Add the foundational types for ADR-049 streaming handlers:
- StreamingHandler, ResponseStream type aliases and HandlerKind enum
(Once | Stream) in registration.rs, with make_streaming_handler() helper
- CallError::invalid_operation_type() in wire.rs (sixth protocol code,
retryable: false)
- HandlerRegistration.handler flipped from Handler to HandlerKind;
HandlerRegistration::new() now takes HandlerKind
- OperationRegistryBuilder absorbs wrapping: with_local/with_leaf/
with_leaf_provenance wrap raw Handler in HandlerKind::Once for
Query/Mutation; new with_local_streaming/with_leaf_streaming take a
StreamingHandler and wrap in HandlerKind::Stream for Subscription.
Builder validates kind matches spec.op_type (mismatch = startup error)
- OperationRegistry::register() returns Result<(), String> with a clear
mismatch message; all call sites updated to handle the Result
- invoke() matches on HandlerKind: Once -> existing path; Stream ->
INVALID_OPERATION_TYPE error envelope (guards against silent
truncation; invoke_streaming() added in a downstream task)
- OverlayOperationEnv::invoke_with_policy matches on HandlerKind:
Once -> dispatch; Stream -> INVALID_OPERATION_TYPE (composition is
request/response-only)
- Migrated every HandlerRegistration::new() construction site (~95)
to wrap raw Handler in HandlerKind::Once(handler); the builder sites
are handled by the builder-absorbs-wrapping change
- Updated two websocket subscription tests that relied on Subscription
ops dispatching via invoke() to expect INVALID_OPERATION_TYPE
- Added unit tests for invoke/register validation and
make_streaming_handler
Create crates/alknet-call with Cargo.toml, lib.rs, and module skeletons
for the registry (spec, context, registration, env, discovery) and
protocol (wire, pending, connection, adapter, abort) subsystems. Add the
crate to the workspace members list. Depends on alknet-core (workspace
path), irpc (workspace dep), tokio, serde, serde_json, async-trait,
tracing, thiserror, uuid, and futures. Implements ProtocolHandler on
ALPN alknet/call per docs/architecture/crates/call.
