refactor(logging): preserve tracebacks and add channel context

- Preserve tracebacks: logger.error in except blocks → logger.exception
- Channel context: BaseChannel injects self.logger = logger.bind(channel=name)
- Third-party bridge: redirect_lib_logging() replaces ad-hoc stdlib-to-loguru bridges
- Log levels: network timeouts downgraded from ERROR → WARNING
- Fix --verbose flag to actually work with loguru (set handler to DEBUG)

nanobot/agent/tools/mcp.py

@@ -198,11 +198,10 @@ class MCPToolWrapper(Tool):
                         await asyncio.sleep(1)  # Brief backoff before retry
                         continue
                     # Second transient failure — give up with retry-specific message
-                    logger.error(
-                        "MCP tool '{}' failed after retry: {}: {}",
+                    logger.exception(
+                        "MCP tool '{}' failed after retry: {}",
                         self._name,
                         type(exc).__name__,
-                        exc,
                     )
                     return f"(MCP tool call failed after retry: {type(exc).__name__})"
                 logger.exception(
@@ -287,11 +286,10 @@ class MCPResourceWrapper(Tool):
                         )
                         await asyncio.sleep(1)
                         continue
-                    logger.error(
-                        "MCP resource '{}' failed after retry: {}: {}",
+                    logger.exception(
+                        "MCP resource '{}' failed after retry: {}",
                         self._name,
                         type(exc).__name__,
-                        exc,
                     )
                     return f"(MCP resource read failed after retry: {type(exc).__name__})"
                 logger.exception(
@@ -383,7 +381,7 @@ class MCPPromptWrapper(Tool):
                 logger.warning("MCP prompt '{}' was cancelled by server/SDK", self._name)
                 return "(MCP prompt call was cancelled)"
             except McpError as exc:
-                logger.error(
+                logger.exception(
                     "MCP prompt '{}' failed: code={} message={}",
                     self._name,
                     exc.error.code,
@@ -400,11 +398,10 @@ class MCPPromptWrapper(Tool):
                         )
                         await asyncio.sleep(1)
                         continue
-                    logger.error(
-                        "MCP prompt '{}' failed after retry: {}: {}",
+                    logger.exception(
+                        "MCP prompt '{}' failed after retry: {}",
                         self._name,
                         type(exc).__name__,
-                        exc,
                     )
                     return f"(MCP prompt call failed after retry: {type(exc).__name__})"
                 logger.exception(
@@ -608,7 +605,7 @@ async def connect_mcp_servers(
                     " Hint: this looks like stdio protocol pollution. Make sure the MCP server writes "
                     "only JSON-RPC to stdout and sends logs/debug output to stderr instead."
                 )
-            logger.error("MCP server '{}': failed to connect: {}{}", name, e, hint)
+            logger.exception("MCP server '{}': failed to connect: {}", name, hint)
             with suppress(Exception):
                 await server_stack.aclose()
             return name, None

nanobot/agent/tools/web.py

@@ -500,10 +500,10 @@ class WebFetchTool(Tool):
                 "untrusted": True, "text": text,
             }, ensure_ascii=False)
         except httpx.ProxyError as e:
-            logger.error("WebFetch proxy error for {}: {}", url, e)
+            logger.exception("WebFetch proxy error for {}", url)
             return json.dumps({"error": f"Proxy error: {e}", "url": url}, ensure_ascii=False)
         except Exception as e:
-            logger.error("WebFetch error for {}: {}", url, e)
+            logger.exception("WebFetch error for {}", url)
             return json.dumps({"error": str(e), "url": url}, ensure_ascii=False)
 
     def _to_markdown(self, html_content: str) -> str: