v0.51.25 — Release C: 6-PR streaming/runtime contributor batch

Theme: Profile-isolated quota probes + request wedge diagnostics + max_turns config honor + per-turn usage overwrite + interim_assistant SSE wiring + workspace-prefix transcript dedup.

Constituent PRs

• #1873 by @franksong2702 — Subprocess-based profile isolation for quota fetches (closes #1831)
• #1860 by @franksong2702 — Request wedge diagnostics for /api/chat/start + /api/sessions (refs #1855)
• #1877 by @Michaelyklam — Honor agent.max_turns in WebUI streaming agents (closes #1876)
• #1861 by @franksong2702 — Per-turn usage overwrite (vs cumulative accumulation) (closes #1857) + Opus-absorbed defensive guard against restart-zeros-totals
• #1865 by @franksong2702 — Wire interim_assistant_callback runtime contract through SSE stream
• #1889 by @ai-ag2026 — Dedup workspace-prefixed user turns during compaction (refs #1217)

Pre-release verification

• Full pytest under HERMES_HOME isolation: 4861 passed, 8 skipped, 1 xfailed, 2 xpassed, 8 subtests passed in 145.96s on Python 3.11.
• Browser API harness (port 8789): all 11 checks PASS.
• node -c on static/messages.js: clean.
• Stage diff: 13 files, +1216/-196.
• Opus advisor pass on stage-320: SHIP with three Medium-severity concerns (one absorbed in-release: #1861 restart-zeros-totals guard; two filed as follow-ups: #1873 worker-pool ops, #1889 regex sentinel).
• Pre-stamp re-fetch of all 6 PR heads: no contributor force-pushes during the Opus window.

Opus-absorbed fixes

#1861 defensive guard — api/streaming.py:2925-2934: added > 0 / is not None guards before overwriting s.input_tokens / s.output_tokens / s.estimated_cost so a rebuilt-from-cache-miss agent (post-restart or post-LRU-eviction) doesn't zero out persisted disk totals on its next turn. Test still passes.

Test count

4858 → 4872 collected, 4861 passing (+14 net new tests).

Closes

• #1831 (PR #1873)
• #1857 (PR #1861)
• #1876 (PR #1877)

Closes #1860, #1861, #1865, #1873, #1877, #1889.