Manage sllidar_ros2 as a git subtree and apply QoS fix

- Add m5p3nc3r/sllidar_ros2 fork as a git subtree at lidar/sllidar_ros2/
- Dockerfile now COPYs source from the workspace instead of cloning at
  build time; git is no longer a build dependency
- Set /scan publisher QoS to BEST_EFFORT (depth 2) for Nav2/RViz2 compat
- Add lidar/README.md documenting the subtree workflow
- Remove lidar/sllidar_ros2/ from .gitignore (no longer needed)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

lidar/Dockerfile

@@ -7,12 +7,12 @@ SHELL ["/bin/bash", "-c"]
 
 RUN apt-get update && apt-get install -y --no-install-recommends \
     python3-colcon-common-extensions \
-    git \
     && rm -rf /var/lib/apt/lists/*
 
 WORKDIR /ws
 
-RUN git clone --depth 1 https://github.com/slamtec/sllidar_ros2.git src/sllidar_ros2
+# Source is managed as a git subtree — copy directly from the workspace
+COPY lidar/sllidar_ros2/ src/sllidar_ros2/
 
 RUN source /opt/ros/${ROS_DISTRO}/setup.bash && \
     colcon build --packages-select sllidar_ros2

lidar/README.md

@@ -0,0 +1,96 @@
+# RPLIDAR A1 — LIDAR Container
+
+ROS 2 container for the Slamtec RPLIDAR A1, built on top of a fork of the
+official `sllidar_ros2` driver.
+
+---
+
+## How the build works
+
+The driver source lives in `lidar/sllidar_ros2/` as a **git subtree** of this
+repository.  The [Dockerfile](Dockerfile) copies it directly from the
+workspace — no network access is required at build time.
+
+```
+Workspace repo                Docker build
+──────────────────────────    ──────────────────────────────────────────
+lidar/sllidar_ros2/      ───> COPY lidar/sllidar_ros2/ src/sllidar_ros2/
+(git subtree of fork)         colcon build --packages-select sllidar_ros2
+```
+
+The upstream fork is maintained at:
+
+    https://github.com/m5p3nc3r/sllidar_ros2
+
+---
+
+## Development workflow
+
+### Pulling upstream changes into the workspace
+
+```bash
+git subtree pull --prefix=lidar/sllidar_ros2 sllidar_ros2 main --squash
+```
+
+This fetches the latest commits from the fork, squashes them into a single
+merge commit, and updates `lidar/sllidar_ros2/` in the workspace.
+
+### Making local changes
+
+Edit files inside `lidar/sllidar_ros2/` as normal, then commit them to the
+workspace repo:
+
+```bash
+git add lidar/sllidar_ros2/
+git commit -m "lidar: describe the change"
+```
+
+### Pushing changes back to the fork
+
+```bash
+git subtree push --prefix=lidar/sllidar_ros2 sllidar_ros2 main
+```
+
+This replays only the commits that touched `lidar/sllidar_ros2/` and pushes
+them to the fork's `main` branch.
+
+### First-time setup on a fresh clone
+
+The subtree files are committed in the workspace repo, so a `git clone` of
+this repo is all that is needed — there is no separate step to initialise the
+subtree.  To be able to pull or push to the fork later, add the remote:
+
+```bash
+git remote add sllidar_ros2 https://github.com/m5p3nc3r/sllidar_ros2.git
+```
+
+---
+
+## Changes relative to upstream
+
+| File | Change |
+|---|---|
+| `src/sllidar_node.cpp` | `/scan` publisher QoS set to `BEST_EFFORT` with depth 2. Required for compatibility with Nav2 and RViz2, which subscribe to `/scan` with `BEST_EFFORT`. The upstream default (`RELIABLE`) causes those consumers to receive no data. |
+
+The upstream Slamtec repository is at:
+
+    https://github.com/slamtec/sllidar_ros2
+
+---
+
+## Published topics
+
+| Topic | Type | Description |
+|---|---|---|
+| `/scan` | `sensor_msgs/LaserScan` | 360° laser scan, `BEST_EFFORT` QoS, depth 2 |
+
+## Device
+
+The RPLIDAR A1 connects via USB serial at `/dev/ttyUSB0` (default), 115200 baud.
+The container receives access to that device via the `devices` mapping in
+[docker-compose.yml](../docker-compose.yml).  To use a different port, set
+`LIDAR_PORT` in your `.env` file:
+
+```bash
+LIDAR_PORT=/dev/ttyUSB1
+```

lidar/sllidar_ros2/src/sllidar_node.cpp

@@ -59,7 +59,7 @@ class SLlidarNode : public rclcpp::Node
     : Node("sllidar_node")
     {
 
-      scan_pub = this->create_publisher<sensor_msgs::msg::LaserScan>("scan", rclcpp::QoS(rclcpp::KeepLast(10)));
+      scan_pub = this->create_publisher<sensor_msgs::msg::LaserScan>("scan", rclcpp::QoS(rclcpp::KeepLast(2)).best_effort());
       
     }