AI Implementation feature(903): Admin Area Challenges: List, Import/Export and Add/Edit Modal 1.03 (#44)

docs/guides/admin-challenges-import.md

@@ -0,0 +1,95 @@
+---
+type: guide
+title: Admin — Challenges Full-Replace Import
+description: How the confirmed challenges import wipes every existing challenge (with cascading files/solves and disk unlink) and inserts the archive contents in one transaction.
+tags: [guide, admin, challenges, import, full-replace, tester]
+timestamp: 2026-07-22T22:17:11Z
+---
+
+# What it is
+
+The **confirmed challenges import** is the second step of the import flow
+on `/admin/challenges` (after the preview). When the admin clicks
+**Overwrite & Import** the client POSTs the already-validated archive to
+`POST /api/v1/admin/challenges/import?confirm=overwrite`. The server
+performs a **full replace** of the challenge set inside one DB
+transaction, then best-effort unlinks the disk files owned by the
+wiped challenges.
+
+# When to use it
+
+Use this when an admin wants to restore the platform challenge set to
+the exact contents of a previously exported JSON archive. The user
+guide for the surrounding flow lives at [Admin —
+Challenges](/guides/admin-challenges.md); this concept focuses on the
+import-specific behavior and its consequences.
+
+# Behavior contract
+
+| Phase | What happens |
+|-------|--------------|
+| Pre-flight | The client already validated the archive against the `IMPORT_VALIDATION_FAILED` Zod schema in [Admin Challenges DTOs](/api/admin.md#challenges). The server re-validates; preview counts (`total`, `conflicts`, `unknownCategories`, `warnings`) are surfaced by the import modal. |
+| Staging | Every `dataBase64` file in the archive is decoded and staged to disk via `ChallengeFilesService.stage(...)`. If any stage fails the server rolls back every previously staged file and re-throws (mirrors the existing `rollbackStaged` safety net). |
+| Transaction (DB) | The server begins a single TypeORM transaction. It loads every existing challenge, captures the disk-bound `stored_filename`s of every existing `ChallengeFile`, then `DELETE`s all existing `ChallengeEntity` rows by id. `ChallengeFileEntity` and `SolveEntity` cascade-delete via FK, so dependent rows disappear too. The archive's challenges are then inserted under their original names. |
+| Post-commit (FS) | For every captured `storedFilename` the server calls `ChallengeFilesService.removeFinal(storedFilename)` (best-effort; failures are logged but do not abort). Each staged file for the imported set is committed to its final filename. |
+| Response | Returns `{ imported, skipped, warnings }`. Known unknown `categorySystemKey`s are reported in `skipped[]` (still wipe everything else). |
+
+# Side effects to expect as a tester
+
+- **Every existing challenge disappears** from the list immediately
+  after the success banner — including rows whose names did not appear
+  in the archive. Use the Players page to confirm that pre-existing
+  `solve` rows for wiped challenges also vanish (they cascade).
+- **Uploaded challenge files** owned by wiped rows are removed from
+  `./data/uploads/challenges/` post-commit. The imported archive's
+  files appear under the same directory using their original
+  filenames encoded onto the wipe.
+- An empty archive (`{ challenges: [] }`) is valid and produces
+  `imported: 0`, an empty list, and zero on-disk challenge files.
+- The **import modal auto-closes on success**; the page-level status
+  banner (`[data-testid="challenges-status"]`) shows the
+  imported/skipped/warning summary. Failures keep the modal open and
+  show the error inline.
+
+# Idempotency
+
+- Re-importing the same archive twice yields the same final DB state.
+- The previous upsert-on-name semantics are gone: even challenges
+  whose names did not appear in the archive are removed.
+
+# Error codes
+
+See [Admin Endpoints](/api/admin.md) and the [Admin —
+Challenges](/guides/admin-challenges.md) guide:
+
+- `IMPORT_VALIDATION_FAILED` (400) — schema failure on preview or
+  confirm.
+- `IMPORT_PARTIAL_FAILURE` is no longer emitted: the response is
+  always 200 with `{ imported, skipped, warnings }` (consistent with
+  partial success being the normal case when unknown categories are
+  present).
+- Any DB transaction failure rolls back every staged file and
+  re-throws the original error, leaving the DB untouched.
+
+# Wiring
+
+| Concern | File |
+|---------|------|
+| Endpoint | `backend/src/modules/admin/admin-challenges.controller.ts` (`POST /api/v1/admin/challenges/import?confirm=overwrite`). |
+| Orchestration | `backend/src/modules/admin/challenges.service.ts` (`importConfirmed`) — full-replace transaction + post-commit unlink. |
+| File staging and disk ops | `backend/src/modules/admin/challenge-files.service.ts` (`stage`, `commit`, `removeFinal`). |
+| Schema | `backend/src/modules/admin/dto/challenges.dto.ts` (`CHALLENGE_FORMAT`, `CHALLENGE_FORMAT_VERSION`, import document schema). |
+| Client UI | `frontend/src/app/features/admin/challenges/challenges.component.ts` (`onImportConfirm`) — refreshes list, sets status, calls `closeImport()`. |
+| Pure helpers | `frontend/src/app/features/admin/challenges/challenges.pure.ts` (`summarizeImportResult`, `importErrorMessage`). |
+| Backend contract tests | `tests/backend/admin-challenges-import-replace.spec.ts` — full-replace, disk-file unlink, empty archive, unknown-category wipe. |
+| Frontend contract tests | `tests/frontend/admin-challenges-import-autoclose.spec.ts` — pure helpers + modal auto-close branch. |
+
+# Notes
+
+- The flag is not in the archive's per-challenge `data`; only admins
+  can read the plaintext, and the export/import preserves the same
+  restriction.
+- Wiping cascades remove `solve` rows for wiped challenges — the
+  scoreboard will recompute on the next render without those entries.
+- The destroy-then-insert happens in one transaction, so a partial
+  failure cannot leave the platform with a mix of old and new rows.