The last slice of the consumer-layer cutover. Teardown only — zero
runtime-logic change; the 494-green suite is the regression gate.
- Drop `httpx-sse` from pyproject + lockfile: slice-6 deleted its last
user, nothing imports `httpx_sse`, the SDK owns SSE parsing now.
- Module boundary (operator decision): KEEP `sessions.py` + `sse_client.py`
as pure caller-semantic type/exception homes (no rename, no fold —
A3 was blocked by the `AgentNotAvailable` name collision + `wt.py`
would mis-home `endpoint_for_plane`). Docstrings updated to stop
claiming "client"; the `AdminEvent`/`SseId`/exception homes stay put
(resolves the slice-6 deferred-home item).
- Retire wire contracts #2 (sessions) + #15 (tier3): DEC-1 phase-2 —
normative authority already transferred to the cutover contract; the
code they specified is gone, so the files are deleted. #1 (SSE event
vocab) and `first_message` stay (ratatoskr-owned, not retired).
- Final coverage-map re-anchor: tools/list_sessions re-homed to `wt.py`;
the Last-Event-ID SSE-resume sub-gap CLOSED (folded into `stream_turn`
auto-resume); Surface-2 SSE parsing re-anchored to the SDK.
- Stale doc-rot fix: the cli.py transport comment no longer calls
`seed_preset_first_message` "not-yet-migrated" (it rides `wt`).
- v0.22.0 (minor, DEC-6, operator-approved): publishes the full 6-slice
cutover milestone.
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