diff --git a/crates/zx_document_core/src/progress.rs b/crates/zx_document_core/src/progress.rs
index 8185835..5643076 100644
--- a/crates/zx_document_core/src/progress.rs
+++ b/crates/zx_document_core/src/progress.rs
@@ -1,102 +1,210 @@
-use serde::{Deserialize, Serialize};
+use serde::{Deserialize, Serialize, Serializer};
 
-#[derive(Debug, Clone, PartialEq, Serialize, Deserialize, uniffi::Enum)]
+/// Clamp a progress value to 0..1. NaN→0, <0→0, >1→1.
+pub fn clamp_progress(v: f32) -> f32 {
+    if v.is_nan() || v < 0.0 { return 0.0; }
+    if v > 1.0 { return 1.0; }
+    v
+}
+
+#[derive(Debug, Clone, PartialEq, Deserialize, uniffi::Enum)]
 #[serde(tag = "type")]
 pub enum ReadingPosition {
     Markdown {
+        #[serde(rename = "blockId")]
         block_id: String,
+        #[serde(rename = "scrollProgress")]
         scroll_progress: f32,
     },
     Text {
+        #[serde(rename = "lineNumber")]
         line_number: u32,
+        #[serde(rename = "scrollProgress")]
         scroll_progress: f32,
     },
     Pdf {
+        #[serde(rename = "pageNumber")]
         page_number: u32,
+        #[serde(rename = "pageProgress")]
         page_progress: f32,
+        #[serde(rename = "overallProgress")]
         overall_progress: f32,
     },
     Image {
+        #[serde(rename = "zoomScale")]
         zoom_scale: f32,
+        #[serde(rename = "offsetX")]
         offset_x: f32,
+        #[serde(rename = "offsetY")]
         offset_y: f32,
     },
     Epub {
+        #[serde(rename = "chapterId")]
         chapter_id: String,
+        #[serde(rename = "chapterProgress")]
         chapter_progress: f32,
+        #[serde(rename = "overallProgress")]
         overall_progress: f32,
     },
     Unknown,
 }
 
+// Manual Serialize to enforce camelCase field names + clamped progress values.
+impl Serialize for ReadingPosition {
+    fn serialize<S: Serializer>(&self, s: S) -> Result<S::Ok, S::Error> {
+        use serde::ser::SerializeStruct;
+        match self {
+            Self::Markdown { block_id, scroll_progress } => {
+                let mut st = s.serialize_struct("Markdown", 3)?;
+                st.serialize_field("type", "Markdown")?;
+                st.serialize_field("blockId", block_id)?;
+                st.serialize_field("scrollProgress", &clamp_progress(*scroll_progress))?;
+                st.end()
+            }
+            Self::Text { line_number, scroll_progress } => {
+                let mut st = s.serialize_struct("Text", 3)?;
+                st.serialize_field("type", "Text")?;
+                st.serialize_field("lineNumber", line_number)?;
+                st.serialize_field("scrollProgress", &clamp_progress(*scroll_progress))?;
+                st.end()
+            }
+            Self::Pdf { page_number, page_progress, overall_progress } => {
+                let mut st = s.serialize_struct("Pdf", 4)?;
+                st.serialize_field("type", "Pdf")?;
+                st.serialize_field("pageNumber", page_number)?;
+                st.serialize_field("pageProgress", &clamp_progress(*page_progress))?;
+                st.serialize_field("overallProgress", &clamp_progress(*overall_progress))?;
+                st.end()
+            }
+            Self::Image { zoom_scale, offset_x, offset_y } => {
+                let mut st = s.serialize_struct("Image", 4)?;
+                st.serialize_field("type", "Image")?;
+                st.serialize_field("zoomScale", zoom_scale)?;
+                st.serialize_field("offsetX", offset_x)?;
+                st.serialize_field("offsetY", offset_y)?;
+                st.end()
+            }
+            Self::Epub { chapter_id, chapter_progress, overall_progress } => {
+                let mut st = s.serialize_struct("Epub", 4)?;
+                st.serialize_field("type", "Epub")?;
+                st.serialize_field("chapterId", chapter_id)?;
+                st.serialize_field("chapterProgress", &clamp_progress(*chapter_progress))?;
+                st.serialize_field("overallProgress", &clamp_progress(*overall_progress))?;
+                st.end()
+            }
+            Self::Unknown => {
+                let mut st = s.serialize_struct("Unknown", 1)?;
+                st.serialize_field("type", "Unknown")?;
+                st.end()
+            }
+        }
+    }
+}
+
+impl ReadingPosition {
+    /// Return a normalized copy with all progress fields clamped to 0..1.
+    pub fn normalized(&self) -> Self {
+        match self {
+            Self::Markdown { block_id, scroll_progress } => Self::Markdown {
+                block_id: block_id.clone(),
+                scroll_progress: clamp_progress(*scroll_progress),
+            },
+            Self::Text { line_number, scroll_progress } => Self::Text {
+                line_number: *line_number,
+                scroll_progress: clamp_progress(*scroll_progress),
+            },
+            Self::Pdf { page_number, page_progress, overall_progress } => Self::Pdf {
+                page_number: *page_number,
+                page_progress: clamp_progress(*page_progress),
+                overall_progress: clamp_progress(*overall_progress),
+            },
+            Self::Image { zoom_scale, offset_x, offset_y } => Self::Image {
+                zoom_scale: *zoom_scale, offset_x: *offset_x, offset_y: *offset_y,
+            },
+            Self::Epub { chapter_id, chapter_progress, overall_progress } => Self::Epub {
+                chapter_id: chapter_id.clone(),
+                chapter_progress: clamp_progress(*chapter_progress),
+                overall_progress: clamp_progress(*overall_progress),
+            },
+            Self::Unknown => Self::Unknown,
+        }
+    }
+
+    pub fn progress_value(&self) -> Option<f32> {
+        match self {
+            Self::Markdown { scroll_progress, .. } => Some(clamp_progress(*scroll_progress)),
+            Self::Text { scroll_progress, .. } => Some(clamp_progress(*scroll_progress)),
+            Self::Pdf { overall_progress, .. } => Some(clamp_progress(*overall_progress)),
+            Self::Epub { overall_progress, .. } => Some(clamp_progress(*overall_progress)),
+            Self::Image { .. } | Self::Unknown => None,
+        }
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
 
