fix(cli): resolve a relative paths.data against the project root

Env::data_path() handed paths.data to the data layer verbatim, so a
relative value resolved against the invoking process's cwd — aura run
from a project subdirectory silently read a different archive location
than from the root, while runs/ stayed anchored. Relative values now
join onto the project root, matching runs_root() and the [nodes]
pointer resolution; absolute values and the no-project default pass
through unchanged. RED-first unit test pins the root-anchored
resolution.

closes #254

crates/aura-cli/src/project.rs

@@ -182,12 +182,23 @@ impl Env {
         TraceStore::open(self.runs_root())
     }
 
-    /// The data archive root: `paths.data` inside a project when set,
+    /// The data archive root: `paths.data` inside a project when set
-    /// the data-server default otherwise.
+    /// (relative values resolved against the project root, same as
+    /// `runs_root()` and the `[nodes]` pointers), the data-server default
+    /// otherwise.
     pub fn data_path(&self) -> String {
         self.project
             .as_ref()
-            .and_then(|p| p.toml.paths.data.clone())
+            .and_then(|p| {
+                p.toml.paths.data.as_ref().map(|data| {
+                    let path = Path::new(data);
+                    if path.is_absolute() {
+                        data.clone()
+                    } else {
+                        p.root.join(path).to_string_lossy().to_string()
+                    }
+                })
+            })
             .unwrap_or_else(|| data_server::DEFAULT_DATA_PATH.to_string())
     }
 
@@ -615,6 +626,21 @@ mod tests {
         std::fs::remove_dir_all(&tmp).ok();
     }
 
+    /// #254: a relative `paths.data` must resolve against the project root
+    /// (`p.root`), matching `runs_root()`'s and the `[nodes]` pointers'
+    /// resolution — not against the invoking process's cwd, which silently
+    /// changes the data location depending on the caller's working directory.
+    #[test]
+    fn data_path_resolves_a_relative_paths_data_against_the_project_root() {
+        let tmp = std::env::temp_dir().join(format!("aura-datarel-{}", std::process::id()));
+        std::fs::create_dir_all(&tmp).unwrap();
+        std::fs::write(tmp.join("Aura.toml"), "[paths]\ndata = \"data\"\n").unwrap();
+        let p = load(&tmp, false).expect("data-only load");
+        let env = Env::with_project(p);
+        assert_eq!(env.data_path(), tmp.join("data").to_string_lossy().to_string());
+        std::fs::remove_dir_all(&tmp).ok();
+    }
+
     #[test]
     fn two_nodes_pointers_refuse_with_multi_crate() {
         let tmp = std::env::temp_dir().join(format!("aura-multi-{}", std::process::id()));

crates/aura-cli/tests/common/mod.rs

@@ -69,8 +69,9 @@ fn mint_tempdir() -> PathBuf {
 /// Writes the `Aura.toml` + `demo_signal.json` common to every fresh project:
 /// an absolute `[nodes]` pointer at the shared, once-built fixture crate, and
 /// — when `data_dir` is `Some` — a `[paths] data` override pointing at it
-/// (relative, resolved against the invocation cwd, which every test that uses
+/// (relative, resolved against the project root — `root` itself — since
-/// this always sets to `root` itself via `.current_dir`).
+/// `Env::data_path` joins a relative `paths.data` onto the project root,
+/// same as `runs_root()` and the `[nodes]` pointers, #254).
 fn write_project_files(root: &Path, data_dir: Option<&str>) {
     let fixture = built_project();
     let data_line = data_dir.map(|d| format!("data = \"{d}\"\n")).unwrap_or_default();