forge: warn when the core avatar marker cannot be written

The one-shot marker was written with create_dir_all(..).ok() and
fs::write(..).ok(), so a failure was invisible and the avatar upload
repeated on every start. Log the path and error; startup still succeeds.

hive-c0re/src/forge/users.rs

@@ -180,14 +180,21 @@ pub(super) async fn ensure_core_avatar(token: &str) -> Result<()> {
     )
     .await?
     .context("set core avatar")?;
-    if let Some(parent) = marker.parent() {
+    if let Err(e) = write_marker(&marker) {
-        std::fs::create_dir_all(parent).ok();
+        tracing::warn!(marker = %marker.display(), error = ?e, "forge: could not write the avatar marker; the upload repeats on the next start");
     }
-    std::fs::write(marker, "").ok();
     tracing::info!("forge: set core user avatar to hyperhive logo");
     Ok(())
 }
 
+/// Create the one-shot marker file, and its directory if needed.
+fn write_marker(marker: &Path) -> std::io::Result<()> {
+    if let Some(parent) = marker.parent() {
+        std::fs::create_dir_all(parent)?;
+    }
+    std::fs::write(marker, "")
+}
+
 /// Outcome of probing whether the persisted core token still works
 /// against the *current* forge. Existence on disk is not validity: a
 /// token minted before a forge rebuild / re-provision is unknown to the
@@ -301,10 +308,28 @@ pub fn core_token() -> Option<String> {
 
 #[cfg(test)]
 mod tests {
-    use super::{CoreTokenCheck, classify_core_token_error};
+    use super::{CoreTokenCheck, classify_core_token_error, write_marker};
     use forgejo_api::{ApiError, ApiErrorKind, ForgejoError};
     use reqwest::StatusCode;
 
+    #[test]
+    fn write_marker_creates_the_missing_parent_dir() {
+        let dir = tempfile::tempdir().expect("tempdir");
+        let marker = dir.path().join("not-yet").join("nested").join("avatar-set");
+        write_marker(&marker).expect("write");
+        assert!(marker.is_file());
+    }
+
+    /// A parent that is a regular file makes `create_dir_all` fail for any
+    /// uid, root included.
+    #[test]
+    fn write_marker_reports_a_path_it_cannot_create() {
+        let dir = tempfile::tempdir().expect("tempdir");
+        let file = dir.path().join("a-file");
+        std::fs::write(&file, "").expect("file");
+        assert!(write_marker(&file.join("sub").join("avatar-set")).is_err());
+    }
+
     fn api_err(kind: ApiErrorKind) -> ForgejoError {
         ForgejoError::ApiError(ApiError {
             message: None,