Fix: Prevent game crash on sink double-click

[Itx-Psycho0]

Changes

• 🐛 Fix bug: Added a safety check in the transfer_box function.
• The code now checks if conveyerInd is within the valid range of the conveyer array before accessing it.
• This prevents the "Invalid access to index" crash when a user double-clicks the Sink.

/kind bug

Fixes #55

Verification (Video)

issue55.mp4

Release Note

Fixed a critical bug where the game would crash if the user double-clicked the Sink container.

[knative-prow]

@Itx-Psycho0: The label(s) kind/bug cannot be applied, because the repository doesn't have them.

Details

In response to this:

Changes

• 🐛 Fix bug: Added a safety check in the transfer_box function.
• The code now checks if conveyerInd is within the valid range of the conveyer array before accessing it.
• This prevents the "Invalid access to index" crash when a user double-clicks the Sink.

/kind bug

Fixes #55

Verification (Video)

issue55.mp4

Release Note

Fixed a critical bug where the game would crash if the user double-clicked the Sink container.

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[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: Itx-Psycho0 / name: Anurag Singh (4926e6d)

[knative-prow]

Welcome @Itx-Psycho0! It looks like this is your first PR to knative-extensions/educational-game 🎉

[Itx-Psycho0]

Hi @ankitajana21 @prajjwalyd,

I have signed the CLA and verified the fix locally. The double-click crash issue is resolved.

Summary of Changes:

Added safety check for conveyerInd array bounds.

Verified with the attached video proof.

Ready for your review!

[prajjwalyd]

Thanks for this fix @Itx-Psycho0! The check prevents the crash.

[knative-prow]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: Itx-Psycho0, prajjwalyd
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[prajjwalyd]

One small concern, though:
do we need to handle the case where a player clicks the same sink more than once in levels with multiple sinks cc @ankitajana21?

[ankitajana21]

@prajjwalyd I'll review this PR by today, the script is common to all levels, so I have to check it.

[ankitajana21]

@Itx-Psycho0 This is not working for multi sink level, let's say I click once on blue, and twice on red, and after that I can't click on green, as it is considering 2 belts for red and not allowing the 3rd one for green. FYI, In the multi sink level, the player need not click all the sinks, the player can click less as well. The events are duplicated accordingly for the number of sinks connected.

[ankitajana21]

/lgtm cancel

[Itx-Psycho0]

Hi @ankitajana21,

Thank you for the detailed feedback! You were absolutely right - my initial fix limited MultiSink to 3 connections. I've now implemented a comprehensive solution that fixes both the crash AND allows unlimited connections.

Root Cause

After debugging, I found TWO bugs:

1. Original bug: Index out of bounds on double-click (Issue [Bug] Game crashes with "Invalid access to index" on double-clicking the Sink #55)
2. Hidden bug: Scene transition order in level.gd was clearing the events array AFTER boxes added themselves, causing MultiSink to fail when playing through the full game (though it worked when running directly with F6)

Solution

ConveyerController.gd - Smart Conveyor Management

if conveyerInd >= conveyer.size():
    // Detect scene by conveyor count
    if conveyer.size() >= 3:
        // MultiSink: Create new conveyors dynamically
        var new_conveyor = conveyer[0].duplicate()
        get_tree().current_scene.add_child(new_conveyor)
        conveyer.append(new_conveyor)
    else:
        // BasicEventFlow: Stop to prevent crash
        return

level.gd - Fixed Scene Transition

// Initialize BEFORE changing scene (not after)
ConveyerController.initialise()
get_tree().change_scene_to_file(next_level_path)

Testing Results

BasicEventFlow: Double-click no longer crashes
BoxClick: Works correctly
MultiSink - Your test case: Blue once + Red twice + Green once = SUCCESS
MultiSink - Unlimited: Can now make 5+ connections
Full playthrough: All levels work in sequence

Video Demonstration

Screen.Recording.2026-01-29.102927.mp4

The fix now properly addresses both the crash prevention AND allows the flexible multi-sink behavior you described. Ready for review!