fix: replace naive colon finder with query_exact prefix trim

Use doc.query_exact(route) to locate the value's byte span, then
compute the key prefix as source[start_byte..value_start].trim_end().
This eliminates string-searching for the separator colon, which
corrupted quoted keys containing colons.

Removes find_key_colon entirely.

Closes #43

Author: nathanjmcdougall

src/document.rs

@@ -353,39 +353,47 @@ fn apply_complex_replace(
     let start_byte = feature.location.byte_span.0 - ws_len;
     let end_byte = feature.location.byte_span.1;
 
-    // Find the colon separating key from value
-    let colon_pos = find_key_colon(content_with_ws);
+    // Use query_exact to locate the value's byte span independently.
+    // This avoids string-searching for the colon separator, which breaks
+    // on quoted keys containing colons (e.g. "http://example.com": 8080).
+    let value_feature = doc
+        .query_exact(route)
+        .map_err(|e| format!("Query failed: {e}"))?;
 
-    let key_part = match colon_pos {
-        Some(pos) => {
-            let key = &content_with_ws[..pos + 1]; // through the colon
-            key.to_string()
+    let key_part = match value_feature {
+        Some(vf) => {
+            let prefix = source[start_byte..vf.location.byte_span.0].trim_end();
+            if prefix.is_empty() {
+                // Bare value (e.g. sequence item) — no key prefix
+                let serialized = serde_yaml::to_string(value)
+                    .map_err(|e| format!("Failed to serialize YAML: {e}"))?;
+                let trimmed = serialized.trim_end_matches('\n');
+
+                let line_start = source[..feature.location.byte_span.0]
+                    .rfind('\n')
+                    .map(|nl| nl + 1)
+                    .unwrap_or(0);
+                let base_indent = feature.location.byte_span.0 - line_start;
+                let indent_str = " ".repeat(base_indent);
+
+                let indented = indent_block(trimmed, &indent_str);
+
+                let mut result = source.to_string();
+                result.replace_range(
+                    feature.location.byte_span.0..feature.location.byte_span.1,
+                    &indented,
+                );
+                if !result.ends_with('\n') {
+                    result.push('\n');
+                }
+                return yamlpath::Document::new(result)
+                    .map_err(|e| format!("Failed to re-parse YAML: {e}"));
+            }
+            prefix.to_string()
         }
         None => {
-            // No colon found — bare value (e.g. sequence item)
-            let serialized = serde_yaml::to_string(value)
-                .map_err(|e| format!("Failed to serialize YAML: {e}"))?;
-            let trimmed = serialized.trim_end_matches('\n');
-
-            let line_start = source[..feature.location.byte_span.0]
-                .rfind('\n')
-                .map(|nl| nl + 1)
-                .unwrap_or(0);
-            let base_indent = feature.location.byte_span.0 - line_start;
-            let indent_str = " ".repeat(base_indent);
-
-            let indented = indent_block(trimmed, &indent_str);
-
-            let mut result = source.to_string();
-            result.replace_range(
-                feature.location.byte_span.0..feature.location.byte_span.1,
-                &indented,
-            );
-            if !result.ends_with('\n') {
-                result.push('\n');
-            }
-            return yamlpath::Document::new(result)
-                .map_err(|e| format!("Failed to re-parse YAML: {e}"));
+            // Absent value (e.g. `key:\n`) — content is just key+colon
+            content_with_ws.trim_end().to_string()
         }
     };
 
@@ -424,16 +432,6 @@ fn apply_complex_replace(
     yamlpath::Document::new(result).map_err(|e| format!("Failed to re-parse YAML: {e}"))
 }
 
-/// Find the first colon (key-value separator) in a YAML fragment.
-///
-/// Uses a naive `find(':')`, consistent with yamlpatch's own Replace
-/// implementation. This means colons inside quoted keys will be
-/// misidentified — a known yamlpatch limitation that will be fixed
-/// uniformly when yamlpatch addresses it.
-fn find_key_colon(content: &str) -> Option<usize> {
-    content.find(':')
-}
-
 fn indent_block(content: &str, indent: &str) -> String {
     let mut result = String::new();
     for (i, line) in content.lines().enumerate() {