Day-2 cut of item B: the reversal path becomes async. Pre-v1.0.7
(and v1.0.7 day 1) the refund handler flipped seller_transfers
straight from completed to reversed without ever calling Stripe —
the ledger said "reversed" while the seller's Stripe balance still
showed the original transfer as settled. The new flow:
refund.succeeded webhook
→ reverseSellerAccounting transitions row: completed → reversal_pending
→ StripeReversalWorker (every REVERSAL_CHECK_INTERVAL, default 1m)
→ calls ReverseTransfer on Stripe
→ success: row → reversed + persist stripe_reversal_id
→ 404 already-reversed (dead code until day 3): row → reversed + log
→ 404 resource_missing (dead code until day 3): row → permanently_failed
→ transient error: stay reversal_pending, bump retry_count,
exponential backoff (base * 2^retry, capped at backoffMax)
→ retries exhausted: row → permanently_failed
→ buyer-facing refund completes immediately regardless of Stripe health
State machine enforcement:
* New `SellerTransfer.TransitionStatus(tx, to, extras)` wraps every
mutation: validates against AllowedTransferTransitions, guarded
UPDATE with WHERE status=<from> (optimistic lock semantics), no
RowsAffected = stale state / concurrent winner detected.
* processSellerTransfers no longer mutates .Status in place —
terminal status is decided before struct construction, so the
row is Created with its final state.
* transfer_retry.retryOne and admin RetryTransfer route through
TransitionStatus. Legacy direct assignment removed.
* TestNoDirectTransferStatusMutation greps the package for any
`st.Status = "..."` / `t.Status = "..."` / GORM
Model(&SellerTransfer{}).Update("status"...) outside the
allowlist and fails if found. Verified by temporarily injecting
a violation during development — test caught it as expected.
Configuration (v1.0.7 item B):
* REVERSAL_WORKER_ENABLED=true (default)
* REVERSAL_MAX_RETRIES=5 (default)
* REVERSAL_CHECK_INTERVAL=1m (default)
* REVERSAL_BACKOFF_BASE=1m (default)
* REVERSAL_BACKOFF_MAX=1h (default, caps exponential growth)
* .env.template documents TRANSFER_RETRY_* and REVERSAL_* env vars
so an ops reader can grep them.
Interface change: TransferService.ReverseTransfer(ctx,
stripe_transfer_id, amount *int64, reason) (reversalID, error)
added. All four mocks extended (process_webhook, transfer_retry,
admin_transfer_handler, payment_flow integration). amount=nil means
full reversal; v1.0.7 always passes nil (partial reversal is future
scope per axis-1 P2).
Stripe 404 disambiguation (ErrTransferAlreadyReversed /
ErrTransferNotFound) is wired in the worker as dead code — the
sentinels are declared and the worker branches on them, but
StripeConnectService.ReverseTransfer doesn't yet emit them. Day 3
will parse stripe.Error.Code and populate the sentinels; no worker
change needed at that point. Keeping the handling skeleton in day 2
so the worker's branch shape doesn't change between days and the
tests can already cover all four paths against the mock.
Worker unit tests (9 cases, all green, sqlite :memory:):
* happy path: reversal_pending → reversed + stripe_reversal_id set
* already reversed (mock returns sentinel): → reversed + log
* not found (mock returns sentinel): → permanently_failed + log
* transient 503: retry_count++, next_retry_at set with backoff,
stays reversal_pending
* backoff capped at backoffMax (verified with base=1s, max=10s,
retry_count=4 → capped at 10s not 16s)
* max retries exhausted: → permanently_failed
* legacy row with empty stripe_transfer_id: → permanently_failed,
does not call Stripe
* only picks up reversal_pending (skips all other statuses)
* respects next_retry_at (future rows skipped)
Existing test updated: TestProcessRefundWebhook_SucceededFinalizesState
now asserts the row lands at reversal_pending with next_retry_at
set (worker's responsibility to drive to reversed), not reversed.
Worker wired in cmd/api/main.go alongside TransferRetryWorker,
sharing the same StripeConnectService instance. Shutdown path
registered for graceful stop.
Cut from day 2 scope (per agreed-upon discipline), landing in day 3:
* Stripe 404 disambiguation implementation (parse error.Code)
* End-to-end smoke probe (refund → reversal_pending → worker
processes → reversed) against local Postgres + mock Stripe
* Batch-size tuning / inter-batch sleep — batchLimit=20 today is
safely under Stripe's 100 req/s default rate limit; revisit if
observed load warrants
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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