     #[test]
-    fn test_markdown_serde() {
-        let pos = ReadingPosition::Markdown {
-            block_id: "h1".into(),
-            scroll_progress: 0.5,
-        };
+    fn test_markdown_camel_case() {
+        let pos = ReadingPosition::Markdown { block_id: "h1".into(), scroll_progress: 0.5 };
         let json = serde_json::to_string(&pos).unwrap();
-        assert!(json.contains("\"type\":\"Markdown\""));
-        let back: ReadingPosition = serde_json::from_str(&json).unwrap();
-        assert_eq!(back, pos);
+        eprintln!("SERIALIZED: {json}");
+        assert!(json.contains("\"type\":\"Markdown\""), "missing type: {json}");
+        assert!(json.contains("\"blockId\":\"h1\""), "missing blockId: {json}");
+        assert!(json.contains("\"scrollProgress\":0.5"), "missing progress: {json}");
     }
 
     #[test]
-    fn test_text_serde() {
-        let pos = ReadingPosition::Text {
-            line_number: 42,
-            scroll_progress: 0.3,
-        };
+    fn test_pdf_camel_case() {
+        let pos = ReadingPosition::Pdf { page_number: 7, page_progress: 0.8, overall_progress: 0.35 };
         let json = serde_json::to_string(&pos).unwrap();
-        let back: ReadingPosition = serde_json::from_str(&json).unwrap();
-        assert_eq!(back, pos);
+        assert!(json.contains("\"pageNumber\":7"));
+        assert!(json.contains("\"pageProgress\":0.8"));
+        assert!(json.contains("\"overallProgress\":0.35"));
     }
 
     #[test]
-    fn test_pdf_serde() {
-        let pos = ReadingPosition::Pdf {
-            page_number: 7,
-            page_progress: 0.8,
-            overall_progress: 0.35,
-        };
+    fn test_clamp_nan() {
+        let pos = ReadingPosition::Markdown { block_id: "h1".into(), scroll_progress: f32::NAN };
         let json = serde_json::to_string(&pos).unwrap();
-        let back: ReadingPosition = serde_json::from_str(&json).unwrap();
-        assert_eq!(back, pos);
+        assert!(json.contains("\"scrollProgress\":0.0"));
     }
 
     #[test]
-    fn test_image_serde() {
-        let pos = ReadingPosition::Image {
-            zoom_scale: 1.5,
-            offset_x: 100.0,
-            offset_y: 200.0,
-        };
+    fn test_clamp_negative() {
+        let pos = ReadingPosition::Text { line_number: 1, scroll_progress: -0.5 };
         let json = serde_json::to_string(&pos).unwrap();
-        let back: ReadingPosition = serde_json::from_str(&json).unwrap();
-        assert_eq!(back, pos);
+        assert!(json.contains("\"scrollProgress\":0.0"));
     }
 
     #[test]
-    fn test_epub_serde() {
-        let pos = ReadingPosition::Epub {
-            chapter_id: "ch3".into(),
-            chapter_progress: 0.6,
-            overall_progress: 0.25,
-        };
+    fn test_clamp_above_one() {
+        let pos = ReadingPosition::Pdf { page_number: 1, page_progress: 2.5, overall_progress: 10.0 };
         let json = serde_json::to_string(&pos).unwrap();
-        let back: ReadingPosition = serde_json::from_str(&json).unwrap();
-        assert_eq!(back, pos);
+        assert!(json.contains("\"pageProgress\":1.0"));
+        assert!(json.contains("\"overallProgress\":1.0"));
     }
 
     #[test]
-    fn test_unknown_serde() {
-        let pos = ReadingPosition::Unknown;
-        let json = serde_json::to_string(&pos).unwrap();
-        let back: ReadingPosition = serde_json::from_str(&json).unwrap();
-        assert_eq!(back, pos);
+    fn test_progress_value() {
+        assert_eq!(ReadingPosition::Unknown.progress_value(), None);
+        let md = ReadingPosition::Markdown { block_id: "h1".into(), scroll_progress: 0.75 };
+        assert_eq!(md.progress_value(), Some(0.75));
+    }
+
+    #[test]
+    fn test_roundtrip() {
+        let positions = vec![
+            ReadingPosition::Markdown { block_id: "h1".into(), scroll_progress: 0.5 },
+            ReadingPosition::Pdf { page_number: 7, page_progress: 0.8, overall_progress: 0.35 },
+            ReadingPosition::Unknown,
+        ];
+        for pos in &positions {
+            let json = serde_json::to_string(pos).unwrap();
+            eprintln!("ROUNDTRIP JSON: {json}");
+            let back: ReadingPosition = serde_json::from_str(&json).unwrap();
+            assert_eq!(&back, pos);
+        }
     }
 }
diff --git a/rust_out b/rust_out
new file mode 100755
index 0000000..5a000ff
Binary files /dev/null and b/rust_out differ