fix(build): honor platform on local single-arch loads

Author: Debug Agent

openhands-agent-server/openhands/agent_server/docker/build.py

@@ -769,6 +769,8 @@ def build_with_telemetry(opts: BuildOptions) -> BuildResult:
     if push:
         args += ["--platform", ",".join(opts.platforms), "--push"]
     else:
+        if len(opts.platforms) == 1:
+            args += ["--platform", opts.platforms[0]]
         args += ["--load"]
 
     for t in tags:
@@ -842,7 +844,7 @@ def build_with_telemetry(opts: BuildOptions) -> BuildResult:
     logger.info(
         f"[build] Building target='{opts.target}' image='{opts.image}' "
         f"custom_tags='{opts.custom_tags}' from base='{opts.base_image}' "
-        f"for platforms='{opts.platforms if push else 'local-arch'}'"
+        f"for platforms='{opts.platforms}'"
     )
     logger.info(
         f"[build] Git ref='{opts.git_ref}' sha='{opts.git_sha}' "

tests/agent_server/test_docker_build.py

@@ -569,13 +569,64 @@ def fake_run(cmd: list[str], cwd: str | None = None):
     cmd, cwd = docker_calls[0]
     assert cwd == str(ctx)
     assert "--load" in cmd
+    assert "--platform" in cmd and "linux/amd64" in cmd
     assert "--target" in cmd and "source-minimal" in cmd
     assert "--build-arg" in cmd
     assert "BASE_IMAGE=python:3.12" in cmd
     for tag in opts.all_tags:
         assert tag in cmd
 
 
+def test_local_build_with_multiple_platforms_skips_platform_flag(tmp_path: Path):
+    from openhands.agent_server.docker.build import (
+        BuildOptions,
+        _default_sdk_project_root,
+        build,
+    )
+
+    ctx = tmp_path / "ctx"
+    ctx.mkdir()
+    docker_calls: list[tuple[list[str], str | None]] = []
+
+    def fake_run(cmd: list[str], cwd: str | None = None):
+        if cmd[:3] != ["docker", "buildx", "build"]:
+            raise AssertionError(f"unexpected command: {cmd}")
+        docker_calls.append((cmd, cwd))
+        return subprocess.CompletedProcess(cmd, 0, stdout="ok", stderr="")
+
+    opts = BuildOptions(
+        base_image="python:3.12",
+        custom_tags="python",
+        git_sha="abc1234567890",
+        git_ref="refs/heads/main",
+        target="source-minimal",
+        platforms=["linux/amd64", "linux/arm64"],
+        push=False,
+        sdk_project_root=_default_sdk_project_root(),
+    )
+
+    with (
+        patch(
+            "openhands.agent_server.docker.build._make_build_context", return_value=ctx
+        ),
+        patch("openhands.agent_server.docker.build._run", side_effect=fake_run),
+        patch(
+            "openhands.agent_server.docker.build._active_buildx_driver",
+            return_value="docker-container",
+        ),
+        patch(
+            "openhands.agent_server.docker.build._default_local_cache_dir",
+            return_value=tmp_path / "cache",
+        ),
+        patch("openhands.agent_server.docker.build.shutil.rmtree"),
+    ):
+        build(opts)
+
+    cmd = docker_calls[0][0]
+    assert "--load" in cmd
+    assert "--platform" not in cmd
+
+
 def test_build_can_reuse_same_prebuilt_sdist_multiple_times(tmp_path: Path):
     from openhands.agent_server.docker.build import (
         BuildOptions,