feat: hot-activate WASM channels, channel-first prompts, unified artifact resolution (#297)

* refactor: unify WASM artifact resolution into registry/artifacts.rs

Consolidate duplicated WASM find/build/install logic from 5+ files into
a single src/registry/artifacts.rs module. This fixes two bugs:
- registry/installer.rs now respects CARGO_TARGET_DIR (was hardcoded)
- channels/wasm/bundled.rs now searches all WASM triples (was wasip2 only)

Also includes: extension manager hot-activation for WASM channels,
extension guidance in LLM prompts, channel manager hot-add support,
webhook router channel lookup, and minor cleanups.

Co-Authored-By: Claude Opus 4.6 <[email protected]>

* fix: send approval prompts as messages on WASM channels (Telegram, Slack)

WASM channels mapped ApprovalNeeded status to a typing indicator,
so users on Telegram never saw tool approval prompts — the agent
got stuck in AwaitingApproval and all subsequent messages failed
with "Waiting for approval".

- Intercept ApprovalNeeded in WasmChannel::handle_status_update and
  send the prompt as an actual message via call_on_respond, showing
  tool name, description, parameters, and yes/no/always instructions
- Guard against empty LLM responses after clean_response() strips
  reasoning_content think-tags (defense-in-depth for reasoning models)
- Add reasoning_content fallback to NearAiChatProvider::complete()
  for consistency with complete_with_tools()
- Add debug logging when empty responses are suppressed
- Improve error logging for channel respond() failures
- Register WASM channel webhook routes before credential checks so
  platforms don't deactivate webhook URLs with 404s

Co-Authored-By: Claude Opus 4.6 <[email protected]>

* fix: address PR #297 review comments

- ChannelManager::add: use async write().await instead of try_write()
- resolve_target_dir: resolve relative CARGO_TARGET_DIR against crate_dir
- install_wasm_files: log warning on capabilities copy failure
- refresh_active_channel: load capabilities file for webhook secret name
- activate_wasm_channel: validate name against path traversal
- Fix cargo fmt formatting in nearai_chat.rs

Co-Authored-By: Claude Opus 4.6 <[email protected]>

* fix: wire up channel runtime for hot-activation and address PR review round 2

- Wire up set_channel_runtime() in main.rs so hot-activation actually works
  (with_channel_runtime was never called — hot-activation was dead code)
- Change ExtensionManager channel runtime fields to RwLock<Option<...>>
  interior mutability so set_channel_runtime(&self) works after Arc wrapping
- Fix artifact tests to use resolve_target_dir() instead of hardcoding
  "target/" (breaks when CARGO_TARGET_DIR is set)
- Fix bundled.rs build hint: cargo component build (not cargo build --target)
- Fix wasm_artifact_path doc: binary_name should not include .wasm extension

Co-Authored-By: Claude Opus 4.6 <[email protected]>

* fix: use char-aware truncation to prevent UTF-8 panic in approval prompt

&s[..77] panics on multi-byte UTF-8 (CJK, emoji). Use s.chars().take(77)
for safe truncation at character boundaries.

Co-Authored-By: Claude Opus 4.6 <[email protected]>

---------

Co-authored-by: Claude Opus 4.6 <[email protected]>

src/extensions/mod.rs

@@ -1,16 +1,19 @@
-//! Unified extension system for discovering, installing, authenticating, and activating
-//! MCP servers and WASM tools through conversational agent interactions.
+//! Lifecycle management for extensions: discovery, installation, authentication,
+//! and activation of channels, tools, and MCP servers.
 //!
-//! Extensions are the user-facing abstraction over MCP servers and WASM tools. The agent
-//! can search a built-in registry (or discover online), install, authenticate, and activate
-//! extensions at runtime without CLI commands.
+//! Extensions are the user-facing abstraction that unifies three runtime kinds:
+//! - **Channels** (Telegram, Slack, Discord) — messaging integrations (WASM)
+//! - **Tools** — sandboxed capabilities (WASM)
+//! - **MCP servers** — external API integrations via Model Context Protocol
+//!
+//! The agent can search a built-in registry (or discover online), install,
+//! authenticate, and activate extensions at runtime without CLI commands.
 //!
 //! ```text
-//!  User: "add notion"
-//!    -> tool_search("notion")      -> finds MCP server in registry
-//!    -> tool_install("notion")     -> saves config to mcp-servers.json
-//!    -> tool_auth("notion")        -> OAuth 2.1 flow, returns URL
-//!    -> tool_activate("notion")    -> connects, registers tools
+//!  User: "add telegram"
+//!    -> tool_search("telegram")    -> finds channel in registry
+//!    -> tool_install("telegram")   -> copies bundled WASM to channels dir
+//!    -> tool_activate("telegram")  -> configures credentials, starts channel
 //! ```
 
 pub mod discovery;
@@ -31,7 +34,7 @@ pub enum ExtensionKind {
     McpServer,
     /// Sandboxed WASM module, file-based, capabilities auth.
     WasmTool,
-    /// WASM channel module (future: dynamic activation, currently needs restart).
+    /// WASM channel module with hot-activation support.
     WasmChannel,
 }
 
@@ -82,6 +85,9 @@ pub enum ExtensionSource {
         repo_url: String,
         #[serde(default)]
         build_dir: Option<String>,
+        /// Crate name used to locate the build artifact binary.
+        #[serde(default)]
+        crate_name: Option<String>,
     },
     /// Discovered online (not yet validated for a specific source type).
     Discovered { url: String },
@@ -169,6 +175,10 @@ pub struct ActivateResult {
     pub message: String,
 }
 
+fn default_true() -> bool {
+    true
+}
+
 /// An installed extension with its current status.
 #[derive(Debug, Clone, Serialize, Deserialize)]
 pub struct InstalledExtension {
@@ -187,6 +197,9 @@ pub struct InstalledExtension {
     /// Whether this extension has a setup schema (required_secrets) that can be configured.
     #[serde(default)]
     pub needs_setup: bool,
+    /// Whether this extension is installed locally (false = available in registry but not installed).
+    #[serde(default = "default_true")]
+    pub installed: bool,
 }
 
 /// Error type for extension operations.
@@ -222,9 +235,6 @@ pub enum ExtensionError {
     #[error("Config error: {0}")]
     Config(String),
 
-    #[error("Channels require restart to activate")]
-    ChannelNeedsRestart,
-
     #[error("{0}")]
     Other(String),
 }