feat(mcp): add mcp_read meta-tool for resource reads

Implements plans/mcp-resources-prompts-design.md section 4.3 (T4):
mcp_read_<server> declaration and handler wired to render.rs, RFC 6570
Level-1-only URI template expansion, defensive ResourceContents parsing,
per-item text paging with pattern filtering, blob spill metadata, an
overall 204800-byte multi-content ceiling, dispatch wiring on both
eval chains, and a render_text paging-stall guard.

src/mcp/render.rs

@@ -1,8 +1,6 @@
 //! Content policy for MCP resource and tool content: UTF-8-boundary-safe text
 //! paging, grep-style pattern filtering, and spill-to-disk for binary blobs.
 
-#![allow(dead_code)]
-
 use crate::config::paths;
 use base64::engine::general_purpose::STANDARD;
 use base64::read::DecoderReader;
@@ -136,6 +134,14 @@ pub fn render_text(
     while !stream.is_char_boundary(end) {
         end -= 1;
     }
+    // A max_bytes smaller than one codepoint would produce an empty page with
+    // next_offset == offset, stalling paging; always advance by at least one.
+    if end == start && start < total_bytes {
+        end += 1;
+        while !stream.is_char_boundary(end) {
+            end += 1;
+        }
+    }
     let truncated = end < total_bytes;
     Ok(RenderedText {
         text: stream[start..end].to_string(),
@@ -428,6 +434,17 @@ mod tests {
         assert!(!rest.truncated);
     }
 
+    #[test]
+    fn max_bytes_below_one_codepoint_still_advances() {
+        // 'é' is 2 bytes; max_bytes 1 must not stall at next_offset == offset.
+        let rendered = render_text("éa", None, 0, Some(1)).unwrap();
+
+        assert_eq!(rendered.text, "é");
+        assert!(rendered.truncated);
+        assert_eq!(rendered.total_bytes, 3);
+        assert_eq!(rendered.next_offset, Some(2));
+    }
+
     #[test]
     fn offset_past_eof_returns_empty() {
         let rendered = render_text("short", None, 100, None).unwrap();