Add bread-launcher: headless app-launcher core + GTK4 results widget

Extracts the app-launcher substance (desktop-entry parsing, fuzzy
matching/ranking, launch history, launching) out of breadbox into a
reusable ecosystem crate, so breadbar's future embedded capsule and
breadbox's overlay window can share one implementation instead of two
(THEME_SYSTEM_PLAN.md Phase 4/6a). The GTK4 results-list widget lives
behind a `gtk` feature, mirroring bread-theme's `gtk`/`adw` gating, so a
headless consumer isn't forced to link GTK.

Adds unit tests for fuzzy_score/matches_term/priority_rank, which were
previously untested pure functions inside breadbox's main.rs.

bread-launcher/src/matching.rs

@@ -0,0 +1,272 @@
+use std::{collections::HashMap, path::PathBuf};
+
+use crate::desktop::{load_all_desktop_entries, DesktopEntry};
+use crate::history::LaunchHistory;
+
+// ---- Fuzzy matching (query filter) ------------------------------------------
+
+/// Subsequence match used to *filter* rows as the user types: every char of
+/// `pattern`, in order, must appear somewhere in `text` (case-insensitive).
+/// Looser than [`fuzzy_score`], which ranks the rows that pass this filter.
+pub fn fuzzy_matches(pattern: &str, text: &str) -> bool {
+    if pattern.is_empty() {
+        return true;
+    }
+    let mut chars = text.chars();
+    for pc in pattern.chars() {
+        let pl = pc.to_lowercase().next().unwrap_or(pc);
+        if !chars
+            .by_ref()
+            .any(|tc| tc.to_lowercase().next().unwrap_or(tc) == pl)
+        {
+            return false;
+        }
+    }
+    true
+}
+
+/// Ranks how well `query` matches `entry` — lower is better. Exact match (by
+/// name or `wm_class`) sorts first, then name-prefix, then name-contains,
+/// then `wm_class`-prefix/contains, then everything else that still passed
+/// [`fuzzy_matches`] (a subsequence match with no stronger relationship).
+pub fn fuzzy_score(query: &str, entry: &DesktopEntry) -> u32 {
+    let q = query.to_lowercase();
+    let name = entry.name.to_lowercase();
+    let wm = entry.wm_class.as_deref().unwrap_or("").to_lowercase();
+    if name == q || wm == q {
+        return 0;
+    }
+    if name.starts_with(&q) {
+        return 1;
+    }
+    if name.contains(&q) {
+        return 2;
+    }
+    if wm.starts_with(&q) || wm.contains(&q) {
+        return 3;
+    }
+    4 // subsequence match
+}
+
+// ---- Priority ranking (empty-query ordering) --------------------------------
+
+/// Whole-word / exact match of `term` within `field` (both lowercase). Avoids
+/// "code" matching "vscodium" while still matching "Code", "code-oss", and
+/// "Visual Studio Code".
+pub fn matches_term(field: &str, term: &str) -> bool {
+    if term.is_empty() || field.is_empty() {
+        return false;
+    }
+    if field == term {
+        return true;
+    }
+    let bytes = field.as_bytes();
+    let tlen = term.len();
+    let mut start = 0;
+    while let Some(pos) = field[start..].find(term) {
+        let i = start + pos;
+        let before_ok = i == 0 || !bytes[i - 1].is_ascii_alphanumeric();
+        let after = i + tlen;
+        let after_ok = after >= bytes.len() || !bytes[after].is_ascii_alphanumeric();
+        if before_ok && after_ok {
+            return true;
+        }
+        start = i + 1;
+        if start >= field.len() {
+            break;
+        }
+    }
+    false
+}
+
+/// Position of `entry` in the (already-lowercased) `priority` list, matched
+/// against either its name or `wm_class`. `None` if `entry` isn't named
+/// there at all.
+pub fn priority_rank(entry: &DesktopEntry, priority_lower: &[String]) -> Option<usize> {
+    let name_l = entry.name.to_lowercase();
+    let wm_l = entry.wm_class.as_deref().unwrap_or("").to_lowercase();
+    priority_lower
+        .iter()
+        .position(|p| matches_term(&name_l, p) || matches_term(&wm_l, p))
+}
+
+/// Loads every known desktop entry, resolves each one's icon path from
+/// `manifest`, and sorts them: entries named in `priority` come first (in
+/// that order), then everything else by most-launched (via `history`), then
+/// alphabetically.
+pub fn load_sorted_entries(
+    manifest: &HashMap<String, PathBuf>,
+    priority: &[String],
+    history: &LaunchHistory,
+) -> Vec<DesktopEntry> {
+    let mut entries = load_all_desktop_entries();
+
+    // Populate icon_path from manifest
+    for entry in &mut entries {
+        if let Some(path) = manifest.get(&entry.icon_name) {
+            if path.exists() {
+                entry.icon_path = Some(path.clone());
+            }
+        }
+    }
+
+    let priority_lower: Vec<String> = priority.iter().map(|s| s.to_lowercase()).collect();
+
+    entries.sort_by(|a, b| {
+        let ai = priority_rank(a, &priority_lower);
+        let bi = priority_rank(b, &priority_lower);
+        match (ai, bi) {
