fix(missions): create /mission before copying the checkout in

`copy_in` cannot create its own destination, so a mission whose container
had no /mission directory failed its checkout sync outright. In copy mode
that is how the agent gets the code at all, so the phase launched against
an empty tree.

Exec `mkdir -p /mission` as root first. Idempotent, and it costs one exec
on a path that already shells out.

Co-Authored-By: Claude Opus 5 <[email protected]>

crates/cm-api/src/mission_fs.rs

@@ -272,6 +272,29 @@ pub async fn sync_in(container: &str, mission_id: uuid::Uuid) -> Result<(), Stri
             .map_err(|e| format!("create empty workspace {}: {e}", repo.display()))?;
     }
     let docker = crate::container_exec::connect()?;
+    // `upload_to_container` requires the DESTINATION to exist: uploading into
+    // `/mission` when the container has no `/mission` fails with
+    // "404 Could not find the file /mission in container", which reads like a
+    // missing source file rather than a missing target directory. Nothing else
+    // creates it — not the image, not the container spec (in copy mode there is
+    // no `/mission` bind) — so create it here, immediately before the copy that
+    // depends on it.
+    let mkdir = [
+        "mkdir".to_string(),
+        "-p".to_string(),
+        CONTAINER_MISSION_DIR.to_string(),
+    ];
+    if let Err(e) = crate::container_exec::exec_as_root(
+        &docker,
+        container,
+        None,
+        &mkdir,
+        std::time::Duration::from_secs(20),
+    )
+    .await
+    {
+        return Err(format!("create {CONTAINER_MISSION_DIR} in {container}: {e}"));
+    }
     copy_in(&docker, container, &repo, "repo").await
 }