Native Iroh client

Build with VGI_RPC_WITH_IROH_CABI=ON and provide the version-matched vgi_iroh.h and vgi_iroh_cabi library. Beginning with the first release after v0.23.3, vgi-rpc-rust releases provide static-library archives for supported native targets. Extract one and pass its prefix as -DVGI_RPC_IROH_CABI_ROOT=/path/to/vgi-iroh-cabi-vX.Y.Z-target. CMake also honors explicit VGI_IROH_CABI_INCLUDE_DIR and VGI_IROH_CABI_LIBRARY values for unpackaged POSIX source builds. When VGI_RPC_IROH_CABI_ROOT is set, discovery is constrained to that prefix and fails closed if its header, library, CMake target, or native link dependencies are incomplete. RpcClient::connect_iroh with native_iroh_transport_provider() then speaks raw vgi-rpc/arrow-mux/1 in-process. The same C ABI also backs HttpClient for httpi:// URLs using iroh-http/2. No executable is downloaded or spawned.

The native provider holds a process-lifetime endpoint pool. Every implicit endpoint instance is derived from one private process-generated key, giving it the same local EndpointId even when relay or timeout settings require another native endpoint instance. Explicit secret_key values remain separate configured identities. remote_relay_url and direct_addresses are per-remote route hints and do not change local endpoint configuration.

Use the ordinary typed HTTP client with an Iroh URL:

vgi_rpc::IrohTransportOptions transport;
transport.remote_relay_url = "https://relay.example";

auto client = vgi_rpc::HttpClient::builder("httpi://<64-hex-endpoint-id>/vgi")
                  .iroh_transport_options(std::move(transport))
                  .build();
auto description = client.describe();

The URI base path is the RPC prefix: /vgi above produces /vgi/health and /vgi/<method> requests, or /vgi/<protocol>/<method> once protocol() names a routing key. A URI without a path uses bare /<method> routes. A later builder prefix() or config() call is an explicit override.

Only the HTTP carrier changes. Capability discovery, request/response size negotiation, Arrow IPC, compression, authentication callbacks, sticky sessions, continuations, typed exchange/producer state, retry gates, and external-location policy all remain in the existing HttpClient state machine. Each request uses a fresh HTTP/1.1 exchange over iroh-http/2, verifies the authenticated remote EndpointId, and bounds response headers and body while reading. CallOptions deadlines and stop tokens are combined with IrohTransportOptions::cancel_check.

httpi:// is already encrypted and mutually authenticates Iroh EndpointIds, so credential headers are allowed without allow_insecure_credentials. TLS settings and TCP SOCKS proxies do not apply and are rejected. The remote worker still decides authorization; when using vgi-iroh-bridge, configure the worker to trust only that adjacent bridge's forwarded-Iroh identity boundary.

Set IrohTransportOptions::cancel_check when a caller needs cooperative cancellation. Native open and write operations use the C ABI cancellation callbacks, while reads poll a bounded native timeout. The callback must be non-blocking; exceptions are treated as cancellation. Raw Arrow I/O failures retain the C ABI stage, category, dispatch certainty, and native message in IrohStatusDetail; HTTP-over-Iroh failures map those dimensions onto the existing HttpClientErrorKind contract.

The installed CMake target links the stable vgi_iroh::cabi target name. The package configuration rediscovers the header and library on the consumer machine, so exported targets contain no build-host archive path. Distributions can place those two artifacts under their own relocatable prefix.