feat(channels): Telegram Guest Mode and Bot-to-Bot communication (Bot API 10.0) (#3748)

Implement two Bot API 10.0 features for zeph-channels:

Guest Mode (#3729): bot responds to @mentions in any Telegram chat without
membership. A local bidirectional axum proxy intercepts getUpdates traffic,
injecting "guest_message" into allowed_updates and forwarding guest_message
updates to the agent via a shared mpsc channel. Responses are routed through
answerGuestQuery (one-shot, no editMessageText). Access control checks
allowed_users before any LLM call. System prompt is annotated with guest
context when is_guest_context is set on ChannelMessage.

Bot-to-Bot communication (#3730): bot can receive and respond to messages
from other Telegram bots. Calls setManagedBotAccessSettings at startup when
bot_to_bot = true. Loop prevention uses dual-check: structural reply chain
depth (spec FR-007, walk reply_to_message bounded by max+1) plus consecutive
bot-reply counter per chat (defense-in-depth). Default max_bot_chain_depth=1
to reflect the Telegram API payload's single nesting level.

New config fields under [telegram]:
  guest_mode = false
  bot_to_bot = false
  allowed_bots = []
  max_bot_chain_depth = 1

New ChannelMessage fields: is_guest_context, is_from_bot.
All 31 construction sites across the workspace updated.
9 new unit tests in zeph-channels (9089 total, +10 vs main).

Closes #3729, Closes #3730

Author: bug-ops

CHANGELOG.md

@@ -28,6 +28,22 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/).
   Unblocks Guest Mode (#3729), Bot-to-Bot communication (#3730), and reaction moderation (#3731).
   Closes #3728.
 
+- feat(channels): add Telegram Guest Mode and Bot-to-Bot communication (`zeph-channels`, `zeph-config`).
+  Guest Mode spawns a transparent local axum HTTP proxy on an ephemeral port that intercepts
+  `getUpdates` responses from `api.telegram.org`, extracts `guest_message` entries (which
+  teloxide-core 0.13 discards as unknown update kinds), and forwards them to the agent — without
+  a second `getUpdates` connection (no 409 Conflict). The `Bot` is redirected to the proxy via
+  `Bot::set_api_url()`. Responds via `answerGuestQuery` in a single call from `flush_chunks`;
+  `send_chunk()` accumulates text only in guest context (NFR-005 compliance). Bot-to-Bot mode
+  registers via `setManagedBotAccessSettings` on startup; `bot_to_bot_active` is set only on
+  success via `Arc<AtomicBool>` (remains false if API call fails). Per-chat consecutive bot reply
+  depth tracked via `BotReplyCounters`; eviction removes one random entry at capacity (not
+  bulk-clear). New config fields: `telegram.guest_mode`, `telegram.bot_to_bot`,
+  `telegram.allowed_bots`, `telegram.max_bot_chain_depth`. Guest context propagated via
+  `ChannelMessage.is_guest_context` → `SessionState.is_guest_context` → volatile system prompt
+  annotation. Fixed missing `is_guest_context`/`is_from_bot` fields in `gateway_spawn.rs` and
+  `daemon.rs`. Closes #3729, #3730.
+
 - feat(memory): add BeliefMem probabilistic edge layer to APEX-MEM (`zeph-memory`). New
   `pending_beliefs` + `belief_evidence` SQLite tables (migration 084) store candidate facts with
   probability weights before commitment. Evidence accumulates via Noisy-OR with optional temporal

crates/zeph-acp/src/agent/mod.rs

@@ -1282,6 +1282,8 @@ impl ZephAcpAgentState {
             .send(ChannelMessage {
                 text: text.clone(),
                 attachments,
+                is_guest_context: false,
+                is_from_bot: false,
             })
             .await
             .map_err(|_| acp::Error::internal_error().data("agent channel closed"))?;
@@ -2005,6 +2007,8 @@ impl ZephAcpAgentState {
                     let _ = tx.try_send(ChannelMessage {
                         text: "/clear".to_owned(),
                         attachments: vec![],
+                        is_guest_context: false,
+                        is_from_bot: false,
                     });
                 }
                 "Session history cleared.".to_owned()
@@ -2067,6 +2071,8 @@ impl ZephAcpAgentState {
             .try_send(ChannelMessage {
                 text: review_prompt,
                 attachments: vec![],
+                is_guest_context: false,
+                is_from_bot: false,
             })
             .is_err()
         {

crates/zeph-bench/src/channel.rs

@@ -204,6 +204,8 @@ impl zeph_core::channel::Channel for BenchmarkChannel {
                 Ok(Some(ChannelMessage {
                     text,
                     attachments: vec![],
+                    is_guest_context: false,
+                    is_from_bot: false,
                 }))
             }
             None => Ok(None),

crates/zeph-channels/Cargo.toml

@@ -15,10 +15,10 @@ readme = "README.md"
 [features]
 profiling = []
 discord = ["dep:tokio-tungstenite", "dep:futures"]
-slack = ["dep:axum", "dep:hmac", "dep:sha2", "dep:subtle"]
+slack = ["dep:hmac", "dep:sha2", "dep:subtle"]
 
 [dependencies]
-axum = { workspace = true, optional = true }
+axum = { workspace = true }
 crossterm.workspace = true
 futures = { workspace = true, optional = true }
 hmac = { workspace = true, optional = true }

crates/zeph-channels/src/cli.rs

@@ -135,6 +135,8 @@ async fn process_line(
     Ok(Some(ChannelMessage {
         text: trimmed.to_string(),
         attachments,
+        is_guest_context: false,
+        is_from_bot: false,
     }))
 }
 
@@ -771,6 +773,8 @@ mod tests {
         tx.send(ChannelMessage {
             text: "hello".to_string(),
             attachments: vec![],
+            is_guest_context: false,
+            is_from_bot: false,
         })
         .await
         .unwrap();

crates/zeph-channels/src/discord/mod.rs

@@ -162,6 +162,8 @@ impl Channel for DiscordChannel {
             return Some(ChannelMessage {
                 text: incoming.content,
                 attachments: vec![],
+                is_guest_context: false,
+                is_from_bot: false,
             });
         }
     }
@@ -188,6 +190,8 @@ impl Channel for DiscordChannel {
             return Ok(Some(ChannelMessage {
                 text: incoming.content,
                 attachments: vec![],
+                is_guest_context: false,
+                is_from_bot: false,
             }));
         }
     }

crates/zeph-channels/src/json_cli.rs

@@ -98,6 +98,8 @@ impl Channel for JsonCliChannel {
                     return Ok(Some(ChannelMessage {
                         text,
                         attachments: Vec::new(),
+                        is_guest_context: false,
+                        is_from_bot: false,
                     }));
                 }
                 Some(None) | None => return Ok(None), // EOF
@@ -119,6 +121,8 @@ impl Channel for JsonCliChannel {
                 Some(ChannelMessage {
                     text: trimmed,
                     attachments: Vec::new(),
+                    is_guest_context: false,
+                    is_from_bot: false,
                 })
             }
             _ => None,

crates/zeph-channels/src/slack/mod.rs

@@ -139,6 +139,8 @@ impl Channel for SlackChannel {
         Some(ChannelMessage {
             text: incoming.text,
             attachments: vec![],
+            is_guest_context: false,
+            is_from_bot: false,
         })
     }
 
@@ -171,6 +173,8 @@ impl Channel for SlackChannel {
         Ok(Some(ChannelMessage {
             text: incoming.text,
             attachments,
+            is_guest_context: false,
+            is_from_bot: false,
         }))
     }