diff --git a/host/src/exec.rs b/host/src/exec.rs
index d8f4f62..cce79ec 100644
--- a/host/src/exec.rs
+++ b/host/src/exec.rs
@@ -10,11 +10,14 @@ pub enum Command {
 }
 
 /// How to run it. `cwd` is a world path. `timeout` ends the command and all its processes.
+/// `conversation` is the harness conversation that runs the command. Its processes and their
+/// descendants carry it, so the host knows the caller (for example in the `wasi:http` hook).
 #[derive(Clone, Debug, Default)]
 pub struct Options {
     pub cwd: String,
     pub env: Vec<(String, String)>,
     pub timeout: Option<Duration>,
+    pub conversation: Option<String>,
 }
 
 /// The stream that one output chunk came from.