Replace hardcoded cache key in ForAgentsController with a config-based
key (`mcp.cache.for_agents_key`) and configurable TTL
(`mcp.cache.for_agents_ttl`). This prevents collisions with other modules
or packages that might use the same flat cache key.
- Add `cacheKey()` method on ForAgentsController, reads from config
- Add `cache` section to config.php with default key and TTL
- Dynamic Cache-Control max-age now follows the configured TTL
- Add ForAgentsControllerTest covering key customisation,
cache storage, invalidation, TTL, and response structure
Refs: TODO.md CQ-003
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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