The body has a self-contained repro snippet, the 122-character heading that triggers it, versions (polaris-types 1.0.7, app-bridge-types 0.7.2, CDN App Bridge), and the three things that make it go away - shorter heading, no accessory, fewer secondary actions.
The framing is that the heading truncating is correct; the bug is that the accessory isn’t counted in the header’s space allocation, so it gets painted over rather than the row reflowing.
