feat(stage1): verify NSDUH youth attempt availability

.learnings/ERRORS.md

@@ -2,6 +2,35 @@
 
 Command failures and integration errors.
 
+---
+## [ERR-20260920-032] samhsa-pdf-direct-fetch-forbidden
+
+**Logged**: 2026-09-20
+**Priority**: medium
+**Status**: resolved
+**Area**: docs
+
+### Summary
+SAMHSA PDF endpoints returned HTTP 403 to the web reader, direct download, and in-app browser during the NSDUH source audit.
+
+### Error
+`403 Forbidden` from the official PDF URLs; the sandboxed first download attempt also had no network route.
+
+### Context
+The official documents remained indexed with searchable text, and SAMHSA HTML methodology pages plus year-specific search extracts exposed the required question, routing, variable, and disclosure-risk statements. No local or remote data were changed by the failed reads.
+
+### Suggested Fix
+Use SAMHSA's indexed official-document text and HTML pages for this audit, retain exact source URLs, and keep page-level PDF visual verification pending rather than claiming it occurred.
+
+### Metadata
+- Reproducible: yes
+- Related Files: `research/stage1/nsduh_youth_attempt_source_audit.md`
+- Pattern-Key: net.access-forbidden
+
+### Resolution
+- **Resolved**: 2026-09-20
+- **Notes**: Triangulated the claim across official 2021–2023 restricted-use codebooks, the 2024 questionnaire, 2024 methodology definitions, the 2024 public-use guide, and the local public-use schema. Direct PDF page rendering remains explicitly unverified.
+
 ---
 ## [ERR-20260920-031] git-https-authentication-rejected