Import Mapping Feedback Loop

Context

Use this when a file import flow must keep its exact-match happy path, but still let users recover from mismatched headers or unknown material names inside the app.

Pattern

1. Keep the default strict. Exact header/material matches should continue to work with zero extra input.
2. Return mapping metadata on every import response. Include detected source columns, required field mapping status, and unique imported material resolutions so the UI can react without inventing its own parser.
3. Suggest, don’t auto-apply. Deterministic header aliases (Part Id → Id, Qty → Quantity) are useful as suggestions, but require an explicit user mapping before import succeeds.
4. Separate pure import from side effects. Let the service layer consume explicit mappings; let the bridge/app layer create missing library entities first, then rerun import with the created ids.
5. Rewrite imported material values to the resolved library name before validation. That keeps downstream project/nesting flows working with canonical material names.
6. Keep the UI two-speed. Let exact header/material files stay on the fast import path, but hold mismatched files in a review session that tracks pending mapping edits, requires an explicit preview refresh after operator changes, and only creates new materials on final commit.

Good signs

• The same import-file route can support first-pass analysis and final import.
• Unknown materials are listed once per source value with a stable status (resolved, unresolved, created).
• Row validation codes stay actionable instead of disappearing behind bridge-only errors.

Anti-patterns

• Auto-mapping fuzzy headers without telling the user.
• Creating materials inside the pure parser/validator service.
• Returning only row errors and forcing the UI to re-open the file itself to learn what headers existed.