Ln 43 Code Modernizer

3. Execute a Bounded Migration

• Test value and boundary: Require every test to detect a concrete defect in this product's business logic and name the protected business outcome. Prefer E2E through user or external-system boundaries; use integration or unit tests only for business scenarios difficult to exercise reliably through E2E. Reject platform, trivial-wiring, implementation-detail, and duplicate proof with no distinct business failure signal.
• Map the current external contract, important failures, and data or configuration compatibility to existing proof; implement KEEP, ADD, UPDATE, MERGE, DELETE, or justified NO_TEST within the approved test scope, remove superseded testware, and give temporary characterization or compatibility evidence a removal trigger.
• Use differential or characterization cases on shared representative and adversarial inputs; the old implementation is comparison evidence, not the authority for known defects or explicitly changed behavior. Resolve differences against the intended contract.
• Introduce the replacement at one clear boundary rather than mixing old and new mechanisms throughout the codebase.
• Use native package-manager and generation commands for dependencies and generated state; do not hand-edit lockfiles or generated artifacts.
• Update callers, types, configuration, dependency injection, routes, events, serialization, tests, build scripts, and documentation required by the bounded capability.
• Preserve backward compatibility only where a real consumer requires it and define the removal condition for every temporary adapter.
• Prepare and test persisted-data or configuration migrations against a disposable copy with explicit ordering, resumability, mixed-version behavior, backup/restore evidence, rollback, and failure recovery; apply them elsewhere only when the user names the target environment and authorizes the rehearsed operation.
• Before removing a dependency or module reported as unused, check dynamic imports, reflection, plugin/config registration, code generation, build scripts, CLIs, and optional runtime paths that static import scans miss.
• Remove the old implementation only after search and runtime wiring checks show no remaining consumer.
• Inspect the diff for unrelated refactoring, formatting churn, duplicate dependencies, debug code, and accidental public contract changes.

4. Verify and Keep or Discard

• Run focused contract and regression tests immediately after each migration step.
• Run the repository's required build, lint, type, test, smoke, packaging, and application-start checks.
• Compare the agreed workflow, maintenance, dependency, bundle, startup, performance, or defect metric with the baseline under equivalent conditions.
• For bundle work, compare real build composition, parsed and compressed size, chunking, loading behavior, and source maps rather than package metadata alone.
• Evaluate entrypoint and route critical paths separately: total bytes may fall while initial transfer, request waterfalls, decompression, parse/compile, execution, or cache invalidation gets worse.
• Verify tree-shaking and deduplication claims against the actual bundler graph, module format, exports, side-effect metadata, and target browsers/runtimes before changing imports or package metadata.
• Check security advisories, licenses, runtime support, package provenance, and new transitive dependencies for the retained design.
• Exercise rollback or removal mechanics when migration failure would be costly or difficult to detect.
• Mark the migration KEEP only when required behavior and verification pass and the defined net value is achieved.
• Resolve bounded migration defects and repeat affected checks before the final decision; mark DISCARD and revert the bounded change when value remains unproven, regressions remain, or net complexity exceeds the agreed tradeoff.
• Remove non-retained adapters, instrumentation, feature flags, packages, and generated artifacts only when their ownership is proven; clean only run-owned ledger paths and exact process IDs, preserving dirty or pre-existing worktrees and reported evidence.

5. Finalize and Report

• Verify that no stale implementation, import, registration, configuration, documentation, or dependency remains after a kept migration.
• Confirm relevant verification covers the final retained state, reusing still-valid results and rerunning checks invalidated by changes or unresolved failures. Compare the final diff with the original modernization scope.
• Reconcile option and migration ledgers with final code, dependencies, measurements, and rollback state.
• Identify residual custom code, compatibility adapters, migration steps, operational changes, and external dependency risks.
• Bind the modernization result to the protected behavior and final implementation state; identify which prior assumptions or verification became stale.
• Use DELIVERED when the selected bounded design is fully retained and verified; use PARTIAL when an independently safe subset is retained with explicit remaining work; use NO_CHANGE when every migration is discarded and the baseline is restored; use BLOCKED when authorization, safety evidence, or required verification is unavailable.

Self-Check

• Reconcile before returning. Check item-level evidence, requirement coverage, contradictions, scope, verdict, and applicable cleanup. Correct the report or authorized artifacts. Reuse valid evidence; do not automatically rescan the repository or rerun successful commands. Repeat checks only for relevant changes, failures, or unresolved evidence. Disclose remaining gaps.

Output Contract

Report in the user's language, in this order; label all five fields and state each fact once. Use controlled plain language: one fact per sentence, usually under 20 words, active voice, and one term per concept, with no synonyms for verdicts, IDs, or states. Small results may use one line per field; omit empty tables and do not copy linked artifacts:

1. Result: The exact skill-specific verdict token first, then the supported outcome.
2. Scope: Reviewed/changed scope, exclusions, baseline, and material assumptions.
3. Evidence: Skill-specific fields below; distinguish facts, inferences, and unverified claims. Link artifacts; use tables when useful.
4. Verification: Checks/results, unavailable evidence, and applicable cleanup/external state.
5. Completion: Checklist: X/Y complete; Incomplete: None or each UNPROVEN item's reason, outcome impact, and exact next action; residual risks and required decisions.

Skill-specific evidence: Capability, protected contract, consumers, current cost, and behavioral/value baselines. Compare considered alternatives and SELECTED / REJECTED reasons. Per migration: changes, verification, comparable value metrics, and KEEP / DISCARD. Include code/dependency and workflow deltas, affected test actions, residual custom code/compatibility, outstanding transition work, and run-owned measurement/diff/rollback/cleanup evidence.