diff --git a/buck/prefix-min/BUCK b/buck/prefix-min/BUCK
index f8b8cffb2..fbcf16a34 100644
--- a/buck/prefix-min/BUCK
+++ b/buck/prefix-min/BUCK
@@ -477,6 +477,9 @@ prefix_tree(
         "libexec/cider/usr/lib/libz.1.dylib": "//vendor/src:z_dylib",
         "libexec/cider/usr/lib/native/libEGL.dylib": "//src/linux/native:EGL_dylib",
         "libexec/cider/usr/lib/native/libFreeType.dylib": "//src/linux/native:FreeType_dylib",
+        "libexec/cider/usr/lib/native/libwayland-client.dylib": "//src/linux/native:wayland-client_dylib",
+        "libexec/cider/usr/lib/native/libwayland-cursor.dylib": "//src/linux/native:wayland-cursor_dylib",
+        "libexec/cider/usr/lib/native/libxkbcommon.dylib": "//src/linux/native:xkbcommon_dylib",
         "libexec/cider/usr/lib/native/libX11.dylib": "//src/linux/native:X11_dylib",
         "libexec/cider/usr/lib/native/libXRandR.dylib": "//src/linux/native:XRandR_dylib",
         "libexec/cider/usr/lib/native/libXcursor.dylib": "//src/linux/native:Xcursor_dylib",
diff --git a/buck/rules/rust.bzl b/buck/rules/rust.bzl
index 649837a5e..278f1ed12 100644
--- a/buck/rules/rust.bzl
+++ b/buck/rules/rust.bzl
@@ -344,18 +344,23 @@ def _darwin_rust_staticlib_impl(ctx):
         cmd.add("--cfg", 'feature="%s"' % f)
     cmd.add(ctx.attrs.rustc_flags)
 
-    # NO MULTI FILE CRATES HERE, and the reason is recorded because it is not obvious.
+    # MULTI FILE CRATES ARE FINE NOW, and the history is kept because the reason was not obvious.
     # rustc finds a `mod` by following it from the crate root, so module files are HIDDEN inputs
     # that never appear in the argv, and `buck2 aquery` reports NO INPUT LIST AT ALL: the
     # attributes of an action are kind, category, identifier, cmd and executor knobs. The Nix
-    # endpoint therefore stages what the argv names and nothing else, and a `mod` file simply is
-    # not there, which surfaces as 205 compiler errors that say nothing about staging.
+    # endpoint therefore staged what the argv named and nothing else, and a `mod` file simply was
+    # not there, which surfaced as 205 compiler errors that said nothing about staging.
     #
     # Passing each src as an inert --cfg was tried and does NOT work: the path ends up embedded
     # inside `cider_module="..."` rather than being an argv token that IS a path.
     #
-    # So a guest crate is ONE FILE until the endpoint can be taught about hidden inputs. The hidden
-    # entry below is still correct for a direct buck2 build, where it drives rebuilds properly.
+    # WHAT FIXED IT was teaching the endpoint instead, which is where the gap always was: srcset.rs
+    # stages the whole DIRECTORY of any .rs in a rustc argv, and had done so for the host rule from
+    # the start; it just matched on the category `rustc` and this rule's category is
+    # darwin_rust_staticlib. Both are matched now. src/darwin/rustprobe is deliberately two files
+    # so the limit cannot come back unnoticed.
+    #
+    # The hidden entry below is what makes a DIRECT buck2 build rebuild on a module change.
     cmd.add(cmd_args(hidden = ctx.attrs.srcs))
     ctx.actions.run(cmd, category = "darwin_rust_staticlib", identifier = ctx.label.name)
     return [
diff --git a/nix/ciderBuildInputs.nix b/nix/ciderBuildInputs.nix
index 00cb160c0..69402937d 100644
--- a/nix/ciderBuildInputs.nix
+++ b/nix/ciderBuildInputs.nix
@@ -23,6 +23,11 @@
   libXrandr,
   libXcursor,
   libxkbfile,
+  # WAYLAND, for the GUI backend that replaces X11 (task #112). wrapgen dlopens the real .so at
+  # BUILD time to read its dynamic symbol table, so these have to be present in the build inputs
+  # and not only at runtime.
+  wayland,
+  libxkbcommon,
   cairo,
   libglvnd,
   fontconfig,
@@ -101,6 +106,8 @@ let
     libXrandr
     libXcursor
     libxkbfile
+    wayland
+    libxkbcommon
     cairo
     libglvnd
     fontconfig
diff --git a/src/darwin/rustprobe/BUCK b/src/darwin/rustprobe/BUCK
index 1f2cf5778..fc4b4a270 100644
--- a/src/darwin/rustprobe/BUCK
+++ b/src/darwin/rustprobe/BUCK
@@ -9,9 +9,13 @@ load("//buck/rules:rust.bzl", "darwin_rust_staticlib")
 # A build that succeeds proves the link, and the link was never the doubtful part. What the run
 # proves is that std works without Rust's lang_start: env_args must equal argc, which means
 # std::env::args found _NSGetArgv, format! reached the allocator, and println! reached stdout.
+# TWO FILES, WHICH IS THE POINT. srcs is what makes a direct buck2 build rebuild when the module
+# changes; the endpoint needs srcset.rs to stage the crate directory, which it now does for this
+# rule's category as well as for the host one.
 darwin_rust_staticlib(
     name = "rustprobe_lib",
     crate_root = "probe.rs",
+    srcs = ["report.rs"],
     visibility = ["PUBLIC"],
 )
 
diff --git a/src/darwin/rustprobe/probe.rs b/src/darwin/rustprobe/probe.rs
index c990a8567..80363dfe0 100644
--- a/src/darwin/rustprobe/probe.rs
+++ b/src/darwin/rustprobe/probe.rs
@@ -9,10 +9,14 @@
 // the allocator. A probe that only returned 0 would link and prove nothing.
 use std::os::raw::{c_char, c_int};
 
