feat(runtime): project process connections through providers

[jdchawla29]

Summary

• let runtime providers supply the hidden read-only mounts required by guarded agent processes
• disable Codex plugin synchronization when it runs behind the process guard
• broker threaded process connections without crossing event-loop ownership
• execute the packaged process guard directly to avoid module re-entry warnings

Validation

• 746 focused agent, eval, environment, capability, client, and CLI tests passed; 1 skipped
• repository CI formatting check passed
• repository CI Ruff check passed
• repository CI full-extra type check passed
• the final Git tree is identical to the previously hosted-E2E-validated SDK tree

Stack

Layer 5 of 5.

1. feat(agents): add first-class Claude Code and Codex CLI runtimes #624 - Claude Code CLI and agent execution contract
2. feat(agents): add first-class Codex CLI runtime #625 - Codex CLI runtime
3. refactor(runtime): separate inference access from reachability #626 - scoped inference routing and reachability separation
4. feat(capabilities): bind connections to trusted processes #627 - trusted process-bound connections
5. feat(runtime): project process connections through providers #623 - runtime-provider projection and hardening

The dependent platform integration is hud-evals/hud-monorepo#1473.

[jdchawla29]

Closing this draft so the replacement final stack layer follows #627 numerically. The branch and code are unchanged.