bug: FSM vending machine buttons re-enable during wait states causing incorrect change calculation

[VaibhavJindal7]

Description

The interactive vending machine FSM has two related
bugs in assets/js/interactive_soda_machine.js

Bug 1 — Buttons re-enable during Wait states

Steps to reproduce:

1. Click "Drop 10¢"
2. Click "Drop 10¢" again (total = 20¢)
3. Machine enters W20 wait state
4. Buttons sometimes still appear
5. If user clicks "Drop 5¢" → gets only soda,
   no change returned
6. If user clicks "Drop 10¢" → gets soda +
   only 5¢ change instead of correct amount

Expected Behavior

Buttons should be completely disabled from the
moment a coin is inserted until the machine
returns to idle state M0

Root Cause in Code

The button enable condition only checks:
if (soda_machine_fsm.state <= 4)

This misses states W15 (5) and W20 (6) where
buttons should still be disabled

Bug 2 — No feedback during processing

When machine is in any Wait state (W5, W10,
W15, W20) the buttons disappear but no message
is shown to the user explaining what is happening

Expected Behavior

Show a clear message like "Processing coin..."
or "Please wait..." during all wait states

Files affected

assets/js/interactive_soda_machine.js

problem.video1.mp4

problem.video.2.mp4

[VaibhavJindal7]

I would like to work on this issue.
I have identified the root cause in
interactive_soda_machine.js where buttons
re-enable incorrectly during Wait states
(state > 4 condition is incomplete).
I will submit a fix shortly.

[VaibhavJindal7]

Partially addressed in PR #771.

Changes made:

1. Added status messages during all Wait states
   so users now see clear feedback:

   • "Processing coin..." when coin is inserted
   • "Coin accepted! Insert more coins" at M5/M10
   • "Processing..." at W15/W20
   • "Returning change!" at M20
   • "Enjoy your soda!" at M15
   • "Insert a coin to start" when back at idle

2. Fixed button re-enable condition - buttons now
   only re-enable at stable states (M0, M5, M10)

The "20" display issue in circles is documented
in the FSM page with a clear explanation.

PR link: #771