Release BE: stage-374 (v0.51.81) — 6-PR batch — cost-history POSIX lock + prompt-cache tokens + Plugins panel i18n + pending placeholder + journal partial recovery + RuntimeAdapter Slice 2

[nesquena-hermes]

v0.51.81 — Release BE (stage-374)

6-PR contributor batch. All authored by contributors, agent-assembled and tested.

Contents

Added

• feat(runtime): add default-off RuntimeAdapter seam #2424 @Michaelyklam — default-off RuntimeAdapter Slice 2 seam (HERMES_WEBUI_RUNTIME_ADAPTER=legacy-journal)
• fix: surface prompt cache usage in WebUI #2421 @Michaelyklam — surface prompt-cache read/write tokens in WebUI usage (fixes Bug: WebUI cost is ~100× CLI cost on same token volume — prompt cache misses on mobile reconnect, agent rebuild, and per-message workspace prefix #2419)
• i18n: add internationalization support for the Settings Plugins panel #2425 @mccxj — i18n for Settings Plugins panel

Fixed

• fix: lock cost history snapshot updates across workers #2418 @Michaelyklam — provider-specific POSIX file lock for cost-history snapshot updates (fixes Cost-history backend: add file-lock for multi-worker WebUI deployments #2402)
• fix: show pending assistant state on chat submit #2431 @Michaelyklam — render assistant-side pending placeholder before /api/chat/start returns (fixes ux(chat): show assistant pending state immediately after submit #2429)
• Recover journaled partial output after WebUI restart #2427 @franksong2702 — recover journaled partial output after WebUI restart (fixes Restore journaled partial timeline after WebUI process restart #2423)

Pre-merge gate

• Pre-Opus checks: JS node -c, Python ast.parse, merge-marker scan (tightened), CHANGELOG placeholder scan, agent self-verify on fix: lock cost history snapshot updates across workers #2418/fix: surface prompt cache usage in WebUI #2421/feat(runtime): add default-off RuntimeAdapter seam #2424/Recover journaled partial output after WebUI restart #2427 — all clean
• pytest: 5814 passed, 6 skipped, 3 xpassed in 115s
• Opus advisor (claude-opus-4-7 with --thinking): VERDICT: ship as-is. No BLOCKER. Two SHOULD-FIX items deferred to v0.51.82 follow-up issues (S1: response-shape contract drift when legacy-journal flag on; S2: narrow journal recovery gap when in-memory messages empty but core transcript populated).

Held this round

• fix: protect pipes in parentheses from table split + KaTeX dollar-sign misparse in tables #2428 (@bengdan, table renderer pipe-protect) — multi-pipe inside a single bracket pair still mis-splits. Detailed regression note + suggested iterative-fix posted; hold applied.

Approval

Contributor PRs — no nesquena-self-built work in this stage, so independent-review gate doesn't apply. #2418 already had a nesquena APPROVED review; the other five passed agent review + the full automated gate above.