Python: add agent-framework-hosting-activity-protocol channel (#5641)

* feat(hosting-activity-protocol): rename Bot Framework channel to ActivityProtocolChannel

The existing Bot-Framework-via-Azure-Bot-Service channel was previously
shipped under the name ``hosting-teams`` / ``TeamsChannel``. That name
is misleading for what the channel actually does -- it speaks the Bot
Framework Activity Protocol against Azure Bot Service, which fans out
across MS Teams, Slack, Webex, Telegram-via-Bot-Service, etc., and does
not provide any Teams-specific affordances.

This PR renames the package atomically and frees the ``hosting-teams``
name for a future Teams-native channel built on
``microsoft-teams-apps`` (PR-5b, spec req #28).

Renames (all in one commit):

- Package: ``agent-framework-hosting-teams`` ->
  ``agent-framework-hosting-activity-protocol``
- Module: ``agent_framework_hosting_teams`` ->
  ``agent_framework_hosting_activity_protocol``
- Channel class: ``TeamsChannel`` -> ``ActivityProtocolChannel``
- Helper: ``teams_isolation_key`` -> ``activity_protocol_isolation_key``
  (isolation key prefix ``teams:`` -> ``activity:``)
- Channel name: ``"teams"`` -> ``"activity"``; default mount path
  ``/teams`` -> ``/activity``
- Internal helper: ``_parse_teams_activity`` -> ``_parse_activity``
- Worker task name + a couple of error strings updated for consistency

Updates README.md and the module docstring to call out:

- this is the channel-neutral Activity Protocol channel,
- it surfaces what every Bot-Service-connected channel has in common
  (text in / text out),
- a forthcoming ``agent-framework-hosting-teams`` package will layer
  Teams-specific affordances (adaptive cards, message extensions,
  dialogs, SSO, ...) on the same Bot Service transport.

Workspace: registers ``agent-framework-hosting-activity-protocol`` in
``python/pyproject.toml`` and adds the matching pyright
``executionEnvironments`` entry.

Behavior is unchanged. Pyright + mypy clean, 11 tests pass.

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

* review: address PR-5 round 2 feedback

- security (#3198327004): add `service_url_allowed_hosts` constructor
  option (default `botframework.com` + `smba.trafficmanager.net`) and
  reject inbound activities whose `serviceUrl` host falls outside it
  with HTTP 400 — without this gate a malicious caller could redirect
  outbound replies (and the attached bearer token) to an
  attacker-controlled host
- security (#3198324219): add `inbound_auth_validator` async callback;
  log a loud WARNING at startup when no validator AND no operator
  reverse-proxy is configured so the dev-mode bypass cannot
  accidentally ship to production. Document the contract: prototype
  intentionally does not ship JWT validation (out of scope); operators
  must plug a validator or terminate auth in front of the channel
- retry semantics (#3198328746): distinguish transient outbound
  failures (httpx network errors, non-2xx from Bot Service) — return
  502 so Bot Service retries — from deterministic agent failures —
  return 200 so Bot Service does not retry the same broken activity
  in a loop
- bug (#3198330424): fix the placeholder-failure deadlock. When
  `send_initial_placeholder` fails, `activity_id` stays `None`, the
  edit-worker loop exit condition (`accumulated == last_sent`) is
  unreachable while no PUT is possible, and the worker would deadlock
  on `wake.wait()` forever after `worker_done` is set. Now: skip the
  worker entirely on placeholder failure and POST a single final
  activity at the end with whatever accumulated
- tests (#3198334465, #3187178091, #3198336045): add coverage for
  - `_is_service_url_allowed` allow/deny matrix + webhook 400 on
    disallowed serviceUrl
  - `inbound_auth_validator` allow/deny/raises paths
  - outbound `Authorization: Bearer <token>` header presence in
    production mode and absence in dev mode
  - the streaming path (`_stream_to_conversation`): placeholder +
    final edit, placeholder-failure fallback (with timeout guard
    against deadlock regression), and empty-stream `(no response)`
    placeholder replacement
  - retry-signal differentiation: outbound `httpx.ConnectError` →
    502; deterministic `ValueError` from the agent → 200

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

* test(hosting): drop redundant @pytest.mark.asyncio decorators

asyncio_mode = "auto" is configured in pyproject.toml across the
hosting packages, so individual @pytest.mark.asyncio decorators are
unnecessary.

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

* feat(hosting-activity-protocol): add response hooks

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

* docs(hosting-activity-protocol): mark constructor keyword args

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

---------

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

python/uv.lock

@@ -51,6 +51,7 @@ members = [
     "agent-framework-hosting-responses",
     "agent-framework-hosting-invocations",
     "agent-framework-hosting-telegram",
+    "agent-framework-hosting-activity-protocol",
     "agent-framework-hyperlight",
     "agent-framework-lab",
     "agent-framework-mem0",
@@ -671,6 +672,17 @@ requires-dist = [
     { name = "openai", specifier = ">=1.99.0,<3" },
 ]
 
+[[package]]
+name = "agent-framework-hosting-activity-protocol"
+version = "1.0.0a260424"
+source = { editable = "packages/hosting-activity-protocol" }
+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 = "azure-identity", marker = "sys_platform == 'darwin' or sys_platform == 'linux' or sys_platform == 'win32'" },
+    { name = "httpx", marker = "sys_platform == 'darwin' or sys_platform == 'linux' or sys_platform == 'win32'" },
+]
+
 [[package]]
 name = "agent-framework-hosting-invocations"
 version = "1.0.0a260424"
@@ -678,6 +690,7 @@ source = { editable = "packages/hosting-invocations" }
 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 = "azure-identity", specifier = ">=1.20,<2" },
     { name = "httpx", specifier = ">=0.27,<1" },
 ]