fix(scrape): repair download memory and dead break guard in amazon config

[arminfauland]

Two independent bugs in config/sites/amazon.jsonc make every run re-download every invoice. Found while investigating why a daily run kept fetching ~830 invoices it already had — the stored list held 12 entries after 830 downloads.

1. alreadyDownloaded matched substrings

amazon.downloadedInvoices is a comma-joined string, but the check was a plain $contains. An invoice key that is a substring of a stored key counts as present and is therefore never downloaded:

list = "…-306-1111111-2222222-10"
key  = "…-306-1111111-2222222-1"    → $contains → true   (wrong)

Affects any order with ten or more invoice links. Both sides are now wrapped in commas so only whole entries match.

Verified with jsonata against the real expressions:

key	should be	old	new
…-2222222-1 (only -10 stored)	false	true	false
…-2222222-10	true	true	true

2. shouldStoreOrderId could never be true

The guard tests firstDownloadedOrderId — but that value is only created by the next action. In JSONata a comparison against an undefined operand yields undefined, so = null or = undefined evaluates to false in both states:

unset → false          set → false

The following skipIf uses skipIfFalse: true, so the step was always skipped and amazon.lastOrderId was never written. That leaves the incremental shouldBreak — which compares the current order against lastOrderId — as dead code, so runs always walk the entire order history instead of stopping at the last known order.

$not($exists(...)) expresses the original intent: true on the first iteration, false afterwards.

Verification

Both expressions were extracted from the file and evaluated with the jsonata package rather than reasoned about. Deployed on my own instance since 2026-08-04: the stored list now grows per invoice instead of per run, three consecutive runs downloaded 19 → 3 → 0 files, and the run time for one account dropped from 13.0 min to 1.7 min.

Related: #149 — without that fix the list is invisible to templates within the same run, so these two fixes only take full effect together.