Per-sheep pen-time metrics, seed support, make webots → menu

* `controllers/shepherd_dog/shepherd_dog.py`
  - Tracks the first step at which each sheep crosses the gate; on
    auto-finish (all sheep penned) prints a `[results]` summary
    block: mode/drive/world/lidar/dogs/seed line, total simulated
    time, per-sheep penning order with absolute step + seconds since
    sim start, and the gate spread between the first and last
    penning.
  - Reads `HERDING_SEED` (env / runtime cfg) and seeds the
    controller's RNG when set. Empty = time-based default = old
    non-deterministic behaviour.
* `controllers/sheep/sheep.py` reads `HERDING_SEED` the same way
  (loading `herding_runtime.cfg` itself so it works even when
  Webots strips env vars) and seeds Python's RNG XOR'd with the
  sheep's name hash, so a fixed seed gives a reproducible flock
  trajectory without all sheep starting from identical wander state.
* `tools/run_webots.sh` writes `HERDING_SEED` into the runtime cfg
  (empty when unset so existing scripts keep their stochastic
  behaviour).
* `tools/webots_menu.sh` gains a Seed prompt (random / fixed
  integer); the launch summary box shows the choice next to the
  perception row.
* `Makefile`
  - `make webots`  now fires the interactive picker (replacing the
    old positional invocation).
  - `make webots_quick MODE=… DRIVE=… WORLD=… N=…` is the old
    positional path, kept for batch / scripted use.

Smoke-tested: menu renders Mode → Drive → World → LiDAR → Dogs
→ Sheep → Perception → Seed → Headless prompts and shows the
selected Seed value in the launch summary. 126 pytest cases still
pass.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

controllers/sheep/sheep.py

@@ -37,6 +37,37 @@ timestep = int(robot.getBasicTimeStep())
 name = robot.getName()
 self_node = robot.getSelf()
 
+# Seed Python's RNG (shared with the dog controller) so a fixed
+# HERDING_SEED produces reproducible runs. Each sheep mixes its name
+# into the seed so the flock isn't all identical.
+def _read_runtime_cfg():
+    cfg_path = os.path.join(_PROJECT_ROOT, "herding_runtime.cfg")
+    out = {}
+    if os.path.exists(cfg_path):
+        try:
+            with open(cfg_path) as f:
+                for line in f:
+                    line = line.strip()
+                    if not line or line.startswith("#") or "=" not in line:
+                        continue
+                    k, _, v = line.partition("=")
+                    out[k.strip().upper()] = v.strip()
+        except OSError:
+            pass
+    return out
+
+_rt = _read_runtime_cfg()
+_seed_raw = (os.environ.get("HERDING_SEED")
+             or _rt.get("HERDING_SEED")
+             or "").strip()
+if _seed_raw:
+    try:
+        # XOR with hash(name) so different sheep have different seeds
+        # but the flock as a whole is deterministic for a given seed.
+        random.seed(int(_seed_raw) ^ (hash(name) & 0x7FFFFFFF))
+    except ValueError:
+        pass
+
 left_motor = robot.getDevice("left wheel motor")
 right_motor = robot.getDevice("right wheel motor")
 left_motor.setPosition(float("inf"))