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/brokerd/tests/serve.rs

@@ -11,7 +11,7 @@ use std::time::{Duration, Instant};
 
 use brokerd::audit::RECOVERED_NOTICE;
 use brokerd::runner::REFUSING;
-use proto::{
+use bxcore::{
     AuditEvent, CallId, DenyReason, Empty, Envelope, ErrorCode, Message, PROTOCOL_VERSION,
     ResultStatus, SessionId, ToolRequest, ToolResponse,
 };
@@ -100,7 +100,11 @@ impl Home {
             .flat_map(|n| {
                 let text = std::fs::read_to_string(dir.join(n)).unwrap();
                 text.lines()
-                    .map(|l| serde_json::from_str::<proto::AuditRecord>(l).unwrap().event)
+                    .map(|l| {
+                        serde_json::from_str::<bxcore::AuditRecord>(l)
+                            .unwrap()
+                            .event
+                    })
                     .collect::<Vec<_>>()
             })
             .collect()
@@ -143,10 +147,10 @@ fn exchange(socket: &Path, id: u64, msg: Message) -> Vec<Envelope> {
         r#final: true,
         msg,
     };
-    proto::write_frame(&mut stream, &env).unwrap();
+    bxcore::write_frame(&mut stream, &env).unwrap();
     let mut frames = Vec::new();
     loop {
-        let env = proto::read_frame(&mut stream).unwrap();
+        let env = bxcore::read_frame(&mut stream).unwrap();
         let last = env.r#final;
         frames.push(env);
         if last {
@@ -296,7 +300,7 @@ fn an_approval_nobody_answers_expires() {
 
 fn copy_case(home: &Home, case: &str, only: &[&str]) {
     let from = format!(
-        "{}/../proto/tests/fixtures/audit/{case}",
+        "{}/../bxcore/tests/fixtures/audit/{case}",
         env!("CARGO_MANIFEST_DIR")
     );
     std::fs::create_dir_all(home.path("audit")).unwrap();