v0.51.76 — Release AZ

Stage-369: 4-PR safe-lane batch.

Composition

PR #2195 by @Michaelyklam (refs #692) — OpenRouter cost history backend. Process-local lock + reset-aware delta computation.

PR #2347 by @franksong2702 (fixes #2344) — Preserve live agent timeline across session switches. Snapshot live assistant turn DOM; merge back on return.
PR #2393 by @Michaelyklam (refs #2313) — Cap live chat stream transports to selected session.
PR #2396 by @starship-s — Preserve session agents for credential pools (stable cache identity for pool routes).

Widened brittle setCompressionUi({ source-string assertion in tests/test_run_journal_frontend_static.py to accept either inline-object or hoisted-variable form (PR #2347 hoisted state to share with appendLiveCompressionCard; behavior identical).
Fixed **PR TBD** placeholder → **PR #2347** in CHANGELOG (Opus catch).

pytest: 5767 passed, 10 skipped, 1 xfailed, 2 xpassed, 8 subtests passed in 144.85s. EXIT=0. Single run, no self-loop (os.execv guard active).
Opus advisor: SHIP verdict. All 5 risk areas verified (cache identity / dataset.sessionId stamping / SSE transport ordering / cost-snapshot lock / cross-PR boundaries). No further SHOULD-FIX.
Agent self-verify (unmocked, against production code):
- #2396 cache signature: pool-rotation invariant ✓, key-change invalidation ✓, pool-removal transition ✓, empty/None equivalence ✓.
- #2195 RMW lock: 20 concurrent appends → 1 coalesced entry ✓. Reset-aware delta: 25 → 5 produces delta=5 (not -20) ✓.

PR #2195 _COST_SNAPSHOT_LOCK is process-local; add file-lock for multi-worker WebUI if/when enabled.
PR #2347 interim_assistant joins with \n\n instead of raw concat — UX pass for sessions with many interim outputs.
PR #2347 _thinkingCardHtml(text, open) template duplication — trivial refactor.

v0.51.76 — Release AZ (stage-369: 4-PR safe-lane batch) by @nesquena-hermes in #2400
Add OpenRouter cost history backend by @Michaelyklam in #2195
Preserve live agent timeline across session switches by @franksong2702 in #2347
fix(streaming): preserve session agents for credential pools by @starship-s in #2396

Full Changelog: v0.51.75...v0.51.76