The CI display helper now uses --start-delay-ms instead of --start-path
because the XCTest sandbox prevents writing to /tmp/. The harness manifest
no longer includes startPath, but the test guard still required it, causing
"Incomplete external display harness configuration" errors.
Make startPath optional in both the manifest and environment variable
harness loading paths, and gate the start signal write on displayStartPath
being non-empty.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
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