The thin client (sbtn) parsed the launcher value flags (-java-home, -mem,
-jvm-debug, -sbt-dir, ...) but then dropped them. The space form was consumed
and discarded; the flag=value form fell through to the residual arguments and
was forwarded to the server verbatim, where --java-home=/path was rejected as a
command (`Not a valid command: --`).
When the client had to start a server (none running, no --server), the consumed
-java-home never reached the forked sbt launcher, so the server came up under
the default JVM and, in CI where the intended JDK is only reachable via
-java-home, failed to connect.
parseArgs now captures the consumed launcher value flags (both `flag value` and
`flag=value`) into Arguments.launcherValueArgs, and the cold-start fork re-passes
them to the sbt launcher so the server runs under the requested JVM. The client
tokenizes arguments by splitting on whitespace, which would otherwise fragment a
value that contains spaces (a Windows path like C:\Program Files\Java); parseArgs
tracks those split boundaries and rejoins a value flag's value. An empty flag=
value and a dangling flag with no value are consumed but not propagated, since
the launcher's require_arg would otherwise fail the fork.
The fork command construction is extracted into a pure, package-visible
serverCommand so a test can assert the propagated flag reaches the started
server. The sbt-launch-jar path is unchanged: it invokes java directly, with no
launcher to interpret the flag.
Fixes#9418
Co-authored-by: Claude Opus 4.8 (1M context) <[email protected]>
