Extensions importing legacy pi UI components (e.g. DynamicBorder from
@earendil-works/pi-coding-agent) receive a second src module graph in
npm-package installs. Host startup assigns the module-level `theme` only
inside the bundled dist copy, so the src-graph copy stays undefined and
DynamicBorder.render dereferenced `theme.boxRound` unconditionally,
throwing "undefined is not an object" and taking down the whole TUI.
Route the default color through the existing `fgOrPlain` guard and fall
back to the default rounded glyph when `theme` is undefined, matching the
`typeof theme === "undefined"` degradation already used by fgOrPlain and
getSettingsListTheme.
Fixes#5366
roboomp
83ed5eef1f