Fix program indexing failure when shortcut key is spammed during startup

[Copilot]

Program indexing fails to complete when users rapidly toggle Flow Launcher during startup or after system resume, causing applications (e.g., Vivaldi, Spotify) to be missing from search results.

Root Cause

Indexing task was fire-and-forget (_ = Task.Run(...)), allowing premature GC or interruption before completion.

Changes

Task Lifecycle Management

• Store indexing task reference and lock for thread-safe access
• Wrap indexing in try-catch with proper error logging

lock (_indexingTaskLock)
{
    _indexingTask = Task.Run(async () =>
    {
        try
        {
            await IndexProgramsAsync().ConfigureAwait(false);
            WatchProgramUpdate();
        }
        catch (Exception e)
        {
            Context.API.LogException(ClassName, "Failed to complete program indexing", e);
        }
    });
}

Query Synchronization

Wait for indexing completion (30s timeout) before processing queries:

if (indexingTask != null && !indexingTask.IsCompleted)
{
    await Task.WhenAny(indexingTask, Task.Delay(TimeSpan.FromSeconds(30), token))
        .ConfigureAwait(false);
}

Disposal Safety

Wait for indexing completion (10s timeout) before cleanup to prevent resource disposal during active indexing.

Impact

• User: Applications now appear reliably after indexing completes
• Code: Single-file change to Program plugin (+62, -4)

Original prompt

---

This section details on the original issue you should resolve

<issue_title>BUG: Flow Launcher doesn't finish indexing programs if spammed the shortcut key to launch it while it's starting</issue_title>
<issue_description>### Checks

• I have checked that this issue has not already been reported.

• I am using the latest version of Flow Launcher.

• I am using the prerelease version of Flow Launcher.

Problem Description

If you spam the Flow Launcher launch shortcut key (Mine is LWin) while it's starting, it will infinitely try to index programs without success. Most of the results will work but all applications will not show up.
Example, Vivaldi will not show up, Spotify neither, but if I search a Windows setting or anything else it will show up.

To Reproduce

1. Run Flow Launcher
2. Spam the launch shortcut key while it's opening
3. Try to search for any application

Screenshots

No response

Flow Launcher Version

1.20.2

Windows Build Number

10.0.26100.5074

Error Log

No error occurs.</issue_description>

Comments on the Issue (you are @copilot in this section)

@Jack251970 Can you check if this can help?

https://ci.appveyor.com/project/JohnTheGr8/flow-launcher/builds/52743730/artifacts</comment_new>
<comment_new>@Jack251970
@rottakore I am not sure if #3978 can help. Could you please check if this can help?

https://github.com/Flow-Launcher/Prereleases/releases/tag/v2.0.0.13849</comment_new>
<comment_new>@Jack251970
Thanks for your reply! I think we need further investigation into this.</comment_new>
<comment_new>@Jack251970
I observed that this problem seems to occur easily when Windows is resumed.</comment_new>

• Fixes BUG: Flow Launcher doesn't finish indexing programs if spammed the shortcut key to launch it while it's starting #3962

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