[DanielThomas]

Summary

Fix installation and dynamic tool discovery when an application requires system modules that are present in the JDK but absent from ja's hosting layer, as reported in #90.

• Inspect the module descriptor before attempting provider discovery, so installing a main-class application does not load its classes unnecessarily.
• Make system modules observable during resolution while preserving the existing parent/path selection policy.
• Detect newly resolved system modules before defining a child layer. Reuse the existing Java launcher, option-inspection entry point, and tool dispatcher to discover and run those providers in a child JVM, where startup assigns system modules to the correct built-in loaders.
• Keep system-installed tools and dynamically discovered tools whose dependencies are already loaded on the existing in-process path. No unconditional java.se/ALL-SYSTEM startup roots or JDK-internal APIs.
• Preserve provider option discovery, runtime-access arguments, source overrides, and warmup metadata across the fallback.

Validation

• Added regressions covering java.sql, java.se, and jdk.xml.dom, both ToolProvider and javax.tools.Tool, activated providers, source overrides, and warmup metadata.
• Real install-and-run tests distinguish provider dispatch from main-class dispatch and assert that installed commands do not fork an additional JVM.
• Explicitly assert that running the system-installed jig does not invoke the Java launcher, and compare process IDs for dynamic tools with and without additional system-module requirements.
• ja test --all: 490/491 passing. The only failure is the pre-existing JmhToolProviderTest.discoversAndRunsAModularBenchmark, whose server-socket bind is denied by the sandbox (SocketException: Operation not permitted).
• After adding the installed-command process-ID assertions: ja test --all com.netflix.tools.ja.test.InstallerTest: 22/22 passing.
• The original SQL provider reproduction succeeds through the current-source CLI for tool execution, installation, and execution of the installed command.
• git diff --check passes.