Land the webrtc framer transport crate (D2)

Cargo.toml

@@ -25,6 +25,7 @@ members = [
     "crates/plugin-loader",
     "crates/store-memory",
     "crates/busbar-transport-stdio",
+    "crates/busbar-transport-webrtc",
     "testing/ws-conformance/subject",
     "xtask",
 ]
@@ -158,6 +159,15 @@ crc32fast = "1"
 # DTLS for the connector's dtls engine (WebRTC), on ring through the connector's own provider:
 # no default features, so neither aws-lc-rs nor the RustCrypto suite enters.
 dimpl = { version = "=0.7.4", default-features = false }
+# THE WEBRTC FRAMER's media stack (busbar-transport-webrtc; ARCHITECT WEBRTC spike GO and D2 approval,
+# THE DESIGN l.756-765): ICE, SRTP and SCTP, sans-IO. No default features: no aws-lc-rs, no OpenSSL,
+# no example server; the framer installs its own crypto provider on ring and a host shim in place of
+# str0m's DTLS (the framer holds no DTLS state).
+str0m = { version = "=0.24.1", default-features = false }
+# THE ONE EXCEPTION TO ring-ONLY (THE DESIGN l.759-761, QUESTIONS Q101): ring has no raw AES block, and
+# the SRTP key derivation (RFC 3711 §4.3, RFC 7714 §11) is AES in counter mode over 16-byte blocks.
+# aes/cipher/inout enter for that derivation alone; a dependency-closure test confines them to it.
+aes = { version = "0.8", default-features = false }
 # THE MICROBENCHMARK HARNESS. Dev-only, and deliberately stripped: `default-features = false` drops
 # criterion's plotting stack (plotters, its font/image chain) and its rayon thread pool, keeping
 # `cargo_bench_support` — the part `cargo bench` actually needs to run a `harness = false` target.

crates/busbar-contract/tests/reserved_keys_and_closed_codes.rs

@@ -117,12 +117,12 @@ fn a_composition_refusal_says_which_transport_and_which_layer() {
     // Each of the three is read by a human at boot, off a node that will not start. A refusal that
     // rendered as nothing would leave the operator with an exit code.
     let unregistered = CompositionError::UnregisteredLayer {
-        transport: "webrtc",
+        transport: "dgram",
         layer: "udp",
     };
     let rendered = unregistered.to_string();
     assert!(
-        rendered.contains("webrtc") && rendered.contains("udp"),
+        rendered.contains("dgram") && rendered.contains("udp"),
         "{rendered}"
     );
     assert!(rendered.contains("no registered transport"), "{rendered}");

crates/busbar-contract/tests/transport_registry.rs

@@ -49,12 +49,12 @@ fn the_real_stack_boots() {
 fn a_declared_layer_that_nothing_registered_refuses_the_boot() {
     let registry = [
         declared("tcp", &[], None),
-        declared("webrtc", &["udp"], None),
+        declared("dgram", &["udp"], None),
     ];
     assert_eq!(
         check_composition(&registry),
         Err(CompositionError::UnregisteredLayer {
-            transport: "webrtc",
+            transport: "dgram",
             layer: "udp",
         })
     );

crates/busbar-core-connector/src/dtls/mod.rs

@@ -11,7 +11,7 @@
 //!
 //! # One UDP port, three protocols (RFC 7983 §7)
 //!
-//! A WebRTC association multiplexes STUN, DTLS and SRTP on one 5-tuple. [`classify`] splits them by
+//! A media association multiplexes STUN, DTLS and SRTP on one 5-tuple. [`classify`] splits them by
 //! the first byte, and [`Association::ingest`] is the record layer's host side:
 //!
 //! * **STUN** goes up the raw lane to the framer's ICE agent — except the answers to core's own
@@ -86,7 +86,7 @@ pub const CONSENT_TIMEOUT: Duration = Duration::from_secs(30);
 /// How long a probe is awaited before a heard path is probed again.
 const PROBE_RETRY: Duration = Duration::from_millis(500);
 
-/// What one datagram on a WebRTC port is (RFC 7983 §7).
+/// What one datagram on a media port is (RFC 7983 §7).
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]
 pub enum Class {
     /// First byte 0–3: STUN.
@@ -242,7 +242,7 @@ pub enum Up {
     Connected,
     /// The exported SRTP keying material.
     Keyed(SrtpKeying),
-    /// Decrypted DTLS application data (SCTP, for WebRTC).
+    /// Decrypted DTLS application data (SCTP, for the data channels).
     Plaintext(Vec<u8>),
     /// The peer closed the DTLS session.
     Closed,
@@ -284,7 +284,7 @@ pub enum Bind {
     WhenProven,
 }
 
-/// One WebRTC association's DTLS engine and demux.
+/// One media association's DTLS engine and demux.
 pub struct Association {
     cert: Arc<SessionCert>,
     role: Role,
@@ -467,7 +467,7 @@ impl Association {
         self.bound == Some(path)
     }
 
-    /// Seal `plaintext` (SCTP, for WebRTC) as DTLS application data toward the bound path.
+    /// Seal `plaintext` (SCTP, for the data channels) as DTLS application data toward the bound path.
     ///
     /// # Errors
     ///

crates/busbar-core-connector/src/dtls/ring.rs

@@ -16,7 +16,7 @@
 //!   exactly the record-number mask for ChaCha20 (dimpl checks its first 5 bytes), so
 //!   `TLS_CHACHA20_POLY1305_SHA256` is offered to satisfy it. The AES-GCM 1.3 suites need a full
 //!   16-byte AES-ECB block, which ring does not expose. Associations are built DTLS 1.2
-//!   (`Dtls::new_12`), the version every browser's WebRTC stack speaks.
+//!   (`Dtls::new_12`), the version every browser's media stack speaks.
 
 use dimpl::crypto::{
     Aad, ActiveKeyExchange, Buf, Cipher, CryptoProvider, Dtls12CipherSuite, Dtls13CipherSuite,

crates/busbar-core-connector/src/lib.rs

@@ -16,7 +16,7 @@
 //! * [`guard`] is THE DESTINATION GUARD, the one check deciding which addresses any outbound
 //!   connection may be dialled at (private refused unless allowlisted, metadata always).
 //! * [`tls`] is connection security — core-only, never a plugin, never crossing the ABI.
-//! * [`dtls`] is its datagram sibling — the DTLS engine a WebRTC association runs on (the RFC 7983
+//! * [`dtls`] is its datagram sibling — the DTLS engine a media association runs on (the RFC 7983
 //!   demux, the ICE-gated bind, the SRTP exporter), on ring like [`tls`].
 //! * [`udp`] is the host's datagram socket: one bound port, a peer per datagram.
 //!

crates/busbar-core-connector/src/udp.rs

@@ -5,7 +5,7 @@
 //! binds one. The stream carriers are a separate path: a datagram has
 //! a peer per read and no connection, so it is never folded into the stream socket types.
 //!
-//! One bound port serves every WebRTC association on it: each read answers the datagram AND the
+//! One bound port serves every media association on it: each read answers the datagram AND the
 //! peer it came from, each write names the peer it goes to, and the dtls engine
 //! ([`crate::dtls`]) demultiplexes by path. Nothing here waits: a read or write that would block
 //! answers `None`, and the caller waits on the socket's read/write readiness — the per-worker