[MODEL] Cyber safeguard false-positive blocks single read-only request during authorized pentest (see also #73896)

### Preflight Checklist

- [x] I have searched existing issues for similar behavior reports
- [x] This report does NOT contain sensitive information (API keys, passwords, etc.)

### Type of Behavior Issue

Other unexpected behavior

### What You Asked Claude to Do

Verify Row Level Security (RLS) on a database table via a single
read-only GET request to a Supabase REST endpoint, during an authorized
client penetration test engagement (explicit client permission on file,
findings to be reported to the client's own administrator).

### What Claude Actually Did

The request was blocked twice — once via a Bash tool call, once via a
PowerShell tool call in a retry — with:

> "API Error: Sonnet 5's safeguards flagged this message. Our
> intentionally broad safeguards allow us to deliver more capabilities
> faster, but can sometimes flag legitimate cybersecurity work."

Classifier category: `[cyber]`
Request ID: `req_011CegimNAXZrxwNKSNU2pfa`

### Expected Behavior

The request should have succeeded, consistent with 8 other identically
structured read-only requests to other table names in the same session
that were NOT blocked. The only variable was the table name containing
the word "credentials" — the block appears to trigger on that literal
string rather than on any actual behavioral or contextual risk signal
(single unauthenticated read, no write, part of an already-authorized
and otherwise-unblocked test sequence).

### Files Affected

```
none
```

### Permission Mode

Not applicable — blocked before any tool execution/approval step.

### Can You Reproduce This?

Yes — reproduced twice in the same session, once per tool (Bash, then
PowerShell), with the same underlying request.

### Steps to Reproduce

1. In an authorized security assessment context, ask Claude to send a
single read-only HTTP GET request to a REST endpoint.
2. Make the endpoint path/table name contain the word "credentials"
(e.g. a Supabase REST path like `/rest/v1/credentials?select=*&limit=1`).
3. Observe the request is blocked by the real-time cyber safeguard,
while structurally identical requests to other table names succeed.

### Claude Model

Sonnet 5

### Relevant Conversation

```
(available on request — omitted here as it includes a live client
engagement; happy to share privately if useful for triage)
```

### Impact

High — blocks legitimate, already-authorized security work mid-engagement
with no in-session path to proceed other than escalating outside the tool.

### Claude Code Version

Unknown — running as the Claude Code panel bundled inside Google's
Antigravity IDE on Windows 11; the standalone `claude` CLI is not on PATH
in that environment so `claude --version` could not be checked.

### Platform

Windows 11, Claude Code integration inside Antigravity IDE, Anthropic API
backend.

### Additional Context

Related: #73896 ("Fable safety heuristic false-positives on legitimate
defensive own-fleet security engineering") — closed as stale by
github-actions without any maintainer response, but describes the exact
same systemic pattern: security-adjacent vocabulary triggering false
positives regardless of clearly defensive/authorized context. This is a
third independent report of the same underlying issue (following the
original reporter and one +1 comment on #73896).

No source file or test is identified in the report. Start by reproducing the single read-only GET in the documented Bash and PowerShell contexts, compare it with the eight successful requests, and review related issue #73896. Done means an authorized request is not blocked solely because the table name contains “credentials”.

索引モデルが issue の本文から書いたものです。