fix(mail): stop Gmail refusing the search, and stop calling that "hittade inget" (#1521)

Pressing Leta produced mails=25, documents=0 on a real two-mailbox run.
Nothing was found because nothing was searched: every request came back
429 "Too many concurrent requests for user".

Two bugs, and the second is the one that matters.

The search fanned out with Promise.all over every message id at once, one
Gmail request per message, per connection. Gmail enforces a per-user
concurrency ceiling as well as a daily quota, and this sailed past it long
before any volume worth worrying about. It now runs through a pool of five
per connection, which is comfortably under and still finishes a page of
results in a couple of round trips.

The catch turned each refusal into an empty array, with a comment saying
one mailbox's failure must not become the company's. Right instinct, wrong
consequence: an empty array is also what an empty mailbox returns, and the
manual hunt loop stops on fetched === 0 because that is its signal for
"the mailboxes hold nothing more for what is open". So a rate-limited
search told the user their receipts do not exist, and stopped looking.

searchFailureCount() now separates "could not look" from "nothing there".
The run route reports it, and the loop treats a pass with failures as
failed rather than finished, so pressing again is the obvious next move
instead of a pointless one.

This is the failure this feature exists to catch, happening inside the
feature: silence that reads as an answer.

Restoring the unbounded fan-out fails one test; removing the failure
counter fails three.

Co-authored-by: Jakob Wennberg <311770904+jakobwennberg-oss@users.noreply.github.com>
Co-authored-by: Claude Opus 5 (1M context) <noreply@anthropic.com>

components/extensions/general/use-receipt-hunt.ts

@@ -27,6 +27,8 @@ export interface HuntResult {
   proposed: number
   remaining: number
   failed?: boolean
+  /** Connections that refused the search. See the stop condition below. */
+  searchFailures?: number
 }
 
 export interface HuntProgress {
@@ -79,6 +81,15 @@ export function useReceiptHunt(onPass?: () => void) {
         onPass?.()
 
         // Nothing new this pass: the mailboxes have no more for what is open.
+        //
+        // Unless a mailbox refused to be read, in which case zero fetched says
+        // nothing about what is in there. Stopping on it, and reporting it as
+        // "hittade inget", would tell the user their receipts do not exist
+        // because Gmail was busy. Treat it as a failure and let them retry.
+        if ((body.data.searchFailures ?? 0) > 0) {
+          setResult({ ...body.data, fetched, proposed, failed: true })
+          return
+        }
         if (body.data.fetched === 0) {
           setResult({ ...body.data, fetched, proposed })
           return