+            (Some(i), Some(j)) => i.cmp(&j),
+            (Some(_), None) => std::cmp::Ordering::Less,
+            (None, Some(_)) => std::cmp::Ordering::Greater,
+            (None, None) => {
+                // Most-launched first, then alphabetical
+                history
+                    .count(&b.name)
+                    .cmp(&history.count(&a.name))
+                    .then(a.name.to_lowercase().cmp(&b.name.to_lowercase()))
+            }
+        }
+    });
+
+    entries
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    fn entry(name: &str, wm_class: Option<&str>) -> DesktopEntry {
+        DesktopEntry {
+            id: format!("{name}.desktop"),
+            name: name.to_string(),
+            exec: "true".to_string(),
+            icon_name: String::new(),
+            icon_path: None,
+            categories: Vec::new(),
+            wm_class: wm_class.map(|s| s.to_string()),
+            terminal: false,
+        }
+    }
+
+    // ---- fuzzy_matches -------------------------------------------------
+
+    #[test]
+    fn fuzzy_matches_empty_pattern_matches_anything() {
+        assert!(fuzzy_matches("", "Firefox"));
+        assert!(fuzzy_matches("", ""));
+    }
+
+    #[test]
+    fn fuzzy_matches_in_order_subsequence() {
+        assert!(fuzzy_matches("ffx", "Firefox"));
+        assert!(fuzzy_matches("frfx", "Firefox"));
+    }
+
+    #[test]
+    fn fuzzy_matches_is_case_insensitive() {
+        assert!(fuzzy_matches("FIREFOX", "firefox"));
+        assert!(fuzzy_matches("firefox", "FireFox"));
+    }
+
+    #[test]
+    fn fuzzy_matches_rejects_out_of_order() {
+        assert!(!fuzzy_matches("xfr", "Firefox"));
+    }
+
+    #[test]
+    fn fuzzy_matches_rejects_missing_chars() {
+        assert!(!fuzzy_matches("firefoxx", "Firefox"));
+    }
+
+    // ---- fuzzy_score -----------------------------------------------------
+
+    #[test]
+    fn fuzzy_score_exact_name_match_is_best() {
+        let e = entry("Firefox", None);
+        assert_eq!(fuzzy_score("firefox", &e), 0);
+    }
+
+    #[test]
+    fn fuzzy_score_exact_wm_class_match_is_best() {
+        let e = entry("Firefox Web Browser", Some("firefox"));
+        assert_eq!(fuzzy_score("firefox", &e), 0);
+    }
+
+    #[test]
+    fn fuzzy_score_name_prefix_beats_name_contains() {
+        let prefix = entry("Firefox", None);
+        let contains = entry("GNU IceCat (Firefox fork)", None);
+        assert_eq!(fuzzy_score("fire", &prefix), 1);
+        assert_eq!(fuzzy_score("fire", &contains), 2);
+        assert!(fuzzy_score("fire", &prefix) < fuzzy_score("fire", &contains));
+    }
+
+    #[test]
+    fn fuzzy_score_wm_class_beats_pure_subsequence() {
+        let wm_hit = entry("Web Browser", Some("firefox"));
+        let subseq_only = entry("Fine Iris Reflex Editor for XML", None);
+        assert_eq!(fuzzy_score("fire", &wm_hit), 3);
+        assert_eq!(fuzzy_score("fire", &subseq_only), 4);
+    }
+
+    // ---- matches_term ------------------------------------------------------
+
+    #[test]
+    fn matches_term_exact_field_matches() {
+        assert!(matches_term("code", "code"));
+    }
+
+    #[test]
+    fn matches_term_whole_word_within_longer_field() {
+        assert!(matches_term("visual studio code", "code"));
+    }
+
+    #[test]
+    fn matches_term_rejects_substring_of_a_larger_word() {
+        // "code" must not match inside "vscodium" — this is the whole
+        // reason matches_term exists instead of a plain `contains`.
+        assert!(!matches_term("vscodium", "code"));
+    }
+
+    #[test]
+    fn matches_term_matches_hyphenated_variant() {
+        assert!(matches_term("code-oss", "code"));
+    }
+
+    #[test]
+    fn matches_term_empty_term_or_field_never_matches() {
+        assert!(!matches_term("code", ""));
+        assert!(!matches_term("", "code"));
+    }
+
+    // ---- priority_rank -----------------------------------------------------
+
+    #[test]
+    fn priority_rank_matches_by_name() {
+        let e = entry("Firefox", None);
+        let priority = vec!["firefox".to_string(), "code".to_string()];
+        assert_eq!(priority_rank(&e, &priority), Some(0));
+    }
+
+    #[test]
+    fn priority_rank_matches_by_wm_class() {
+        let e = entry("Web Browser", Some("firefox"));
+        let priority = vec!["code".to_string(), "firefox".to_string()];
+        assert_eq!(priority_rank(&e, &priority), Some(1));
+    }
+
+    #[test]
+    fn priority_rank_none_when_unlisted() {
+        let e = entry("Nautilus", None);
+        let priority = vec!["firefox".to_string()];
+        assert_eq!(priority_rank(&e, &priority), None);
+    }
+
+    #[test]
+    fn priority_rank_does_not_match_substring_of_a_word() {
+        let e = entry("VSCodium", None);
+        let priority = vec!["code".to_string()];
+        assert_eq!(priority_rank(&e, &priority), None);
+    }
+}