test(e2e): add ctrl-c tests for labeled mode and cached tasks (#307)

## Summary
- Add ctrl-c e2e tests for `--log=labeled` mode and cache-enabled tasks
- Move SIGINT ignore handler from program startup to right before plan
execution, so interactive task selection (`vp run`) remains cancellable
with Ctrl+C
- Add `println!()` after milestone in `exit-on-ctrlc` tool so milestone
bytes flush through line-buffered writers in labeled mode

## Test plan
- [x] All e2e snapshot tests pass on macOS
- [x] ctrl-c tests pass on Windows VM
- [ ] CI passes

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: branchseer

Cargo.lock

@@ -17,6 +17,7 @@ async-trait = { workspace = true }
 bincode = { workspace = true, features = ["derive"] }
 bstr = { workspace = true }
 clap = { workspace = true, features = ["derive"] }
+ctrlc = { workspace = true }
 derive_more = { workspace = true, features = ["from"] }
 fspy = { workspace = true }
 futures-util = { workspace = true }

crates/vite_task/Cargo.toml

@@ -327,6 +327,13 @@ impl<'a> Session<'a> {
                     Some(self.make_summary_writer()),
                     self.program_name.clone(),
                 ));
+                // Ignore SIGINT/CTRL_C before executing tasks. Child tasks
+                // receive the signal directly from the terminal driver and handle
+                // it themselves. This lets the runner wait for tasks to exit and
+                // report their actual exit status rather than being killed
+                // mid-flight.
+                let _ = ctrlc::set_handler(|| {});
+
                 self.execute_graph(graph, builder).await.map_err(SessionError::EarlyExit)
             }
         }

crates/vite_task/src/session/mod.rs

@@ -3,12 +3,6 @@ use vite_task::{Command, ExitStatus, Session};
 use vite_task_bin::OwnedSessionConfig;
 
 fn main() -> ! {
-    // Ignore SIGINT/CTRL_C before the tokio runtime starts. Child tasks
-    // receive the signal directly from the terminal driver and handle it
-    // themselves. This lets the runner wait for tasks to exit and report
-    // their actual exit status rather than being killed mid-flight.
-    let _ = ctrlc::set_handler(|| {});
-
     let exit_code: i32 =
         tokio::runtime::Builder::new_multi_thread().enable_all().build().unwrap().block_on(async {
             match run().await {

crates/vite_task_bin/src/main.rs

@@ -33,6 +33,9 @@ pub fn run() -> Result<(), Box<dyn std::error::Error>> {
     })?;
 
     pty_terminal_test_client::mark_milestone("ready");
+    // Print a newline so the milestone bytes get flushed through line-buffered
+    // writers (labeled/grouped log modes).
+    println!();
 
     loop {
         std::thread::park();

crates/vite_task_bin/src/vtt/exit_on_ctrlc.rs

@@ -12,3 +12,30 @@ steps = [
     { "write-key" = "ctrl-c" },
   ] },
 ]
+
+[[e2e]]
+name = "ctrl-c terminates running tasks (labeled)"
+steps = [
+  { argv = [
+    "vt",
+    "run",
+    "--log=labeled",
+    "dev",
+  ], interactions = [
+    { "expect-milestone" = "ready" },
+    { "write-key" = "ctrl-c" },
+  ] },
+]
+
+[[e2e]]
+name = "ctrl-c terminates running tasks (cached)"
+steps = [
+  { argv = [
+    "vt",
+    "run",
+    "dev-cached",
+  ], interactions = [
+    { "expect-milestone" = "ready" },
+    { "write-key" = "ctrl-c" },
+  ] },
+]

crates/vite_task_bin/tests/e2e_snapshots/fixtures/ctrl-c/snapshots.toml

@@ -0,0 +1,11 @@
+---
+source: crates/vite_task_bin/tests/e2e_snapshots/main.rs
+expression: e2e_outputs
+---
+> vt run dev-cached
+@ expect-milestone: ready
+$ vtt exit-on-ctrlc
+@ write-key: ctrl-c
+$ vtt exit-on-ctrlc
+
+ctrl-c received

crates/vite_task_bin/tests/e2e_snapshots/fixtures/ctrl-c/snapshots/ctrl-c terminates running tasks (cached).snap

@@ -0,0 +1,13 @@
+---
+source: crates/vite_task_bin/tests/e2e_snapshots/main.rs
+expression: e2e_outputs
+---
+> vt run --log=labeled dev
+@ expect-milestone: ready
+[ctrl-c-test#dev] $ vtt exit-on-ctrlc ⊘ cache disabled
+[ctrl-c-test#dev] 
+@ write-key: ctrl-c
+[ctrl-c-test#dev] $ vtt exit-on-ctrlc ⊘ cache disabled
+[ctrl-c-test#dev] 
+
+[ctrl-c-test#dev] ctrl-c received

crates/vite_task_bin/tests/e2e_snapshots/fixtures/ctrl-c/snapshots/ctrl-c terminates running tasks (labeled).snap

@@ -7,4 +7,5 @@ expression: e2e_outputs
 $ vtt exit-on-ctrlc ⊘ cache disabled
 @ write-key: ctrl-c
 $ vtt exit-on-ctrlc ⊘ cache disabled
+
 ctrl-c received

crates/vite_task_bin/tests/e2e_snapshots/fixtures/ctrl-c/snapshots/ctrl-c terminates running tasks.snap

@@ -1,8 +1,13 @@
 {
-  "cache": false,
+  "cache": true,
   "tasks": {
     "dev": {
-      "command": "vtt exit-on-ctrlc"
+      "command": "vtt exit-on-ctrlc",
+      "cache": false
+    },
+    "dev-cached": {
+      "command": "vtt exit-on-ctrlc",
+      "cache": true
     }
   }
 }