desktop: use tokio::fs for Sora and Midjourney file I/O (Sonar S7493) (#2804)

## Summary

Replaces blocking `std::fs` calls inside `async fn`s in the desktop
crate with `tokio::fs`. SonarCloud reports these as **rust:S7493** ("use
an asynchronous file API instead of this blocking file operation"). This
PR resolves 17 of the 26 desktop findings.

| File (under `crates/desktop/artcraft/src/services/`) | Findings |
Change |

|----------------------------------------------------------------|----------|----------------------------------------------------------------------------|
| `sora/state/read_sora_credentials_from_disk_with_upgrade.rs` | 10 |
`read_to_string` and `OpenOptions`+`write_all`+`flush` →
`tokio::fs::{read_to_string, write}` |
| `sora/state/initialize_sora_jwt_bearer_token.rs` | 2 |
`std::fs::{read_to_string, write}` → `tokio::fs` |
| `sora/state/sora_credential_manager.rs` (`call_sentinel_refresh`) | 2
| `OpenOptions`+`write_all`+`flush` → `tokio::fs::write` |
| `midjourney/utils/download_midjourney_image.rs` | 2 |
`File::create`+`write_all` → `tokio::fs::write` |
| `midjourney/threads/upload_midjourney_batch.rs` | 1 |
`std::fs::remove_file` → `tokio::fs::remove_file(..).await` |

`tokio::fs::write` creates or truncates the file and writes everything.
That is the same as the
`OpenOptions::new().create(true).write(true).truncate(true)` +
`write_all` + `flush` sequence it replaces. The synchronous helpers in
`sora_credential_manager.rs` (`persist_*_to_disk`) are not `async`, are
not flagged, and are left unchanged. The `.exists()` guards are also
left as they are. The desktop crate already depends on `tokio` with the
`fs` feature, so no manifest or lockfile changes.

## Not included (overlap with open PRs)

The remaining 9 desktop S7493 findings are in files that open PRs are
rewriting. They are left alone to avoid conflicting changes:

- `core/utils/simple_http_download.rs`,
`sora/.../handle_successful_generations.rs`,
`worldlabs/threads/worldlabs_marble_task_polling.rs`: #2777 (fail
downloads on non-2xx responses).
- `core/threads/.../fal/handle_fal_complete.rs`: #2550, #2373.
- `core/utils/auto_download.rs`: #2785, #2686, #2393.

The api_clients findings are in #2803.

## Testing

- Each changed file parses with `rustfmt --check`. The formatting diffs
it reports already exist on `main`, and no files were reformatted.
- **I could not build the desktop crate locally.** `cargo check -p
artcraft` stops at `libdbus-sys` because the build machine lacks the
GTK, WebKit and D-Bus system libraries Tauri needs. Please rely on CI
for compilation before marking this ready.
- No new tests are added. This is a behaviour-preserving switch to
non-blocking I/O, so no test fails before the change and passes after
it, and these paths have no existing offline tests.


<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->

<!-- coderabbit-ai-generated:v1 -->

## Summary by CodeRabbit

* **Chores**
* Updated background handling for saved images, checkpoints, and account
credentials. Existing cleanup, credential processing, and error
reporting behavior remain unchanged.
* These maintenance updates do not change the app’s available features
or how people interact with it.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

crates/desktop/artcraft/src/services/midjourney/threads/upload_midjourney_batch.rs

@@ -119,7 +119,7 @@ pub(super) async fn upload_midjourney_batch(maybe_app_handle: Option<&AppHandle>
     }
   }
 
-  if let Err(err) = std::fs::remove_file(MidjourneyUploadCheckpoint::path(app_data_root, local_task)) {
+  if let Err(err) = tokio::fs::remove_file(MidjourneyUploadCheckpoint::path(app_data_root, local_task)).await {
     log::warn!("Could not remove completed Midjourney upload checkpoint: {}", err);
   }
   Ok(())

crates/desktop/artcraft/src/services/midjourney/utils/download_midjourney_image.rs

@@ -2,8 +2,6 @@ use crate::core::state::data_dir::app_data_root::AppDataRoot;
 use crate::core::state::data_dir::trait_data_subdir::DataSubdir;
 use errors::AnyhowResult;
 use midjourney_client::utils::get_image_url::get_image_url;
-use std::fs::File;
-use std::io::Write;
 use std::path::PathBuf;
 use url::Url;
 use midjourney_client::utils::image_downloader_client::ImageDownloaderClient;
@@ -28,8 +26,7 @@ pub async fn download_midjourney_image(
   let download_filename = format!("{}_{}.{}", job_id, index, ext);
   let download_path = tempdir.join(download_filename);
 
-  let mut file = File::create(&download_path)?;
-  file.write_all(&image_bytes)?;
+  tokio::fs::write(&download_path, &image_bytes).await?;
 
   Ok(download_path)
 }

crates/desktop/artcraft/src/services/sora/state/initialize_sora_jwt_bearer_token.rs

@@ -14,7 +14,7 @@ pub async fn initialize_sora_jwt_bearer_token(app_data_root: &AppDataRoot) -> An
     return Ok(()); // Bearer token already exists.
   }
 
