Reference solution
The findings below are ordered by priority.
Findings
1. Repository writes begin before the whole file is known to be valid
Location: src/member-import.ts:49-73
Each clean chunk is inserted immediately, while duplicate validation for later chunks has not happened yet. If a later chunk contains an error, the function returns ok: false after earlier members have already been committed. A rejection from a later insertMany call likewise leaves earlier calls committed, so both validation and write failures violate the all-or-nothing guarantee.
Parse, normalize, and validate the entire file without writes first. Only when no errors remain should the importer make one atomic insertMany call for the complete member set.
2. In-file identity checks happen before address normalization
Location: src/member-import.ts:26-30,54-59
The duplicate set compares raw row.address strings, and normalization happens only when a clean chunk is prepared for insertion. Addresses such as Alice@Example.com and alice@example.com therefore look different during validation but become the same stored identity.
Normalize every address before any uniqueness comparison, retain the source row alongside it, and use that normalized value for both validation and insertion.
3. Existing-member lookup receives unnormalized addresses
Location: src/member-import.ts:43-45
The repository lookup is called with the raw parsed strings even though its interface expects normalized identities and existing addresses are stored normalized. A case or surrounding-space variation can bypass the existing-member check and then collide when its normalized form is inserted.
Send the full set of normalized addresses to findExistingAddresses and compare its normalized results against the corresponding source rows.
4. The duplicate set is reset at every chunk boundary
Location: src/member-import.ts:49-59
seenAddresses is created inside the chunk loop. Even exact duplicate strings are missed when the first occurs in one 100-row chunk and the second occurs in another, so chunk placement changes whether the same file is accepted.
Maintain one normalized-address set for the complete input while validating all rows before writing.
5. Error rows are off by one because the header is not counted
Location: src/member-import.ts:20-23
The first data line is assigned row 1 even though the display_name|address header already occupies physical row 1. Duplicate errors therefore point administrators to the line above the offending member.
Assign data-row numbers as index + 2; continue reserving row 0 for the file-level size error.
Reasonable non-findings
- The 500-data-row maximum is enforced before repository access.
- Trimming and lowercasing addresses is the required normalization; the defect is that identity checks happen earlier.
- Trimming display names before insertion is correct.
- Splitting on the fixed delimiter is acceptable because the request layer guarantees the documented unquoted input format.
- A repository
insertMany call is atomic as stated; atomicity is lost because the importer makes separate calls before validation finishes.