Quick repeated calls to await @Fetch*.load(...).task inside .task modifier can result in stale query results #557

Description

(originally reported in Slack #sqlite-data channel)

Quick repeating calls to load can occur naturally in situations like handling a deep link on application start: the application first loads the initial/default query, followed by a quick reload to process the deep link.

Investigation reveals that awaiting the FetchSubscription.task is what triggers this bug. There's a race between the cancellation of the task (which will occur when the await is situated inside a view's .task modifier) and the handling of the new load. If the cancel wins, it prevents the new load from succeeding, resulting in stale data.

See attached demo app for a controllable repro - SubscriptionTaskReloadRaceApp_1.12.0.zip. The app cycles between query states A -> B -> C -> D, which each have their respective expected results ([A,A..], [B, B, ..], etc.). The app will halt whenever displayed results do not match expected results based on the most recent load call. Lowering the "Replacement load delay" to below 100ms reliably triggers the mismatch/stale results state. repro video

Checklist

• I wrote this in my own words, and aimed to be as succinct as possible, even if I used AI to help research its content.
• I have determined whether this bug is also reproducible in a vanilla SwiftUI project.
• I have determined whether this bug is also reproducible in a vanilla GRDB project.
• If possible, I've reproduced the issue using the main branch of this package.
• This issue hasn't been addressed in an existing GitHub issue or discussion.

Expected behavior

Results provided by the @Fetch* wrapper always match with the latest load call.

Actual behavior

Results provided by the @Fetch* wrapper can get stuck on results corresponding to a previous load call instead of the latest.

Reproducing project

SubscriptionTaskReloadRaceApp_1.12.0.zip

SQLiteData version information

1.12.0

Sharing version information

2.10.1

GRDB version information

7.11.1

Destination operating system

iOS 27

Xcode version information

27.0

Swift Compiler version information

6.4