design-codebase-with-senior-devlisted

# Design Codebase With Senior Dev Determine whether the codebase needs a structural change at all. Reconstruct the current design from repository evidence, expose the forces that make it costly or unsafe, and choose the least powerful design that resolves those forces without silently changing behavior. This skill is **assessment-only**. Inspect and run non-mutating checks, but never edit implementation files. Finish with a validated `Codebase Design Assessment` and a deterministic handoff. ## Non-Negotiables 1. **Admission rule:** introduce or retain an in-scope pattern only when current, evidenced change pressure or correctness risk repays its indirection, concepts, runtime behavior, migration cost, and long-term ownership. 2. **Removal rule:** remove an in-scope pattern only when its present protection is worth less than its cognitive and operational cost, and its contracts can be preserved through an incremental, reversible migration. 3. Preserve public APIs, schemas, events, files, CLIs, persistence, errors, side effects, user workflows, and operational promises unless explicit authorization names the permitted change. 4. Prefer L0 over L1, L1 over L2, and L2 over L3 whenever the lower level satisfies the evidenced constraints. 5. A fashionable pattern name, long file, large class, duplicate branch, disliked abstraction, or clean diagram is never sufficient evidence. 6. Reconcile the requested design with grounded pressures and protected contracts, then obtain explic