fix(cli): check final exec status and warn on partial input (#3803)

* feat(cli): stream non-TTY exec input before EOF

Add --stream-stdin using the existing interactive exec RPC without a PTY. Preserve separate output streams and enforce the existing 4 MiB cumulative input cap while forwarding input.

Require explicit clean stdin EOF and drain the response through its final gRPC status. Cover held-open input, limits, cancellation, trailers, and default finite-input behavior with subprocess and live sandbox regressions.

Signed-off-by: Shiju <shiju@nvidia.com>

* test(cli): distinguish exec cancellation from stdin EOF

Treat transport termination and response cancellation as separate test observations. Verify explicit stdin EOF through the shared frame writer and cover cancellation in the pinned Tonic decoder.

Signed-off-by: Shiju <shiju@nvidia.com>

* style(cli): use lazy optional stdin dispatch

Signed-off-by: Shiju <shiju@nvidia.com>

* test(cli): use imported duration in stdin EOF regression

Signed-off-by: Shiju <shiju@nvidia.com>

---------

Signed-off-by: Shiju <shiju@nvidia.com>

Author: shiju-nv

crates/openshell-cli/src/run.rs

@@ -2506,7 +2506,7 @@ async fn sandbox_exec_streaming_grpc(
                     if forwarded > MAX_EXEC_STDIN_BYTES {
                         return Err(std::io::Error::new(
                             ErrorKind::InvalidInput,
-                            piped_stdin_limit_error().to_string(),
+                            "streamed stdin exceeds the 4 MiB limit; the command may have processed partial input; use `sandbox upload` for larger input",
                         ));
                     }
                     if stdin_tx
@@ -2648,7 +2648,9 @@ async fn sandbox_exec_streaming_grpc(
             Some(exec_sandbox_event::Payload::Exit(exit)) => {
                 exit_code = exit.exit_code;
                 exit_seen = true;
-                break;
+                // Process exit does not complete the RPC. Keep draining so a
+                // failing final gRPC status cannot turn partial output into
+                // a successful execution result.
             }
             None => {}
         }