refactor: extract loop service seam by splitting runtime into dedicated modules

[chriswritescode-dev]

Summary

Extracts the loop service seam by splitting the monolithic runtime.ts into focused modules for prompt construction, usage tracking, and workspace management. This improves separation of concerns and testability.

Changes

Added

• src/loop/runtime-prompt.ts — extracted prompt construction logic
• src/loop/runtime-usage.ts — extracted usage tracking logic
• src/loop/runtime-workspace.ts — extracted workspace management logic
• test/loop/runtime-service-seam.test.ts — test coverage for the service seam

Updated

• src/loop/runtime.ts — refactored to delegate to new modules (-427 lines)
• src/loop/service.ts — refactored to use extracted modules (-82 lines)
• src/services/execution.ts — service seam integration
• src/services/session-loop-resolver.ts — service seam integration
• Multiple hooks, tools, and test files updated to match new interfaces

Removed

• Duplicated runtime logic between runtime.ts and service.ts

Breaking changes

None.