultServiceHandle`). It is already implemented and stable, pending the ADR-025 refactor to drop irpc.
 
 The question (OQ-08) was: how does the rest of the alknet system access alknet-vault's capabilities? The options were:
 
-1. **irpc service over `alknet/call`**: Other services call vault operations through the call protocol.
+1. **Call protocol exposure**: Other services call vault operations through the call protocol.
 2. **ALPN handler on `alknet/secret`**: alknet-vault implements ProtocolHandler and gets its own ALPN.
 3. **Direct library dependency**: alknet-core or handler crates depend on alknet-vault directly, breaking its independence.
 4. **CLI-embedded with call protocol exposure**: The CLI binary instantiates VaultServiceHandle locally and registers vault operations in the call protocol's registry.
@@ -64,9 +64,9 @@ This is analogous to the reverse-proxy admin key pattern (ADR-028 in the reverse
 ## References
 
 - ADR-003: Crate decomposition (alknet-vault is standalone)
-- ADR-005: irpc as call protocol foundation
+- ADR-005: irpc as call protocol foundation (for alknet-call; the vault no longer uses irpc — see ADR-025)
 - ADR-009: One-way door decision framework
 - ADR-014: Secret material flow and capability injection (specifies the mechanism this ADR described in prose)
+- ADR-025: Vault local-only dispatch (dropped irpc from the vault; direct method calls only)
 - OQ-08: Secret service integration point (resolved by this ADR, refined by ADR-014)
-- alknet-vault implementation: `crates/alknet-vault/`
-- Reverse-proxy ADR-028: Admin HTTP API (analogous key management pattern)
+- alknet-vault implementation: `crates/alknet-vault/`