proto becomes bxcore, the one shared crate (M5b task 00)

Done the way the owner asked and the spike mapped: the crate and the
manifests renamed, then what the build reported fixed. Layers: 138
"proto unresolved" errors across 169 files; cargo fmt reordering
imports; six fixture paths built as strings in brokerd's and bxctl's
tests, which the compiler cannot see, and comments naming
crates/proto/; the crate-dependency check and its self-test. One more
the spike did not reach: a `\nproto =` key inside a printf format in
the self-test, which a word-boundary replacement skips because `n` and
`p` are both word characters.

make gate: gate: ok, 944 tests; no new entry in /tmp.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

crates/loopd/tests/pointers.rs

@@ -8,12 +8,12 @@ use std::path::Path;
 use std::process::{Child, Command, Stdio};
 use std::time::Duration;
 
+use bxcore::SessionId;
 use loopd::baseline::Baseline;
 use loopd::broker_port::{not_configured_line, unavailable_line};
 use loopd::memory::{MemoryPort, MemorySource};
 use loopd::session::{Session, SessionError};
 use loopd::tools::Registry;
-use proto::SessionId;
 use support::{FakeServer, Home, Reply};
 
 // `want` is the whole pointer, written out: scripts/check-runbook.sh reads the anchors of every
@@ -78,17 +78,17 @@ fn memoryd_unreachable_or_refusing_names_the_memory_entry() {
     let listener = std::os::unix::net::UnixListener::bind(&socket).unwrap();
     std::thread::spawn(move || {
         let (mut stream, _) = listener.accept().unwrap();
-        let env = proto::read_frame(&mut stream).unwrap();
-        let reply = proto::Envelope {
+        let env = bxcore::read_frame(&mut stream).unwrap();
+        let reply = bxcore::Envelope {
             v: 1,
             id: env.id,
             r#final: true,
-            msg: proto::Message::Error(proto::WireError {
-                code: proto::ErrorCode::Internal,
+            msg: bxcore::Message::Error(bxcore::WireError {
+                code: bxcore::ErrorCode::Internal,
                 detail: "memory/user.md: 1,376 characters; its limit is 1,375".to_string(),
             }),
         };
-        proto::write_frame(&mut stream, &reply).unwrap();
+        bxcore::write_frame(&mut stream, &reply).unwrap();
     });
     let message = MemoryPort::new(socket, Duration::from_secs(5))
         .block()