diff --git a/rust/crates/runtime/src/lib.rs b/rust/crates/runtime/src/lib.rs
index b6660a95..b94cc474 100644
--- a/rust/crates/runtime/src/lib.rs
+++ b/rust/crates/runtime/src/lib.rs
@@ -20,6 +20,7 @@ pub mod green_contract;
 mod hooks;
 mod json;
 mod lane_events;
+pub mod line_range_selector;
 pub mod lsp_client;
 mod mcp;
 mod mcp_client;
diff --git a/rust/crates/runtime/src/line_range_selector.rs b/rust/crates/runtime/src/line_range_selector.rs
new file mode 100644
index 00000000..cd2abe5f
--- /dev/null
+++ b/rust/crates/runtime/src/line_range_selector.rs
@@ -0,0 +1,342 @@
+/// GJC-compatible line range selector parsing for the read tool.
+///
+/// Supports selector syntax:
+/// - `:50` = start at line 50
+/// - `:50-200` = lines 50-200 inclusive
+/// - `:50+150` = 150 lines starting at 50
+/// - `:50+1` = exactly one line
+/// - `:5-16,960-973` = multiple ranges
+/// - `:raw` = full verbatim
+/// - `:conflicts` = git merge conflicts only
+
+use std::num::ParseIntError;
+
+/// Parsed line range specification.
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub enum LineRangeSelector {
+    /// Full file verbatim (`:raw`)
+    Raw,
+    /// Git merge conflict sections only (`:conflicts`)
+    Conflicts,
+    /// Line range(s) (`:L-L+N` syntax)
+    Lines(Vec<LineRange>),
+    /// No selector (full file, may be truncated by default budget)
+    None,
+}
+
+/// A single line range, zero-indexed internally but displayed as 1-indexed.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub struct LineRange {
+    /// Start line (1-indexed, user-facing)
+    pub start_line: usize,
+    /// End line inclusive (1-indexed, user-facing)
+    pub end_line: usize,
+}
+
+impl LineRange {
+    /// Create a new line range (1-indexed).
+    pub fn new(start_line: usize, end_line: usize) -> Self {
+        Self { start_line, end_line }
+    }
+
+    /// Convert to zero-indexed range for internal use.
+    pub fn zero_indexed(&self) -> (usize, usize) {
+        (self.start_line.saturating_sub(1), self.end_line.saturating_sub(1))
+    }
+
+    /// Get the number of lines in this range.
+    pub fn len(&self) -> usize {
+        if self.start_line <= self.end_line {
+            self.end_line - self.start_line + 1
+        } else {
+            0
+        }
+    }
+
+    /// Check if this range is valid.
+    pub fn is_valid(&self) -> bool {
+        self.start_line > 0 && self.end_line > 0 && self.start_line <= self.end_line
+    }
+}
+
+/// Parse error types for line range selectors.
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub enum ParseError {
+    InvalidFormat(String),
+    InvalidNumber(ParseIntError),
+    InvalidRange(String),
+}
+
+impl std::fmt::Display for ParseError {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            ParseError::InvalidFormat(msg) => write!(f, "Invalid format: {}", msg),
+            ParseError::InvalidNumber(e) => write!(f, "Invalid number: {}", e),
+            ParseError::InvalidRange(msg) => write!(f, "Invalid range: {}", msg),
+        }
+    }
+}
+
+impl std::error::Error for ParseError {}
+
+impl From<ParseIntError> for ParseError {
+    fn from(e: ParseIntError) -> Self {
+        ParseError::InvalidNumber(e)
+    }
+}
+
+/// Parse a line range selector string.
