fix: use leaf graph path for stdio suggestion (#167)

## Technical changes
- Replaced the labeled reporter's global `spawn_leaf_count` stdio heuristic with per-leaf evaluation based on graph structure along each `LeafExecutionPath`.
- Added `LeafExecutionPath::all_containing_graphs_single_node(...)` to determine whether a leaf is inside only single-node graphs (root + expanded ancestors).
- Moved stdio suggestion selection to `new_leaf_execution(...)`, storing the computed suggestion on `LabeledLeafReporter` and using it in `start(...)`.
- Removed now-obsolete `count_spawn_leaves(...)` logic and rewrote labeled reporter unit tests to validate graph-path criteria and ancestor behavior.
- Added a new e2e fixture `stdio-graph-criteria` that exercises mixed `&&` + expanded graph cases and verifies tty behavior via snapshots.
- Updated stdin-inheritance fixture documentation to match the new criteria wording.

## User-facing changes
- Commands now suggest inherited stdio when they run in a single-node graph chain, even if a sibling `&&` branch expands into a multi-node graph.
- Commands now suggest piped stdio whenever they are in a multi-node graph or nested under any multi-node ancestor graph.
- This makes tty behavior for nested `vp run ...` expansions align with execution semantics in mixed sequential/expanded plans.

## Validation
- `cargo test -p vite_task labeled_reporter`
- `cargo test -p vite_task_bin --test e2e_snapshots -- stdio-graph-criteria`
- `cargo test -p vite_task_bin --test e2e_snapshots -- stdin-inheritance`

Author: branchseer

crates/vite_task/src/session/reporter/labeled.rs

@@ -180,6 +180,49 @@ impl LeafExecutionPath {
         }
         unreachable!("LeafExecutionPath: empty path")
     }
+
+    /// Return true when this leaf is contained in a chain of execution graphs where
+    /// every graph (root + all nested `Expanded` ancestors) has exactly one node.
+    ///
+    /// This is used by the labeled reporter to determine whether inherited stdio can
+    /// be suggested for spawned processes.
+    ///
+    /// # Panics
+    ///
+    /// - If the path is empty (indicates a bug in path construction).
+    /// - If an intermediate path element points to a `Leaf` item instead of
+    ///   `Expanded`.
+    fn all_containing_graphs_single_node(&self, root_graph: &ExecutionGraph) -> bool {
+        let Some((last_path_item, parent_path_items)) = self.0.split_last() else {
+            unreachable!("LeafExecutionPath: empty path")
+        };
+
+        let mut current_graph = root_graph;
+        if current_graph.node_count() != 1 {
+            return false;
+        }
+
+        for (depth, path_item) in parent_path_items.iter().enumerate() {
+            let item = path_item.resolve(current_graph);
+            match &item.kind {
+                ExecutionItemKind::Expanded(nested_graph) => {
+                    current_graph = nested_graph;
+                    if current_graph.node_count() != 1 {
+                        return false;
+                    }
+                }
+                ExecutionItemKind::Leaf(_) => {
+                    unreachable!(
+                        "LeafExecutionPath: intermediate element at depth {depth} is a Leaf, expected Expanded"
+                    )
+                }
+            }
+        }
+
+        // Validate that the final path item resolves in the containing graph.
+        let _ = last_path_item.resolve(current_graph);
+        true
+    }
 }
 
 impl std::ops::Index<&LeafExecutionPath> for ExecutionGraph {

crates/vite_task/src/session/reporter/mod.rs

@@ -1,7 +1,8 @@
 # Tests stdin inheritance behavior for spawned tasks.
 #
 # Stdin is inherited from the parent process only when BOTH conditions are met:
-# 1. The reporter suggests inherited stdin (single spawn leaf in the graph, or synthetic execution)
+# 1. The reporter suggests inherited stdin (the leaf is in a single-node graph chain,
+#    or the execution uses PlainReporter for synthetic execution)
 # 2. Caching is disabled for the task (cache_metadata is None)
 #
 # Otherwise, stdin is set to /dev/null.

crates/vite_task_bin/tests/e2e_snapshots/fixtures/stdin-inheritance/snapshots.toml

@@ -0,0 +1,4 @@
+{
+  "name": "stdio-graph-criteria-test",
+  "private": true
+}

crates/vite_task_bin/tests/e2e_snapshots/fixtures/stdio-graph-criteria/package.json

