List all bank securities positions

Verified non-API-key staff or services holding ledger:read or ledger:securities:read (the reporting service reads it for Schedule RC-B); customers and API keys are refused 403 even locally. as_of names a business date whose original ledger closing completed, else 409 ledger.period_not_ready. Every lot held on the date (traded on or before it and not disposed of by it) or carried by that closing is placed with its version-one closing cost, fair-value adjustment and allowance; amortized cost is checked against the contractual schedule through the close; fair value comes only from an independently approved day_close valuation as of the date whose balances the closing carries, otherwise the position names it missing, never zero; the classification in force is the approved version effective on or before the date. A position whose lot record and closing disagree (booked or disposed of after the close, a valuation restated after it) names the exception. No signed receipt, dealer or bank statement evidence is included; responses are bounded at 16 MiB.