Closes#62088
When `buildActionOpts` returns undefined (default account, no token
override), `downloadSlackFile` calls `resolveToken(undefined, undefined)`
which re-reads raw config via `loadConfig()`. If botToken is a SecretRef
object, `normalizeResolvedSecretInputString` rejects it because it
expects a string — the download silently fails.
This injects the already-resolved botToken from the gateway runtime
snapshot into the download opts as a fallback, bypassing the raw config
re-read. Same root cause as the Discord fix in b51214ec3e.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>