Terminate complete stack process trees during tool indexing

[rudijetson]

Problem

Tool discovery can return after signaling only the direct stack process. An uncooperative wrapper or descendant MCP server can survive a successful discovery or timeout, leaving stale index process trees behind.

Scope

• launch POSIX stack servers in dedicated process groups
• converge success, error, exit, and timeout paths on one bounded cleanup routine
• close RPC resources, terminate the complete process group, wait, and escalate when needed
• validate timing options and handle invalid or already-exited child PIDs safely
• add behavior-level process-tree tests

Acceptance

• success returns only after parent and descendants exit
• timeout returns only after parent and descendants exit
• focused and full CLI tests pass
• generated bundle is reproducible
• debt scan, package dry run, and diff checks pass

The Admin Mac already proved the runtime behavior in docs/swe-compliance/2026-08-06-admin-mac-rudi-cleanup.md; this issue publishes the source repair on the current CLI stack.