debug_stand_in_policy() -> PromptCachePolicyBuild the placeholder policy used by DEEPAGENTS_CODE_DEBUG_COLD_CACHE.
Keeps the modal reachable on providers with no documented cache policy.
Lives here rather than in the caller so the Anthropic window and minimum
stay tied to _ANTHROPIC_MIDDLEWARE_TTL_SECONDS and
_ANTHROPIC_DEFAULT_MINIMUM_TOKENS instead of being re-hardcoded, which
would silently drift the moment either constant is revised.
The provider name is deliberately Anthropic's: under the debug flag the modal may therefore cite Anthropic retention while a different provider is active. The figures are illustrative in that mode, not real estimates.