Reporting cost == max_perf puts an occupied worker at exactly 100%
utilization, which the autoscaler reads as "at target, no action."
The 3rd session_create then 429s on both active workers and stalls in
the global queue instead of triggering a cold-worker activation
(observed: 1→2 active scales fine, 2→3 does not).
Bumping cost to 2 * max_perf makes each session look like more than
one worker's work, so the autoscaler always keeps an extra active
worker hot. Slight over-provisioning, but the 3rd reservation lands
directly on a free worker rather than queueing.
Expose --session-cost on the client so the value can be swept without
edits. README documents the trade-off.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
