COMMENT review - non-gating. The human decides the merge gate.

Verdict: clean, correct bug fix. I traced the root cause and both changes and they hold up.

Verified-good

• writeOneFile (line 338): the old callback-based fs.writeFile was fire-and-forget, so await writeOneFile(...) resolved before the bytes hit disk. migration.service.ts awaits createAssets and then immediately runs createEntry (lines 523 -> 535, and 948), and the entries step reads assets.json to resolve asset references - a write/read race that matches the reported "stuck / partial state" symptom. Switching to await fs.promises.writeFile fixes it. writeOneFile is module-private (not exported), and all three call sites - 361 inside writeFile's try/catch, and 800 & 814 inside createAssets' try/catch - already handle a rejection, so the now-throwing behavior introduces no unhandled rejection.
• mkdir(assetsSave, { recursive: true }) (line 797): necessary and correctly placed. Lines 800 & 814 write via writeOneFile directly, which does NOT mkdir (unlike the writeFile helper at line 355 used on line 816). assetsSave is otherwise only created as a side effect of a successful per-asset write (saveAsset, line 722, on the files/<id> subdir). If every asset fails or throws before any success, assetsSave would not exist and the two direct writeOneFile writes would ENOENT - exactly what this guards.

Non-blocking

• question - error swallowing after the fix: see inline on line 800.
• nit - no automated test accompanies an IO-ordering fix (author acknowledged this in the checklist). Given the race nature, a test asserting assets.json exists once createAssets resolves would lock in the fix and prevent regression.

Scope: diff is a single file in api, matching the stated Affected Area and the ticket. No unrelated churn.

Re-review at head 86c00d7d (COMMENT — non-gating)

Re-reviewed after the new commit 86c00d7d "fix(contentful): rethrow from createAssets so write failures surface" landed on top of the previously-reviewed 0757fd0e. The only change since the last review is the single added line throw err; in the createAssets catch block. The diff is still confined to api/src/services/contentful.service.ts (3 hunks) — scope is clean and matches the api Affected Area.

Status of the three points from the prior review (0757fd0e):

1. nit — writeOneFile now rejects instead of swallowing. Resolved by design. All three call sites (createAssets L800/L814 inside its try, and writeFile L361 inside its own try) are covered by a catch, and the new throw err is exactly what makes a writeOneFile rejection surface. Correct.
2. question — does downstream createEntry tolerate a missing/partial assets.json after a failed write? Effectively addressed for the same run: startTestMigration/startMigration run the Contentful steps as a sequential await chain, so a throw from createAssets now aborts before createTaxonomy/createEntry/createVersionFile run — createEntry is no longer reached with a half-written assets.json. See the blocker below for the caveat on how that abort surfaces.
3. nit — no accompanying test. Still not addressed; no test file in the diff. Non-blocking (see body note).

Blocking

• contentful.service.ts:833 — the propagated error lands on a fire-and-forget promise with no handler. The controller invokes migrationService.startTestMigration(req) / startMigration(req) without await and without .catch() (api/src/controllers/migration.controller.ts:27 and :40), responds 200 immediately, and the migration runs detached. There is no global process.on('unhandledRejection') anywhere in api and no --unhandled-rejections flag in the start scripts. So the new throw err turns an asset write/mkdir/read failure into an unhandled promise rejection, which on Node's default (throw, v15+) terminates the whole API process — taking down every in-flight migration — while the client already got a 200 and never learns it failed. Before this PR, createAssets swallowed the error and continued. Details/fix options inline.

Non-blocking

• No test (prior nit #3, still open). The author's checklist rationale (race-condition/IO fix) is now weaker: with the await + throw, the behavior is deterministic and unit-testable (e.g. stub fs.promises.writeFile to reject and assert createAssets rejects; stub it to resolve and assert assets.json content). A small test would lock in the fix.

Verified good

• writeOneFile await fs.promises.writeFile (L338) — the previous callback form genuinely resolved the outer await before the write completed; this is a real fix.
• mkdir(assetsSave, { recursive: true }) (L797) — necessary and correct: when every asset fails, saveAsset never creates a dir under assetsSave (it only mkdirs assetPath on the success path), so the subsequent writeOneFile(assets.json) would ENOENT without this. recursive makes it idempotent for the normal path.
• The failure is still logged via customLogger immediately before the throw, so it is not silent in the logs — the gap is purely the missing top-level handler.

Out-of-diff notes (can't anchor inline)

• The fire-and-forget controller (migration.controller.ts:27/:40) and the absence of a global rejection handler are pre-existing and systemic — aem.service.ts createAssets already propagates (no outer try/catch), so this PR brings Contentful in line with that pattern rather than inventing it. That's why the recommended fix likely belongs in startTestMigration/startMigration (wrap the switch, mark the project failed, log) or in the controller, not necessarily in this file.