fix(runtime): bound proxy processes and compressed requests

[drewstone]

What changed

• Reserve compressed-request capacity before buffering and cap compressed wire and decoded bodies at 32 MiB.
• Terminate a surviving process group even when its original leader already exited.
• Cover saturation recovery, expansion bombs, oversized wire bodies, and asynchronous/synchronous teardown.

Proof

• pnpm typecheck
• pnpm test -- --run: 969 passed, 12 skipped, 53 files
• focused leader-exit tests: 2 passed
• independent adversarial review requested before merge