Python: add agent-framework-hosting-responses channel (#5639)

* feat(hosting-responses): add OpenAI Responses-shaped channel package

New ``agent-framework-hosting-responses`` package implementing the
OpenAI Responses-shaped HTTP channel for the Hosting framework. Mounts
``POST /responses`` (and a ``/responses/{response_id}`` GET) onto an
``AgentFrameworkHost`` and translates the OpenAI Responses wire shape
to/from the channel-neutral ``ChannelRequest`` / ``HostedRunResult``
plumbing.

Surface (re-exported from ``agent_framework_hosting_responses``):

- ``ResponsesChannel`` -- concrete ``Channel`` implementation. Owns the
  Starlette route(s), parses inbound JSON into ``ChannelRequest``, runs
  the optional ``ChannelRunHook``, calls back into the
  ``ChannelContext`` to invoke the agent target, builds Responses
  envelopes (sync JSON or SSE), and respects
  ``DeliveryReport.include_originating`` so cross-channel push routes
  only ack to the originating Responses caller.
- The minted ``response_id`` is propagated via the host's ContextVar
  machinery so storage-side history providers (e.g.
  ``FoundryHostedAgentHistoryProvider``) persist envelopes against the
  same id the channel returns.
- 48 unit tests covering route wiring, parsing of each Responses input
  shape, hook composition, sync vs streaming paths, and originating
  vs non-originating delivery branches.

Registers the package in ``python/pyproject.toml`` ``[tool.uv.sources]``
and adds the matching pyright ``executionEnvironments`` entry.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* review: address PR-3 round 2 feedback

- consume IsolationKeys.chat_key from the host-bound contextvar instead
  of the raw `x-agent-chat-isolation-key` header off the wire so the
  host's ASGI isolation middleware (or any operator-supplied
  replacement) is the authoritative point at which the caller is
  authenticated and the bucket key is established
- expand `response_id_factory` docstring to call out partition
  co-location vs. partition-ownership enforcement: the channel forwards
  `previous_response_id` as a hint to the factory; the storage layer
  validates the embedded partition against the bound user/chat
  isolation keys
- on mid-stream failure, call `deliver_response` with the accumulated
  text before emitting `response.failed` so host-side history /
  push-channel state stays consistent with the partial deltas the
  client already saw

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* docs(hosting-responses): fix quickstart to use current Agent API

ChatAgent was renamed to Agent and ChatMessage to Message. Update the
README quickstart to use client.as_agent(...) and refresh the stale
docstring reference in _channel.py.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* fix(hosting-responses): adapt to hosted run result wrapper

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* feat(hosting-responses): add response hooks

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* fix(hosting-responses): keep instructions in chat options

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

---------

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

python/uv.lock

@@ -48,6 +48,7 @@ members = [
     "agent-framework-gemini",
     "agent-framework-github-copilot",
     "agent-framework-hosting",
+    "agent-framework-hosting-responses",
     "agent-framework-hyperlight",
     "agent-framework-lab",
     "agent-framework-mem0",
@@ -642,6 +643,23 @@ provides-extras = ["serve", "disk"]
 [package.metadata.requires-dev]
 dev = [{ name = "httpx", specifier = ">=0.28.1" }]
 
+[[package]]
+name = "agent-framework-hosting-responses"
+version = "1.0.0a260424"
+source = { editable = "packages/hosting-responses" }
+dependencies = [
+    { name = "agent-framework-core", marker = "sys_platform == 'darwin' or sys_platform == 'linux' or sys_platform == 'win32'" },
+    { name = "agent-framework-hosting", marker = "sys_platform == 'darwin' or sys_platform == 'linux' or sys_platform == 'win32'" },
+    { name = "openai", marker = "sys_platform == 'darwin' or sys_platform == 'linux' or sys_platform == 'win32'" },
+]
+
+[package.metadata]
+requires-dist = [
+    { name = "agent-framework-core", editable = "packages/core" },
+    { name = "agent-framework-hosting", editable = "packages/hosting" },
+    { name = "openai", specifier = ">=1.99.0,<3" },
+]
+
 [[package]]
 name = "agent-framework-hyperlight"
 version = "1.0.0b260521"