feat(retained): make interaction responses durable

[drewstone]

Outcome

• Retain exact native Pi sessions across turns and replay canonical events.
• Persist interaction responses before native delivery and return idempotent acknowledgements.
• Fail closed when restart, process identity, or finalization cannot prove the native effect.
• Bind controls to the exact provider, environment, run, session, turn, and interaction.

Proof

• pnpm test: 945 passed, 12 skipped, 51 files passed.
• pnpm typecheck: passed.
• pnpm build: passed.
• git diff --check: passed.