diff --git a/test/flows/assembly-webhook-controller.integration.test.ts b/test/flows/assembly-webhook-controller.integration.test.ts
index 37fd99c..66af83d 100644
--- a/test/flows/assembly-webhook-controller.integration.test.ts
+++ b/test/flows/assembly-webhook-controller.integration.test.ts
@@ -230,4 +230,44 @@ describe('Assembly webhook: deciding whether to sync to Dropbox', () => {
 
     expect(res.status).toBe(404)
   })
+
+  it('waits 800ms before processing to avoid a webhook ping-pong', async () => {
+    const { channel } = await seedActive()
+    const sleepSpy = mockSleepInstant()
+    const data = copilotFileFactory.build({ channelId: channel.assemblyChannelId, path: 'x.txt' })
+
+    // A non-handleable event returns early, but the 800ms guard runs first for every request.
+    await post('link.created', data)
+
+    expect(sleepSpy).toHaveBeenCalledWith(800)
+    expect(sleepSpy).not.toHaveBeenCalledWith(5000)
+  })
+
+  it('skips a create for a file that was already soft-deleted (lookup ignores deletedAt)', async () => {
+    const { channel } = await seedActive()
+    mockSleepInstant()
+    // A tombstoned row still matches the assemblyFileId lookup, so the create is treated
+    // as existing and skipped — this is what prevents resyncing a soft-deleted file.
+    const row = await fileSyncSeeder.create({
+      ...synced(),
+      ...tombstone(),
+      channelSyncId: channel.id,
+      itemPath: '/back.txt',
+      dbxFileId: 'dbx:back',
+      object: ObjectType.FILE,
+    })
+    const data = copilotFileFactory.build({
+      id: row.assemblyFileId as string,
+      channelId: channel.assemblyChannelId,
+      path: 'back.txt',
+    })
+
+    // No Dropbox mocks: a stray create would trip onUnhandledRequest:'error'.
+    const res = await post('file.created', data)
+
+    expect(res.status).toBe(200)
+    const rows = await rowsFor(channel.id)
+    expect(rows).toHaveLength(1) // only the tombstone; no new row created
+    expect(rows[0].id).toBe(row.id)
+  })
 })
diff --git a/test/flows/resync-sweep.integration.test.ts b/test/flows/resync-sweep.integration.test.ts
index 31b1b2b..f5f1fc4 100644
--- a/test/flows/resync-sweep.integration.test.ts
+++ b/test/flows/resync-sweep.integration.test.ts
@@ -366,4 +366,44 @@ describe('resync sweep', () => {
     const [ch] = await db.select().from(channelSync).where(eq(channelSync.id, channel.id))
     expect(ch.resyncingAt).toBeNull() // orchestrator's finally cleared the in-progress flag
   })
+
+  it('does nothing when the portal has no Dropbox connection', async () => {
+    const { channel } = await seed()
+    const row = await fileSyncSeeder.create({
+      ...pendingDelete(PendingActionTarget.DROPBOX),
+      channelSyncId: channel.id,
+      itemPath: '/orphan.txt',
+      dbxFileId: 'dbx:orphan',
+      object: ObjectType.FILE,
+      pendingActionLastAttemptAt: minutesAgo(6),
+    })
+
+    // A portal id with no connection → early return before any row is processed.
+    await retryFailedSyncsForPortal(randomUUID(), [row])
+
+    const after = await rowById(row.id)
+    expect(after.deletedAt).toBeNull()
+    expect(after.pendingAction).toBe('delete') // untouched
+    expect(after.pendingActionLastError).toBeNull()
+  })
+
+  it('marks a row failed when its action/target combo is unrecognised', async () => {
+    const { connection, channel } = await seed()
+    const row = await fileSyncSeeder.create({
+      ...pendingDelete(PendingActionTarget.ASSEMBLY),
+      channelSyncId: channel.id,
+      itemPath: '/weird.txt',
+      dbxFileId: 'dbx:weird',
+      object: ObjectType.FILE,
+      pendingActionLastAttemptAt: minutesAgo(6),
+    })
+    // Hand the dispatcher a row whose target is out of range; the DB row keeps a valid combo.
