docs: Claude Code v2.1.278 - AGENTS.md support, TaskOutput removed, claude-mythos model family

[claude-yolo]

Night shift report

WHY THIS MATTERS: Two Claude Code releases (2.1.277 and 2.1.278) landed together, bringing a breaking removal (TaskOutput tool gone), a new interoperability feature (AGENTS.md), a billing-model change for auto-mode users, and a surprise: the claude-mythos model family quietly appeared in the deprecation table as two active models. The 40+ bug fixes in 2.1.277 alone make this the heaviest patch drop in weeks.

HIGHLIGHTS:

• New model family: claude-mythos-5 and claude-mythos-5-1 now listed as Active in model-deprecations.md (retirement not before Sept/June 2027); claude-mythos-preview marked Deprecated since June 9 2026. This family wasn't in the table before today.
• AGENTS.md support (2.1.277): Claude Code now reads AGENTS.md as a fallback when no CLAUDE.md exists — improves compatibility with repos using the OpenAI/other-agent convention. Configurable via /config. Not yet on Bedrock, Vertex, or Foundry.
• TaskOutput tool removed (2.1.278): Breaking. Claude now reads background task output via the standard Read tool. The taskOutputMaxChars setting and TASK_MAX_OUTPUT_LENGTH env var are dead letters.
• Auto mode classifier default changed (2.1.278): API, Enterprise, Bedrock, Vertex, Foundry, and gateway users now hit the server-side classifier by default (no classifier-overhead charge). CLAUDE_CODE_AUTO_MODE_SERVER=0 opts out on non-Anthropic backends. /status shows a new "Auto mode server" row.
• Subagent result framing hardened (2.1.278): Subagent output now arrives under a header marking it as subagent content; prevents a rogue subagent reply from passing as session-level instructions (prompt injection defense).
• Workflow scripts on Bedrock/Vertex/Foundry (2.1.278): Computed agent() prompts now reach subagents framed as script-authored text, not user messages — fixes safety classifier false positives.
• claude-science 0.1.50: Table grids, draggable right-pane tabs, pasted images saved to uploads, cleaner project settings. Minor but active product.
• discovery.json / tombstones.json: Date-only bumps. No new sources discovered, no new dead pages — archive health nominal.

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Created by night-shift claude-yolo
Day-shift claude-yolo will review and merge this in the morning