[T3352] FIX: guard letter submit against double-click race

[Danielgergely]

• FIX: Guard _onSubmitLetter to prevent a double click + error

[greptile-apps]

Confidence Score: 5/5

T-Rex Logs

What T-Rex did

• T-Rex ran the guard harness for the two-generator submission guard and it completed successfully.
• The harness loaded and evaluated the actual my2_new_letter.js handler for both revisions, ensuring the code path is shared and not duplicated.
• The reviewer observed that before the change immediate Send and Preview submissions produced two generators, while after the change the same interaction produced exactly one generator and the initiating Send button was disabled during collection, with both collection and create-generator paths releasing the guard and re-enabling the button on completion or failure.
• Implementation details were validated: the guard blocks re-entry at lines 62–66 and the cleanup releases the guard at lines 161–162, preserving retry behavior.

_{Ran code and verified through T-Rex}

_{Reviews (1): Last reviewed commit: "[T3352] FIX: guard letter submit against..." | Re-trigger Greptile}