OUT-3800: dedupe parallel folder creation in Dropbox→Assembly sync

[SandipBajracharya]

Problem

Sibling files syncing in parallel (e.g. /abc/file1.txt, /abc/file2.txt) both try to create their shared parent folder /abc. Assembly's folder create is path-idempotent and returns the same assemblyFileId to both racers, so the second insertFileMap collided on the file_folder_sync_portal_channel_assembly_unique partial index and threw the Failed query: insert into file_folder_sync ... error in Sentry.

Fix

• insertFileMap now uses onConflictDoNothing against the existing assembly unique index (no new index added) and returns null on conflict. The synced-files count only increments when a row was actually inserted.
• createAndUploadFileToAssembly pre-checks the mapping table by path (getDbxMappedFileFromPath) to skip the redundant Assembly create in the common sequential case. onConflictDoNothing is the safety net for the true concurrent race.
• Insert-race-loser now stamps dbxFileId via handleFolderCreatedCase, so a folder entry that loses the insert race to an intermediate-segment writer isn't left with dbxFileId=null (which would break later deletes/moves).
• Refactor: split the long createAndUploadFileToAssembly into createLeafFileInAssembly and createFolderInAssembly; the public method is now a thin dispatcher.

Notes

• No migration / no new index — reuses file_folder_sync_portal_channel_assembly_unique.
• Relies on Assembly returning the same assemblyFileId for a duplicate folder (confirmed by the Sentry error). The existing "Folder already exists" catch covers the sequential variant.

Tests

Added coverage in MapFiles.tombstone.test.ts for the conflict target columns, the partial-index predicate, and the inserted / null-on-conflict return paths. pnpm typecheck, pnpm lint, and all 14 tests pass.

🤖 Generated with Claude Code

[linear-code]

OUT-3800

[vercel]

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Project	Deployment	Actions	Updated (UTC)
dropbox-integration	Ready	Preview, Comment	Jun 1, 2026 11:33am

[greptile-apps]

Greptile Summary

Fixes a file_folder_sync unique-index collision that occurred when sibling files syncing in parallel both tried to create their shared parent folder in Assembly, which is path-idempotent and returns the same assemblyFileId to both racers.

• insertFileMap gains an onConflictDoNothing targeting the existing file_folder_sync_portal_channel_assembly_unique partial index (columns portalId, channelSyncId, assemblyFileId with predicate deletedAt IS NULL AND assemblyFileId IS NOT NULL), returning null on conflict. The synced-files counter is only incremented for the winning insert.
• createAndUploadFileToAssembly is split into createLeafFileInAssembly and createFolderInAssembly; the folder path adds a path-based pre-check via getDbxMappedFileFromPath to short-circuit the common sequential case, while onConflictDoNothing serves as the safety net for the true concurrent race.
• The insert-race loser now calls handleFolderCreatedCase to stamp dbxFileId onto the winning row, preventing null from being left when an intermediate-segment writer wins the insert for a folder entry that carries a Dropbox file ID.

Confidence Score: 4/5

Safe to merge; the deduplication logic is correct, the partial-index predicate exactly mirrors the schema, and the synced-files count increments exactly once per unique folder.

The partial-index predicate in insertFileMap exactly mirrors the schema so the deduplication fires correctly in Postgres. The entire concurrent-race branch relies on Assembly returning the same assemblyFileId for the same folder path, a property confirmed empirically but not enforced in code. If that contract breaks, silent duplicate rows could be inserted. Test coverage for the new insertFileMap behaviour is thorough.

src/features/sync/lib/Sync.service.ts — specifically the concurrent folder-creation path in createFolderInAssembly and the assumptions around Assembly idempotency.

Important Files Changed

Filename	Overview
src/features/sync/lib/MapFiles.service.ts	insertFileMap now returns null on onConflictDoNothing; partial-index target and WHERE predicate exactly match the schema definition
src/features/sync/lib/Sync.service.ts	createAndUploadFileToAssembly split into createLeafFileInAssembly / createFolderInAssembly; path-based pre-check + onConflictDoNothing deduplication is logically sound but relies on Assembly returning the same assemblyFileId for concurrent folder creates
src/features/sync/lib/tests/MapFiles.tombstone.test.ts	New insertFileMap tests cover conflict-target columns, partial-index predicate, successful insert, and null-on-conflict return; insertReturning fixture shared correctly via module-level let

_{Reviews (1): Last reviewed commit: "fix(OUT-3800): dedupe parallel folder cr..." | Re-trigger Greptile}

[arpandhakal]

good to go. Lets reduce the number of comments and make them simple. claude pollutes the codebase with extra comments as of now.