Correct overwrite_existing_file description for Export Vector Container to ASCII File #103

Problem

The API reference describes ExportVectorContainerToAsciiFile's overwrite_existing_file (overwriteExistingFile) as "False appends to the existing file." That is wrong for both SA targets. Installed SA documentation says a false value makes the step fail when the file already exists, and nothing is written.

The briosa source was corrected in spatialanalyzer/briosa#300 (merged as a3864ed, Refs spatialanalyzer/briosa#299). The new wording in both targets' file_operations.proto and the migration ledger is:

False fails if the file already exists; it does not append.

briosa-docs has no automated sync from briosa, so this needs a docs change here.

Do not change

The gRPC "MP label" column value Overwrite existing file? (FALSE = Append) is the exact SDK argument label that Briosa sends, and it is correct. Only the description text is wrong.

Working pages (published at the next release snapshot)

Replace the description with the wording above in:

• api/dotnet/file-operations.md and api/dotnet/sa-2024.1.0508.5/file-operations.md
• api/grpc/file-operations.md and api/grpc/sa-2024.1.0508.5/file-operations.md (the description row only, not the label row)
• api/javascript/file-operations.md and api/javascript/sa-2024.1.0508.5/file-operations.md
• api/python/file-operations.md and api/python/sa-2024.1.0508.5/file-operations.md
• docs/mp-argument-name-migration.md (rename table, "Meaning" cell)

Decision needed: currently published snapshots

The live site serves the Server 0.9.0 and client 0.4.0 snapshots, which carry the same wrong description:

• grpc_versioned_docs/version-0.9.0/{,sa-2024.1.0508.5/}file-operations.md
• {dotnet,javascript,python}_versioned_docs/version-0.4.0/{,sa-2024.1.0508.5/}file-operations.md

Those snapshots faithfully reproduce the released 0.9.0 proto comment. But the comment misdescribes SpatialAnalyzer behavior that did not change between releases, and the error matters to callers: someone who sets false expecting an append gets a failure. Decide whether to correct these snapshots as errata (the snapshot rule only forbids relabeling) or to leave them until the next release snapshot supersedes them. Older snapshots (0.3.0 clients, 0.8.0 server, and earlier) carry the same text and fall under the same decision.

Done when

• The working pages use the corrected description.
• The snapshot decision is recorded and applied.
• Correct overwrite_existing_file description for Export Vector Container to ASCII File briosa#299 can be closed.