[Bug] Claude Code 2.1.186: Assistant ignores CLAUDE.md preferences and explicit user instructions

Bug Description
Since updating to Claude Code CLI 2.1.186 (installed 2026-06-23 ~16:37 CEST), the assistant has become noticeably more likely to ignore configured preferences (CLAUDE.md) and explicit in-conversation instructions, and to diverge from the action actually requested. The same configuration was reliably followed on the prior versions (2.1.181–2.1.185). I can't prove causation — reporting this as a correlation observed since the update. Concrete examples from a single session today: 1. Deviated from a documented, project-specific procedure in CLAUDE.md (a prescribed exact REST auth invocation). It substituted a refactored shell-variable form that broke authentication, then misdiagnosed the resulting error (concluded a project/permission did not exist) instead of checking its own broken call. 2. Repeatedly ran read-only investigation/exploration after being explicitly told "don't investigate, just do X" — several times in a row. 3. Switched tools to the browser (CDP) when explicitly asked to use REST. 4. Ended nearly every response with unsolicited follow-up offers, despite an explicit "tight responses, do what's asked, no extra offers" preference. 5. Ignored an explicit efficiency rule ("use the cheapest tool that covers the task; ask the admin who already knows the location before multi-step exploration"), instead brute-forcing pagination over ~2000 fields and guessing API endpoints until repeated 404s. Expected: configured CLAUDE.md preferences and explicit user instructions are honored, and the assistant performs the requested action without substituting its own agenda. Actual (since 2.1.186): preferences and explicit instructions are overridden more frequently, and the assistant goes off in a different direction than asked. Environment: macOS, Claude Code CLI native install, model Opus 4.8 (claude-opus-4-8). Same CLAUDE.md/settings as on the prior versions where behavior was correct.

Environment Info

• Platform: darwin
• Terminal: iTerm.app
• Version: 2.1.185
• Feedback ID: 355c11f6-68cf-4e9b-a6a5-d54d5687a0f3

Errors

[{"error":"Error: 500 {\"type\":\"error\",\"error\":{\"type\":\"api_error\",\"message\":\"Internal server error\"},\"request_id\":\"req_011CcLN4eLNh2kZL66cH15Yg\"}\n    at generate (/$bunfs/root/src/entrypoints/cli.js:12:69182)\n    at makeRequest (/$bunfs/root/src/entrypoints/cli.js:52:7688)\n    at processTicksAndRejections (native:7:39)","timestamp":"2026-06-23T14:39:33.160Z"},{"error":"Error: 500 {\"type\":\"error\",\"error\":{\"type\":\"api_error\",\"message\":\"Internal server error\"},\"request_id\":\"req_011CcLN9LetrgGCsceD6WW3r\"}\n    at generate (/$bunfs/root/src/entrypoints/cli.js:12:69182)\n    at makeRequest (/$bunfs/root/src/entrypoints/cli.js:52:7688)\n    at processTicksAndRejections (native:7:39)","timestamp":"2026-06-23T14:40:37.136Z"}]