Enable SVG decode via librsvg, read-only

[Meldiron]

What does this PR do?

Makes Imagick able to decode SVG so Appwrite's /preview endpoint can rasterize SVG uploads and apply the full transformation pipeline (crop, rotate, borders, output=png, …). Today SVG previews fall back to a placeholder icon because the image cannot open SVG at all — two independent blockers:

1. Alpine's imagemagick package is installed without the imagemagick-svg subpackage, so there is no SVG decode delegate (no decode delegate for this image format 'SVG' even with the policy lifted).
2. policy.xml denies the SVG/SVGZ/MSVG coders and module.

Changes:

• Install imagemagick-svg, which decodes through librsvg — the memory-safe Rust renderer — never ImageMagick's internal MSVG coder.
• Grant the SVG/SVGZ coders read-only rights in policy.xml.
• The policy install step now decodes a probe SVG, so the build fails loudly if the delegate or policy regresses.
• Structure tests: SVG/SVGZ in registered formats, the rights: Read ↔ {SVG,SVGZ} policy pairing, and a real decode through the PHP imagick extension.

What stays blocked (the reasons SVG was denied in the first place):

Guard	Status
HTTP/HTTPS delegates (SSRF via external hrefs)	still denied
@* path reads (local file disclosure)	still denied
MSVG internal renderer (riskier fallback if librsvg is absent)	still denied
SVG encode	denied — the grant is read-only
Resource bombs	existing width/height/disk/memory limits apply to the rasterized output

Test Plan

Validated against a container from appwrite/base:2.0.0 with imagemagick-svg installed and this exact policy.xml:

• SVG decode + rotate + PNG encode through the PHP imagick extension works (also verified end-to-end through Utopia\Image\Image crop/rotate/output('png') — the exact Appwrite preview pipeline)
• SVG encode is denied
• MSVG decode is denied
• identify -list policy output matches the new structure-test regex

All three new/extended tests.yaml assertions were validated against real container output.

Related PRs and Issues

• Rasterize SVG files in the file preview endpoint appwrite#13392 — SVG support in /preview; will be reworked to rasterize through Imagick once a base release with this change is available

🤖 Generated with Claude Code

[greptile-apps]

Greptile Summary

The PR adds librsvg-backed SVG decoding to the runtime image and grants SVG/SVGZ read-only ImageMagick access while retaining existing resource, network-delegate, path, and MSVG restrictions.

• Installs the Alpine imagemagick-svg package.
• Adds build-time and container-structure probes for basic SVG decoding.
• Updates the changelog and policy documentation for the new capability.

Confidence Score: 4/5

The PR appears safe to merge, with a non-blocking recommendation to test the external-resource restrictions that now protect SVG decoding.

The package, policy, build probe, and runtime capability test are aligned for basic SVG decoding; the remaining concern is that validation proves successful decoding but not continued enforcement of the security controls surrounding hostile SVG references.

Files Needing Attention: tests.yaml

Security Review

No concrete vulnerability was established. The new tests should additionally exercise the external-resource restrictions that now protect the enabled SVG path, so later package or policy regressions cannot pass validation unnoticed.

Important Files Changed

Filename	Overview
Dockerfile	Installs the SVG delegate and adds a successful basic SVG decode as a build-time capability check.
policy.xml	Re-enables SVG/SVGZ decoding with read-only coder rights while retaining MSVG, network-delegate, indirect-path, and resource restrictions.
tests.yaml	Verifies format registration, policy rights, and basic Imagick decoding, but does not validate the external-resource restrictions protecting the newly enabled input path.
CHANGES.md	Documents the new SVG capability and the security controls intended to remain in force.

Prompt To Fix All With AI

### Issue 1
tests.yaml:115-118
**External-resource guards untested**

The new test decodes only an empty inline SVG, so image validation does not exercise the HTTP/HTTPS and indirect-path restrictions protecting the newly enabled untrusted SVG path. A later package or policy regression can leave basic decoding green while those security controls no longer isolate external resources.

---

For each issue above, determine whether it is valid and should be fixed. If so, fix it directly.

_{Reviews (1): Last reviewed commit: "Enable SVG decode via librsvg, read-only" | Re-trigger Greptile}