feat(multi-camera): pick cameras and record them one at a time

CHANGELOG.md

@@ -9,6 +9,21 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Added
 
+- **Pick cameras, and record them one at a time, in Multi-Camera Recording.**
+  Each row of the status table now has a checkbox and its own **Record** /
+  **Stop** button. Unticking a camera disconnects it, which frees its USB
+  bandwidth, so it is neither previewed nor recorded. The choice is remembered
+  in `~/.glider/camera_selection.json`, and the camera panel's Multi-Camera mode
+  leaves those cameras out too, so an experiment does not record them. A row's
+  button starts or stops that camera alone and leaves the others as they are.
+  Each camera shows its own take time, and its file is finished in the
+  background so the other previews keep running. **Record All** adds any
+  cameras not yet recording to the run that is going, and **Stop All** stops
+  every camera. A camera restarted within the same second gets a `_take2` file
+  instead of overwriting the first, and cameras are listed in number order
+  (cam_2 before cam_10). The preview tiles now show each camera's frame rate
+  instead of "-- FPS".
+
 - **Pup retrieval scoring.** A **Pup Retrieval** protocol (picked in the
   Experiment form's **Protocol** dropdown, by the Run tab's built-in Pup
   Retrieval preset, or in Session Review's new **Protocol** selector, one value

src/glider/gui/multi_camera/camera_selection.py

@@ -0,0 +1,87 @@
+"""Which cameras in a rig are switched on.
+
+A rig is rarely "every camera the computer can see": a laptop's built-in
+webcam enumerates alongside the arena cameras, and a sixteen-camera rig running
+a four-animal session has twelve cameras spending USB bandwidth on empty
+arenas. A camera switched off here is not connected at all, so it is neither
+previewed nor recorded and its bandwidth goes to the cameras that matter.
+
+What is stored is the cameras switched *off*, so a camera plugged in later
+appears switched on, as every camera did before this existed. Persisted in
+``~/.glider/camera_selection.json`` for the same reason the names are: arena 3
+is arena 3 next week, and re-picking cameras every session is how one gets
+forgotten.
+"""
+
+from __future__ import annotations
+
+import json
+import logging
+from pathlib import Path
+
+logger = logging.getLogger(__name__)
+
+__all__ = ["CameraSelection"]
+
+SELECTION_FILENAME = "camera_selection.json"
+
+
+class CameraSelection:
+    """The cameras the operator has switched off, remembered between sessions."""
+
+    def __init__(self, path: Path | None = None):
+        self._path = Path(path) if path is not None else self._default_path()
+        self._disabled: set[str] = set()
+        self.load()
+
+    @staticmethod
+    def _default_path() -> Path:
+        from glider.core.config import get_config
+
+        return get_config().paths.user_config_dir / SELECTION_FILENAME
+
+    # ------------------------------------------------------------------
+
+    def load(self) -> None:
+        """Read the stored selection. A missing or unreadable file means every
+        camera is on - never an error, because the window has to open regardless."""
+        try:
+            data = json.loads(self._path.read_text(encoding="utf-8"))
+        except (OSError, ValueError):
+            self._disabled = set()
+            return
+        disabled = data.get("disabled") if isinstance(data, dict) else None
+        self._disabled = {str(c) for c in disabled} if isinstance(disabled, list) else set()
+
+    def save(self) -> bool:
+        """Write the selection. False if it could not be stored.
+
+        Best-effort, like the camera names: a read-only home directory must not
+        stop anyone recording. The cost is re-picking cameras next session.
+        """
+        try:
+            self._path.parent.mkdir(parents=True, exist_ok=True)
+            self._path.write_text(
+                json.dumps({"disabled": sorted(self._disabled)}, indent=2) + "\n",
+                encoding="utf-8",
+            )
+        except OSError as e:
+            logger.warning("could not save camera selection to %s: %s", self._path, e)
+            return False
+        return True
+
+    # ------------------------------------------------------------------
+
+    def is_enabled(self, camera_id: str) -> bool:
+        return camera_id not in self._disabled
+
+    def set_enabled(self, camera_id: str, enabled: bool) -> None:
+        """Switch a camera on or off, and store it."""
+        if enabled:
+            self._disabled.discard(camera_id)
+        else:
+            self._disabled.add(camera_id)
+        self.save()
+
+    def disabled(self) -> set[str]:
+        return set(self._disabled)