+///
+/// Examples:
+/// - `"50"` → `LineRangeSelector::Lines(vec![LineRange::new(50, 50)])`
+/// - `"50-200"` → `LineRangeSelector::Lines(vec![LineRange::new(50, 200)])`
+/// - `"50+150"` → `LineRangeSelector::Lines(vec![LineRange::new(50, 199)])`
+/// - `"raw"` → `LineRangeSelector::Raw`
+/// - `"conflicts"` → `LineRangeSelector::Conflicts`
+pub fn parse_selector(selector: &str) -> Result<LineRangeSelector, ParseError> {
+    if selector.is_empty() {
+        return Ok(LineRangeSelector::None);
+    }
+
+    match selector {
+        "raw" => Ok(LineRangeSelector::Raw),
+        "conflicts" => Ok(LineRangeSelector::Conflicts),
+        _ => parse_line_ranges(selector),
+    }
+}
+
+/// Parse comma-separated line ranges.
+fn parse_line_ranges(selector: &str) -> Result<LineRangeSelector, ParseError> {
+    let mut ranges = Vec::new();
+
+    for range_str in selector.split(',') {
+        let range_str = range_str.trim();
+        if range_str.is_empty() {
+            continue;
+        }
+
+        let range = parse_single_range(range_str)?;
+        ranges.push(range);
+    }
+
+    if ranges.is_empty() {
+        Ok(LineRangeSelector::None)
+    } else {
+        // Merge overlapping/adjacent ranges
+        ranges.sort_by_key(|r| r.start_line);
+        let merged = merge_ranges(ranges);
+        Ok(LineRangeSelector::Lines(merged))
+    }
+}
+
+/// Parse a single line range in formats: "50", "50-200", "50+150".
+fn parse_single_range(range_str: &str) -> Result<LineRange, ParseError> {
+    // Try "50+150" format first (start+count)
+    if let Some(plus_idx) = range_str.find('+') {
+        let start_str = &range_str[..plus_idx];
+        let count_str = &range_str[plus_idx + 1..];
+
+        if start_str.is_empty() || count_str.is_empty() {
+            return Err(ParseError::InvalidFormat(range_str.to_string()));
+        }
+
+        let start = start_str.parse::<usize>()?;
+        let count = count_str.parse::<usize>()?;
+
+        if start == 0 || count == 0 {
+            return Err(ParseError::InvalidRange(
+                "Line numbers and counts must be >= 1".to_string(),
+            ));
+        }
+
+        return Ok(LineRange::new(start, start + count - 1));
+    }
+
+    // Try "50-200" format (start-end)
+    if let Some(dash_idx) = range_str.find('-') {
+        // Skip leading dash (negative numbers aren't valid here)
+        if dash_idx == 0 {
+            return Err(ParseError::InvalidFormat(range_str.to_string()));
+        }
+
+        let start_str = &range_str[..dash_idx];
+        let end_str = &range_str[dash_idx + 1..];
+
+        if start_str.is_empty() || end_str.is_empty() {
+            return Err(ParseError::InvalidFormat(range_str.to_string()));
+        }
+
+        let start = start_str.parse::<usize>()?;
+        let end = end_str.parse::<usize>()?;
+
+        if start == 0 || end == 0 {
+            return Err(ParseError::InvalidRange(
+                "Line numbers must be >= 1".to_string(),
+            ));
+        }
+
+        if start > end {
+            return Err(ParseError::InvalidRange(format!(
+                "Start line {} cannot be greater than end line {}",
+                start, end
+            )));
+        }
+
+        return Ok(LineRange::new(start, end));
+    }
+
+    // Try plain "50" format (single line)
+    let line_num = range_str.parse::<usize>()?;
+    if line_num == 0 {
+        return Err(ParseError::InvalidRange(
+            "Line number must be >= 1".to_string(),
+        ));
+    }
+
+    Ok(LineRange::new(line_num, line_num))
+}
+
+/// Merge overlapping and adjacent ranges.
