ca-pi: empty ExtensionAPI stub suppresses typing at the Pi host boundary (typesafety-001)

[SUaDtL]

Branch: feat/pi-support · Tribunal run 2026-07-17-pi-support-branch · Finding: findings/typesafety/typesafety-001.json
pi-api.d.ts:1-7 empty stub forces 'as unknown as' ports and one 'as never' (extension.ts:441). Fix: structural port interfaces.

[SUaDtL]

Verified against PR #313 head 9ed248f4: pi-api.d.ts now defines the structural ExtensionAPI surface consumed by the parent and child adapters, including event, tool, command, message, session, command-list, and tool-list ports. The boundary casts cited in extension.ts are gone, and every hosted Pi adapter and typecheck lane is green. This finding is implemented on #313, which now carries Closes #318.