fix(sdk): enable rustls' ring provider and install it in the init path

GREEN. rustls 0.23 selects its CryptoProvider from its own 'ring' /
'aws-lc-rs' crate features. Arti reaches rustls through tor-rtcompat with
default-features = false and nothing in this workspace turned a provider
feature on, so rustls was compiled with zero providers and the first TLS
config built from the process default panicked:

    Could not automatically determine the process-level CryptoProvider from
    Rustls crate features. ...

That is the 'Failed to start' screen on the unlock path. The 'ring' crate
being present in the graph (via snow, for Noise) never had anything to do
with it.

'ring', not 'aws-lc-rs': aws-lc-rs wants CMake and a C toolchain for the
NDK and fights the cross-compile.

Belt and braces: open_wire() now calls install_crypto_provider() before
Node::start_with_passphrase, a OnceLock-guarded
ring::default_provider().install_default() with the already-installed Err
ignored. That keeps the cdylib correct regardless of how a consumer's
feature graph resolves rustls.

aws-lc-rs is absent from the lock, so there is no two-provider conflict to
report.

Evidence:
  cargo test --release --test provider_resolution
    before: panicked at rustls-0.23.44/src/crypto/mod.rs:249 (device message)
    after:  1 passed
  cargo tree -f '{p} [{f}]' -p rustls
    rustls v0.23.44 [log,logging,ring,std,tls12]

crates/onionwire-sdk/Cargo.lock

@@ -3588,6 +3588,7 @@ checksum = "6725596c3f2c3a0aef021139e145d4eafe314a6623e4680ca83852b2c67ab2ba"
 dependencies = [
  "log",
  "once_cell",
+ "ring",
  "rustls-pki-types",
  "rustls-webpki",
  "subtle",

crates/onionwire-sdk/Cargo.toml

@@ -35,11 +35,14 @@ tokio = { version = "1", features = ["rt-multi-thread", "time"] }
 # rustls 0.23 resolves its provider from its OWN `ring` / `aws-lc-rs` features,
 # never from whichever crypto crates happen to be linked in the graph. Arti
 # pulls rustls in through `tor-rtcompat` with `default-features = false`, so
-# unless this crate turns a provider feature on, rustls compiles with zero
-# providers and the first TLS config built from the process default fails at
-# runtime. (Currently: no provider feature — see the regression test in
-# `tests/provider_resolution.rs`.)
-rustls = { version = "0.23", default-features = false }
+# without this line rustls compiles with zero providers and the first TLS config
+# built from the process default fails at runtime — the "Failed to start /
+# Could not automatically determine the process-level CryptoProvider" screen.
+#
+# `ring`, not `aws-lc-rs`: aws-lc-rs needs CMake and a C toolchain for the NDK
+# and fights the Android cross-compile. The `ring` crate was already in the
+# graph (via `snow`, for Noise) but that is a different thing entirely.
+rustls = { version = "0.23", default-features = false, features = ["ring"] }
 uniffi = { version = "0.32", features = ["cli", "tokio"] }
 thiserror = "2"
 

crates/onionwire-sdk/src/lib.rs

@@ -17,13 +17,38 @@
 //! no TUI/ratatui type leaks into the AAR.
 
 use std::path::PathBuf;
-use std::sync::Arc;
+use std::sync::{Arc, OnceLock};
 
 use onionwire::node::Node;
 use onionwire::qr;
 
 uniffi::setup_scaffolding!();
 
+/// Install rustls's process-level default `CryptoProvider`, exactly once.
+///
+/// Belt and braces. `Cargo.toml` pins `rustls` with the `ring` feature, which
+/// is what actually fixes the missing-provider failure: with it, rustls
+/// resolves a provider from crate features on its own. This function exists
+/// because the cdylib is loaded into a process we do not own — an explicitly
+/// installed provider makes the SDK independent of how the surrounding app's
+/// feature graph happens to resolve rustls.
+///
+/// Idempotent and cheap after the first call (`OnceLock` short-circuits it).
+/// An `Err` means some provider is already installed process-wide, which is the
+/// outcome we want, so it is deliberately ignored — including the case of a
+/// consumer that installed `aws-lc-rs` itself. A genuine *conflict* — both
+/// provider features compiled in — is a build-graph bug, not something to
+/// paper over here; `Cargo.toml` enables `ring` only.
+///
+/// Not exported over UniFFI: it is Rust-side plumbing, not part of the Kotlin
+/// surface.
+pub fn install_crypto_provider() {
+    static INSTALLED: OnceLock<()> = OnceLock::new();
+    INSTALLED.get_or_init(|| {
+        let _ = rustls::crypto::ring::default_provider().install_default();
+    });
+}
+
 #[derive(Debug, thiserror::Error, uniffi::Error)]
 #[uniffi(flat_error)]
 pub enum WireError {
@@ -88,6 +113,10 @@ pub struct Wire {
 /// that is minutes, not seconds. Call it off the main thread.
 #[uniffi::export(async_runtime = "tokio")]
 pub async fn open_wire(home: String, passphrase: String) -> WResult<Arc<Wire>> {
+    // Before anything that can build a TLS config: Arti's rustls backend dies
+    // with "Could not automatically determine the process-level CryptoProvider"
+    // if no provider is resolvable. See `install_crypto_provider`.
+    install_crypto_provider();
     let node = Node::start_with_passphrase(PathBuf::from(home), &passphrase)
         .await
         .map_err(WireError::new)?;

crates/onionwire-sdk/tests/init_provider.rs

@@ -0,0 +1,30 @@
+//! `open_wire` must not depend on how the consumer's feature graph resolves a
+//! rustls provider — it installs the process default itself, first.
+//!
+//! This is the belt-and-braces half of the fix for the on-device "Failed to
+//! start / Could not automatically determine the process-level CryptoProvider"
+//! screen; the primary fix is the `rustls` `ring` feature in `Cargo.toml`,
+//! covered by `tests/provider_resolution.rs`. Kept in its own test binary on
+//! purpose: installing a provider here would mask that test if they shared a
+//! process.
+
+#[test]
+fn sdk_installs_the_process_default_provider() {
+    assert!(
+        rustls::crypto::CryptoProvider::get_default().is_none(),
+        "this test must start with no provider installed"
+    );
+
+    onionwire_sdk::install_crypto_provider();
+
+    assert!(
+        rustls::crypto::CryptoProvider::get_default().is_some(),
+        "install_crypto_provider() left the process without a default provider"
+    );
+
+    // Second call: idempotent, not a panic and not an error.
+    onionwire_sdk::install_crypto_provider();
+
+    // The call Arti makes that blew up on device.
+    let _ = rustls::ClientConfig::builder();
+}