docs(architecture): add ADR-022, resolve OQ-23 — handler registration, provenance, and composition authority

ADR-022 wires the three controls ADR-015 specified but left without
registration paths (C1-C4 from review #001): composition authority,
scoped env, and capabilities now enter through a HandlerRegistration
bundle. Provenance (Local, FromOpenAPI, FromMCP, FromCall, Session)
determines which ops can compose — leaves don't get composition
authority. CompositionAuthority replaces handler_identity: Identity
(it's a declared authority bundle, not a peer identity). Capabilities
are per-request from the bundle (resolves closure-capture vs context
ambiguity). Kernel/user analogy: user's authority checked at External
gate; handler's composition authority used inside; scoped env bounds
reachability.

Also fixes W1 (stale ADR-020 path example) and W3 (from_mcp missing
from adapter lists in operation-registry.md).

Spec updates: operation-registry.md (OperationRegistry,
HandlerRegistration, OperationContext, OperationEnv, registration
example, capability injection), call-protocol.md (build_root_context),
README.md, overview.md, open-questions.md (OQ-23), call/README.md.

docs/architecture/decisions/020-hd-derivation-for-encryption-keys.md

@@ -67,9 +67,10 @@ credential encryption:
    decrypting multiple credentials at startup.
 
 4. **Domain separation via paths.** Different encryption purposes can use
-   different derivation paths (`m/74'/2'/0'/0'` for v1, `m/74'/2'/1'/0'`
-   for a future v2). PBKDF2 has no equivalent — the only versioning knob is
-   the iteration count or the password.
+   different derivation paths (`m/74'/2'/0'/0'` for v2, `m/74'/2'/0'/1'`
+   for a future v3). PBKDF2 has no equivalent — the only versioning knob is
+   the iteration count or the password. See ADR-021 for the version-indexed
+   path scheme.
 
 5. **The salt becomes unnecessary for key derivation.** HD derivation
    doesn't need a salt — the path provides domain separation. The salt