[Maintenance]: Cover shared runtime and tools in CI and release gates

[rwang23]

Parent

None — standalone audit-remediation item.

What to build

Extend pull-request CI and the release gate to cover the shared runtime/ and
tools/ surfaces already used by the repository, without adding a new runtime
dependency.

Acceptance criteria

• Node syntax checks include runtime/ and tools/ alongside platform code.
• Existing tools/*.test.mjs tests run in pull-request CI and the release gate.
• Workflow syntax and existing regression suites remain green.
• The change does not alter product runtime behavior.

Blocked by

None.

Implementation

Draft implementation PR: #289. This issue was created after the audit so the
independently reviewable remediation has a dedicated tracking record. It should
close only when the linked PR merges.