Fix crate-name import resolution for bin+lib crates

Register the Cargo package name (normalized - -> _) as an alias for
src/lib.rs in the resolver, so 'use <crate>::{...}' in src/main.rs
resolves to src/lib.rs. Adds rustdemo/Cargo.toml fixture and test
coverage; updates blast-radius test for the new transitive edge.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

src/index/imports.rs

@@ -294,7 +294,7 @@ fn clean(target: &str) -> Option<String> {
 }
 
 impl Resolver {
-    pub fn build(files: Vec<(String, i64)>) -> Self {
+    pub fn build(files: Vec<(String, i64)>, crate_name: Option<&str>) -> Self {
         let mut by_path = HashMap::new();
         let mut by_name = HashMap::new();
         let mut by_stem = HashMap::new();
@@ -308,6 +308,17 @@ impl Resolver {
                 .unwrap_or(name);
             by_stem.entry(stem).or_insert(id);
         }
+        // `use <crate>::…` names the crate's own lib root, which always lives
+        // at src/lib.rs — there is no `<crate>.rs` file. Register the package
+        // name as an alias so bin→lib edges resolve. Workspaces (no [package]
+        // name) are skipped.
+        if let Some(name) = crate_name.filter(|n| !n.is_empty())
+            && let Some(id) = by_path.get("src/lib.rs").copied()
+        {
+            by_path.insert(name.to_string(), id);
+            by_name.entry(name.to_string()).or_insert(id);
+            by_stem.entry(name.to_string()).or_insert(id);
+        }
         Resolver {
             by_path,
             by_name,

src/index/pipeline.rs

@@ -18,6 +18,30 @@ pub struct IndexStats {
     pub imports: i64,
 }
 
+/// Read the `[package] name` from `Cargo.toml`, normalized to the crate
+/// identifier (`-` → `_`) used in `use <crate>::…`.
+fn read_crate_name(project: &Path) -> Option<String> {
+    let toml = std::fs::read_to_string(project.join("Cargo.toml")).ok()?;
+    let mut in_package = false;
+    for line in toml.lines() {
+        let l = line.trim();
+        if l.starts_with('[') {
+            in_package = l == "[package]";
+            continue;
+        }
+        if in_package
+            && let Some(v) = l.strip_prefix("name").map(str::trim)
+            && let Some(v) = v.strip_prefix('=').map(str::trim)
+        {
+            let name = v.trim_matches('"');
+            if !name.is_empty() {
+                return Some(name.replace('-', "_"));
+            }
+        }
+    }
+    None
+}
+
 /// (Re)index a project. `recreate` drops any existing index first.
 pub fn run(project: &Path, db_path: &Path, recreate: bool) -> Result<IndexStats> {
     if recreate && db_path.exists() {
@@ -83,8 +107,10 @@ pub fn run(project: &Path, db_path: &Path, recreate: bool) -> Result<IndexStats>
         }
     }
 
-    let resolver =
-        imports::Resolver::build(file_ids.iter().map(|(k, v)| (k.clone(), *v)).collect());
+    let resolver = imports::Resolver::build(
+        file_ids.iter().map(|(k, v)| (k.clone(), *v)).collect(),
+        read_crate_name(project).as_deref(),
+    );
 
     for f in &changed {
         let fid = file_ids[&f.rel];