fix(PPT-764): Prefer AVIF over WebP in format auto-selection

[adityaverm-a]

Summary

• Reorder FORMAT_PRIORITY from webp > avif to avif > webp in the container auto-optimizer and the CloudFront dit-header-normalization function
• When a client sends Accept: image/avif,image/webp,..., DIT now selects AVIF instead of always falling back to WebP
• Sharp AVIF encoding was already supported; the bug was priority ordering in format selection at both the edge and container layers

Root cause

FORMAT_PRIORITY ranked WebP above AVIF in two places:

• source/container/.../auto-optimizer.ts — container format auto-selection
• source/constructs/lib/v8/functions/dit-header-normalization.js — CF Function collapses Accept → single dit-accept header

If only the container changed, production would still serve WebP because the CF Function strips image/avif before the request reaches the container.

Test plan

• Unit tests: auto-optimizer.test.ts — avif preferred when both avif+webp accepted
• Unit tests: dit-function.test.ts — Accept image/avif,image/webp,image/png → dit-accept: image/avif
• Local dev: explicit ?format=avif&quality=80 → valid AVIF output (547 B from test.png)
• Local dev: auto-format with dit-accept: image/avif,image/webp → AVIF (547 B), not WebP (370 B)
• Post-deploy: verify CF Function + container both deployed together
• Post-deploy: curl -H "Accept: image/avif,image/webp,image/*" <dit-url> returns AVIF

Deploy note

Both the CloudFront Function and the container image must ship together. Deploying only one layer leaves AVIF broken.

Known follow-up

Sharp reports AVIF output as Content-Type: image/heif; Chrome may download instead of inline-render when hitting the URL directly. File bytes are valid AVIF. Consider mapping heif → avif in response headers as a separate fix.

Made with Cursor

[Copilot]

Pull request overview

This PR fixes automatic image format selection so that AVIF is preferred over WebP when a client supports both, keeping CloudFront header normalization and the container auto-optimizer in sync.

Changes:

• Reordered FORMAT_PRIORITY to prefer avif over webp in both the container auto-optimizer and the CloudFront dit-header-normalization function.
• Updated/added unit tests to assert AVIF is chosen when both AVIF and WebP are accepted.
• Updated the infrastructure snapshot to reflect the CloudFront Function code change.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
source/container/src/services/transformation-resolver/auto-optimization/auto-optimizer.ts	Changes container-side FORMAT_PRIORITY so auto format selection picks AVIF before WebP.
source/container/src/services/transformation-resolver/auto-optimization/auto-optimizer.test.ts	Updates/adds unit tests to validate AVIF preference in auto-selection.
source/constructs/lib/v8/functions/dit-header-normalization.js	Changes edge-side FORMAT_PRIORITY so Accept normalization selects AVIF first.
source/constructs/lib/v8/test/unit/dit-function.test.ts	Updates unit test expectation for AVIF vs WebP selection from Accept.
source/constructs/lib/v8/test/snapshot/snapshots/image-processing-stack.test.ts.snap	Updates snapshot to match the new CloudFront Function priority ordering.

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