svc-vision: camera live view, moved from app-flutter's test tool

Camera-agnostic (--camera auto finds any V4L2 capture device and finds it again after a replug; non-MJPEG cameras are encoded), says when the camera is unavailable, paced per decision 28. Python, standard library only. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01DDwfd6Ki8UfG4hK6W5YpJz
2026-10-12 16:14:03 +09:00
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+---
+type: guidelines
+---
+# Vision guidelines
+
+## 1. Camera-agnostic
+- Any V4L2 capture device works. Never hard-code a node such as `/dev/video0`:
+  numbering follows enumeration order. Take a `/dev/v4l/by-id/` path, or find
+  the camera at runtime (`--camera auto`).  
+- Use what the camera offers. MJPEG passes through untouched; anything else is
+  encoded here. A requested size or rate the camera lacks falls back to its own
+  default rather than failing.  
+- UVC control names differ between cameras and kernels. Look them up on the
+  device; reply that a control is missing rather than guessing.
+
+## 2. One process owns the camera
+- V4L2 capture is single-reader. This service opens the device; recording and
+  inference take frames from it, never from the device.  
+- UVC controls reset when the camera re-enumerates. Set them on open, not once.
+
+## 3. The tablet link is the constraint
+- Every socket to a display is paced (`SO_MAX_PACING_RATE`, project-yukart
+  decision 28). Unpaced bursts stall the USB link for seconds.  
+- Latest frame wins. A slow client skips frames; it never gets a queue of old ones.  
+- Say when there is no camera. A client must be able to tell "unavailable" from
+  "slow".
+
+## 4. Python, on purpose
+- Python 3.10 (the Orin's), standard library only; GStreamer and v4l-utils come
+  from the host. The exception to Rust for Orin services is decision 29: camera
+  pipelines and inference live in the Python ecosystem.  
+- No pip installs on the car Orin until there is a reason; then a venv under
+  `~/infra/svc-vision/`, never the system Python.
+
+## 5. To be added