Accounts inventory repeats full credential-store reads for every provider projection

Observable defect

The real accounts inventory API repeatedly reloads every provider credential while rendering one settings response. At 58cc489bb65e67db4cdb8cf70b6431d217599d72, a local real-browser/API/encrypted-disk diagnostic measured 14 pool list calls, 14 selection-state calls and one expiry sweep per GET: 29 complete credential-store reads. A two-account GET took 2251ms; a priority PATCH queued behind that GET took 2346ms, while the following PATCH took 159ms.

The hosted Accounts lane at the same revision failed its existing reorder check after only the first PATCH completed server-side. A client timeout caused by inventory contention is provisional: the hosted artifact did not retain requestfailed events. This issue independently tracks the measured redundant read amplification, not an asserted infrastructure failure or the unrelated mobile layout fix.

Scope and acceptance

Use one request-scoped validated inventory for provider list and selection projections after expiry reconciliation. Preserve authenticated decoding, malformed-record failures, migration, eligibility, selection reasons and subsequent-request freshness. Do not introduce a persistent cache, increase timeouts or weaken assertions.

Validate real credential storage and HTTP/browser behavior, selection parity/error cases, and the unchanged full Accounts UI acceptance. Preserve timing and original failure evidence.