fix camera recovery blocking the dora event loop

Camera::open() retried forever inside a fixed sleep, so a camera that did not
come back left the node stuck there: it stopped reading dora events and no
longer honoured Stop or AllInputsClosed.

Recovery is now a state machine over ticks. open() makes one attempt and
returns; the loop decides when to try again from a 1/2/5/10 s backoff deadline,
and nothing sleeps, so events keep being read while the camera is down. The
first attempt closes the handle; past that the device is wedged and the node
escalates to sl::Camera::reboot(), guarded to the ZED 2 and newer since it does
nothing on the ZED and ZED Mini. Reopening pins the serial so recovery gets the
same physical camera back.

Set async_grab_camera_recovery so a link hiccup returns CAMERA_REBOOTING
immediately instead of blocking the grab for ~17 s, and enable_image_validity_
check so the SDK flags frames a stalled camera hands back looking valid. Those
transient errors no longer drop the handle, since the SDK is already
reconnecting it.

An all-black frame now counts as a failed grab rather than being published, and
a camera delivering nothing usable for 5 s (30 s while the SDK reports it is
reconnecting) triggers recovery. A new camera_state output publishes
opening/streaming/recovering so a downstream node can tell "no frame yet" from
"camera lost".

ZED_RETRY_INTERVAL_SECONDS is replaced by the backoff.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Y7g2cBJ5e3r15ZbJ9WZn8c

AGENTS.md

@@ -36,9 +36,9 @@ Camera behavior is configured entirely through environment variables (see README
 ## Architecture
 
 - **`src/util/env.h`** — Shared inline env-variable parsing helpers (`get_env_int`, `get_env_str`, `get_env_bool`, `get_env_float`).
-- **`src/zed/camera.h`** — `zed::Config`, `zed::Calibration`, and `zed::Camera` class. Camera wraps the ZED SDK lifecycle: open (with retry loop), warmup, grab (image + depth + point cloud), calibration, device timestamp, and close. Exposes `handle()` for engine access.
+- **`src/zed/camera.h`** — `zed::Config`, `zed::Calibration`, and `zed::Camera` class. Camera wraps the ZED SDK lifecycle: `open()` (one attempt, returns success), warmup, grab (image + depth + point cloud), calibration, device timestamp, blank-frame check, `close()` and `reset()` (close plus `sl::Camera::reboot()` where the model allows it). Exposes `handle()` for engine access.
 - **`src/zed/camera.cc`** — Implementation. SDK enum parsers live in an anonymous namespace. `parse_depth_mode` runs in `Config::from_env()`, not in the constructor, so an unrecognised `ZED_DEPTH_MODE` exits before the node joins the dataflow rather than falling back to a default.
-- **`src/main.cc`** — Dora event loop. Parses `ZED_PC_MODE` (`FULL`/`HALF`) once before the loop. On any input event (intended to be driven by a tick timer; the id is not inspected): calls `camera.grab()`, then sends `image_bgr` and `depth`, plus `point_cloud` when `ZED_POINT_CLOUD` is on and `camera_info` on the first frame of a camera session (`camera_info_pending`, re-armed on reconnection). `pack_depth` copies the depth map into a tightly packed `[H, W]` float buffer (sl::Mat rows can be padded) and clears `inf`/`nan` to `0`. `set_intrinsics` and `set_frame_stamps` stamp every output of a frame with the same intrinsics, `frame_id` and the two timestamps (`device_timestamp_ns`, `host_timestamp_ns`; both Unix-epoch nanoseconds). Point cloud output varies by mode: `FULL` sends the raw `sl::Mat` pointer (no copy); `HALF` downsamples by 2 in each dimension. Handles reconnection on grab failure.
+- **`src/main.cc`** — Dora event loop. Parses `ZED_PC_MODE` (`FULL`/`HALF`) once before the loop. On any input event (intended to be driven by a tick timer; the id is not inspected): calls `camera.grab()`, then sends `image_bgr` and `depth`, plus `point_cloud` when `ZED_POINT_CLOUD` is on and `camera_info` on the first frame of a camera session (`camera_info_pending`, re-armed on reconnection). `pack_depth` copies the depth map into a tightly packed `[H, W]` float buffer (sl::Mat rows can be padded) and clears `inf`/`nan` to `0`. `set_intrinsics` and `set_frame_stamps` stamp every output of a frame with the same intrinsics, `frame_id` and the two timestamps (`device_timestamp_ns`, `host_timestamp_ns`; both Unix-epoch nanoseconds). Point cloud output varies by mode: `FULL` sends the raw `sl::Mat` pointer (no copy); `HALF` downsamples by 2 in each dimension. Recovery is a state machine over ticks rather than a blocking retry: the camera is opened from inside the loop, `begin_recovery` closes (first attempt) or resets (later ones) and sets a backoff deadline, and `camera_state` is published on each transition. Nothing sleeps, so `Stop` is honoured while the camera is down.
 - **`DoraTargets.cmake`** — Handles building or fetching dora-rs and generating the CXX bridge files. Two paths: local (`DORA_ROOT_DIR`) or git clone. Produces `dora_node_api_cxx` library and the `node_bridge.cc` glue.
 - **`scripts/build.sh`** — Configure/compile/install in one shell-free-callable step. Referenced by `dataflow.yml`, the `Dockerfile` and the README.
 - **`dataflow.yml`** — Example dora dataflow definition using the `git:` source format, pinned with `tag:` — dora 1.0 pins a source with the mutually exclusive `tag:`, `rev:` or `branch:`.