Module crypto/tls

TLS client streams over OpenSSL — plans/archive/D6_TLS_PLAN.md (the O2 decision: one TlsStream implementing the D5 Reader/Writer traits).

On unix targets this requires OpenSSL 1.1.1+/3.x at BUILD time: the compiler probes pkg-config openssl (with Homebrew keg fallbacks) and adds the include and link flags; without it, importing this module fails at the C step with the linker naming the missing library. Windows needs no OpenSSL — it gets a Schannel/SSPI backend behind the same fifteen __yo_tls_* functions (shipped in v0.2.26, plans/archive/D6_TLS_PLAN.md). On wasm there is no backend and tls_available() answers false.

Integration model: the TCP socket belongs to Yo's per-thread async runtime, so OpenSSL never sees the fd. The SSL object speaks through two MEMORY BIOs; this module pumps ciphertext between them and the TcpStream around every handshake/read/write step.

{ TlsStream } :: import "std/crypto/tls";
s := io.await(TlsStream.connect(`example.com`.to_string(), u16(443), io), e);
_n := io.await(s.write_str("GET / HTTP/1.1\r\nHost: example.com\r\n\r\n", io), e);
n := io.await(s.read(buf.ptr().unwrap(), buf.capacity(), io), e);
io.await(s.close(io), e);

Stability

unstable — the transport works on every supported target (D6 closed 2026-09-04; the compiler's own downloader runs over it) and both backends verify the chain against the system trust store and check the hostname, so what is unstable is how narrow the surface is. There is exactly one entry point, TlsStream.connect(host, port, io), and no way to say anything else: no options value, so no custom CA bundle, no client certificate, no ALPN (which HTTP/2 would need), no session resumption, no "accept this self-signed certificate for a test", and no server side. Every one of those arrives as a new parameter or a new options type, which is why connect's signature is not frozen. Certificate REVOCATION is deliberately not checked on either backend, matching them to each other rather than to a policy. Freezing follows the first of those features, not a release count.