Fix docker image pull progress blocked by small layers

Small Docker layers (typically <100 bytes) can skip the downloading phase
entirely, going directly from "Pulling fs layer" to "Download complete"
without emitting any progress events with byte counts. This caused the
aggregate progress calculation to block indefinitely, as it required all
layer jobs to have their `extra` field populated with byte counts before
proceeding.

The issue manifested as parent job progress jumping from 0% to 97.9% after
long delays, as seen when a 96-byte layer held up progress reporting for
~50 seconds until it finally reached the "Extracting" phase.

Set a minimal `extra` field (current=1, total=1) when layers reach
"Download complete" without having gone through the downloading phase.
This allows the aggregate progress calculation to proceed immediately
while still correctly representing the layer as 100% downloaded.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

tests/docker/test_interface.py

@@ -569,3 +569,81 @@ async def test_install_progress_handles_download_restart(
         await event.wait()
 
     capture_exception.assert_not_called()
+
+
+async def test_install_progress_handles_layers_skipping_download(
+    coresys: CoreSys,
+    test_docker_interface: DockerInterface,
+    capture_exception: Mock,
+):
+    """Test install handles small layers that skip downloading phase and go directly to download complete."""
+    coresys.core.set_state(CoreState.RUNNING)
+    # Simulate multiple layers where one small layer (96 bytes) skips the downloading phase
+    # This layer should not block progress reporting for the parent job
+    coresys.docker.docker.api.pull.return_value = [
+        {"status": "Pulling from test/image", "id": "latest"},
+        # Layer 1: Normal layer with downloading phase
+        {"status": "Pulling fs layer", "progressDetail": {}, "id": "layer1"},
+        {
+            "status": "Downloading",
+            "progressDetail": {"current": 100, "total": 1000},
+            "progress": "[=====>                                             ]     100B/1000B",
+            "id": "layer1",
+        },
+        {
+            "status": "Downloading",
+            "progressDetail": {"current": 1000, "total": 1000},
+            "progress": "[==================================================>]    1000B/1000B",
+            "id": "layer1",
+        },
+        {"status": "Download complete", "progressDetail": {}, "id": "layer1"},
+        {
+            "status": "Extracting",
+            "progressDetail": {"current": 1000, "total": 1000},
+            "progress": "[==================================================>]    1000B/1000B",
+            "id": "layer1",
+        },
+        {"status": "Pull complete", "progressDetail": {}, "id": "layer1"},
+        # Layer 2: Small layer that skips downloading (like 02a6e69d8d00 from the logs)
+        {"status": "Pulling fs layer", "progressDetail": {}, "id": "layer2"},
+        {"status": "Waiting", "progressDetail": {}, "id": "layer2"},
+        # Goes straight to Download complete without Downloading phase
+        {"status": "Download complete", "progressDetail": {}, "id": "layer2"},
+        {
+            "status": "Extracting",
+            "progressDetail": {"current": 96, "total": 96},
+            "progress": "[==================================================>]      96B/96B",
+            "id": "layer2",
+        },
+        {"status": "Pull complete", "progressDetail": {}, "id": "layer2"},
+        {"status": "Digest: sha256:test"},
+        {"status": "Status: Downloaded newer image for test/image:latest"},
+    ]
+
+    with patch.object(
+        type(coresys.supervisor), "arch", PropertyMock(return_value="amd64")
+    ):
+        # Schedule job so we can observe that it completes successfully
+        event = asyncio.Event()
+        job, install_task = coresys.jobs.schedule_job(
+            test_docker_interface.install,
+            JobSchedulerOptions(),
+            AwesomeVersion("1.2.3"),
+            "test",
+        )
+
+        async def listen_for_job_end(reference: SupervisorJob):
+            if reference.uuid != job.uuid:
+                return
+            event.set()
+
+        coresys.bus.register_event(BusEvent.SUPERVISOR_JOB_END, listen_for_job_end)
+        await install_task
+        await event.wait()
+
+    # The key assertion: Job should complete successfully without errors
+    # Without the fix, layer2 would block all progress reporting until it reached Extracting,
+    # preventing the aggregate progress calculation from running
+    assert job.done is True
+    assert job.progress == 100
+    capture_exception.assert_not_called()