Python: Channels

[eavanvalkenburg]

Tracking issue for the Python hosting core + pluggable channels work.

Design: docs/specs/002-python-hosting-channels.md
Overall PR: #6031 (feature/python-hosting → main)

Hosting core (agent-framework-hosting)

• AgentFrameworkHost(target=..., channels=[...]) — one Starlette app, agent or Workflow target
• Channel protocol + ChannelContribution (routes/middleware/commands/lifecycle)
• Host-neutral ChannelRequest envelope + per-request run_hook
• Session control per request (session_mode auto/required/disabled)
• Channel-neutral session identity via ChannelSession.isolation_key
• IdentityResolver seam (channel-native id → isolation_key)
• IdentityLinker seam (begin/complete link ceremony)
• ResponseTarget (originating / active / channel / channels / identities / all_linked / none)
• ChannelPush capability for proactive/cross-channel delivery
• Background runs (run_in_background → ContinuationToken, poll routes)
• Active-channel tracking per isolation_key
• Host-level Starlette middleware + host.serve(...) / host.app
• File-based HostStateStore default (survives restart); in-memory for tests
• Runtime modes (long_running vs ephemeral) + durable task runner seam

Channels

• ResponsesChannel (agent-framework-hosting-responses) — HTTP+SSE (+ WebSocket transport)
• InvocationsChannel (agent-framework-hosting-invocations)
• TelegramChannel (agent-framework-hosting-telegram) — polling + webhook, ChannelCommand catalog, silent attributed echoes
• ActivityChannel (agent-framework-hosting-activity-protocol) — Azure Bot Service / Teams, push via ConversationReference, slash commands, markdown rendering
• DiscordChannel (agent-framework-hosting-discord) — interactions + slash commands (Python: add agent-framework-hosting-discord channel #6081)
• TeamsChannel (agent-framework-hosting-teams) — Teams-native via microsoft/teams.py (Python: add agent-framework-hosting-teams channel (microsoft-teams-apps SDK) #5642)
• A2AChannel (agent-framework-hosting-a2a)
• MCPToolChannel (agent-framework-hosting-mcp)

Identity, linking & policy

• Entra identity linker helper (agent-framework-hosting-entra)
• One-time-code cross-channel linking ceremony
• Cross-channel continuity (same isolation_key across channels on one host)
• LinkPolicy + confidentiality_tier (AllowAll / SameTier / ExplicitAllowList / DenyAll)
• Authorization profiles (open / forced-link / allowlist) + IdentityAllowlist seam

Cross-channel delivery

• all_linked fan-out + input replay (echo_input) with per-channel attribution
• Per-channel response formatting variants (single structured-output call) — sample
• Unlink eviction hardening (stop delivery after unlink)
• Identity registry persistence (Cosmos-backed write-through; on-disk fallback)

Samples & docs

• Hosting Channels sample apps (Python: add hosting Channels sample apps #5645)
• Self-contained multi-channel Personal Assistant container sample (Telegram + Discord + Activity/Teams + Responses, Entra auth, disk/Cosmos storage, web search + Monty CodeAct)
• Spec 002-python-hosting-channels.md + hosting channels ADR

Fast-follow / stretch

• Generic auth helpers (HMAC signature, bearer token middleware)
• Pluggable cross-host state store (Cosmos / SQL HostStateStore)
• WhatsApp channel package
• Direct-to-Teams channel (speculative — Bot-Service-free transport)