tests/test_dsh_plugin_core_parity.py asserts that the DSH copy of
core.ts is byte-identical to the OpenCode core, that cordis.patch.yml
inserts the package by name, that package.json declares
dsh.bundle.patch and ships dist and the patch, that dist/ is neither
tracked nor trackable, and that the plugin never registers /plan or
/plan-status: dsh owns /plan for its plan mode.
The tests workflow gains a vitest (DSH plugin) job mirroring the
OpenCode one: npm ci, tsc build against the published types, vitest.