fix(task): validate monorepo-relative task refs

e2e/tasks/test_task_validate

@@ -253,6 +253,52 @@ assert_contains "mise tasks validate multiple-alias 2>&1 || true" "Cannot define
 # Clean up
 rm -rf mise-tasks
 
+# Test monorepo config_root dependency validation matches runtime resolution
+rm -f mise.toml
+mkdir -p monorepo-validate/pkg
+cat <<'EOF' >monorepo-validate/mise.toml
+experimental_monorepo_root = true
+
+[settings]
+experimental = true
+
+[monorepo]
+config_roots = ["pkg"]
+EOF
+
+cat <<'EOF' >monorepo-validate/pkg/mise.toml
+[tasks._dep]
+hide = true
+alias = "dep-alias"
+usage = 'arg "<name>"'
+run = 'echo "arg=$usage_name"'
+
+[tasks.w_bare]
+depends = ["_dep bare"]
+
+[tasks.w_colon]
+depends = [":_dep colon"]
+
+[tasks.w_full]
+depends = ["//pkg:_dep full"]
+
+[tasks.w_alias]
+depends = ["dep-alias alias"]
+EOF
+
+(
+  cd monorepo-validate/pkg
+  assert_contains "mise tasks validate" "✓ All 5 task(s) validated successfully"
+)
+
+assert_contains "mise -C monorepo-validate run //pkg:w_bare" "arg=bare"
+assert_contains "mise -C monorepo-validate run //pkg:w_colon" "arg=colon"
+assert_contains "mise -C monorepo-validate run //pkg:w_full" "arg=full"
+assert_contains "mise -C monorepo-validate run //pkg:w_alias" "arg=alias"
+
+# Clean up
+rm -rf monorepo-validate
+
 # Test that run.tasks entries with inline arguments are accepted
 mkdir -p mise-tasks
 cat <<'SCRIPT' >mise-tasks/test

src/cli/tasks/validate.rs

@@ -5,8 +5,8 @@ use std::sync::Arc;
 use crate::config::Config;
 use crate::duration;
 use crate::file;
-use crate::task::Task;
 use crate::task::task_fetcher::TaskFetcher;
+use crate::task::{GetMatchingExt, Task, build_task_ref_map, resolve_task_pattern};
 use crate::tera::contains_template_syntax;
 use crate::ui::style;
 use console::style as console_style;
@@ -226,13 +226,15 @@ impl TasksValidate {
         issues
     }
 
-    /// Check if a task exists by name, display_name, or alias
-    fn task_exists(all_tasks: &BTreeMap<String, Task>, task_name: &str) -> bool {
-        all_tasks.contains_key(task_name)
-            || all_tasks.values().any(|t| t.display_name == task_name)
-            || all_tasks
-                .values()
-                .any(|t| t.aliases.contains(&task_name.to_string()))
+    /// Check if a task exists by name, display_name, or alias.
+    /// Monorepo-relative references are resolved the same way runtime task matching resolves them.
+    fn task_exists(all_tasks: &BTreeMap<String, Task>, task_name: &str, parent: &Task) -> bool {
+        let resolved_name = resolve_task_pattern(task_name, Some(parent));
+        let task_refs = build_task_ref_map(all_tasks.iter());
+        task_refs
+            .get_matching(&resolved_name)
+            .is_ok_and(|matches| !matches.is_empty())
+            || all_tasks.values().any(|t| t.display_name == resolved_name)
     }
 
     fn validate_missing_references(
@@ -257,7 +259,7 @@ impl TasksValidate {
             }
 
             // Check if task exists
-            if !Self::task_exists(all_tasks, dep_name) {
+            if !Self::task_exists(all_tasks, dep_name, task) {
                 issues.push(ValidationIssue {
                     task: task.name.clone(),
                     severity: Severity::Error,
@@ -561,7 +563,7 @@ impl TasksValidate {
                 } => {
                     // Strip inline arguments before checking existence, matching runtime behavior
                     let (name, _) = crate::task::task_list::split_task_spec(task_name);
-                    if !Self::task_exists(all_tasks, name) {
+                    if !Self::task_exists(all_tasks, name, task) {
                         issues.push(ValidationIssue {
                             task: task.name.clone(),
                             severity: Severity::Error,
@@ -575,7 +577,7 @@ impl TasksValidate {
                     // Strip inline arguments before checking existence, matching runtime behavior
                     for task_name in tasks {
                         let (name, _) = crate::task::task_list::split_task_spec(task_name);
-                        if !Self::task_exists(all_tasks, name) {
+                        if !Self::task_exists(all_tasks, name, task) {
                             issues.push(ValidationIssue {
                                 task: task.name.clone(),
                                 severity: Severity::Error,