+    const mangled = { ...row, pendingActionTarget: 'BOGUS' } as unknown as typeof row
+
+    await retryFailedSyncsForPortal(connection.portalId, [mangled])
+
+    const after = await rowById(row.id)
+    expect(after.pendingActionLastError).toContain('unrecognised')
+    expect(after.deletedAt).toBeNull() // never dispatched to a real handler
+  })
 })
diff --git a/test/flows/sync-error-shape.integration.test.ts b/test/flows/sync-error-shape.integration.test.ts
new file mode 100644
index 0000000..8d6ee0f
--- /dev/null
+++ b/test/flows/sync-error-shape.integration.test.ts
@@ -0,0 +1,199 @@
+import { eq } from 'drizzle-orm'
+import { describe, expect, it } from 'vitest'
+import db from '@/db'
+import { ObjectType, type ObjectTypeValue } from '@/db/constants'
+import { fileFolderSync } from '@/db/schema/fileFolderSync.schema'
+import { SyncService } from '@/features/sync/lib/Sync.service'
+import type { DropboxFileListFolderSingleEntry } from '@/features/sync/types'
+import User from '@/lib/copilot/models/User.model'
+import type { CopilotFileRetrieve, Token } from '@/lib/copilot/types'
+import { copilotFileFactory } from '../factories'
+import {
+  copilotError,
+  copilotNotFound,
+  type DropboxMeta,
+  dropboxPathLookupNotFound,
+  dropboxRpcError,
+  mockCopilotDeleteFile,
+  mockDropboxDeleteFile,
+  mockDropboxGetMetadata,
+} from '../msw'
+import { channelSeeder, dropboxConnectionSeeder, fileSyncSeeder, synced } from '../seeders'
+
+const CONNECTION_TOKEN = { refreshToken: 'rt', accountId: 'acc', rootNamespaceId: 'ns' }
+
+function makeService(portalId: string) {
+  const user = new User('test-token', { workspaceId: portalId } as Token)
+  return new SyncService(user, CONNECTION_TOKEN)
+}
+
+async function seed() {
+  const connection = await dropboxConnectionSeeder.create({
+    accountId: 'acc',
+    rootNamespaceId: 'ns',
+    refreshToken: 'rt',
+  })
+  const channel = await channelSeeder.create({
+    portalId: connection.portalId,
+    dbxRootPath: '/root',
+  })
+  return { connection, channel, svc: makeService(connection.portalId) }
+}
+
+const rowById = async (id: string) => {
+  const [row] = await db.select().from(fileFolderSync).where(eq(fileFolderSync.id, id))
+  return row
+}
+
+// createAndUploadFileInDropbox returns undefined on the dead-end branches; the caller
+// (completePendingDropboxCreate) turns that into a throw.
+describe('Dropbox create-vs-update: dead-end branches throw', () => {
+  it('throws when the existing Dropbox item has an unexpected tag (not file or folder)', async () => {
+    const svc = makeService('portal-x')
+    const file = copilotFileFactory.build({ path: 'weird.txt' }) as CopilotFileRetrieve & {
+      object: ObjectTypeValue
+    }
+    // filesGetMetadata resolves with a deleted-tag item → neither folder nor file branch.
