feat: graph module with wikilink extraction and query term helpers

Byte-scanning wikilink extractor handles [[target]], [[target|display]],
[[target#heading]], skips embeds (![[...]]). Deduplicates targets.
Query term extraction for graph agent relevance filtering.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: devwhodevs

src/graph.rs

@@ -0,0 +1,101 @@
+use std::collections::HashSet;
+
+/// Extract unique wikilink targets from text.
+/// Handles [[Target]], [[Target|Display]], [[Target#Heading]].
+/// Skips embeds (![[...]]).
+pub fn extract_wikilink_targets(text: &str) -> Vec<String> {
+    let bytes = text.as_bytes();
+    let mut targets = Vec::new();
+    let mut seen = HashSet::new();
+    let mut i = 0;
+
+    while i + 1 < bytes.len() {
+        if bytes[i] == b'[' && bytes[i + 1] == b'[' {
+            // Check for embed prefix (! before [[)
+            let is_embed = i > 0 && bytes[i - 1] == b'!';
+            if let Some(rest) = text.get(i + 2..)
+                && let Some(close) = rest.find("]]")
+            {
+                let inner = &rest[..close];
+                if !is_embed && !inner.is_empty() && !inner.contains('\n') {
+                    // Strip heading: [[Note#Section]] → "Note"
+                    let target = inner.split('#').next().unwrap_or(inner);
+                    // Strip display: [[Note|Display]] → "Note"
+                    let target = target.split('|').next().unwrap_or(target);
+                    let target = target.trim().to_string();
+                    if !target.is_empty() && seen.insert(target.clone()) {
+                        targets.push(target);
+                    }
+                }
+                i += 2 + close + 2;
+                continue;
+            }
+        }
+        i += 1;
+    }
+    targets
+}
+
+/// Extract query terms for relevance filtering.
+/// Splits on whitespace, lowercases, drops terms shorter than 3 chars.
+pub fn extract_query_terms(query: &str) -> Vec<String> {
+    query
+        .split_whitespace()
+        .map(|t| t.to_lowercase())
+        .filter(|t| t.len() >= 3)
+        .collect()
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_extract_wikilink_targets() {
+        let text =
+            "See [[Note One]] and [[Note Two|display]] for details. Also [[Note One]] again.";
+        let targets = extract_wikilink_targets(text);
+        assert!(targets.contains(&"Note One".to_string()));
+        assert!(targets.contains(&"Note Two".to_string()));
+        assert_eq!(targets.len(), 2); // deduplicated
+    }
+
+    #[test]
+    fn test_extract_wikilinks_with_headings() {
+        let text = "Link to [[Note#Section]] here.";
+        let targets = extract_wikilink_targets(text);
+        assert_eq!(targets, vec!["Note"]);
+    }
+
+    #[test]
+    fn test_extract_wikilinks_empty() {
+        assert!(extract_wikilink_targets("no links here").is_empty());
+        assert!(extract_wikilink_targets("").is_empty());
+    }
+
+    #[test]
+    fn test_extract_wikilinks_skip_embeds() {
+        let text = "![[embedded image.png]] and [[real link]]";
+        let targets = extract_wikilink_targets(text);
+        assert_eq!(targets, vec!["real link"]);
+    }
+
+    #[test]
+    fn test_extract_wikilinks_heading_and_display() {
+        let text = "[[Note#Section|Custom Display]]";
+        let targets = extract_wikilink_targets(text);
+        assert_eq!(targets, vec!["Note"]); // strip both heading and display
+    }
+
+    #[test]
+    fn test_extract_query_terms() {
+        let terms = extract_query_terms("BRE-2579 delivery date");
+        assert_eq!(terms, vec!["bre-2579", "delivery", "date"]);
+    }
+
+    #[test]
+    fn test_extract_query_terms_short_words_dropped() {
+        let terms = extract_query_terms("a is the big query");
+        assert_eq!(terms, vec!["the", "big", "query"]);
+    }
+}

src/lib.rs

@@ -4,6 +4,7 @@ pub mod docid;
 pub mod embedder;
 pub mod fts;
 pub mod fusion;
+pub mod graph;
 pub mod hnsw;
 pub mod indexer;
 pub mod model;