The launcher runs the runtime as a spawnSync CHILD of node(mosaic) (deliberate,
per launch.ts:99 — parent survives to propagate signals), so
MOSAIC_LEASE_SESSION_ID lives on the claude child, not the pane's root pid. The
transport read only pane.pid's /proc/environ and returned RESOLVE_FAILED for
every real 'mosaic claude' seat. Now BFS the pane's process subtree (bounded,
injectable children-reader) and read the first descendant that carries a valid
lease id; fail-closed if none. Unit tests now exercise the real walk (pane=node
without lease -> child=claude with lease) rather than mocking the resolution.
Found by scooby greenfield E2E on fomo-lin with proc-level evidence.
Co-Authored-By: Claude Opus 4.8 <[email protected]>
Claude-Session: https://claude.ai/code/session_013SAYFkRhQfhguY7AHfiUC8
