slice 1.0.4: agent loop runner — provider + tool dispatch + event emit

[sausi-7]

Phase 1.0 demo slice · Difficulty: D2

Scope

The minimum loop: take a system prompt + user prompt + provider + tool registry; stream events; dispatch tool calls; feed results back; terminate on done.

No token-budget trimming, no conversation persistence, no multi-turn — that's deferred.

Acceptance criteria

• Async function returning an AsyncIterator[Event].
• Tool-call → tool-result round-trip works against write_file and read_file.
• Loop terminates cleanly on done or error.
• Smoke test against a FakeProvider that scripts a write_file call.