docs(architecture): resolve review #003 — type/API surface completeness

Review #003 found 11 critical, 14 warning, and 6 suggestion findings
after reviews #001 (governance/security) and #002 (cross-document
consistency/two-way-door audit) were resolved. The theme: types and
APIs that were *referenced* but never *defined*, and stale ADR sketches
that didn't match the now-updated spec docs.

Critical fixes (11):

- C1: DerivedKey #[derive(Deserialize)] contradicted the custom
  Deserialize that rejects "[REDACTED]" — dropped the derive, added
  explicit manual Serialize/Deserialize impls (protocol.md).
- C2: encrypt prose said "derived at PATHS::ENCRYPTION" but the
  signature takes key_version — updated to encryption_path_for_version
  (service.md).
- C3: derive_encryption_key returned DerivedKey, derive_encryption_key
  _for_version returned EncryptionKey (same cache) — unified on
  DerivedKey, defined CachedKey (service.md).
- C4: tokio vs std::sync::RwLock contradiction — specified
  std::sync::RwLock, dropped tokio from vault deps (ADR-018, ADR-025,
  service.md).
- C5: Missing drift rows in vault README — added #9 (key_version
  ignored) and #10 (rotate not implemented).
- C6: ADR-022 build_root_context and invoke() sketches omitted
  abort_policy (9 fields vs 10) — added the field to both sketches.
- C7: Capabilities type referenced 20+ times, never defined — added
  struct definition to core-types.md with Clone+Send+Sync, Zeroize,
  sealed builder API, immutability guard.
- C8: SessionOverlaySource on CallAdapter but never defined, crate
  violation (alknet-call can't depend on alknet-agent) — defined the
  trait in alknet-call (call-protocol.md), matching the IdentityProvider
  pattern.
- C9: CompositeOperationEnv dispatch fall-through was "a two-way door"
  — added contains() to OperationEnv trait, made the composite probe
  before dispatching, eliminating the sentinel ambiguity.
- C10: No API for Layer 2 (connection overlay) registration, CallConnection
  undefined — defined CallConnection struct + register_imported() API
  (call-protocol.md).
- C11: with_local signature diverged between two examples (4 args vs 5)
  — added capabilities as the 5th arg, made both examples consistent.

Warning fixes (14):

- W1: invoke_with_policy restructured as required method, invoke gets a
  default impl delegating to it — eliminates duplication across impls.
- W2: CachedKey defined (service.md).
- W3: EncryptionKey constructor/glue specified, added to re-export list.
- W4: Secp256k1ExtendedPrivKey defined, derive_ethereum_key glue shown.
- W5: encryption_path_for_version rejects version < 2 (v1 is TS PBKDF2).
- W6: Wire payload schemas for all event types + ResponseEnvelope →
  EventEnvelope conversion table (call-protocol.md).
- W7: Timeout section — deadline on OperationContext, composed calls
  inherit parent's deadline, CallAdapter::with_timeout().
- W8: Request ID generation spec — UUID v4 for composed calls, wire ID
  vs internal ID relationship for abort cascade.
- W9: unlock_new already-unlocked behavior specified (returns
  AlreadyUnlocked).
- W10: KeyType Serialize/Deserialize justification corrected (stale
  irpc reference removed).
- W11: OperationProvenance and CompositionAuthority defined inline in
  operation-registry.md (were only in ADR-022).
- W12: encrypt/decrypt free functions marked pub(crate), relationship
  to VaultServiceHandle methods stated.
- W13: rotate signature removed from encryption.md (it's a
  VaultServiceHandle method, not a free function).
- W14: CallAdapter::new() + with_session_source() + with_timeout()
  constructors shown.

Suggestion fixes (6): Seed: Clone note, VaultServiceInner invariant,
ExtendedPrivKey accessor signatures, CURRENT_KEY_VERSION location, ADR-018
stale actor text, derivation helpers re-export note.

docs/architecture/decisions/025-vault-local-only-dispatch.md

@@ -164,11 +164,12 @@ auth-wrapping handler, and the operation filtering (Unlock/Lock local-only).
 ### 5. The vault's dependency footprint shrinks
 
 The vault drops: `irpc`, `irpc-derive`, `postcard` (for remote), `noq`
-(via irpc), `iroh` (via irpc-iroh). It retains: `bip39`, `ed25519-bip32`,
-`aes-gcm`, `sha2`, `hmac`, `secp256k1` (feature-gated), `tokio` (for
-`RwLock` sync primitives, not for channels), `serde` (for `DerivedKey`
-redaction and `EncryptedData` wire format), `zeroize`, `thiserror`, `base64`,
-`rand`.
+(via irpc), `iroh` (via irpc-iroh), and `tokio` (the actor's
+`tokio::sync::mpsc` channels are gone; all vault methods are synchronous
+and use `std::sync::RwLock` for thread safety). It retains: `bip39`,
+`ed25519-bip32`, `aes-gcm`, `sha2`, `hmac`, `secp256k1` (feature-gated),
+`serde` (for `DerivedKey` redaction and `EncryptedData` wire format),
+`zeroize`, `thiserror`, `base64`, `rand`.
 
 ADR-018's "zero alknet crate dependencies" becomes "zero alknet crate
 dependencies and zero RPC framework dependencies." This is the cleanest