Improve prompt error handling and relative path support (#153) #264

Job	Run time
CODEQL_PATH Tests (macos-latest)	1m 30s
CODEQL_PATH Tests (ubuntu-latest)	1m 1s
CODEQL_PATH Tests (windows-latest)	1m 26s
Integration Tests (ubuntu-latest, stdio)	11m 4s
Integration Tests (windows-latest, stdio)	15m 0s
Integration Tests (ubuntu-latest, http)	10m 59s
Integration Tests (windows-latest, http)	13m 36s
	54m 36s

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