chore(easytier): gate hotpath-rs 0.19 dependency and off-mode shim

Re-enable the hotpath profiler as an optional dependency gated behind the
 feature (default off). In off builds the crate stays out of the
dependency graph entirely:  plus a local
 module provide no-op // macros so
call sites compile unchanged. Also add a  guarding the
mutual exclusivity of  with the / global
allocators.

easytier/Cargo.toml

@@ -58,6 +58,8 @@ chrono = { version = "0.4.37", features = ["serde"] }
 guarden = "0.2"
 quanta = "0.12"
 
+hotpath = { version = "0.19", default-features = false, optional = true }
+
 delegate = "0.13.5"
 
 itertools = "0.14.0"
@@ -410,11 +412,14 @@ tracing = ["tokio/tracing", "dep:console-subscriber"]
 magic-dns = ["dep:hickory-client", "dep:hickory-server"]
 faketcp = ["dep:flume"]
 zstd = ["dep:zstd"]
-# Deprecated: hotpath profiling has been removed. These feature aliases are
-# retained as no-ops so existing build scripts using `--features hotpath*`
-# continue to work without pulling in any dependencies.
-hotpath = []
-hotpath-cpu = ["hotpath"]
-hotpath-alloc = ["hotpath"]
+hotpath = [
+    "dep:hotpath",
+    "hotpath/hotpath",
+    "hotpath/tokio",
+    "hotpath/parking_lot",
+    "hotpath/flume",
+]
+hotpath-cpu = ["hotpath", "hotpath/hotpath-cpu"]
+hotpath-alloc = ["hotpath", "hotpath/hotpath-alloc"]
 # For Network Extension on macOS
 macos-ne = []

easytier/src/hotpath_off.rs

@@ -0,0 +1,40 @@
+//! No-op stand-in for the `hotpath` macros used by this crate, selected when
+//! the `hotpath` feature is disabled.
+//!
+//! Keeping `hotpath` as an optional dependency means default builds do not pull
+//! the profiler (or any of its transitive dependencies) into the dependency
+//! graph. These macros expand to their input unchanged, mirroring `hotpath`'s
+//! own disabled mode so call sites compile identically with or without the
+//! feature.
+//!
+//! The macros are `#[macro_export]`-ed so that `lib.rs`' `extern crate self as
+//! hotpath` alias exposes them through the same `hotpath::...` paths used when
+//! the feature is enabled.
+
+/// No-op mirroring `hotpath::channel!`: returns the channel expression
+/// unchanged (dropping any optional trailing `label`/`log`/`capacity` args).
+#[doc(hidden)]
+#[macro_export]
+macro_rules! channel {
+    ($expr:expr $(, $($rest:tt)*)?) => {
+        $expr
+    };
+}
+
+/// No-op mirroring `hotpath::mutex!`: returns the expression unchanged.
+#[doc(hidden)]
+#[macro_export]
+macro_rules! mutex {
+    ($expr:expr $(, $($rest:tt)*)?) => {
+        $expr
+    };
+}
+
+/// No-op mirroring `hotpath::rw_lock!`: returns the expression unchanged.
+#[doc(hidden)]
+#[macro_export]
+macro_rules! rw_lock {
+    ($expr:expr $(, $($rest:tt)*)?) => {
+        $expr
+    };
+}

easytier/src/lib.rs

@@ -5,6 +5,20 @@ use std::io;
 use clap::Command;
 use clap_complete::{Generator, Shell};
 
+// When the `hotpath` feature is off, alias the current crate as `hotpath` so
+// call sites keep using `hotpath::...` paths, and provide a local no-op shim
+// for the profiling macros. This keeps `hotpath` an optional dependency: the
+// profiler is absent from the dependency graph entirely in default builds.
+#[cfg(not(feature = "hotpath"))]
+extern crate self as hotpath;
+#[cfg(not(feature = "hotpath"))]
+mod hotpath_off;
+
+// `hotpath-alloc` registers a global profiling allocator, which is mutually
+// exclusive with the `jemalloc`/`mimalloc` global allocators.
+#[cfg(all(feature = "hotpath-alloc", any(feature = "jemalloc", feature = "mimalloc")))]
+compile_error!("feature `hotpath-alloc` cannot be enabled together with `jemalloc` or `mimalloc`");
+
 // Re-export `Instant` at the crate root so public APIs that expose it
 // (e.g. `Route::get_peer_info_last_update_time`) reference a deliberate
 // public type rather than leaking an inaccessible one.