A server process that watches an incoming folder can notice a new filename before all its contents have arrived. A completed transfer at the end does not undo a consumer that already tried to process a partial file. Agree on a readiness convention with the receiving system's owner.

WinSCP can upload under a temporary name, then rename it after completion. This feature requires SFTP binary transfers and a consumer configured to ignore temporary names. A suffix alone does not establish that rule.

Check the rule for small files as well as large ones

In preferences, inspect Endurance. Temporary-name transfer has an initial 100 KB threshold and can be enabled for all files. A large-file test cannot establish the smaller-file behaviour while a threshold remains.

An interrupted transfer can leave a .filepart file. Distinguish it from a completed final-name file; do not rename uncertain partial content just to trigger processing.

Temporary-file creation needs appropriate directory permission. Replacement can change ownership or other attributes of an existing target. Confirm these requirements with the server owner before production use.

Rehearse the consumer's actual decision

Use an isolated test folder and two harmless samples, one small and one larger than the configured threshold. Have the receiving-system owner observe which filenames the consumer attempts to process and when the final result becomes available.

For each sample, confirm that no processing began under the temporary name, the final name appeared after transfer, and the consumer accepted the complete expected content. Record any unexpected behaviour rather than assuming the rename supplies an all-purpose transaction guarantee.

Keep the client setting and consumer ignore rule documented together. If either changes, repeat the two-size rehearsal. This convention controls when a file becomes eligible for that consumer; it does not by itself prove application validation, exactly-once processing or identical behaviour from every program watching the directory.

Sources: WinSCP documentation.