refactor: driver SDK layout and DriverModule registry

[deymosh]

Summary

This is the "Driver SDK layout and DriverModule registry" step of docs/AGENT-CANDIDATES.md. It shapes the agent host for install on demand and for further agents. Loading and warm-up behave exactly as before.

• Layout: src/host/ holds the process, routing and the module list; src/sdk/ the driver SDK; src/install/ the pinned-runtime installer; drivers live in src/drivers/<agent>/. src/generated/ stays put, since the Rust type generator and CI's drift check write and check it there. The bundle entry is now src/host/main.ts; the output is still dist/main.js, so the image and release archives are unchanged.
• DriverModule (sdk/module.ts): each driver folder exports one from module.ts. It holds:
  • the agent's id and label;
  • the environment variables that are its alone, claimed before any driver is built (the DeepSeek Harness's endpoint and key);
  • how to build the driver;
  • its runtime: what the machine already has, and how to install the pinned one.
• Module list: host/modules.ts replaces the two switch statements in main.ts. Loading and the warm-up mode iterate it, and install on demand will too.
• Layout test (host/__tests__/layout.test.ts) fails when:
  • a driver imports anything outside sdk/, install/, generated/ or its own folder;
  • sdk/ or install/ imports the host or a driver;
  • anything but the module list names a driver;
  • a driver folder has no registered module.
• Docs: docs/PROTOCOL.md "Adding an agent" and docs/AGENT-CANDIDATES.md "Package layout" describe the new shape.

Verification

• The agent host's typecheck and tests (521, including the new module and layout tests) and its build pass. cargo test for the driver-protocol spawn test and the bridge end-to-end test pass against the new bundle (-- --ignored).
• Live, in the bridge container, with the new bundle:
  • a DeepSeek Harness session on deepseek-v4.1-flash ran a turn, and its conversation delete still works;
  • warm-up mode resolved all three agents' runtimes.

🤖 Generated with Claude Code