test(security): use claude-code/testing tool noun in public-surface-scrub tests #1855

What should happen

The register() tests in plugins/magpie-security/hooks/public-surface-scrub.test.ts should dispatch tool calls via claude-code/testing's native tool noun ($.tool.call({ tool: 'Bash', command: '...' })) rather than hand-building mock on and $ fixtures.

Why

Follow-up to merged PR #1676 (noted by maintainer @potiuk in his approval review):

"One follow-up, not blocking: the register() tests still hand-build on and $ rather than using claude-code/testing's tool noun, so a drift between the mock event and the real one (like the earlier e.input.command bug) would not be caught."

Using $.tool.call tests the real event dispatch pipeline and ensures any future harness event schema drift is caught deterministically.

Which layer

Other / unsure

Boundary conditions

Host APIs invoked by the mod hook ($.session.root(), $.fs.read(), $.env.get()) should be mocked using standard on('session.root', ...) / on('fs.read', ...) / on('env.get', ...) event handlers, with on('tool.call', ...) providing the downstream next(e) fallback target.

Out of scope

No modifications to the public-surface-scrub.ts runtime logic itself; this is strictly a test suite refactoring to eliminate hand-synthesized event objects.

References

• Follow-up to PR feat(security): add deterministic public-surface scrub Claude Code mod (part of #1497) #1676
• Part of issue Explore Claude Code mods across the skill families #1497