Settings -> Models grows a Context compaction card next to Token savings:
the trigger % of the context window (10-95), the absolute token cap
(clamped 10k-2M), and the summarizer-model pin (default: the session's
own model). POST /v1/settings/compaction persists them; engines read the
knobs live per check, so changes apply to running sessions immediately.
The "context compacted" divider rides the existing notice machinery: the
persisted `compacted` notice replays on reload (itemsFromMessages) and
the live COMPACTED event appends the same info notice mid-turn. The
transcript itself stays intact - outbound-only by construction.
Covered by vitest (marker replay), a settings-card e2e (defaults +
clamped POSTs + model pin), and a mid-session divider e2e driven by the
fixtures' scripted `compacted` event.
Minimal engine footprint: a checkpoint at each iteration top (between tool
turns and before a new turn), the usage signal captured per round-trip
(context_tokens; chars/4 estimate when never reported), and
_outbound_messages consulting the boundary. The summarizer runs off-loop
through the normal provider router, so the Settings model pin is just an
id.
Failure policy per spec: retry once in both modes; attended sessions get
the Retry / Trim-oldest-10% prompt (via the ask_user plumbing, gated by an
is_attended callback the WS surface wires); unattended runs auto-trim and
continue — never parked on internal bookkeeping. Raw context-overflow 400s
from the main model route into the same policy, progress-guarded so a
still-overflowing model terminates in the error path.
CompactionState persists on the session record (new sqlite column, same
defensive parse as grants), so reloads keep the compacted view. A
persisted compacted notice + a new COMPACTED event mark the spot for
the GUI divider (rendered in commit 3).
Rohit C Prasad