Release BC / v0.51.79 — stage-372 (5-PR review-bypass batch: text-mode image fix + Activity-group compression + custom provider routing + quota chip toggle + RFC docs)

[nesquena-hermes]

Release BC / v0.51.79 — stage-372 (5-PR review-bypass batch)

Review-bypass batch release: all 5 constituent PRs are individually nesquena-APPROVED (per ~/WebUI/docs/agent-memory/batch-release-rules.md § review-bypass rule). This release PR ships the squashed batch without requiring another full review round.

Constituents (all nesquena APPROVED)

PR	Author	What
#2407	@Michaelyklam	RFC docs update — #1925 runtime-adapter gate advanced to Slice 2-ready
#2406	@Michaelyklam	Sync POST /api/chat route passes cfg= into history sanitizer (closes #2398)
#2408	@Michaelyklam	Auto-compression cards close current live Activity group (closes #2404)
#2411	@Michaelyklam	Named custom:* providers preserve vendor-prefixed model selections (closes #2405)
#2413	nesquena-hermes (self-built)	Quota chip Settings toggle, default off (regression fix for v0.51.78's #2082)

Pre-merge gates

• pytest: 5794 passed, 6 skipped, 3 xpassed, 8 subtests passed, 0 failed in 115.66s
• Pre-Opus gate: JS + Python syntax clean, no merge markers, no CHANGELOG placeholders
• Opus advisor: SHIP, no SHOULD-FIX, no DEFER. Two optional symmetry follow-ups noted (dead _isNamedCustomActiveProvider branch in _isPortalFetch, missing label.textContent clear in refresher disabled short-circuit) — neither is user-visible or merge-blocking.
• Cross-PR ui.js audit (3 PRs touch the file): Opus confirmed no function-boundary overlap, no contradictory edits. fix: split live Activity groups at auto-compression #2408 lives at ~4820/4951, fix: preserve named custom provider model selections #2411 at ~745/1020/1105/4601, feat(quota-chip): add Settings toggle, flip default to off #2413 at 676–701.
• Browser QA: smoke-verified at 1920×1080 on stage-372 build — quota chip hidden by default (the regression fix), Settings field present with description.
• CHANGELOG: each PR linked to its correct tracking issue (Follow-up: complete #2297 coverage in _handle_chat_sync (POST /api/chat) #2398, Auto-compression card mid-turn should close current live Activity group #2404, bug(ui): custom:* provider model selection rejected by false-positive mismatch warning and forced fallback reset #2405, RFC: Make WebUI a thin observability/control client over Hermes Agent runtime #1925, feat: show ambient provider quota indicator #2082).

Conflict resolution

CHANGELOG conflicts on #2406, #2408, #2411 (each added an ## [Unreleased] entry; v0.51.78 sliced a new release block between them and HEAD). Resolved by consolidating all three Fixed entries into one ## [Unreleased] block then sliced under the new ## [v0.51.79] release header during the stamping commit. ui.js auto-merged cleanly on all three contributor PRs.

What this closes

• Follow-up: complete #2297 coverage in _handle_chat_sync (POST /api/chat) #2398 (text-mode image history sanitizer on sync route)
• Auto-compression card mid-turn should close current live Activity group #2404 (auto-compression mid-turn Activity boundary)
• bug(ui): custom:* provider model selection rejected by false-positive mismatch warning and forced fallback reset #2405 (named custom provider model selection persistence)
• Quota chip default-on regression from v0.51.78 (feat: show ambient provider quota indicator #2082 follow-up)

Stage-372 worktree

Branch: stage-372 (this PR's head)
Tag target: v0.51.79