feat(channels): adopt Telegram Bot API 10.1 rich-text formatting and fix guest-mode escaping

CHANGELOG.md

@@ -5,6 +5,44 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/).
 
 ## [Unreleased]
+### Fixed
+
+- `zeph-channels`: Telegram guest-mode responses (`TelegramChannel::flush_chunks`) are now
+  formatted through the same `markdown_to_telegram` renderer used by regular messages, and
+  sent with `parse_mode = "MarkdownV2"` instead of an unconverted `"HTML"` call — raw LLM
+  Markdown could previously break Telegram's HTML parser or render literal markup to guest
+  users (issue #6541, spec 007-3-telegram-rich-text). `TelegramRenderer` also now prefixes
+  every line of a multi-line blockquote with `>` (`markdown.rs`); previously only the first
+  line of a multi-line quote was actually quoted by Telegram's client. Nested blockquotes now
+  flatten to a single `>`-per-line level instead of accumulating an unescaped `>>` — Telegram
+  MarkdownV2 has no nested-blockquote grammar and rejects a doubled `>` outright (`400 can't
+  parse entities`, dropping the whole message); a nesting-depth cap
+  (`MAX_BLOCKQUOTE_NESTING_DEPTH = 512`, same defence-in-depth pattern as `MAX_CHUNK_DEPTH`,
+  #6595) bounds the tracked-mark memory for adversarially deep nested input.
+- `src/channel.rs`: `create_channel` now wires `TelegramConfig.guest_mode` and `.bot_to_bot`
+  (plus `allowed_bots`/`max_bot_chain_depth`) into `TelegramChannel` — previously these config
+  fields were accepted but never threaded into the builder, so Guest Mode and Bot-to-Bot were
+  unreachable in a real running agent even with both enabled in config (pre-existing gap,
+  found during review of #6541; not previously filed as its own issue).
+- `zeph-channels`: `TelegramChannel::start`'s Guest Mode proxy (`spawn_guest_proxy`) now calls
+  `set_nonblocking(true)` on the bound `std::net::TcpListener` before handing it to
+  `tokio::net::TcpListener::from_std` — tokio requires a non-blocking socket for that
+  conversion, and a recent tokio release turned the previous silent misbehavior into a hard
+  panic ("Registering a blocking socket with the tokio runtime is unsupported", see
+  tokio-rs/tokio#7172). Latent since Guest Mode's original implementation; unreachable in
+  tests or production until the `guest_mode` wiring fix above made this code path actually
+  run — without this fix, enabling `guest_mode = true` would have crashed the process.
+
+### Added
+
+- `zeph-channels`/`zeph-config`: adopt Telegram Bot API 10.1 expandable blockquotes
+  (issue #6541, spec 007-3-telegram-rich-text). New `TelegramConfig.expandable_blockquote_min_lines`
+  (default `10`) renders blockquotes at or above the configured line count as the expandable
+  (collapsed-by-default) form (`**>` … `\|\|`); `0` disables the expandable form
+  unconditionally. New `markdown::markdown_to_telegram_with_config` accepts an explicit
+  threshold; `markdown_to_telegram` is unchanged and delegates to it with the default of 10.
+  Wired into `--init` and `--migrate-config`.
+
 ### Removed
 
 - `zeph-agent-tools`: removed the unused `AgentChannel` sealed trait and its supporting

book/src/guides/telegram.md

@@ -44,7 +44,8 @@ Telegram has API rate limits, so streaming works differently from CLI. Zeph batc
 - Subsequent chunks accumulate and edit the existing message in-place
 - Edit interval is configurable via `stream_interval_ms` (default 3000ms, minimum 500ms)
 - Long messages (>4096 chars) are automatically split
-- MarkdownV2 formatting is applied automatically
+- MarkdownV2 formatting is applied automatically, including multi-line blockquotes — every
+  quoted line renders inside Telegram's blockquote UI, not just the first
 
 ### Configuring Stream Interval
 
@@ -61,6 +62,21 @@ stream_interval_ms = 3000  # Edit every 3 seconds (default)
 
 Lower values provide more responsive feedback but consume more API quota. Higher values reduce API calls but responses appear less fluid. Start with the default and adjust based on your network speed and API rate limit tolerance.
 
+### Configuring Expandable Blockquotes
+
+Long blockquotes can render collapsed by default, using Telegram's expandable blockquote UI (Bot API 10.1):
+
+```toml
+[telegram]
+expandable_blockquote_min_lines = 10  # default
+# Collapse quotes of 5+ lines instead:
+# expandable_blockquote_min_lines = 5
+# Disable the expandable form entirely — always render fully expanded:
+# expandable_blockquote_min_lines = 0
+```
+
+Blockquotes with at least `expandable_blockquote_min_lines` lines render collapsed, with a "Show more" affordance in the Telegram client; shorter quotes render as a regular (always-expanded) blockquote. Setting this to `0` disables the expandable form unconditionally, regardless of quote length.
+
 ## Guest Mode and Bot-to-Bot Communication
 
 Zeph supports advanced Telegram modes for integration with other bots and guest users.

config/default.toml

@@ -1062,6 +1062,9 @@ circuit_breaker_cooldown_secs = 30
 # token = "your-bot-token"
 # Allowed usernames (empty = allow all except for /start command)
 # allowed_users = ["username1", "username2"]
+# Blockquotes with this many lines or more render as an expandable (collapsed-by-default)
+# blockquote (Bot API 10.1 expandable_blockquote). 0 disables the expandable form entirely.
+# expandable_blockquote_min_lines = 10
 
 [timeouts]
 # LLM chat completion timeout in seconds