fix(terminal): preserve partial output when command times out (#3868)

When a command timed out, all captured output was discarded — the agent
only saw 'Command timed out after Xs' with zero context. Now returns
the buffered output followed by a timeout marker, matching the existing
interrupt path behavior.

Salvaged from PR #3286 by @binhnt92.

Co-authored-by: nguyen binh <binhnt92@users.noreply.github.com>

tests/tools/test_terminal_timeout_output.py

@@ -0,0 +1,27 @@
+"""Verify that terminal command timeouts preserve partial output."""
+from tools.environments.local import LocalEnvironment
+
+
+class TestTimeoutPreservesPartialOutput:
+    """When a command times out, any output captured before the deadline
+    should be included in the result — not discarded."""
+
+    def test_timeout_includes_partial_output(self):
+        """A command that prints then sleeps past the deadline should
+        return both the printed text and the timeout notice."""
+        env = LocalEnvironment()
+        result = env.execute("echo 'hello from test' && sleep 30", timeout=2)
+
+        assert result["returncode"] == 124
+        assert "hello from test" in result["output"]
+        assert "timed out" in result["output"].lower()
+
+    def test_timeout_with_no_output(self):
+        """A command that produces nothing before timeout should still
+        return a clean timeout message."""
+        env = LocalEnvironment()
+        result = env.execute("sleep 30", timeout=1)
+
+        assert result["returncode"] == 124
+        assert "timed out" in result["output"].lower()
+        assert not result["output"].startswith("\n")