docs: 2026-10-14 session-death incident, guards, resolution findings

Document the new exit codes (76/77), the wrapper/unit fix, recovery steps, the
verbose output, and the archive-resolution check (images match a logged-in
fetch; 1080p VP9 exists for newer videos; iOS plays VP9+Opus webm but not
VP9+AAC mp4). Correct the stale "timers are disabled" line, and flag that the
repo's weekly profiles timer was never installed on the host.

docs/gallery-dl.md

@@ -146,6 +146,19 @@ Anonymous access is **not** a viable fallback: it serves lower-resolution media,
 caps profile pagination at 12 posts, and returns `AuthRequired` for stories and
 highlights.
 
+(Observed 2026-10-07, after the session died: with no `sessionid` gallery-dl did
+not fall back to anonymous downloads at all — most sources failed with
+`HTTP redirect to login page` / `HTTP redirect to home page`, and stories came
+back as "No results". The lower-resolution claim above was **not** re-measured
+then; what *was* measured is that archived image sizes match a logged-in fetch.)
+
+**The session can die silently, and nothing about the browser window shows it** —
+an open Instagram tab keeps rendering its logged-in UI until its next failed
+request. The only reliable signal is the cookie DB: `scripts/check-session.py`
+looks for an unexpired `sessionid` in this same profile, and `gdl-cron.sh` runs
+it before every scheduled run (exit 76 = refuse to scrape). See `TOOLING.md`,
+"2026-10-14".
+
 ## Output format
 
 The viewer's parser is the contract, not JD2's exact bytes. `EXPORT_RE` in