v0.51.26 — Release D: 5-PR follow-on contributor batch

Theme: Profile-isolation hardening (cache + skills + gateway-health) + context-length config-override threading + sidebar segment-count UI polish.

Constituent PRs

• #1901 by @Michaelyklam — Use root-level Hermes home for gateway health status (closes #1878)
• #1906 by @dso2ng (first-time contributor) — Sidebar UI polish: show collapsed session segment count
• #1903 by @Michaelyklam — Scope skills endpoints to active profile (closes #1880)
• #1898 by @nesquena-hermes (production) + #1904 by @Michaelyklam (functional test, absorbed via Co-authored-by) — Profile-home in agent cache signature (closes #1897, P0 reported by @AvidFuturist)
• #1900 by @nesquena-hermes — Pass config overrides into context-length fallback (closes #1896, P0 cascading-failure reported by @AvidFuturist)

Pre-release verification

• Full pytest under HERMES_HOME isolation: 4879 passed, 8 skipped, 1 xfailed, 2 xpassed, 8 subtests passed in 136.03s on Python 3.11.
• Browser API harness (port 8789): all 11 endpoints + 20 QA tests PASS.
• node -c on static/i18n.js, static/sessions.js: clean.
• Stage diff: 13 files, +1220/-32.
• Opus advisor pass on stage-321: SHIP. All 5 PRs verified correct with solid test coverage.
• v0.51.25 fixes verified preserved across rebase (every PR was originally based on pre-v0.51.25 master and all were rebased onto current master before staging — no silent reverts).
• Pre-stamp re-fetch of all 6 PR heads: no contributor force-pushes during the Opus window.

Test count

4872 → 4890 collected, 4879 passing (+18 net new).

Closes

• #1878 (PR #1901)
• #1880 (PR #1903)
• #1896 (PR #1900)
• #1897 (PR #1898)

Closes #1898, #1900, #1901, #1903, #1904, #1906.

Notes

• #1905 closed as superseded by #1900 (same-author parallel-iteration pattern; #1900 was already approved).
• #1898+#1904 absorption: #1898's production fix shipped with #1904's superior functional regression test (Michaelyklam Co-authored-by trailer preserves attribution).