Pre-release Opus + nesquena review on v0.50.246 caught that PR #1341
added the data-structure scaffolding (Session.__init__ accepts the 3
fields, save() persists them, compact() exposes them, GET /api/session
returns them) but did NOT add the writer that actually populates them.
Without a writer, the user-visible bug (context-ring shows 0% after
page reload) was NOT fixed by #1341 alone — the fields stayed None
forever because nothing wrote to s.context_length anywhere.
Adds the writer at api/streaming.py:2188 (post-merge per-turn save block,
before s.save()) so the values from agent.context_compressor land on
disk and survive page reloads.
Also moves the SSE usage payload comment to clarify that the live SSE
payload and the session-level persistence are now distinct paths
(payload below, persistence above).
Adds tests/test_pr1341_context_window_persistence.py — 6 structural +
round-trip tests covering Session __init__/save/compact, the routes
response, and the streaming.py writer placement.
Closes#1318 (the actual user-visible bug, not just the scaffolding).
a5c10d594d