Code Modernizer

Code Modernizer

Goal: Modernize a bounded capability only when the new design measurably reduces human workflow friction, maintenance, risk, dependency duplication, or delivered artifact cost. Preserve behavior, isolate migrations, and revert changes that do not create net value.

Execution contract: The ordered checkboxes are the Definition of Done. Track every item internally as PENDING, PROVEN with concrete evidence, CLEARED with evidence that its condition is absent, or UNPROVEN with a gap; reading, delegation, or tool failure is not proof. Reconcile items after each section. Before returning, resolve all PENDING and count only PROVEN and CLEARED; apply the skill's verdict and approval rules to every gap. Preserve user intent, scope, and existing authorization. Continue authorized work; ask only for consequential unresolved choices or required external approval. Scale depth to material risk without silently skipping checks. Preserve dependency and safety ordering; otherwise choose the verification method appropriate to each obligation.

Tool Routing

Do not replace working custom code merely because an external package exists. Do not introduce an unmaintained dependency, accept incompatible licensing, or remove the old path until all consumers and rollback conditions are understood.

Evidence Rules

• Compare net system complexity: removed code and risk minus new dependency, adapter, operational, and migration costs.
• External candidate claims require current primary evidence for maintenance, security, license, runtime support, and API fit.
• Bundle or performance value requires comparable measurements; line-count reduction alone does not prove a better design.
• Preserve public behavior unless the request explicitly authorizes a contract migration.

Checklist

1. Define the Modernization Target

• Resolve the bounded capability, protected outcome, current pain, affected users, developers, or operators, success metric, constraints, and explicit non-goals; label unsupported intent inferences.
• Read repository instructions and inspect Git state, generated files, package-manager policy, and current user changes.
• Inventory the current implementation, public contracts, consumers, configuration, persisted data, runtime registration, tests, and operational procedures.
• Identify the specific workflow, maintenance, security, compatibility, duplication, bundle, startup, or delivery cost that must improve.
• Establish behavioral and relevant quantitative baselines before changing code; for human workflows use reproducible observations such as required steps or concepts, time to first meaningful result, error comprehension, and recovery effort.
• Isolate the work so each migration step can be reverted without touching unrelated or user-owned changes.
• Start a run-owned resource ledger with every created absolute path, worktree, process ID, cache, report, and temporary artifact; never register pre-existing resources as cleanup targets.
• Use NO_CHANGE when evidence shows no worthwhile in-scope modernization; use BLOCKED when a plausible requested benefit cannot be evaluated because essential evidence is unavailable.