Improve prompt error handling and relative path support #244

Job	Run time
Integration Tests (windows-latest, http)	14m 55s
CODEQL_PATH Tests (windows-latest)	1m 26s
CODEQL_PATH Tests (macos-latest)	1m 30s
Integration Tests (ubuntu-latest, stdio)	11m 26s
Integration Tests (ubuntu-latest, http)	9m 3s
CODEQL_PATH Tests (ubuntu-latest)	49s
Integration Tests (windows-latest, stdio)	13m 46s
	52m 55s

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