v0.31.0 — Sprint 32 close (HTTP/2 stream-info)

Sprint 32 close — HTTP/2 stream-info ASGI extensions. Moves
the existing RFC 9218 priority hint from scope['http2_priority']
under scope['extensions'] per ASGI convention and adds a new
HTTP/2 stream-info extension exposing stream_id and send-side
flow-control state. Lays the foundation for future gRPC over
HTTP/2 work; no gRPC code in this release, but a written
assessment is included.

Added

• scope['extensions']['http.response.priority'] — RFC 9218
  priority hint at the conventional ASGI scope-extensions
  location. Field name matches gunicorn's beta HTTP/2 surface;
  the contents are RFC 9218 urgency/incremental rather than the
  RFC 7540 weight/depends_on tree that RFC 9113 §5.3.2
  deprecated. Shape: {'urgency': int 0-7, 'incremental': bool}.
• scope['extensions']['http.response.http2_stream'] — new
  BlackBull HTTP/2 stream-info extension. Snapshot at scope
  build time of {'stream_id': int, 'send_window_remaining': int, 'connection_send_window_remaining': int}. Peer
  recv-window is intentionally absent (we send WINDOW_UPDATE per
  consumed DATA frame, so there's no scalar to snapshot).
• docs/about/grpc-assessment.md — written assessment of
  what gRPC over BlackBull would need, what's available today,
  what Sprint 32 unlocks (server-streaming back-pressure
  visibility), and what's still missing for a minimum gRPC
  server. No commitment; the document is decision input for a
  future sprint.

Changed

• docs/guide/http2.md leads with the new
  scope['extensions']['http.response.priority'] location. A
  Migrating from scope['http2_priority'] subsection explains
  the rename.
• examples/PriorityExample/ updated to read priority from
  the new extension location. The example no longer reads
  scope['http2_priority']; that key remains populated only for
  the deprecation window.

Deprecated

• scope['http2_priority'] — the top-level scope key that
  carried the same RFC 9218 urgency/incremental dict. Still
  populated for backwards compatibility during the v0.31 cycle
  and scheduled for removal in 0.32.0. Apps should read
  scope['extensions']['http.response.priority'] instead.

Tests

• 9 new unit tests in tests/unit/test_http2_extensions.py
  pinning the helper's per-request fresh-dict semantics,
  the priority extension contents (RFC 9218 default + explicit
  pass-through), and the http2_stream snapshot fields.
• 3 new integration tests in
  tests/integration/test_http2_advanced.py confirming the new
  extension keys show up in a real HTTP/2 scope and agree with
  the deprecation alias.

Notes for adopters

• Migrating from scope['http2_priority']. Replace
  scope.get('http2_priority', DEFAULT) with
  (scope.get('extensions') or {}).get('http.response.priority', DEFAULT).
  The dict shape is unchanged.
• HTTP/1.1 requests do not advertise the new HTTP/2
  extensions. scope['extensions'] will contain
  http.response.pathsend (from v0.30) but not
  http.response.priority / http.response.http2_stream.
• Window snapshot caveat. The send-window fields are taken
  at scope-build time; they shift as the response body streams.
  Live readings (e.g. for iterative gRPC server-streaming
  back-pressure) need a future sprint — see Open question in
  docs/about/grpc-assessment.md.

Out of scope / deferred

• HTTP/2 mutation API — set-priority-on-push, app-driven
  window updates, dependency edits. Wait for an adopter need.
• gRPC implementation — only the assessment doc this sprint.
  A real gRPC server is 1-3 sprints of work on top of these
  primitives; the assessment doc spells out the breakdown.
• scope['http2_priority'] removal — happens in v0.32.0;
  retained this release to give adopters one cycle to migrate.
• RFC 7540 weight/depends_on parity with gunicorn — RFC 9113
  deprecated those; modern clients don't send them.