+    const deletedMeta: DropboxMeta = {
+      '.tag': 'deleted',
+      id: 'id:x',
+      name: 'weird.txt',
+      path_display: '/root/weird.txt',
+      path_lower: '/root/weird.txt',
+    }
+    mockDropboxGetMetadata({ '/root/weird.txt': deletedMeta })
+
+    await expect(
+      svc.completePendingDropboxCreate({
+        pendingRowId: 'row-x',
+        channelSyncId: 'chan-x',
+        dbxRootPath: '/root',
+        file,
+      }),
+    ).rejects.toThrow('returned undefined')
+  })
+
+  it('throws when the file type is out of range (not file or folder)', async () => {
+    const svc = makeService('portal-x')
+    const file = copilotFileFactory.build({
+      path: 'odd.txt',
+      object: 'link', // out-of-range object → falls through both create branches
+    }) as CopilotFileRetrieve & { object: ObjectTypeValue }
+    mockDropboxGetMetadata({}) // not_found → item does not exist yet
+
+    await expect(
+      svc.completePendingDropboxCreate({
+        pendingRowId: 'row-x',
+        channelSyncId: 'chan-x',
+        dbxRootPath: '/root',
+        file,
+      }),
+    ).rejects.toThrow('returned undefined')
+  })
+})
+
+// deleteDropboxFileQuietly swallows a "already gone" 409, rethrows anything else.
+describe('deleteDropboxFileQuietly error handling (via removeFileFromDropbox)', () => {
+  async function seedDropboxRow() {
+    const { connection, channel, svc } = await seed()
+    const row = await fileSyncSeeder.create({
+      ...synced(),
+      channelSyncId: channel.id,
+      itemPath: '/gone.txt',
+      dbxFileId: 'dbx:gone',
+      object: ObjectType.FILE,
+      contentHash: 'h',
+    })
+    const file = copilotFileFactory.build({
+      id: row.assemblyFileId as string,
+      channelId: channel.assemblyChannelId,
+      path: 'gone.txt',
+    }) as CopilotFileRetrieve & { object: ObjectTypeValue }
+    const payload = {
+      file,
+      opts: {
+        channelSyncId: channel.id,
+        dbxRootPath: '/root',
+        assemblyChannelId: channel.assemblyChannelId,
+        // opts.user/connectionToken are unused by removeFileFromDropbox; present to satisfy the type.
+        user: new User('test-token', { workspaceId: connection.portalId } as Token),
+        connectionToken: CONNECTION_TOKEN,
+      },
+    }
+    return { svc, row, payload }
+  }
+
+  it('swallows a 409 path_lookup/not_found and still soft-deletes the row', async () => {
+    const { svc, row, payload } = await seedDropboxRow()
+    mockDropboxDeleteFile({ error: dropboxPathLookupNotFound })
+
+    await expect(svc.removeFileFromDropbox(payload)).resolves.toBeUndefined()
+
+    const after = await rowById(row.id)
+    expect(after.deletedAt).not.toBeNull()
+    expect(after.pendingAction).toBeNull()
+  })
+
+  it('rethrows a different 409 and marks the row failed', async () => {
+    const { svc, row, payload } = await seedDropboxRow()
+    mockDropboxDeleteFile({
+      error: () =>
+        dropboxRpcError({
+          status: 409,
+          errorSummary: 'path/conflict/..',
+          error: { '.tag': 'path', path: { '.tag': 'conflict' } },
+        }),
+    })
+
+    await expect(svc.removeFileFromDropbox(payload)).rejects.toThrow()
+
+    const after = await rowById(row.id)
+    expect(after.deletedAt).toBeNull()
+    expect(after.pendingActionLastError).not.toBeNull()
+  })
+})
+
+// deleteAssemblyFileQuietly swallows a Copilot 404, rethrows anything else.
