diff --git a/PATCHES.md b/PATCHES.md
index 0f193d3..1c0cdd1 100644
--- a/PATCHES.md
+++ b/PATCHES.md
@@ -35,7 +35,10 @@ in-tree means the patch can't be lost to a dependency re-resolve.
    readability handler is never wired and the agent's stdin is never delivered (it hangs) or its
    stdout is never read (the "no output, just a spinner" symptom in Nucleic Control containers).
    Behavior is unchanged; it only surfaces the failing stream. Marked `[Nucleic vendored patch]`
-   (the `import os`, the `nucleicIOLog` static, and the per-stream check in `setupIO`).
+   (the `import os`, the `nucleicIOLog` static, and the per-stream check in `setupIO`). All three are
+   wrapped in `#if canImport(os)` — the swiftly toolchain used by `.github/workflows/vminit-image.yml`
+   resolves Foundation/Virtualization but not the `os` overlay, so the diagnostic degrades to a no-op
+   there instead of failing the build; Xcode (local) builds keep it.
 
 4. **Trimmed for footprint (no behavior change).** `Tests/`, `docs/`, `examples/`, and `images/`
    were dropped, and the corresponding `.testTarget(...)` entries removed from `Package.swift`. The
diff --git a/Sources/Containerization/LinuxProcess.swift b/Sources/Containerization/LinuxProcess.swift
index 7f21306..bbc15f9 100644
--- a/Sources/Containerization/LinuxProcess.swift
+++ b/Sources/Containerization/LinuxProcess.swift
@@ -21,13 +21,22 @@ import ContainerizationOS
 import Foundation
 import Logging
 import Synchronization
-import os  // [Nucleic vendored patch] stdio-connection diagnostics
+
+// [Nucleic vendored patch] stdio-connection diagnostics. Guarded: the `os` overlay isn't importable
+// under every toolchain that builds this package (e.g. the swiftly Swift used by the vminit-image CI,
+// which resolves Foundation/Virtualization but not `os`), so the diagnostic degrades to a no-op there
+// rather than failing the build. Local (Xcode) builds keep it.
+#if canImport(os)
+import os
+#endif
 
 /// `LinuxProcess` represents a Linux process and is used to
 /// setup and control the full lifecycle for the process.
 public final class LinuxProcess: Sendable {
     /// [Nucleic vendored patch] Diagnostic log for stdio stream-connection failures (see `setupIO`).
+    #if canImport(os)
     static let nucleicIOLog = os.Logger(subsystem: "com.nucleic", category: "container-io")
+    #endif
 
     /// The ID of the process. This is purely metadata for the caller.
     public let id: String
@@ -191,12 +200,15 @@ extension LinuxProcess {
         // never wired — the agent's stdin is then never delivered (it hangs waiting for input) or
         // its stdout is never read ("no output, just a spinner"). Log that specific failure (Console
         // / `log show`, subsystem com.nucleic, category container-io) so a stall pinpoints the stream
-        // instead of proceeding silently. Log-only; behavior is unchanged.
+        // instead of proceeding silently. Log-only; behavior is unchanged. Guarded on `canImport(os)`
+        // (see the import) so a toolchain without the `os` overlay still builds.
+        #if canImport(os)
         let configured = [self.ioSetup.stdin != nil, self.ioSetup.stdout != nil, self.ioSetup.stderr != nil]
         for (index, label) in [(0, "stdin"), (1, "stdout"), (2, "stderr")] where configured[index] && handles[index] == nil {
             Self.nucleicIOLog.error(
                 "setupIO[\(self.id, privacy: .public)]: \(label, privacy: .public) stream never connected from the guest — agent stdio will stall")
         }
+        #endif
 
         // Note: stdin relay is started separately via startStdinRelay() after
         // the process has started, to avoid a deadlock where closeStdin is