fix(rust): add fallback to Podman sockets for docker_environments

docs/notes/2.34.x.md

@@ -22,6 +22,7 @@ Fixed an issue where `pants --changed-since` would unnecessarily invalidate all
 
 The `indicatif-spinner` `dynamic_ui_renderer` (default), now renders on a dedicated thread.  This should reduce jitter and display a smoother spinner under heavy load.
 
+The Rust engine now automatically falls back to common Podman socket paths (rootless and rootful) for `docker_environments` if the default Docker socket is unavailable.
 
 ### Goals
 

src/rust/process_execution/docker/src/docker.rs

@@ -95,8 +95,29 @@ impl DockerOnceCell {
         self
       .cell
       .get_or_try_init(async move {
-        let docker = Docker::connect_with_local_defaults()
-          .map_err(|err| format!("Failed to connect to local Docker: {err}"))?;
+        let docker = Docker::connect_with_local_defaults().or_else(|original_err| {
+            if let Ok(xdg) = std::env::var("XDG_RUNTIME_DIR") {
+                let podman_sock = format!("{}/podman/podman.sock", xdg);
+                if std::path::Path::new(&podman_sock).exists() {
+                    let podman_uri = format!("unix://{}", podman_sock);
+                    return Docker::connect_with_socket(
+                        &podman_uri,
+                        120,
+                        bollard::API_DEFAULT_VERSION
+                    );
+                }
+            }
+
+            if std::path::Path::new("/run/podman/podman.sock").exists() {
+                return Docker::connect_with_socket(
+                    "unix:///run/podman/podman.sock",
+                    120,
+                    bollard::API_DEFAULT_VERSION
+                );
+            }
+
+            Err(original_err)
+        }).map_err(|err| format!("Failed to connect to local Docker/Podman: {err}"))?;
 
         let version = docker.version().await
           .map_err(|err| format!("Failed to obtain version from local Docker: {err}"))?;