fix(automation): a missing path under --root says where it was looked for (#1890) (#1907)

A relative path that doesn't exist below the root was refused with the path
as typed and the system's localised message, so a script written for
another working directory ("sub/a.pdf" with --root sub) gave nothing to
correct from. The refusal now names the resolved path and the root; paths
outside the root keep their uniform refusal.


Claude-Session: https://claude.ai/code/session_01RUNQSPVXx3dDBabRZHAnjz

Co-authored-by: Claude Fable 5.1 <noreply@anthropic.com>

crates/automation/src/lib.rs

@@ -1938,8 +1938,17 @@ impl Automation {
             return Err(outside());
         }
         if !rest.is_empty() && !for_write {
-            // Missing, below a folder inside the root: say why, as the system reports it.
-            real = joined.canonicalize().map_err(|e| failed(format!("{path}: {e}")))?;
+            // Missing, below a folder inside the root: say where it was looked for, so a path
+            // written for another working directory can be corrected (#1890), and otherwise
+            // why, as the system reports it. `joined` is under the root, so naming it reveals
+            // nothing outside.
+            real = joined.canonicalize().map_err(|e| {
+                let (looked, root) = (joined.display(), root.display());
+                match e.kind() {
+                    std::io::ErrorKind::NotFound => failed(format!("{path} not found (looked for {looked}, --root {root})")),
+                    _ => failed(format!("{path}: {e} (looked for {looked}, --root {root})")),
+                }
+            })?;
             if !real.starts_with(root) {
                 return Err(outside()); // it appeared, as a link out, since the check above
             }

crates/automation/tests/automation.rs

@@ -857,7 +857,10 @@ fn root_refusals_do_not_reveal_what_exists_outside() {
     // Inside the root nothing changes: missing files say so, and existing ones open and save,
     // however the path is spelled.
     let missing = a.call("doc_open", &json!({ "path": "missing-inside.pdf" })).unwrap_err();
-    assert!(matches!(&missing, ToolError::Failed(m) if m.starts_with("missing-inside.pdf: ") && !m.contains("outside")), "{missing:?}");
+    assert!(
+        matches!(&missing, ToolError::Failed(m) if m.starts_with("missing-inside.pdf not found (looked for ") && !m.contains("outside")),
+        "{missing:?}"
+    );
     let not_dir = a.call("doc_open", &json!({ "path": "inside.pdf/x" })).unwrap_err();
     assert!(matches!(&not_dir, ToolError::Failed(m) if !m.contains("outside")), "{not_dir:?}");
     #[cfg_attr(not(windows), allow(unused_mut))]
@@ -5939,3 +5942,23 @@ fn absolute_gotor_consent_does_not_bypass_validation_or_passwords() {
     assert_eq!(opened["document"]["encrypted"], true);
     assert_eq!(opened["destination_applied"], true);
 }
+
+#[test]
+fn a_missing_path_under_the_root_names_where_it_was_looked_for() {
+    // #1890: a script written from another working directory repeats the root's folder in its
+    // paths. The refusal names the resolved path and the root, so there is something to correct.
+    let (base, root) = sandbox("resolved-path");
+    let mut a = auto(&root);
+    let looked = |rel: &str| root.join(rel).display().to_string();
+    for (path, rel) in
+        [("root/inside.pdf", "root/inside.pdf"), ("missing/deeper/x.pdf", "missing/deeper/x.pdf"), ("./sub/../root/inside.pdf", "root/inside.pdf")]
+    {
+        let ToolError::Failed(m) = err(&mut a, "doc_open", json!({ "path": path })) else { panic!("{path}: not a failure") };
+        assert_eq!(m, format!("{path} not found (looked for {}, --root {})", looked(rel), root.display()));
+    }
+    // The same mistake with a file that does exist outside still gets the plain refusal (#136).
+    let ToolError::Failed(m) = err(&mut a, "doc_open", json!({ "path": "../outside/secret.pdf" })) else { panic!("not a failure") };
+    assert!(!m.contains("looked for"), "{m}");
+    ok(&mut a, "doc_open", json!({ "path": "inside.pdf" }));
+    let _ = std::fs::remove_dir_all(base);
+}