[Channel RFC] Telegram adapter migration (shim → full TelegramChannelAdapter)

[eanzhao]

Parent RFC: #254

Scope

从 TelegramPlatformAdapter（shim 级）迁移到 TelegramChannelAdapter（full adapter 实现）。

Deliverables

Package: agents/channels/Aevatar.GAgents.Channel.Telegram

底层 SDK: Telegram.Bot（11k+ stars，最成熟 .NET Telegram library）

Main class: TelegramChannelAdapter : IChannelTransport, IChannelOutboundPort

• 迁移自 TelegramPlatformAdapter
• Transport 双模式：Webhook 优先 / long-polling fallback（开发模式）
• Group / supergroup / channel 的区分（ConversationReference.TelegramGroup / .TelegramChannel / .TelegramPrivate）

Composer: TelegramMessageComposer : IMessageComposer

• intent → text + inline keyboard
• Attachments: upload via sendPhoto / sendDocument multipart

Capability declaration:

• SupportsEphemeral = false / SupportsThread = false / SupportsModal = false / SupportsConfirmDialog = false
• SupportsStreaming = EditLoopRateLimited（editMessageText 20/min per chat 硬限）
• SupportsActionButtons = true（inline keyboard）

Streaming support:

• BeginStreamingReplyAsync 实现用 editMessageText + rate-limited debounce（RecommendedStreamDebounceMs = 3000）

Acceptance

• TelegramChannelAdapter 过 Conformance Suite（[Channel RFC] Conformance + Fault Injection test suite (Aevatar.GAgents.Channel.Testing) #264）
• Webhook + long-polling 模式均能启动
• 当前 Telegram bot 的 behavior parity
• Group / supergroup / channel 消息都能被路由到对应 canonical conversation

References

• RFC §10.2 Telegram

Dependencies

• Depends on: [Channel RFC] Phase 0 infra prerequisites (DeleteAsync / EventHubs harness / secret manager) #255, [Channel RFC] Proto schema definitions (7 proto files) #256, [Channel RFC] Core abstractions package (Aevatar.GAgents.Channel.Abstractions) #257, [Channel RFC] Runtime package (grains / middleware / durable inbox integration) #258, [Channel RFC] Conformance + Fault Injection test suite (Aevatar.GAgents.Channel.Testing) #264
• Should land after [Channel RFC] Lark adapter migration (LarkPlatformAdapter → LarkChannelAdapter + group chat + streaming) #261（Lark 作为 ref impl 先稳定，Telegram 作为第二 adapter 验证抽象不是 Lark-overfit）