[Bug] Opus 5 reasoning_extraction safeguard blocks benign first message, recurs across fresh sessions (Windows)

**Environment**
- Product: Claude Code, Claude Desktop app (Code tab)
- OS: Windows 11
- Claude Code version: 2.1.274
- Model: Opus 5, Max plan
- Project: local git repo with an extensive custom CLAUDE.md/AGENTS.md instruction set (personal + project-level config, written in Russian)

**What happened**

The very first message of a brand-new Claude Code session — "read the CLAUDE.md file in the project root", nothing else — is refused with:

> API Error: Opus 5's safeguards flagged this message (https://www.anthropic.com/legal/aup). This sometimes happens with safe, normal conversations. Claude Code can't respond to this message with Opus 5.
> Try rephrasing the request in a new session or change your model.
> Details: `[reasoning_extraction]`

Request ID: `req_011Cf8QFpGpgqkp2sk8E4yEk`
Time: 2026-09-17 ~11:44 ICT (UTC+7)

**Recurrence**

This is the 3rd confirmed occurrence in the same project, always on a completely benign message, always in a fresh session:
- Support ticket 215475965088729 was closed on 2026-09-15 marking this issue as resolved.
- The identical block recurred on 2026-09-17, after updating Claude Code to 2.1.274 (support suggested the update as a possible fix — it did not help).
- Follow-up support ticket: 215475975624667.

Switching to Sonnet 5 in the same project/session works with no issue — identical files, no block.

**Why this looks like a false positive**

The triggering message contains no request to reveal reasoning, chain-of-thought, or system instructions — it's a plain file-read instruction. Matches other reports of the same classifier misfiring on unrelated benign content:

- #94775 — benign bug-report sentence and Claude Code's own shipped `workflow-authoring` skill docs blocked, also on Windows, also resolved only by switching to Sonnet 5
- #94210 — block persisting across sessions once tripped, matching the "same project, fresh session, still blocked" pattern here
- #87640 — one-word greeting ("Hi") blocked

**Ask**

Could someone confirm whether this is an account/project-level flag that needs manual clearing, or a classifier bug being tracked? Happy to share the full CLAUDE.md/AGENTS.md content privately if it helps reproduce — didn't want to paste project-specific instruction files into a public issue.

Start by comparing this Windows/Opus 5 report with issues #94775, #94210, and #87640, then review the reported difference between Opus 5 and Sonnet 5 in fresh sessions. Confirm whether the repeated refusal is tied to the project or account, or whether it is a classifier false positive; done means documenting the cause and the appropriate resolution or tracking issue.

Written by the indexing model from the issue text.