bug: RetryInfo delay of '0s' is treated as missing, misclassifying retryable rate limits as terminal #29049

What happened?

classifyGoogleError() parses RetryInfo.retryDelay via parseDurationInSeconds(), then guards with if (parsedDelay) — treating a successful parse of "0s"/"0ms" as a failure because 0 is falsy. delaySeconds stays undefined, so a RATE_LIMIT_EXCEEDED error carrying "retry immediately" semantics falls into the terminal branch instead of the retryable one: retries are aborted and the fallback/credits flow fires for a routine rate limit.

Affected code

packages/core/src/utils/googleQuotaErrors.ts:340-345:

if (retryInfo?.retryDelay) {
  const parsedDelay = parseDurationInSeconds(retryInfo.retryDelay);
  if (parsedDelay) {            // <-- 0 is falsy
    delaySeconds = parsedDelay;
  }
}

packages/core/src/utils/googleQuotaErrors.ts:103-113:

function parseDurationInSeconds(duration: string): number | null {
  // ...
  if (duration.endsWith('s')) {
    const seconds = parseFloat(duration.slice(0, -1));
    return isNaN(seconds) ? null : seconds;   // returns 0 for "0s"
  }

The same truthiness guard recurs at ~line 411 (retryInfo?.retryDelay && delaySeconds).

How can this be reproduced?

Return a 429 with body containing ErrorInfo { reason: "RATE_LIMIT_EXCEEDED" } and RetryInfo { retryDelay: "0s" }. Observed: TerminalQuotaError (terminal). Expected: RetryableQuotaError with immediate/small delay.

What did you expect to happen?

A parsed delay of exactly 0 should be honored ("retry now"), not treated as unparseable.

Suggested direction

Use the documented sentinel contract: const parsed = parseDurationInSeconds(...); if (parsed !== null) { delaySeconds = parsed; } at both occurrences.

Found by source audit on current main (commit 5411f113c); platform-independent. No open issue/PR covering this was found (searched: retry delay rate limit terminal).