Literal query commas were treated as collection separators, so ?ids=1,2 became ?ids=1&ids=2. Primitive-array query-map values and default array expressions also sent Java array identity strings instead of their elements.

Preserve literal/scalar query values and expand arrays through the existing element encoders. Collection expressions keep their current CollectionFormat behavior, and custom Param.Expander implementations still receive arrays as whole values. Add regression coverage plus README and 13.18 changelog notes. Mixed literal-comma/collection templates keep their existing expansion behavior, as documented.

Validation:

• Core: mvn -Pdev -pl core test — 795 tests, no failures, 4 existing skips; Java 8 main toolchain and JDK 27 test JVM.
• Root: mvn -Pdev validate passed with a task-local toolchains file registering the installed JDK 11 alongside the existing toolchains.
• Baseline failures reproduced before the fix; independent source review completed.

Fixes #3623

Remote Actions currently reports action_required with no jobs executed; local validation is complete.