+fn merge_ranges(ranges: Vec<LineRange>) -> Vec<LineRange> {
+    let mut merged: Vec<LineRange> = Vec::new();
+
+    for range in ranges {
+        if let Some(last) = merged.last_mut() {
+            // If ranges overlap or are adjacent, merge them
+            if range.start_line <= last.end_line + 1 {
+                last.end_line = last.end_line.max(range.end_line);
+            } else {
+                merged.push(range);
+            }
+        } else {
+            merged.push(range);
+        }
+    }
+
+    merged
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_parse_raw() {
+        assert_eq!(parse_selector("raw").unwrap(), LineRangeSelector::Raw);
+    }
+
+    #[test]
+    fn test_parse_conflicts() {
+        assert_eq!(
+            parse_selector("conflicts").unwrap(),
+            LineRangeSelector::Conflicts
+        );
+    }
+
+    #[test]
+    fn test_parse_single_line() {
+        match parse_selector("50").unwrap() {
+            LineRangeSelector::Lines(ranges) => {
+                assert_eq!(ranges.len(), 1);
+                assert_eq!(ranges[0].start_line, 50);
+                assert_eq!(ranges[0].end_line, 50);
+            }
+            _ => panic!("Expected Lines variant"),
+        }
+    }
+
+    #[test]
+    fn test_parse_range_start_dash_end() {
+        match parse_selector("50-200").unwrap() {
+            LineRangeSelector::Lines(ranges) => {
+                assert_eq!(ranges.len(), 1);
+                assert_eq!(ranges[0].start_line, 50);
+                assert_eq!(ranges[0].end_line, 200);
+            }
+            _ => panic!("Expected Lines variant"),
+        }
+    }
+
+    #[test]
+    fn test_parse_range_start_plus_count() {
+        match parse_selector("50+150").unwrap() {
+            LineRangeSelector::Lines(ranges) => {
+                assert_eq!(ranges.len(), 1);
+                assert_eq!(ranges[0].start_line, 50);
+                assert_eq!(ranges[0].end_line, 199);
+            }
+            _ => panic!("Expected Lines variant"),
+        }
+    }
+
+    #[test]
+    fn test_parse_multiple_ranges() {
+        match parse_selector("5-16,960-973").unwrap() {
+            LineRangeSelector::Lines(ranges) => {
+                assert_eq!(ranges.len(), 2);
+                assert_eq!(ranges[0].start_line, 5);
+                assert_eq!(ranges[0].end_line, 16);
+                assert_eq!(ranges[1].start_line, 960);
+                assert_eq!(ranges[1].end_line, 973);
+            }
+            _ => panic!("Expected Lines variant"),
+        }
+    }
+
+    #[test]
+    fn test_merge_overlapping_ranges() {
+        // "5-16,10-20" should merge into "5-20"
+        match parse_selector("5-16,10-20").unwrap() {
+            LineRangeSelector::Lines(ranges) => {
+                assert_eq!(ranges.len(), 1);
+                assert_eq!(ranges[0].start_line, 5);
+                assert_eq!(ranges[0].end_line, 20);
+            }
+            _ => panic!("Expected Lines variant"),
+        }
+    }
+
+    #[test]
+    fn test_merge_adjacent_ranges() {
+        // "5-16,17-20" should merge into "5-20"
+        match parse_selector("5-16,17-20").unwrap() {
+            LineRangeSelector::Lines(ranges) => {
+                assert_eq!(ranges.len(), 1);
+                assert_eq!(ranges[0].start_line, 5);
+                assert_eq!(ranges[0].end_line, 20);
+            }
+            _ => panic!("Expected Lines variant"),
+        }
+    }
+
+    #[test]
+    fn test_invalid_range_start_greater_than_end() {
+        let result = parse_selector("200-50");
+        assert!(result.is_err());
+    }
+
+    #[test]
+    fn test_invalid_zero_line() {
+        let result = parse_selector("0");
+        assert!(result.is_err());
+    }
+
+    #[test]
+    fn test_empty_selector() {
+        assert_eq!(parse_selector("").unwrap(), LineRangeSelector::None);
+    }
+
+    #[test]
+    fn test_line_range_zero_indexed() {
+        let range = LineRange::new(50, 200);
+        let (start, end) = range.zero_indexed();
+        assert_eq!(start, 49);
+        assert_eq!(end, 199);
+    }
+
+    #[test]
+    fn test_line_range_len() {
+        assert_eq!(LineRange::new(50, 200).len(), 151);
+        assert_eq!(LineRange::new(50, 50).len(), 1);
+    }
+}