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/crates/vault/README.md

@@ -1,6 +1,6 @@
 ---
 status: draft
-last_updated: 2026-06-22-25
+last_updated: 2026-06-23
 ---
 
 # alknet-vault
@@ -128,6 +128,8 @@ truth for drift tracking — if an item is fixed in source, update this table.
 | 6 | `HashMap::clear` zeroization | `KeyCache::clear()` removes entries and relies on `CachedKey`'s `Drop` impl for zeroization | Verify `HashMap::clear()` actually drops values (it does, but worth a test) | `cache.rs` | [service.md → Security Constraints](service.md#security-constraints) |
 | 7 | `derive_password` / `site_password_path` | `derive_password`, `derive_password_string`, `site_password_path` methods exist | Remove entirely — password-manager pattern not relevant to RPC system's vault (ADR-025, resolves C9) | `service.rs`, `mnemonic-derivation.rs` | [ADR-025](../../decisions/025-vault-local-only-dispatch.md) |
 | 8 | `unlock_new` return type | Returns `String` (not zeroized on drop) | Return `Zeroizing<String>` — the mnemonic is the root of trust and must not linger in freed memory (resolves W7) | `service.rs` | [service.md → unlock_new](service.md#unlock_newword_count--phrase) |
+| 9 | `key_version` ignored in encrypt/decrypt | `encrypt`/`decrypt` always derive at `PATHS::ENCRYPTION` regardless of `key_version` | Derive at `encryption_path_for_version(key_version)` — encrypt stamps the passed version, decrypt selects the key by the blob's version (ADR-021) | `service.rs` | [service.md → encrypt](service.md#encryptplaintext-key_version--encrypteddata), [ADR-021](../../decisions/021-key-rotation-via-version-indexed-paths.md) |
+| 10 | `rotate` not implemented | No `rotate` method exists | Implement `rotate(encrypted, to_version)` — decrypt with old version's key, re-encrypt with new version's key (ADR-021) | `service.rs` | [service.md → rotate](service.md#rotateencrypted-to_version--encrypteddata), [ADR-021](../../decisions/021-key-rotation-via-version-indexed-paths.md) |
 
 ## Public API
 
@@ -139,9 +141,14 @@ pub use mnemonic::{Language, Mnemonic, Seed};
 
 // Derivation
 pub use derivation::{DerivationError, ExtendedPrivKey, PATHS};
+// Derivation helpers (derive_path_from_seed, parse_derivation_path,
+// device_path, encryption_path_for_version) are accessible as
+// alknet_vault::derivation::* — not re-exported at crate root to avoid
+// clutter, but fully public.
 
 // Encryption
-pub use encryption::{EncryptedData, EncryptionError};
+pub use encryption::{EncryptedData, EncryptionError, EncryptionKey};
+pub use encryption::CURRENT_KEY_VERSION;
 
 // Key types (DerivedKey, KeyType)
 pub use protocol::{DerivedKey, KeyType};