[Bug] Web search claims to read pages that return DNS errors (NXDOMAIN) — fabricated source citations

Bug description

When using web search in claude.ai chat (Opus 4.6), Claude claims to have read web pages that are completely unreachable (DNS_PROBE_FINISHED_NXDOMAIN), then cites specific data from those dead domains as if the fetch succeeded.

Steps to reproduce

1. Open claude.ai chat with Opus 4.6
2. Ask: "Búscame pkg ps4 pluto tv 6.00"
3. Claude responds with "Leídas 3 páginas, web buscada" (Read 3 pages, web searched)
4. One of the cited sources is ps4database.io with specific data: "System Version 7.51, 49.1 MB"
5. Navigate to ps4database.io → DNS_PROBE_FINISHED_NXDOMAIN (domain does not resolve)

Expected behavior

Claude should report that a source is unreachable and NOT cite data from domains that fail DNS resolution. The "Leídas 3 páginas" indicator should only count pages that were actually successfully fetched.

Actual behavior

Claude presents data from a dead domain with the same confidence as data from live sources. The user has no way to distinguish verified data from fabricated citations.

Evidence

Screenshots attached showing:

1. Claude citing ps4database.io with specific version data after claiming "Leídas 3 páginas"
2. Browser showing ps4database.io returns DNS_PROBE_FINISHED_NXDOMAIN

Environment

• Platform: claude.ai web
• Model: Opus 4.6
• Account: Pro subscriber
• Date: September 25, 2026

Additional context

Related to broader regression since ~Sep 16, 2026. See also: #96308, #96329, #96745, #96892, #96897, #97113