akvo / iwsims / #107

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Pull #31

coveralls-python

[#30] Make form submissions idempotent with a per-submission key

Synced from akvo-mis #255 (72fe9f23, aa0b4515, 030c2358):
- FormData.submission_key: nullable unique CharField(64); unique index
  built CONCURRENTLY so the data table is never locked (migration
  renumbered to 0004, depending on 0003_add_visualization_indexes)
- SubmitPendingFormSerializer.create() returns the existing row on a
  replayed key and survives the concurrent-retry race via a savepointed
  IntegrityError catch
- /device/sync accepts and forwards submission_key from the mobile app
- Webform mints one key per submission attempt and clears it only after
  the backend confirms
- Covered by 13 new idempotency tests; full v1_data + v1_mobile suite
  passes (479 tests)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

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