RFC: optional onboard camera for the S3 CSI node (XIAO ESP32S3 Sense)

Feature proposal — marked RFC because it adds a new hardware capability rather than fixing a defect. Happy to adjust scope/naming to taste.

Motivation

The Seeed XIAO ESP32S3 Sense is an S3 CSI node with a free OV3660 camera on board. Having the same node serve ground-truth snapshots/video alongside its CSI stream is directly useful for labeling and sanity-checking pose/presence work (e.g. ADR-150-style training captures) without adding a second device to the rig.

What this adds

• main/camera_node.c / camera_node.h (~190 lines): OV3660 init with the hardware-verified XIAO ESP32S3 Sense pin map (sensor PID 0x3660), plus an HTTP server with
  • GET /snap — single fresh JPEG (one stale framebuffer discarded first)
  • GET /stream — multipart MJPEG at ~5 fps
• Kconfig menu: CONFIG_CAMERA_ENABLE (default n, depends on IDF_TARGET_ESP32S3) and CONFIG_CAMERA_HTTP_PORT (default 8081 — the OTA/WASM server owns 8032; httpd ctrl_port offset to 32769 since the OTA instance owns 32768)
• idf_component.yml: espressif/esp32-camera ^2.0.0 with rules: if target == esp32s3, so non-S3 builds never fetch it
• sdkconfig.defaults.s3cam build overlay: octal PSRAM (required for framebuffers), display/WASM trimmed (those pins collide with the camera on the XIAO)
• main.c: starts the camera after WiFi is up; init failure is non-fatal by design — logs a warning and CSI streaming continues unaffected

CSI-coexistence design notes

• QVGA JPEG, fb_count=2, CAMERA_GRAB_LATEST, quality 12 in PSRAM is the proven-reliable config from a probe firmware (SVGA with fb_count=1 overflowed: FB-OVF); bounded per-frame airtime keeps the CSI promiscuous callback from being starved
• httpd tasks pinned to core 1, away from WiFi/CSI work on core 0
• Zero impact when disabled: camera_node.c is only compiled under CONFIG_CAMERA_ENABLE, and the default for every existing target/overlay is off — the C6 and stock S3 builds are byte-identical to main

Hardware/test evidence

• Built clean on ESP-IDF v5.5.2, target esp32s3, using the documented two-step idf.py -B build-s3cam overlay invocation (no host-side Rust changes in this PR)
• Flashed and exercised on a XIAO ESP32S3 Sense: camera comes up with PID 0x3660, /snap returns fresh JPEGs and /stream sustains ~5 fps while the node keeps streaming CSI
• Companion context: this node fed the live HE20 capture/training work referenced in ADR-151 calibrate cannot ingest real ESP32-C6 HE20 CSI: n_subcarriers parsed as u8 (overflows at 256) + he20 tier expects 242 but wire delivers 256 bins #1009 / wifi-densepose-train tch-backend: does not compile against workspace-pinned tch 0.24; clamp(1.0, f64::MAX) runtime panic on PyTorch ≥2.x; no real-validation path (checkpoint selection blind on real data) #1010

🤖 Generated with claude-flow