## Why
Syncing was a growing `if/elseif` chain in
`SyncBankingConnectionJob::handle()` plus one private method per
provider. Every new provider meant editing the job, and the file mixed
provider-specific logic with cross-cutting orchestration. This does not
scale to dozens/hundreds of providers.
## What
Introduces a **factory + strategy** pattern:
- **`App\Contracts\BankingConnectionSyncer`** — interface: `sync()`,
`expires()`, `notifiesOnAuthFailure()`.
- **`AbstractBankingConnectionSyncer`** — defaults for the common case
(API-key provider: never expires, notifies on auth failure). A new
provider usually only implements `sync()`.
- **`BankingConnectionSyncerFactory`** — maps `connection.provider` to
its syncer (resolved from the container, so dependencies are injected).
- **Six syncers** — `IndexaCapitalSyncer`, `BinanceSyncer`,
`WiseSyncer`, `BitpandaSyncer`, `CoinbaseSyncer`, `EnableBankingSyncer`.
Each fully owns its provider behavior, including EnableBanking's daily
email and first-sync cutoff.
`SyncBankingConnectionJob` drops from ~520 to ~190 lines and now only
orchestrates: deleted-user/expiry/rate-limit checks, error handling,
retries, logging, and status updates. It asks the syncer `expires()` /
`notifiesOnAuthFailure()` instead of hardcoding provider lists.
### Adding a provider now
1. Create `XSyncer extends AbstractBankingConnectionSyncer` implementing
`sync()`.
2. Add one line to the factory map.
No changes to the job.
## Tests
- Existing job tests (`SyncBankingConnectionJobTest`,
`SyncRetryAndLoggingTest`) migrated through a shared `runSync()` helper
in `tests/Pest.php`; all original assertions preserved.
- New `BankingConnectionSyncerFactoryTest`: provider→syncer resolution,
unknown-provider exception, and the capability flags.
- Full suite green: **1604 passed**, 0 failures. PHPStan clean, Pint
applied.
## Docs
Adds `docs/adding-a-banking-provider.md` — a step-by-step developer
guide (usable by a human or an AI agent) covering the sync provider and
the broader end-to-end integration touchpoints.
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