Fix "Invalid base URL" when creating card def inheriting from cross-realm spec

[lucaslyl]

linear: https://linear.app/cardstack/issue/CS-10590/create-new-card-def-from-listing-hit-invalid-base-url

When creating a new Card Definition and selecting "Inherits From" a spec from another realm (e.g. Listing from catalog realm), the modal threw TypeError: Failed to construct 'URL': Invalid base URL.

Screen.Recording.2026-04-07.at.10.34.00.PM.mov

Fix:

1. Use spec.moduleHref which internally calls resolveCardReference() to resolve prefix IDs to real URLs before constructing the URL.
2. Use cardIdToURL() which handles prefix-to-URL resolution for spec IDs.

[lucaslyl]

@codex review

[github-actions]

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[github-actions]

Host Test Results

2 185 tests  ±0   2 170 ✅ ±0   2h 21m 45s ⏱️ -20s
    1 suites ±0      15 💤 ±0 
    1 files   ±0       0 ❌ ±0 

Results for commit 0647a41. ± Comparison against base commit 2e77b8f.

♻️ This comment has been updated with latest results.

[github-actions]

Realm Server Test Results

  1 files  ±0    1 suites  ±0   13m 14s ⏱️ -24s
836 tests ±0  836 ✅ ±0  0 💤 ±0  0 ❌ ±0 
907 runs  ±0  907 ✅ ±0  0 💤 ±0  0 ❌ ±0 

Results for commit 0647a41. ± Comparison against base commit 2e77b8f.

♻️ This comment has been updated with latest results.

[habdelra]

I would like to see a regression test for this. please include a test that fails without this fix but passes with it.

[Copilot]

Pull request overview

Fixes a runtime “Invalid base URL” error in the Host operator-mode “Create File” modal when creating new definitions that inherit from specs located in another realm (notably when the spec uses an @cardstack/... prefix-form ID).

Changes:

• Switches module URL construction to use spec.moduleHref (which resolves prefix/relative references before calling new URL()).
• Uses cardIdToURL(spec.id) instead of new URL(spec.id) to correctly handle prefix-form spec IDs when building relativeTo for codeRefWithAbsoluteURL().

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[Copilot]

cardIdToURL is already exported from @cardstack/runtime-common (the file already imports from that barrel). Consider importing it from the existing @cardstack/runtime-common import list instead of a separate deep import to keep imports consistent and avoid relying on internal module paths.

[Copilot]

This fixes URL construction for cross-realm/prefix-form spec IDs, but there doesn’t appear to be acceptance coverage for the specific failure mode described in CS-10590 (selecting an "Inherits From" spec from another realm that uses an @cardstack/... prefix ID). Adding a test that picks a catalog spec (prefix ID) and creates a card definition would help prevent regressions.

Suggested change

	// Use spec.moduleHref which correctly resolves relative module paths
	// via resolveCardReference (handles @cardstack/catalog/... prefix IDs).
	// Without this, new URL(relativeModule, prefixId) throws "Invalid base URL".
	let absoluteModule = spec?.moduleHref
	? new URL(spec.moduleHref)
	: new URL(module);
	// Use spec.moduleHref when available because it is already fully resolved.
	// Otherwise normalize the code ref against the selected realm so relative
	// and prefix-form module IDs (for example @cardstack/...) become absolute
	// URLs before passing them to maybeRelativeURL.
	let absoluteModule = spec?.moduleHref
	? new URL(spec.moduleHref)
	: new URL(
	codeRefWithAbsoluteURL(
	{ module, name: exportName },
	new URL(this.selectedRealmURL),
	).module,
	);