Claude Code 2.1.274 adds a bounded MCP startup wait, a managed-settings OTel event, and stops corrupted transcripts from retrying a 400 forever
The 17 September entry is one of the largest in the changelog's recent history. Three items are directly actionable for anyone running headless or scheduled sessions: CLAUDE_CODE_MCP_STARTUP_WAIT_MS bounds how long the first non-interactive turn blocks on connecting MCP servers (0 means do not wait), sessions stuck endlessly retrying 'unexpected tool_use_id' 400 errors now self-heal or fail with a /rewind hint instead of looping, and headless and SDK sessions no longer make a separate model call for every finished background task. Also shipped: an effort attribute on the claude_code.llm_request OTel span, a claude_code.managed_settings_resolved OTel event gated behind OTEL_LOG_MANAGED_SETTINGS=1, an index.jsonl linking OTEL_LOG_RAW_API_BODIES files to their requests, /code-review switching to leaner inline prompts instead of spawning many subagents on untuned models, and Bedrock/Vertex/Foundry installs defaulting to the v2 MCP client with 2026-07-28 negotiation.
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