fix: fallback to docker-container driver when default builder uses docker driver

[dephiros]

Problem

When the Blacksmith remote builder setup fails (e.g. sticky disk API timeout), the fallback path at src/main.ts:644 checks for an existing builder via toolkit.builder.inspect(). The default builder always exists and uses the docker driver, so the condition if (builder) is always true.

This means the code never reaches the else branch that creates a docker-container builder. The docker driver doesn't support attestation (provenance/sbom), causing builds to fail with:

ERROR: Attestation is not supported for the docker driver.
Switch to a different driver, or turn on the containerd image store, and try again.

Fix

Check the builder's driver property, not just its existence. If the existing builder uses the docker driver, create a docker-container builder instead, which supports all buildx features including attestation.

- if (builder) {
-   core.info(\`Found configured builder: \${builder.name}\`);
+ if (builder && builder.driver !== "docker") {
+   core.info(\`Found configured builder: \${builder.name} (driver: \${builder.driver})\`);

---

[eltonkl]

Thanks for the contribution!

The logging statement on src/main.ts line 656 is not reflected in dist/index.js yet.

Could you update dist/index.js slightly?

sed -i '' 's/Created and set a local builder for use/Created and set a local docker-container builder/g' dist/index.js

[dephiros]

Thanks for the contribution!

Thanks for the review @eltonkl and sorry for missing that since I had to update the dist file manually(missing private deps locally)
Updated ✅

[devin-ai-integration]

✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no potential bugs to report.

View in Devin Review to see 2 additional findings.

[adityamaru]

@dephiros this seems like a good change but I would rather y'all not fallback at all! Let me also look into what error you're seeing when interacting with the stickydisk API

[dephiros]

I saw this PR should be superseded by #86.
Thank you for getting the fix in 🙏 🎉