diff --git a/crates/agcanvas/Cargo.toml b/crates/agcanvas/Cargo.toml
index 222a92e..1d4f8da 100644
--- a/crates/agcanvas/Cargo.toml
+++ b/crates/agcanvas/Cargo.toml
@@ -33,7 +33,7 @@ tokio-tungstenite = "0.24"
 futures-util = "0.3"
 
 # Mermaid diagram rendering
-mermaid-rs-renderer = { version = "0.1.2", default-features = false }
+mermaid-rs-renderer = { git = "https://github.com/1jehuang/mermaid-rs-renderer", tag = "v0.2.0", default-features = false }
 
 # Logging
 tracing = "0.1"
diff --git a/crates/agcanvas/src/mermaid.rs b/crates/agcanvas/src/mermaid.rs
index dd476f1..d2975e0 100644
--- a/crates/agcanvas/src/mermaid.rs
+++ b/crates/agcanvas/src/mermaid.rs
@@ -1,9 +1,67 @@
+use std::panic;
+
 use anyhow::Result;
+use mermaid_rs_renderer::RenderOptions;
 
 pub fn render_mermaid_to_svg(mermaid_source: &str) -> Result<String> {
-    let svg = mermaid_rs_renderer::render(mermaid_source)
-        .map_err(|e| anyhow::anyhow!("Mermaid render failed: {}", e))?;
-    Ok(svg)
+    let source = mermaid_source.to_string();
+
+    let mut options = RenderOptions::modern();
+    options.theme.font_family =
+        "Inter, ui-sans-serif, system-ui, -apple-system, Segoe UI, sans-serif".to_string();
+
+    let result = panic::catch_unwind(|| mermaid_rs_renderer::render_with_options(&source, options));
+    match result {
+        Ok(Ok(svg)) => Ok(sanitize_svg_font_families(&svg)),
+        Ok(Err(e)) => Err(anyhow::anyhow!("Mermaid render failed: {}", e)),
+        Err(_) => Err(anyhow::anyhow!(
+            "Mermaid renderer panicked (unsupported syntax)"
+        )),
+    }
+}
+
+/// Strips nested double quotes inside `font-family` XML attributes.
+///
+/// mermaid-rs-renderer v0.2.0 emits `font-family="..., "Segoe UI", ..."`
+/// which is invalid XML — usvg rejects it. This rewrites those attributes
+/// so the inner quotes are removed.
+fn sanitize_svg_font_families(svg: &str) -> String {
+    let mut result = String::with_capacity(svg.len());
+    let mut chars = svg.chars().peekable();
+
+    while let Some(ch) = chars.next() {
+        result.push(ch);
+
+        if ch == 'f' && result.ends_with("font-family=\"") {
+            let mut value = String::new();
+            loop {
+                match chars.next() {
+                    Some('"') => {
+                        if let Some(&next) = chars.peek() {
+                            if next == ' ' || next == '/' || next == '>' || next == '\n' {
+                                result.push_str(&value);
+                                result.push('"');
+                                break;
+                            } else {
+                                continue;
+                            }
+                        } else {
+                            result.push_str(&value);
+                            result.push('"');
+                            break;
+                        }
+                    }
+                    Some(c) => value.push(c),
+                    None => {
+                        result.push_str(&value);
+                        break;
+                    }
+                }
+            }
+        }
+    }
+
+    result
 }
 
 #[cfg(test)]
@@ -21,4 +79,23 @@ mod tests {
         let svg = render_mermaid_to_svg("sequenceDiagram\n    Alice->>Bob: Hello").unwrap();
         assert!(svg.contains("<svg"));
     }
+
+    #[test]
+    fn renders_edge_labels() {
+        let svg = render_mermaid_to_svg(
+            "flowchart LR\n    A{Decision} -->|Yes| B[OK]\n    A -->|No| C[Cancel]",
+        )
+        .unwrap();
+        assert!(svg.contains("<svg"));
+        assert!(svg.contains("Yes"));
+        assert!(svg.contains("No"));
+    }
+
+    #[test]
+    fn sanitized_svg_is_valid_xml() {
+        let svg = render_mermaid_to_svg("flowchart LR\n    A-->B").unwrap();
+        let mut options = usvg::Options::default();
+        options.fontdb_mut().load_system_fonts();
+        usvg::Tree::from_str(&svg, &options).expect("sanitized SVG should parse with usvg");
+    }
 }