Web ad-hoc builds serve stale code (v2 shows v1's changes)

[melvin-bot]

Problem

Ad-hoc web builds appear to serve stale artifacts across successive builds on the same PR.

Steps that reproduce it on Expensify/App#95631:

1. Trigger an ad-hoc build (v1).
2. Push a few more commits to the PR.
3. Trigger another ad-hoc build (v2).

Expected: v2 reflects the newest commits.
Actual: v2 still shows the code/changes from v1 — the new commits are not visible. Something appears to be cached where it shouldn't be.

Using the "Force a full native build, bypassing Rock remote cache" option does not help — the stale output persists.

Notes

• This looks related to the ad-hoc build / Rock caching behavior previously seen in Expensify/App#81466 ("Ad-hoc builds sometimes have the completely wrong code"), where the workflow relied on Rock's fingerprint to identify build artifacts and hit cache collisions. That issue was closed, but the symptom here (v2 serving v1's code, and the force-full-build toggle not helping) suggests the web ad-hoc path may still have a caching problem.

Reported in Slack by mjasikowski.

[rinej]

@mjasikowski

I created the draft PR with the changes:

• Switched S3 upload to set Cache-Control: no-cache, no-store, must-revalidate for index.html, service-worker.js, and workbox-*.js, while keeping long-lived immutable caching for hashed assets. Since these files have fixed names, they were the most likely reason testers kept getting the previous build.
• Replaced aws s3 cp --recursive with aws s3 sync --delete so old chunks are removed instead of accumulating between builds.

If this isn't enough, the next step would be to add a CloudFront invalidation for the PR path after each deploy.
That requires the distribution ID and IAM permissions, so I'd rather verify this simpler fix first before adding more complexity.

How do we want to test it? Maybe you can add those changes into your branch and run adhoc and check if works properly?

PR -> #97243

[mjasikowski]

@rinej I'll try to test this today on a throwaway PR

[mjasikowski]

@rinej tested in #97672, unfortunately it doesn't work as it should

1. Changed green buttons to blue in v1
2. Created an ad hoc build
3. Changed blue buttons to pink in v2
4. Created an ad hoc build

Buttons are still blue. Tested across browsers to make sure nothing is cached