+// SECOND FILE, DELIBERATELY. See report.rs: a `mod` in its own file is the hidden input the
+// endpoint could not see, and this crate is now the check that it can.
+mod report;
+
 #[unsafe(no_mangle)]
 pub extern "C" fn main(argc: c_int, _argv: *const *const c_char) -> c_int {
     let from_env = std::env::args().count();
-    let msg = format!("cider-rust-probe argc={argc} env_args={from_env}");
+    let msg = report::line(argc, from_env);
     println!("{msg}");
     if from_env as c_int == argc { 0 } else { 1 }
 }
diff --git a/src/darwin/rustprobe/report.rs b/src/darwin/rustprobe/report.rs
new file mode 100644
index 000000000..e8c237844
--- /dev/null
+++ b/src/darwin/rustprobe/report.rs
@@ -0,0 +1,16 @@
+// A SECOND FILE ON PURPOSE, and it is a check rather than a convenience.
+//
+// rustc finds this through `mod report;` in probe.rs, so it is a HIDDEN input: it appears in no
+// argv and, because buck2 aquery reports no input list at all, in nothing the Nix endpoint can
+// see either. Staging the crate ROOT and nothing else is what made a guest crate ONE FILE, and
+// that limit is recorded in buck/rules/rust.bzl. srcset.rs now takes the whole directory for a
+// darwin_rust_staticlib action, the same way it always has for a host rustc action.
+//
+// So if the endpoint ever regresses to staging only the root, this file stops existing during
+// the build and the probe fails to compile with "file not found for module `report`". That is
+// the point: the check is the crate itself, and it cannot pass by accident.
+
+/// The line the runtime check greps for, built here so the module is genuinely used.
+pub fn line(argc: i32, from_env: usize) -> String {
+    format!("cider-rust-probe argc={argc} env_args={from_env}")
+}
diff --git a/src/linux/buildtools/graph-specs/src/srcset.rs b/src/linux/buildtools/graph-specs/src/srcset.rs
index ba9d52a03..9ba19e8b6 100644
--- a/src/linux/buildtools/graph-specs/src/srcset.rs
+++ b/src/linux/buildtools/graph-specs/src/srcset.rs
@@ -463,7 +463,14 @@ pub fn target_sources(
         // "file not found for module `xnu`" after 1,462 green builders.
         for &i in acts {
             let ident = actions[i].get("identity").and_then(|v| v.as_str()).unwrap_or("");
-            if !ident.contains("(rustc ") {
+            // BOTH RUST CATEGORIES, and the second one is why guest crates were single file.
+            // The host rule runs its action as category `rustc`; the guest rule
+            // (darwin_rust_staticlib in buck/rules/rust.bzl) runs its own, so a guest crate
+            // matched nothing here and got its crate ROOT staged and no `mod` files. That file
+            // records the consequence as "a guest crate is ONE FILE until the endpoint can be
+            // taught about hidden inputs" -- this is that lesson, and it is the same directory
+            // rule the host has always had.
+            if !ident.contains("(rustc ") && !ident.contains("(darwin_rust_staticlib ") {
                 continue;
             }
             for tok in strs(&actions[i], "argv") {
diff --git a/src/linux/native/BUCK b/src/linux/native/BUCK
index 92a698e25..9cabf339f 100644
--- a/src/linux/native/BUCK
+++ b/src/linux/native/BUCK
@@ -30,6 +30,12 @@ _NATIVE = [
     ("XRandR", "libXrandr.so", "/usr/lib/native"),
     ("Xcursor", "libXcursor.so", "/usr/lib/native"),
     ("xkbfile", "libxkbfile.so", "/usr/lib/native"),
+    # WAYLAND (#112). The GUI backend that replaces X11 reaches the compositor through these
+    # exactly the way the X11 backend reaches the X server: a generated Mach-O stub per library
+    # that forwards through libelfloader, so nothing has to be ported.
+    ("wayland-client", "libwayland-client.so", "/usr/lib/native"),
+    ("wayland-cursor", "libwayland-cursor.so", "/usr/lib/native"),
+    ("xkbcommon", "libxkbcommon.so", "/usr/lib/native"),
     ("cairo", "libcairo.so", "/usr/lib/native"),
     ("dbus", "libdbus-1.so", "/usr/lib/native"),
     # OpenGL's two live inside the framework rather than in /usr/lib/native, which is the
@@ -57,6 +63,9 @@ _NATIVE = [
 # buck-registry: libXRandR.dylib = XRandR_dylib
 # buck-registry: libXcursor.dylib = Xcursor_dylib
 # buck-registry: libxkbfile.dylib = xkbfile_dylib
+# buck-registry: libwayland-client.dylib = wayland-client_dylib
+# buck-registry: libwayland-cursor.dylib = wayland-cursor_dylib
+# buck-registry: libxkbcommon.dylib = xkbcommon_dylib
 # buck-registry: libcairo.dylib = cairo_dylib
 # buck-registry: libdbus.dylib = dbus_dylib
 # buck-registry: libGL.dylib = GL_dylib