docs(docker): refresh the container-listing doc, drop a stale telemetry test comment

The container-listing section still described the removed `ls -1` parse,
`pkg/queue`, and the old `[]container.PathStat` return. Update it to the current
`find -print0` + errgroup fan-out returning `ContainerDirListing{Files, Failures,
Truncated}`. Also remove the stale `WithBlock`/`DefaultDialTimeout` paragraph left
above the non-blocking `grpc.NewClient` test — its own next paragraph already
contradicted it.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

backend/docs/docker.md

@@ -216,7 +216,7 @@ type DockerClient interface {
 
     // File operations
     ContainerStatPath(ctx context.Context, containerID string, path string) (container.PathStat, error)
-    ListContainerDir(ctx context.Context, containerID string, dirPath string) ([]container.PathStat, error)
+    ListContainerDir(ctx context.Context, containerID string, dirPath string) (ContainerDirListing, error)
     CopyToContainer(ctx context.Context, containerID string, dstPath string, content io.Reader, options container.CopyToContainerOptions) error
     CopyFromContainer(ctx context.Context, containerID string, srcPath string) (io.ReadCloser, container.PathStat, error)
 
@@ -560,11 +560,10 @@ entries, err := dockerClient.ListContainerDir(ctx, containerID, "/work")
 `ListContainerDir` performs a non-recursive directory listing inside a running container:
 
 1. Uses `ContainerStatPath` to verify that `dirPath` exists and is a directory.
-2. Executes `ls -1 -- <dirPath>` inside the container to get direct entry names.
-3. Calls `ContainerStatPath` for every entry to return Docker `container.PathStat` metadata.
-4. Runs entry stat calls through `pkg/queue` with `containerListWorkers = 20` workers to reduce latency for large directories.
+2. Executes `find <dirPath> -maxdepth 1 -mindepth 1 ! -name '.*' -print0` (no TTY) inside the container. `find -print0` emits literal, NUL-delimited entry paths, so names with spaces, newlines, or non-UTF8 bytes survive intact — the old `ls -1` parse mangled them.
+3. Stats every entry concurrently through an `errgroup` bounded to `containerListWorkers = 20`, preserving input order.
 
-The method returns `[]container.PathStat`. The caller is responsible for joining the returned entry name with the requested base path when it needs full paths.
+The method returns a `ContainerDirListing`: `Files` are the readable entries' `container.PathStat` metadata, `Failures` carries any per-entry stat errors so a live directory degrades to a partial listing instead of failing outright, and `Truncated` is set when the directory held more than the entry cap and only the first page was listed.
 
 If `dirPath` is empty, it defaults to `WorkFolderPathInContainer` (`/work`).
 

backend/pkg/observability/otelclient_test.go

@@ -76,10 +76,6 @@ func TestNewTelemetryClient_SuccessPathExportsAndShutsDown(t *testing.T) {
 	}
 }
 
-// A set-but-unreachable collector must not hang startup. The endpoint
-// accepts the TCP connection but never completes the gRPC handshake, so a
-// WithBlock dial would wait forever without the internal DefaultDialTimeout that
-// this bounds — the caller's context has no deadline.
 // A set-but-unreachable collector must not stall startup: grpc.NewClient is
 // non-blocking, so the client is returned immediately and connects in the
 // background if the collector later comes up.