Pick the fallback search word deterministically

Splitting the stripped line on whitespace left inline syntax attached to
the words, so a link's label never produced a usable term, and the
tie-break between equally long words fell out of `max_by_key` returning
the last maximum. Split on non-alphanumerics and keep the earliest of
the longest words.

Co-Authored-By: Warp Agent <agent@warp.dev>

Author: oz-agent

app/src/notebooks/file/mod.rs

@@ -1354,10 +1354,19 @@ fn rendered_search_terms_for_source_line(markdown: &str, line_num: usize) -> Vec
     };
 
     let stripped = strip_markdown_syntax(line);
+    // Split on non-alphanumerics rather than whitespace so a word survives the
+    // inline syntax `strip_markdown_syntax` leaves behind, such as a link's
+    // `[label](target)`. Ties keep the earliest word, so the chosen term does
+    // not hinge on which extreme the iterator happens to return.
     let longest_word = stripped
-        .split_whitespace()
-        .map(|word| word.trim_matches(|c: char| !c.is_alphanumeric()))
-        .max_by_key(|word| word.chars().count())
+        .split(|c: char| !c.is_alphanumeric())
+        .reduce(|longest, word| {
+            if word.chars().count() > longest.chars().count() {
+                word
+            } else {
+                longest
+            }
+        })
         .unwrap_or_default();
 
     [line.trim(), stripped.as_str(), longest_word]

app/src/notebooks/file/mod_tests.rs

@@ -451,15 +451,15 @@ fn test_rendered_search_terms_for_source_line() {
     let markdown = "# Heading one\n\n- a **bold** item\n\n```rust\nlet total = compute();\n```\n\n> quoted line here\n";
 
     // Headings, list bullets and emphasis are stripped so the term matches the
-    // rendered text; the longest word is kept as a last resort. Equally long
-    // words are just as usable as each other, so the last one wins.
+    // rendered text; the longest word is kept as a last resort, and equally
+    // long words resolve to the earliest one.
     assert_eq!(
         rendered_search_terms_for_source_line(markdown, 1),
         ["# Heading one", "Heading one", "Heading"]
     );
     assert_eq!(
         rendered_search_terms_for_source_line(markdown, 3),
-        ["- a **bold** item", "a bold item", "item"]
+        ["- a **bold** item", "a bold item", "bold"]
     );
     assert_eq!(
         rendered_search_terms_for_source_line(markdown, 9),
@@ -472,6 +472,16 @@ fn test_rendered_search_terms_for_source_line() {
         ["let total = compute();", "compute"]
     );
 
+    // A link's visible label survives, even though the surrounding syntax does
+    // not, because words are split on non-alphanumerics.
+    assert_eq!(
+        rendered_search_terms_for_source_line("See [the configuration guide](./config.md).", 1),
+        [
+            "See [the configuration guide](./config.md).",
+            "configuration"
+        ]
+    );
+
     // Nothing visible to search for.
     assert!(rendered_search_terms_for_source_line(markdown, 2).is_empty());
     assert!(rendered_search_terms_for_source_line(markdown, 999).is_empty());