Guard default card/field templates against a transiently undefined model

[lukemelia]

Problem

The production host intermittently crashes while rendering a card:

TypeError: Cannot read properties of undefined (reading 'constructor')
    at get cardInfoFieldDisplayNames (.../default-templates/isolated-and-edit)
    at get displayFields (.../default-templates/isolated-and-edit)

The default isolated/edit and field-edit templates derive the card/field class from this.args.model.constructor inside tracked getters, and dereference this.args.fields unguarded. The host can invoke a format component for a tick while the model instance is still resolving — on initial load, and on a store re-resolve when an incremental index invalidation lands under an open card — so the first tracked getter throws and takes down the render. Glimmer templates are null-safe on undefined paths; JS getters are not.

Fix

Read the field definitions off the card/field class instead of the model instance. The render path already threads the class in as @cardOrField — a stable value independent of the model: getBoxComponent receives it, field-component.gts passes it to every CardOrFieldFormatComponent, and BaseDefComponent already declares it in its Args. getField() accepts a class directly, so getField(this.args.cardOrField, …) is a drop-in for getField(this.args.model.constructor, …) that never touches the transient model.

The @fields-dependent paths are guarded too:

• displayFields returns early when @fields is absent
• isThemeCard coalesces to {}
• the CardInfo edit header renders only when @fields.cardInfo exists
• the notes footer is wrapped in {{#if @fields.cardInfo.notes}} — invoking <@fields.cardInfo.notes /> with undefined @fields throws "attempted to invoke undefined component"

Behavior is unchanged when the model and fields are present.

This supersedes the earlier #5608, which was closed because it was authored alongside unrelated userland work; this reapplies the @cardOrField approach cleanly on current main.

Notes

• atom.gts has the same model.constructor shape but already guards with an early if (!this.args.model) return;, so it is not vulnerable and is left unchanged.
• The crash is a transient-resolution race that only reproduces under live invalidation in production, so there is no deterministic unit test for the timing window (the tracking issue's own render-suite investigation reached the same conclusion). Verified via ember-template-lint (clean) and host lint:types (no errors); behavior-preserving for the normal load path.

🤖 Generated with Claude Code

[github-actions]

Host Test Results

    1 files      1 suites   2h 53m 11s ⏱️
3 813 tests 3 799 ✅ 14 💤 0 ❌
3 832 runs  3 818 ✅ 14 💤 0 ❌

Results for commit 7f3c78f.

[Copilot]

Pull request overview

Updates the base realm’s default card and field edit templates to be resilient when the host briefly renders them before the backing model/fields are fully available, avoiding crashes from JS-side dereferences.

Changes:

• Use the stable @cardOrField class arg for getField(...) lookups instead of @model.constructor.
• Add guards/conditional rendering around @fields-dependent paths (displayFields, theme detection, cardInfo edit header, notes footer).
• Thread cardOrField into the affected template signatures to support the above change.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
packages/base/default-templates/isolated-and-edit.gts	Switch field-definition reads to @cardOrField, and guard @fields accesses/conditional subrenders to prevent transient-resolution crashes.
packages/base/default-templates/field-edit.gts	Switch field-icon lookup to use @cardOrField instead of @model.constructor to avoid dereferencing an undefined model.

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