+describe('deleteAssemblyFileQuietly error handling (via removeFileFromAssembly)', () => {
+  async function seedAssemblyRow() {
+    const { channel, svc } = await seed()
+    const row = await fileSyncSeeder.create({
+      ...synced(),
+      channelSyncId: channel.id,
+      itemPath: '/gone.txt',
+      dbxFileId: 'dbx:gone',
+      object: ObjectType.FILE,
+      contentHash: 'h',
+    })
+    const entry: DropboxFileListFolderSingleEntry = {
+      '.tag': 'file',
+      id: 'dbx:gone',
+      name: 'gone.txt',
+      path_display: '/root/gone.txt',
+      content_hash: 'h',
+    }
+    return { svc, channel, row, entry }
+  }
+
+  it('swallows a Copilot 404 and still soft-deletes the row', async () => {
+    const { svc, channel, row, entry } = await seedAssemblyRow()
+    mockCopilotDeleteFile({ error: copilotNotFound })
+
+    await expect(svc.removeFileFromAssembly(channel.id, '/root', entry)).resolves.toBeUndefined()
+
+    const after = await rowById(row.id)
+    expect(after.deletedAt).not.toBeNull()
+    expect(after.pendingAction).toBeNull()
+  })
+
+  it('rethrows a non-404 Copilot error and marks the row failed', async () => {
+    const { svc, channel, row, entry } = await seedAssemblyRow()
+    mockCopilotDeleteFile({ error: () => copilotError({ status: 400, body: { message: 'boom' } }) })
+
+    await expect(svc.removeFileFromAssembly(channel.id, '/root', entry)).rejects.toThrow()
+
+    const after = await rowById(row.id)
+    expect(after.deletedAt).toBeNull()
+    expect(after.pendingActionLastError).not.toBeNull()
+  })
+})
diff --git a/test/msw/write.ts b/test/msw/write.ts
index 3177100..a91f185 100644
--- a/test/msw/write.ts
+++ b/test/msw/write.ts
@@ -8,7 +8,9 @@ import { mockCopilot, mockDropboxContent, mockDropboxRpc } from './overrides'
 import { server } from './server'
 
 export interface DropboxMeta {
-  '.tag': 'file' | 'folder'
+  // 'deleted' lets a fixture stand in for a DeletedMetadataReference (get_metadata's
+  // unexpected-tag branch); file/folder-only fields stay optional for that case.
+  '.tag': 'file' | 'folder' | 'deleted'
   id: string
   name: string
   path_display: string
@@ -142,13 +144,18 @@ export function mockDropboxLatestCursor(cursor = 'cursor:latest'): void {
   mockDropboxRpc('/2/files/list_folder/get_latest_cursor', () => HttpResponse.json({ cursor }))
 }
 
-// Dropbox delete_v2. Records the deleted paths so a test can check which path was deleted.
+// Dropbox delete_v2. Records the attempted delete paths (recorded even when `error` is set)
+// so a test can check which path was targeted.
 // Per the Dropbox API spec, delete_v2 returns the item's file/folder metadata (not a "deleted" tag).
-export function mockDropboxDeleteFile(): { deletedPaths: string[] } {
+// Pass `error` to make every call fail (e.g. dropboxPathLookupNotFound for the quiet-delete swallow path).
+export function mockDropboxDeleteFile(opts: { error?: () => Response } = {}): {
+  deletedPaths: string[]
+} {
   const deletedPaths: string[] = []
   mockDropboxRpc('/2/files/delete_v2', async ({ request }) => {
     const { path } = (await request.json()) as { path: string }
     deletedPaths.push(path)
+    if (opts.error) return opts.error()
     return HttpResponse.json({ metadata: dropboxFileMetadata({ path_display: path }) })
   })
   return { deletedPaths }
@@ -167,14 +174,18 @@ export function mockCopilotRetrieveFile(byId: Record<string, CopilotFileRetrieve
 }
 
 // Copilot file delete (DELETE /v1/files/{id}) — used by the delete + content-change leaves.
-// Returns { deletedIds } capturing the ids sent, so tests can verify WHICH file was
-// deleted and how many times (the DB row's soft-delete alone can't see the outbound id).
-export function mockCopilotDeleteFile(): { deletedIds: string[] } {
+// Returns { deletedIds } capturing the ids sent (recorded even when `error` is set), so tests
+// can verify WHICH file was targeted and how many times (the DB row alone can't see the outbound id).
+// Pass `error` to make every call fail (e.g. copilotNotFound for the quiet-delete swallow path).
+export function mockCopilotDeleteFile(opts: { error?: () => Response } = {}): {
+  deletedIds: string[]
+} {
   const deletedIds: string[] = []
   mockCopilot(
     '/v1/files/:id',
     ({ params }) => {
       deletedIds.push(params.id as string)
+      if (opts.error) return opts.error()
       return HttpResponse.json({})
     },
     'delete',