OUT-4101: Process webhook changes per channel instead of a global serializer

[SandipBajracharya]

Removes the global one-at-a-time serialization in the Dropbox webhook change path so different channels/accounts process in parallel.

What changed

• handleChannelFileChanges (queue concurrencyLimit: 1, previously triggered unkeyed → one channel's change-processing at a time across the whole system) is now triggered with { concurrencyKey: channelSyncId } → channels/accounts process in parallel, still serial per channel.
• Inside it, the delete / create / content-update dispatches all go through fanOutAndWait(task, items, channelSyncId) (was: unkeyed batchTriggerAndWait for delete/create, a serial for…of for content-updates). This keys them per channel and — bonus — chunks within Trigger.dev's 500-item batch limit (a big folder rename could exceed it before). Delete→create→update ordering is preserved by awaiting each step.
• updateDropboxFileInAssembly keys its inner delete+recreate by channelSyncId, and the recreate is now triggerAndWait (was fire-and-forget) so the mapping row is committed before the update reports done.

Duplicate protection (from review)

Two doors that could create a file twice (Assembly or Dropbox) are closed:

• Within one delta: classifyDbxChanges now applies dedupeByIdKeepLast per bucket — duplicate dbxFileId entries in one batch can't fan out concurrent same-file syncs. Per-bucket so a rename's delete+create pair (same id, different buckets) is preserved.
• Across webhooks: awaiting the recreate + processDropboxChanges's per-account concurrencyLimit: 1 means a follow-up webhook for the same account can't read stale state and re-dispatch the same file.

Testing

• New classifyDbxChanges tests: content-update / created / deleted bucket dedup, and rename-pair preservation.
• Full suite green: 273 unit + 179 integration, pnpm typecheck + pnpm lint clean.

Note for OUT-4102

Keying syncDropboxFileToAssembly per channel (here) / per portal (OUT-4100) means its concurrencyLimit: 25 is no longer a global ceiling — total concurrent syncs now scale with active channels/portals. Intended fairness tradeoff; right-sizing the limit + confirming the DB pool holds up is OUT-4102.

Follow-ups (not in this PR)

• fanOutAndWait discards per-item batch failures (pre-existing, shared by 4 call sites) — tighten in a dedicated ticket.
• The per-channel concurrencyKey serialization can't be observed by the inline test double; confirm on a real Trigger.dev run.

🤖 Generated with Claude Code

[linear-code]

OUT-4101

[vercel]

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Project	Deployment	Actions	Updated (UTC)
dropbox-integration	Ready	Preview	Aug 26, 2026 3:10pm

[greptile-apps]

Greptile Summary

This PR replaces global Dropbox change serialization with per-channel serialization while preserving delete-before-create ordering. It also batches content updates, waits for replacement recreation, and deduplicates repeated Dropbox IDs within each classification bucket.

• Adds channel-scoped concurrency keys to Dropbox change processing and replacement child tasks.
• Routes delete, create, and content-update work through chunked keyed fan-out.
• Deduplicates each change bucket while preserving rename delete/create pairs.
• Adds unit coverage for bucket deduplication and rename preservation.

Confidence Score: 5/5

The PR appears safe to merge; no changed-code-triggered blocking or independently actionable non-blocking issue was identified.

Per-channel keying preserves the required channel isolation and delete-before-create sequence, replacement work now waits for recreation, and bucket-local deduplication does not violate downstream ordering assumptions.

Important Files Changed

Filename	Overview
src/features/webhook/dropbox/lib/webhook.service.ts	Keys channel change coordination by channelSyncId while retaining the existing result check before cursor advancement.
src/trigger/processFileSync.ts	Replaces global/serial dispatch with channel-keyed chunked fan-out and waits for both stages of content replacement.
src/utils/classify-dbx-changes.ts	Deduplicates repeated Dropbox IDs independently within delete, create, and content-update buckets.
src/utils/tests/classify-dbx-changes.test.ts	Covers deduplication in every bucket and confirms that rename delete/create pairs remain intact.

Sequence Diagram

sequenceDiagram
    participant D as Dropbox webhook
    participant A as Account processor
    participant C as Channel-keyed coordinator
    participant F as File tasks
    participant DB as Mapping database
    D->>A: Account change notification
    A->>A: Read cursor pages
    A->>C: triggerAndWait(changes, channelSyncId)
    C->>C: Classify and dedupe per bucket
    C->>F: Fan out deletes
    F->>DB: Remove counterparts and settle mappings
    F-->>C: Delete batch complete
    C->>F: Fan out creates
    F->>DB: Create counterparts and settle mappings
    F-->>C: Create batch complete
    C->>F: Fan out content replacements
    F->>F: Delete then recreate
    F->>DB: Commit replacement mappings
    F-->>C: Update batch complete
    C-->>A: Channel processing complete
    A->>DB: Advance channel cursor

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[priosshrsth]

lgtm