docs(architecture): add ADR-017 call protocol client and adapter contract, resolve OQ-15

ADR-017 locks the client/adapter architecture:
- CallClient opens QUIC connections, shares dispatch loop with CallAdapter
- Connection direction independent of call direction (both sides can call)
- from_call adapter: discovers remote ops via services/list + services/schema,
  registers with forwarding handlers (same pattern as from_openapi/from_mcp)
- to_openapi/to_mcp: project local ops to external protocols
- OperationAdapter trait: produces (OperationSpec, Handler) pairs
- Cross-node call tree: abort cascade propagates through from_call handlers
- Credentials from capabilities (ADR-014), adapter ops Internal by default (ADR-015)

The dispatch POC at /workspace/@alkdev/dispatch demonstrated head/worker over
SSH+axum; under the call protocol it's cross-node composition via from_call.
Connection topology (who advertises, who opens) is independent of call
direction — runner pattern, dispatch pattern, and P2P all work.

docs/architecture/README.md

@@ -1,15 +1,15 @@
 ---
 status: draft
-last_updated: 2026-06-20
+last_updated: 2026-06-21
 ---
 
 # Alknet Architecture
 
 ## Current State
 
-**Pre-implementation.** The project has completed a pivot from a three-layer model to an ALPN-as-service model. The greenfield workspace contains only `alknet-vault` (stable) and research/reference material. Foundational ADRs (001–016) are in place, including the BiStream type definition (ADR-007), vault integration (ADR-008), ALPN router/endpoint (ADR-010), AuthContext structure (ADR-011), call protocol stream model (ADR-012), Rust as canonical implementation language (ADR-013), secret material flow with capability injection (ADR-014), privilege model with authority context (ADR-015), and abort cascade for nested calls (ADR-016). The alknet-core and alknet-call crate specs are in draft.
+**Pre-implementation.** The project has completed a pivot from a three-layer model to an ALPN-as-service model. The greenfield workspace contains only `alknet-vault` (stable) and research/reference material. Foundational ADRs (001–017) are in place, including the BiStream type definition (ADR-007), vault integration (ADR-008), ALPN router/endpoint (ADR-010), AuthContext structure (ADR-011), call protocol stream model (ADR-012), Rust as canonical implementation language (ADR-013), secret material flow with capability injection (ADR-014), privilege model with authority context (ADR-015), abort cascade for nested calls (ADR-016), and call protocol client and adapter contract (ADR-017). The alknet-core and alknet-call crate specs are in draft.
 
-**Next step**: Review alknet-call spec documents, then begin implementation. OQ-11 (handler-level auth resolution observability) and OQ-15 (call protocol client and adapter contract) will be resolved during or before implementation.
+**Next step**: Review alknet-call spec documents, then begin implementation. OQ-11 (handler-level auth resolution observability) will be resolved during implementation.
 
 ## Architecture Documents
 
@@ -46,6 +46,7 @@ last_updated: 2026-06-20
 | [014](decisions/014-secret-material-flow-and-capability-injection.md) | Secret Material Flow and Capability Injection | Accepted |
 | [015](decisions/015-privilege-model-and-authority-context.md) | Privilege Model and Authority Context | Accepted |
 | [016](decisions/016-abort-cascade-for-nested-calls.md) | Abort Cascade for Nested Calls | Accepted |
+| [017](decisions/017-call-protocol-client-and-adapter-contract.md) | Call Protocol Client and Adapter Contract | Accepted |
 
 ## Open Questions
 
@@ -61,6 +62,7 @@ See [open-questions.md](open-questions.md) for the full tracker.
 - **OQ-16**: Safe vault operations for call protocol exposure — none for now (ADR-014)
 - **OQ-18**: Privilege model — `internal` = authority switch, External/Internal visibility, handler identity + scoped env (ADR-015)
 - **OQ-17**: Abort cascade — `call.aborted` cascades to descendants; default `abort-dependents`, `continue-running` opt-in (ADR-016)
+- **OQ-15**: Call protocol client and adapter contract — `CallClient` opens connections; `from_call` imports remote ops; connection direction independent of call direction (ADR-017)
 
 **Resolved two-way doors:**
 - **OQ-04**: Dynamic handler registration — static at startup (ADR-010)
@@ -72,10 +74,6 @@ See [open-questions.md](open-questions.md) for the full tracker.
 **Open two-way doors (resolved during implementation):**
 - **OQ-11**: Handler-level auth resolution observability — decide during implementation
 
-**Open one-way doors (need ADR before implementation):**
-- **OQ-15**: Call protocol client and adapter contract — alknet-call needs both the server (CallAdapter) and client (call invocation over QUIC), plus the adapter contract traits (from_*, to_*) that enable composition. ADR-014 constrains the adapter contract: adapters take credential sources from the assembly layer, not static tokens. ADR-015 constrains: adapter-registered operations are `Internal` by default.
-- **OQ-19**: Session-scoped operation registries — agent-written operations in a quickjs sandbox, overlaid on the global registry via `OperationEnv` trait layering. Protocol doesn't need changes; the one-way door is not closing the trait-based composition point. Promotion from session to core requires curation review.
-
 **Deferred (not active):**
 - **OQ-09**: WASM target boundaries — design constraint, not deliverable
 - **OQ-10**: Git adapter scope — start with smart protocol, add ERC721 later