[plainprogrammer]

Closes #39.

A collector uploads an export file at /collection/import_preview/new (account menu and More, after "Export collection") and sees what applying it would do. Nothing is written. The page shows lots added, changed, unchanged, held by a problem row, and removed, with their copies, plus profile notes. Each row that can't be applied gets its own problem with a rule and a place. A file that can't be read at all is refused with a 422, giving the reason. Applying is #40; this preview exposes each row's outcome and the held lot it names, so #40 isn't blocked.

• Spec: docs/specs/025-import-preview/spec.md (v1.5.0, approved)
• Plan: docs/specs/025-import-preview/plan.md
• ADR: 0021, json_schemer and an in-app copy of the schema
• Verification: docs/specs/025-import-preview/verification.md, which includes 12 screenshots in screenshots/

Maintainer rulings (2026-10-15)

• Replace semantics. A problem row blocks applying. A file in another currency is refused whole. Applying never changes the collector's name or email; it takes collection_view (decisions 1–4).

• Where the rules live. json_schemer is in the app bundle with a copy of the schema kept byte-identical, and the rules moved to ExportFormat::Rules (decision 5, ADR 0021).

• The upload. It is read in the request and never stored. It is judged by its content and refused over 32 MB. Request bodies over 40 MB are refused by Puma, Thruster (MAX_REQUEST_BODY) and kamal-proxy (max_request_body) (decision 6).

• Lists. Each shows its first 100 entries, then "and N more" (decision 11).

• Performance bars. A 50,000-row preview must finish in under 30 s (decision 12) and grow memory by under 500 MB (decision 13). The first measurement missed the memory bar at about 1 GB. The maintainer ruled the plan's fallback: check the header with lots: [], then each lot against $defs/lot (f8ca320, 861f076, ADR 0021 amended). Re-measured against bin/dev with a fresh server for each file:

  File	Time	Memory growth
  Resolvable	10.6 s	+316 MB
  Unresolvable	8.3 s	+139 MB
  Bad price	8.6 s	+120 MB

• Spec 022 isn't edited. Spec 025 records that it supersedes spec 022 decision 6's menu order, and docs/specs/README.md records it in both directions (decision 14).

Checks

• bin/ci at 861f076, the last commit that changes code, passed: 1583 examples, 0 failures, 1 pending (pre-existing), seed 22429. Later commits change documents only, plus a merge of origin/main, which was also documents only.
• A 41 MB POST gets a plain 413 from Puma (AC-3.4, run by hand).
• The implementation review (Mode B, Opus, read-only) found the code SPEC-ALIGNED, with no Critical findings.

Deviations from the plan

All are listed in verification.md:

• Phase 2: Row#text is parenthesised, and read_rows leaves duplicate_lot pointers out of its failed set.
• Phase 3: the AC-1.2 request example builds its held lots in a loop, to stay within RuboCop's 15-line limit. The AC-1.8 example builds the file before taking its snapshot.
• Phase 6: the per-lot schema check described above.

Follow-ups (from the review, not fixed here)

• Problem counts aren't capped. The list of problem counts has one entry per distinct bad value, such as each unknown finish, so it can grow long. The spec asks for this as written, so changing it needs a spec change.
• Prices too large to store. A price_paid too large for a 64-bit count of cents previews as applicable. Adding a row problem for it belongs with Apply an import #40.
• Plan retirement. The plan is owed retirement after this PR merges (distill-feature). Spec 025's areas, data portability and release and deploy, have no area doc yet; Area doc: data portability #108 and Area doc: release and deploy #109 will write them.

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