fix(agent): cap inspection cursors per owner and session

Cursors shared one global FIFO of 1,024 and were never retired on use, so one
agent polling every second evicted every other caller's cursors after about
17 minutes. Each owner and session now keeps its newest 8 cursors, older ones
retired first, under the same global backstop; the cursor just used stays
among the newest, so a retry of the last call still works.

plugins/codeman/skills/codeman/reference/inspection-and-staging.md

@@ -45,8 +45,8 @@ these reads do not provide authoritative current-thread tracking.
 Terminal resizes preserve inspection cursors. Cursors are opaque, scoped to the
 requesting identity, session, pane lifecycle generation
 and attributed transcript, expire after 15 minutes, and disappear on server
-restart. At most 1024 are retained; capacity eviction can invalidate an older
-cursor. A replaced/truncated/rewritten source, reassociated session, foreign cursor
+restart. Each caller and session keeps its newest 8 (so retrying the last call
+works), at most 1024 in all; an older cursor can be retired. A replaced/truncated/rewritten source, reassociated session, foreign cursor
 or unavailable native source returns `409 CONFLICT`. Inspect again without
 `--since` to establish a new tail baseline; this may omit older evidence.