[codex] ROY-27: improve codebase architecture

[zhangweijian97]

Linear issue: ROY-27

This PR was created by the Agent-Driven Development Hub (ADHD.ai) workflow.

Includes:

• plan + implement session output
• separate review/testing session

[zhangweijian97]

ADHD.ai review for ROY-27

Result: FAIL

Token usage: input 29398, output 3662, total 33060

The codebase architecture refactoring successfully modularizes config loading, adds comprehensive error handling classes, and consolidates duplicate parsing logic from agent adapters. All 149 tests pass, type checking succeeds, and no regressions were found. The refactoring improves maintainability by separating concerns (env resolution, merging, validation) into focused modules. However, commit c75f3ce has a misleading message claiming to add a healthcheck endpoint when the actual changes are adapter refactoring.

Bugs were detected and sent back to implementation.

[zhangweijian97]

Closing this PR. The refactoring approach (config split, error classes, shared parsing module) is good, but the branch is stale — it's based on pre-ROY-28 code and has merge conflicts with the current main. Additionally: 1) it mixes an unrelated ROY-32 commit, 2) the change to make updateDraftPrFromWorktree throw instead of return false introduced a bug that caused ROY-32 and ROY-27 to both get blocked. This issue should be re-executed by ADHD.ai against the latest main.