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>

tools/environments/local.py

@@ -473,7 +473,12 @@ class LocalEnvironment(PersistentShellMixin, BaseEnvironment):
                 except (ProcessLookupError, PermissionError):
                     proc.kill()
                 reader.join(timeout=2)
-                return self._timeout_result(effective_timeout)
+                partial = "".join(_output_chunks)
+                timeout_msg = f"\n[Command timed out after {effective_timeout}s]"
+                return {
+                    "output": partial + timeout_msg if partial else timeout_msg.lstrip(),
+                    "returncode": 124,
+                }
             time.sleep(0.2)
 
         reader.join(timeout=5)