Debug a specific, reproducible bug without triggering a rewrite

StudyBot (the Discord reminder bot) is a working app you (or an earlier session) already built in Replit. It has one specific, reproducible bug. Fix exactly that bug with the smallest correct change — this is a debugging pass, not an invitation to refactor or rewrite anything else you notice along the way.

THE BUG
The /remind command sometimes posts the reminder twice in the channel

STEPS TO REPRODUCE
Run /remind with a time less than 60 seconds away, then wait for it to fire — about 1 in 3 attempts posts the message twice, roughly 2 seconds apart

EXPECTED VS ACTUAL
Expected: exactly one reminder message posted at the scheduled time
Actual: occasionally two identical reminder messages posted a couple seconds apart

DEBUGGING DISCIPLINE
Before changing any code, reproduce the bug yourself using the steps above and confirm you're seeing the same actual behavior I'm describing — if you can't reproduce it with these exact steps, say so and ask what's different about my environment rather than guessing at a fix for a bug you haven't actually observed. Once reproduced, trace the actual root cause — the specific line, the specific piece of state, the specific request that's wrong — and explain it in plain language before touching any code, the same way a human engineer would explain a diagnosis before writing a fix. Do not fix the bug by wrapping the symptom in a defensive check that hides it (a try/catch that silently swallows the error, an if-statement that skips the broken code path) unless that genuinely is the correct fix — if the underlying cause is something else entirely and a defensive check would just mask it, say so and fix the actual cause instead. Make the smallest change that fixes the root cause. If you notice unrelated code nearby that looks wrong or outdated while you're in there, do not fix it as part of this change — name it separately, at the end, as something worth a future look, and leave it untouched.

VERIFICATION
After the fix, walk back through the exact repro steps above and confirm the actual behavior now matches expected. Then check the two or three most obviously related flows that touch the same code path — the /schedule command (uses the same scheduling function) and the daily automated reminder job — and confirm the fix didn't change their behavior, since a fix scoped to one exact symptom can still have side effects on a shared function or shared piece of state used elsewhere.

OUTPUT
1. The root cause, in plain language.
2. The diff — only the lines that changed, nothing reformatted or touched that didn't need to be.
3. Confirmation that the original repro steps now produce the expected behavior.
4. Anything unrelated you noticed but deliberately left alone, per the rule above.