The natural smallest unit to TDD against per design-brief §3. Bundles
stream_turn + reconnect_turn + cancel_turn + private _parse_sse_id into
one module because the SSE-resume flow is structurally coupled — cancel
needs the turn_id parsed from the SSE wire id:, reconnect re-uses the
same parsed SseId, and stream_turn is what produces them.
Hard invariant INV-002 forces every yielded Event to carry a parsed
SseId(turn_id, seq) lifted from the composite {turn_id}:{seq} id:
wire field. This closes the foot-gun design-brief §3 explicitly names:
hand-rolled data:-only parsing silently drops the id: line and breaks
SSE-resume invisibly.
v2.1 format used; test categories adversarial/scenario/trace flagged
warn-only by the v2.0 parser (CONTRACT-FORMAT §2.1.L H10 is a known
Brokkr-side parser follow-up). FN block list parses cleanly.
Scaffold also verified at this commit: uv pip install -e ".[dev]"
resolves clean against the lockfile (now committed), and the boundary
smoke test (tests/test_no_worldtree_imports.py) passes.
