plan-seam — Seam-Driven Refactoring & Expand-Contract Strategy

Domain Rubric

1. Seam Coordinates & Isolation Mechanism

Identify interception seams at interface, dependency injection, or package boundaries. Select a zero-downtime isolation mechanism: Interface Adapter, Feature Flag, Shadow Proxy, or Branch by Abstraction.

2. Expand-Contract Triad Invariants

1. Phase 1: Expand (Additive Non-Breaking): Introduce new interfaces, schemas, or shadow services alongside legacy code. Caller signatures and legacy test suites remain unmodified and GREEN.
2. Phase 2: Migrate (Progressive Cutover): Reroute callers individually to the new abstraction via feature flags or adapters. Rollback to legacy path must execute instantly via flag toggle without code redeployment.
3. Phase 3: Contract (Pruning & Cleanup): Remove legacy implementations, delete temporary flags, and purge obsolete branches and shims once full regression tests pass.

3. State

• STAGED: The 3-phase migration strategy and rollback coordinates are staged for human review.
• UNRESOLVED: Tightly coupled code prevents seam identification without a foundational redesign.

Canonical Output Contract