@@ -0,0 +1,3 @@
+{
+  "name": "other"
+}

crates/vite_task_bin/tests/e2e_snapshots/fixtures/stdio-graph-criteria/packages/other/package.json

@@ -0,0 +1,16 @@
+{
+  "tasks": {
+    "check-tty": {
+      "command": "check-tty",
+      "cache": false
+    },
+    "bar": {
+      "command": "check-tty",
+      "cache": false
+    },
+    "foo-nested": {
+      "command": "vp run bar",
+      "cache": false
+    }
+  }
+}

crates/vite_task_bin/tests/e2e_snapshots/fixtures/stdio-graph-criteria/packages/other/vite-task.json

@@ -0,0 +1,2 @@
+packages:
+  - packages/*

crates/vite_task_bin/tests/e2e_snapshots/fixtures/stdio-graph-criteria/pnpm-workspace.yaml

@@ -0,0 +1,19 @@
+# Tests stdio suggestion criteria based on graph shape along each leaf path.
+#
+# Rules under test:
+# - Suggest piped when the leaf's containing graph has more than one node, or
+#   any ancestor graph on its path has more than one node.
+# - Suggest inherited only when every graph on the path (root + nested Expanded
+#   graphs) has exactly one node.
+
+[[e2e]]
+name = "single-node chains inherit even with multi-node sibling graph"
+steps = [
+  "vp run foo",
+]
+
+[[e2e]]
+name = "multi-node ancestor forces piped for nested single-node graph"
+steps = [
+  "vp run -r foo-nested",
+]

crates/vite_task_bin/tests/e2e_snapshots/fixtures/stdio-graph-criteria/snapshots.toml

@@ -0,0 +1,31 @@
+---
+source: crates/vite_task_bin/tests/e2e_snapshots/main.rs
+expression: e2e_outputs
+---
+> vp run -r foo-nested
+~/packages/other$ check-tty ⊘ cache disabled: no cache config
+stdin:not-tty
+stdout:not-tty
+stderr:not-tty
+
+$ check-tty ⊘ cache disabled: no cache config
+stdin:not-tty
+stdout:not-tty
+stderr:not-tty
+
+
+━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
+    Vite+ Task Runner • Execution Summary
+━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
+
+Statistics:   2 tasks • 0 cache hits • 0 cache misses • 2 cache disabled
+Performance:  0% cache hit rate
+
+Task Details:
+────────────────────────────────────────────────
+  [1] other#bar: ~/packages/other$ check-tty ✓
+      → Cache disabled in task configuration
+  ·······················································
+  [2] stdio-graph-criteria-test#bar: $ check-tty ✓
+      → Cache disabled in task configuration
+━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

crates/vite_task_bin/tests/e2e_snapshots/fixtures/stdio-graph-criteria/snapshots/multi-node ancestor forces piped for nested single-node graph.snap

@@ -0,0 +1,47 @@
+---
+source: crates/vite_task_bin/tests/e2e_snapshots/main.rs
+expression: e2e_outputs
+---
+> vp run foo
+$ check-tty ⊘ cache disabled: no cache config
+stdin:tty
+stdout:tty
+stderr:tty
+
+$ check-tty ⊘ cache disabled: no cache config
+stdin:tty
+stdout:tty
+stderr:tty
+
+~/packages/other$ check-tty ⊘ cache disabled: no cache config
+stdin:not-tty
+stdout:not-tty
+stderr:not-tty
+
+$ check-tty ⊘ cache disabled: no cache config
+stdin:not-tty
+stdout:not-tty
+stderr:not-tty
+
+
+━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
+    Vite+ Task Runner • Execution Summary
+━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
+
+Statistics:   4 tasks • 0 cache hits • 0 cache misses • 4 cache disabled
+Performance:  0% cache hit rate
+
+Task Details:
+────────────────────────────────────────────────
+  [1] stdio-graph-criteria-test#foo: $ check-tty ✓
+      → Cache disabled in task configuration
+  ·······················································
+  [2] stdio-graph-criteria-test#bar: $ check-tty ✓
+      → Cache disabled in task configuration
+  ·······················································
+  [3] other#check-tty: ~/packages/other$ check-tty ✓
+      → Cache disabled in task configuration
+  ·······················································
+  [4] stdio-graph-criteria-test#check-tty: $ check-tty ✓
+      → Cache disabled in task configuration
+━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━