fix: clarify task output forwarding errors

Co-authored-by: GPT-5.6 Codex <codex@openai.com>

Author: wan9chi

CHANGELOG.md

@@ -1,5 +1,6 @@
 # Changelog
 
+- **Fixed** Failures while forwarding output from a started task process no longer incorrectly say the process failed to spawn ([#506](https://github.com/voidzero-dev/vite-task/issues/506)).
 - **Fixed** An issue where Bun tasks on macOS did not rerun when files they read, wrote, or listed changed ([#532](https://github.com/voidzero-dev/vite-task/issues/532), [#542](https://github.com/voidzero-dev/vite-task/pull/542)).
 - **Improved** Windows file-access tracking now uses sparse temporary backing files where supported, avoiding upfront allocation of the full backing file on disk ([#524](https://github.com/voidzero-dev/vite-task/pull/524)).
 - **Fixed** Automatic file-access tracking on Linux now works in containers and Kubernetes runners with limited `/dev/shm` space ([#353](https://github.com/voidzero-dev/vite-task/issues/353), [#523](https://github.com/voidzero-dev/vite-task/pull/523)).

crates/vite_task/src/session/event.rs

@@ -41,6 +41,10 @@ pub enum ExecutionError {
     #[error("Failed to spawn process")]
     Spawn(#[source] anyhow::Error),
 
+    /// The child process started, but the runner failed while forwarding its output.
+    #[error("Failed to forward task process output")]
+    ForwardTaskProcessOutput(#[source] anyhow::Error),
+
     /// The child process started, but the runner failed while waiting for it to exit.
     #[error("Failed to wait for task process to exit")]
     WaitForTaskProcessExit(#[source] anyhow::Error),

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

@@ -598,7 +598,7 @@ async fn run_child(
             reason = "pipe_stdio streams child I/O and creates a large future"
         )]
         let r = pipe_stdio(stdout, stderr, sinks, fast_fail_token.clone()).await;
-        r.map_err(|err| ExecutionError::Spawn(err.into()))
+        r.map_err(|err| ExecutionError::ForwardTaskProcessOutput(err.into()))
     } else {
         Ok(())
     };

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

@@ -121,7 +121,7 @@ pub enum SpawnOutcome {
     /// No `infra_error` field: cache operations are skipped on non-zero exit.
     Failed { exit_code: NonZeroI32 },
 
-    /// Could not start the process (e.g., command not found).
+    /// Execution failed without a usable process exit status.
     SpawnError(SavedExecutionError),
 }
 
@@ -152,6 +152,7 @@ pub enum SavedCacheMissReason {
 pub enum SavedExecutionError {
     Cache { kind: SavedCacheErrorKind, message: Str },
     Spawn { message: Str },
+    ForwardTaskProcessOutput { message: Str },
     WaitForTaskProcessExit { message: Str },
     PostRunFingerprint { message: Str },
     IpcServerBind { message: Str },
@@ -239,6 +240,9 @@ impl SavedExecutionError {
             ExecutionError::Spawn(source) => {
                 Self::Spawn { message: vite_str::format!("{source:#}") }
             }
+            ExecutionError::ForwardTaskProcessOutput(source) => {
+                Self::ForwardTaskProcessOutput { message: vite_str::format!("{source:#}") }
+            }
             ExecutionError::WaitForTaskProcessExit(source) => {
                 Self::WaitForTaskProcessExit { message: vite_str::format!("{source:#}") }
             }
@@ -264,6 +268,9 @@ impl SavedExecutionError {
             Self::Spawn { message } => {
                 vite_str::format!("Failed to spawn process: {message}")
             }
+            Self::ForwardTaskProcessOutput { message } => {
+                vite_str::format!("Failed to forward task process output: {message}")
+            }
             Self::WaitForTaskProcessExit { message } => {
                 vite_str::format!("Failed to wait for task process to exit: {message}")
             }
@@ -916,3 +923,27 @@ fn format_input_modified_notice(buf: &mut Vec<u8>, task_names: &[Str]) {
         let _ = write!(buf, " not cached because they modified their inputs.");
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn output_forwarding_error_has_distinct_message() {
+        let error = ExecutionError::ForwardTaskProcessOutput(anyhow::anyhow!(
+            "Resource temporarily unavailable (os error 11)"
+        ));
+
+        let saved = SavedExecutionError::from_execution_error(&error);
+
+        assert!(matches!(
+            &saved,
+            SavedExecutionError::ForwardTaskProcessOutput { message }
+                if message.as_str() == "Resource temporarily unavailable (os error 11)"
+        ));
+        assert_eq!(
+            saved.display_message().as_str(),
+            "Failed to forward task process output: Resource temporarily unavailable (os error 11)"
+        );
+    }
+}