The last Open-driver-work bullet. `-c -o <name>` replaces the fixed
<package>.test stem for exactly one package; the coordinator rejects a
multi-package fan-out ("cannot use -o with multiple packages", Go's
`go test -o` rule) and -o without -c is rejected at the driver
("needs -c for a package target" — a plain run executes from the temp
root, so a caller-owned name has nothing to name). Both driver stages
byte-identical wording; -S keeps its single-file-only reject.
package_test gains the contract row (naming, fixed-stem absence,
artifact runs, both rejects, both drivers); the tree-mode -o row's
pinned wording follows the contract.
Single-directory package-test planner: discovers *.ww, groups white-box
and external <pkg>_test sources, composes the combined test package,
builds it through the sibling ww driver, and runs it with the runtime's
-package/-list/-timeout-ms contract. test/package holds its E2E corpus
and the manual runtime fixture set.
