/api/sessions re-ran the expensive CLI/cron session projection on every
poll while a turn was streaming — a major cause of the multi-second sidebar
latency + 100% CPU on cron-heavy installs (continuing #4672/#4808/#4889).
Root cause: the CLI/cron projection is gated by _CLI_SESSIONS_CACHE, whose
key folds in _sqlite_file_stat_cache_key -> _sqlite_content_fingerprint
(MAX(rowid) FROM messages). During a live turn the gateway writes a message
row per streamed delta, so that fingerprint advances on essentially every
~5s poll — busting the cache and re-running the full candidate-join +
projection (and the lineage-metadata pass) on every poll, contending for the
same SQLite/global lock the streaming worker holds.
The route-level session-list cache already froze its key during streaming
(#4808 _session_list_cache_streaming_freeze_marker), but that freeze never
reached this inner CLI-sessions cache, so the heavy CLI/cron query still
re-ran whenever the outer cache validated.
Fix: while any stream is active, the CLI-sessions cache key folds in the same
stable streaming-freeze marker (keyed only on the set of active stream ids)
instead of the volatile content fingerprint, and the cache TTL widens to a
streaming window. The projection is reused across polls mid-stream and
rebuilt at most once per window. The instant a stream starts/stops the marker
changes, so freshly-finished rows surface promptly. Structural mutations
(cron completion, new/renamed/archived sessions, attention) now also clear
the CLI cache via the existing session-list-changed listener — those signals
never fire per streamed token, which is what makes the freeze safe.
Idle behavior is byte-identical (freeze only engages with active streams).
Applies to both the active-profile and all-profiles cache paths.
Adds tests/test_issue4842_cli_sessions_streaming_freeze.py (6 tests): marker
idle/stable/changes semantics, the core 'key stable across message writes
while streaming' guarantee, idle key still advances with the fingerprint,
streaming TTL > idle TTL, and the structural-mutation listener clears the
CLI cache.
