A conversation failed every turn with a 400 when the API rejected an MCP tool input schema; CC now sends that tool without parameters for the rest of the conversation. yoyo: unprobed. Same session-killing shape as the builtin-name collision (Tool names must be unique) that yoyo guards pre-flight; no schema-rejection guard found by grep (no input_schema handling in src/).
Claude not told about an MCP server tools/instructions until the next tool call when the server finished connecting after a compaction (MCP visibility class; yoyo tells the model about failed connects once per session, Day 181).
Resumed headless sessions lost compaction-kept messages when the compaction followed a reply cut at the output token limit (output-limit class, cf yoyo #1026).
SessionEnd hooks sometimes not running when exiting while a background command still runs.
--help naming a removed tool in its description of --restricted (doc drift on a safety flag).
Codex CLI October 2026: rust-v0.161 made GPT-6.1 Sol the default (yoyo deliberately defaults openai to gpt-6-sol because gpt-6.1-sol has no yoagent preset); /mcp login <name>; managed git worktree tools; 0.163 (Oct 15) adds steering while thinking, parallel execution for read-only tools (#52245), application network policy enforced in standalone MCP commands.