-  let cookie = std::fs::read_to_string(app_data_root.get_sora_cookie_file_path())?
+  let cookie = tokio::fs::read_to_string(app_data_root.get_sora_cookie_file_path()).await?
       .trim()
       .to_string();
 
@@ -22,7 +22,7 @@ pub async fn initialize_sora_jwt_bearer_token(app_data_root: &AppDataRoot) -> An
 
   let bearer = generate_bearer_jwt_with_cookie(&cookie).await?;
 
-  std::fs::write(app_data_root.get_sora_bearer_token_file_path(), bearer)?;
+  tokio::fs::write(app_data_root.get_sora_bearer_token_file_path(), bearer).await?;
 
   Ok(())
 }

crates/desktop/artcraft/src/services/sora/state/read_sora_credentials_from_disk_with_upgrade.rs

@@ -8,8 +8,7 @@ use openai_sora_client::creds::sora_jwt_bearer_token::SoraJwtBearerToken;
 use openai_sora_client::creds::sora_sentinel::SoraSentinel;
 use openai_sora_client::creds::sora_sentinel_token::SoraSentinelToken;
 use openai_sora_client::recipes::maybe_upgrade_or_renew_session::maybe_upgrade_or_renew_session;
-use std::fs::{read_to_string, OpenOptions};
-use std::io::Write;
+use tokio::fs::{read_to_string, write};
 
 pub async fn read_sora_credentials_from_disk_with_upgrade(app_data_root: &AppDataRoot) -> AnyhowResult<SoraCredentialSet> {
   let cookie_file = app_data_root.get_sora_cookie_file_path();
@@ -21,7 +20,7 @@ pub async fn read_sora_credentials_from_disk_with_upgrade(app_data_root: &AppDat
     return Err(anyhow!("Cookie file does not exist: {:?}", cookie_file));
   }
 
-  let value = read_to_string(cookie_file)?
+  let value = read_to_string(cookie_file).await?
       .trim()
       .to_string();
 
@@ -32,14 +31,14 @@ pub async fn read_sora_credentials_from_disk_with_upgrade(app_data_root: &AppDat
   let mut sentinel_token = None;
 
   if bearer_file.exists() {
-    let value = read_to_string(&bearer_file)?
+    let value = read_to_string(&bearer_file).await?
         .trim()
         .to_string();
     bearer = Some(SoraJwtBearerToken::new(value)?);
   }
 
   if legacy_sentinel_file.exists() {
-    let value = read_to_string(&legacy_sentinel_file)?
+    let value = read_to_string(&legacy_sentinel_file).await?
         .trim()
         .to_string();
 
@@ -47,7 +46,7 @@ pub async fn read_sora_credentials_from_disk_with_upgrade(app_data_root: &AppDat
   }
 
   if sentinel_token_file.exists() {
-    let value = read_to_string(&sentinel_token_file)?
+    let value = read_to_string(&sentinel_token_file).await?
         .trim()
         .to_string();
 
@@ -73,14 +72,7 @@ pub async fn read_sora_credentials_from_disk_with_upgrade(app_data_root: &AppDat
       info!("Persisting bearer token value...");
       let value = bearer.token_str();
 
-      let mut file = OpenOptions::new()
-          .create(true)
-          .write(true)
-          .truncate(true)
-          .open(&bearer_file)?;
-
-      file.write_all(value.as_bytes())?;
-      file.flush()?;
+      write(&bearer_file, value.as_bytes()).await?;
     }
   }
 
@@ -89,14 +81,7 @@ pub async fn read_sora_credentials_from_disk_with_upgrade(app_data_root: &AppDat
       info!("Persisting sentinel value...");
       let value = sentinel.get_sentinel();
 
-      let mut file = OpenOptions::new()
-          .create(true)
-          .write(true)
-          .truncate(true)
-          .open(&legacy_sentinel_file)?;
-
-      file.write_all(value.as_bytes())?;
-      file.flush()?;
+      write(&legacy_sentinel_file, value.as_bytes()).await?;
     }
   }
   
@@ -105,14 +90,7 @@ pub async fn read_sora_credentials_from_disk_with_upgrade(app_data_root: &AppDat
       info!("Persisting sentinel token...");
       let value = sentinel_token.to_persistent_storage_json()?;
 
-      let mut file = OpenOptions::new()
-          .create(true)
-          .write(true)
-          .truncate(true)
-          .open(&sentinel_token_file)?;
-
-      file.write_all(value.as_bytes())?;
-      file.flush()?;
+      write(&sentinel_token_file, value.as_bytes()).await?;
     }
   }
 

crates/desktop/artcraft/src/services/sora/state/sora_credential_manager.rs

@@ -162,14 +162,7 @@ impl SoraCredentialManager {
 
     self.holder.set_credentials(&creds)?;
 
-    let mut file = OpenOptions::new()
-        .create(true)
-        .write(true)
-        .truncate(true)
-        .open(self.app_data_root.get_sora_legacy_sentinel_file_path())?;
-
-    file.write_all(sentinel.as_bytes())?;
-    file.flush()?;
+    tokio::fs::write(self.app_data_root.get_sora_legacy_sentinel_file_path(), sentinel.as_bytes()).await?;
 
     Ok(creds)
   }