Release v0.27.26

What's Changed

• fix(cli): honor non-retryable LLM metadata by @overlord-letta in #3230
• feat: route headless messages through environments by @sarahwooders in #3229
• feat(slack): auto-subscribe to threads the agent sends messages to by @overlord-letta in #3073
• feat(reflection): isolate MemFS writes in worktrees by @devanshrj in #3125
• chore: bump version to 0.27.26 by @github-actions[bot] in #3237

Full Changelog: v0.27.25...v0.27.26