[#72454] Fix CollapsibleHeader title truncation when multi_line: false

[myabc]

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https://community.openproject.org/wp/72454

Risk Assessment

• Low risk the change is small, highly observable, and easily rolled back.
• Medium risk changes that are isolated, reduced in scope or could impact few users. The change will not impact library availability.
• High risk changes are those that could impact customers and SLOs, low or no test coverage, low observability, or slow to rollback.

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• Fixes axe scan violation - This change fixes an existing axe scan violation.
• No new axe scan violation - This change does not introduce any new axe scan violations.
• New axe violation - This change introduces a new axe scan violation. Please describe why the violation cannot be resolved below.

Merge checklist

• Added/updated tests
• Added/updated documentation
• Added/updated previews (Lookbook)
• Tested in Chrome
• Tested in Firefox
• Tested in Safari
• Tested in Edge

[changeset-bot]

🦋 Changeset detected

Latest commit: f45501e

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@openproject/primer-view-components	Patch

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[Copilot]

Pull request overview

Fixes Primer::OpenProject::BorderBox::CollapsibleHeader title truncation when rendered in single-line mode (multi_line: false) in the OpenProject-specific Primer fork.

Changes:

• Render the header title using Primer::Beta::Truncate to enable ellipsis truncation.
• Adjust CollapsibleHeader flex/overflow styling to allow the title row to shrink and truncate correctly.
• Add a changeset documenting the patch release.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.

File	Description
app/components/primer/open_project/border_box/collapsible_header.rb	Switches the title slot component from Primer::Beta::Heading to Beta::Truncate to support truncation.
app/components/primer/open_project/border_box/collapsible_header.pcss	Updates overflow/flex sizing rules to make the title line truncatable in single-line layout.
.changeset/easy-cobras-design.md	Declares a patch release and describes the truncation fix.

[Copilot]

.CollapsibleHeader-title-line { flex-basis: 66%; } is a hard-coded percentage that affects the flex item’s main size. Since the trigger area switches to flex-direction: column in the container query and in --multi-line mode, this flex-basis can become confusing and may behave inconsistently across browsers (percentage basis on an auto-sized column flex container). Consider replacing this with a more explicit/robust sizing approach (e.g., flex grow/shrink rules) or scoping the percentage sizing to only the row layout.

[github-actions]

⚠️ Visual or ARIA snapshot differences found

Our visual and ARIA snapshot tests found UI differences. Please review the differences by viewing the files changed tab to ensure that the changes were intentional.

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