Follow-ups from #878: real-owner flag values through the sanitizer and the launcher #883

Follow-ups from the review of #878 (non-blocking), tracked here as one issue:

1. A slash-containing flag value is dropped before it is parsed. The test-home guard's sanitizer drops TPS_TEST_REQUIRE_REAL_OWNER values that contain / (for example 1/0), so the variable arrives unset and the real-owner case runs as optional. The fix makes the guard keep or refuse such a value for this variable so a malformed value fails instead of becoming unset. The Docker lane's configured value is already pinned, so this only affects a hand-set value.
2. Pin the invalid-value failure through the real launcher. The typo test calls the parse helper directly. The fix adds a regression that runs the heartbeat test module through the suite launcher with an invalid value and asserts the run fails at module load.

Refs #816, #878.