The Orin camera works: it was a missing overlay, not dead hardware

An IMX219 is live on the Orin's CAM0 at /dev/video0, verified by capture rather
than by a bound driver: a 16,163,840-byte frame, exactly 3280x2464x2 for
10-bit Bayer, 99.8% non-zero across 40 distinct values. Real sensor data, not
an allocated buffer.

⚠ The fault was configuration, and it is indistinguishable from dead hardware.
The Pi auto-detects cameras; the Jetson does not. Until the sensor's device-tree
overlay is selected there is no /dev/video0, no sensor line in dmesg and nothing
on i2c — the same evidence a broken cable produces, which is how it got blamed
on a cable here. Fixed with config-by-hardware.py, and the README now says to
check the OVERLAYS line BEFORE suspecting hardware.

Two traps recorded with it: the -n flag needs the header number (2= for the CSI
connector) or it defaults to the 40-pin header and reports the module as
unsupported, and v4l-utils is not installed by default so v4l2-ctl reports
"command not found", which reads as "no camera".

The Pi 5 fault was genuinely a cable and is kept for contrast, along with why
its lit IR LEDs proved nothing: the illuminator sits on the 3.3V rail
independently of the i2c and CSI lanes, so it lights whenever the ribbon carries
power, even when the traces detection needs are broken.

AGENTS.md also gains the rules that came out of a 27-attempt loop in this repo:
write files with apply_patch and never write_stdin, never invent or increment a
session id, stop after two identical failures instead of retrying, and emit tool
calls as JSON arguments rather than leaking <parameter=...> markup into strings.

AGENTS.md

@@ -25,23 +25,47 @@ above capture — streaming, UI, recognition — depends only on "a source of fr
 TensorRT on GPU/DLA; on the Pi it is CPU-only and will not hold a live stream. Never present a Pi
 timing as evidence the target is fast enough, and say which board a measurement came from.
 
-## No camera is connected yet
+## Camera state
 
-No working camera has been attached to either board. The first module was not detected on the Pi 5 at
-all — traced to a cable fault, with the module possibly damaged too. See README.md for the evidence
-and the check commands.
+**Orin Nano: working.** IMX219 on CAM0 at `/dev/video0`, format `RG10` (10-bit Bayer), full frame
+captured and verified as real data. This is the board to develop capture against.
 
-⚠ **You cannot fix camera detection from software.** Do not add `dtoverlay=` lines, edit
-`/boot/firmware/config.txt`, or install packages to make a sensor appear. On the Pi,
-`camera_auto_detect=1` is already correct; a silent `dmesg` and a missing i2c bus mean the sensor is
-not being reached electrically. Report the state and stop.
+**Pi 5: dead.** Not detected; a cable fault, with the module possibly damaged. Nothing to do there
+until the hardware is replaced.
 
-⚠ **`/dev/video*` is not evidence of a camera** — those nodes exist on both boards with nothing
+⚠ **The two boards failed for completely different reasons, and the fixes do not transfer.** The
+Orin was a missing device-tree overlay — a configuration fault that looks exactly like dead hardware.
+The Pi was genuinely a broken cable. See README.md.
+
+⚠ **On the Pi, you cannot fix camera detection from software.** Do not add `dtoverlay=` lines or edit
+`/boot/firmware/config.txt`; `camera_auto_detect=1` is already correct there. On the Orin the overlay
+*is* the mechanism, but it is already configured — do not change it without being asked.
+
+⚠ **`/dev/video*` is not evidence of a camera.** Those nodes exist on both boards with nothing
 attached.
 
-Work that does not need live capture is still available: the capture interface and a synthetic or
-still-image backend, the streaming plumbing, the web UI, project structure, tests. **Say plainly when
-you are working against a placeholder** rather than a real frame.
+If you are ever on a board with no working camera, work that does not need live capture is still
+available: the capture interface and a synthetic backend, streaming plumbing, the web UI, tests.
+**Say plainly when you are working against a placeholder** rather than a real frame.
+
+## ⚠ Writing files, and not looping
+
+**Write files with `apply_patch`**, or a heredoc through the shell. **Never** use `write_stdin` to
+create file contents — it writes to the stdin of an already-running process, which is a different
+thing and will not create anything. `write_stdin` takes a session id that an actual `exec_command`
+returned to you; never invent one and never increment one.
+
+**If the same tool call fails twice with the same error, STOP and report it.** Do not retry, and do
+not vary an identifier hoping one works. A repeated identical failure means the assumption is wrong,
+not that the call needs another attempt.
+
+This happened here, in this repo. A session got as far as creating `src/camera_webui/capture/`, then
+tried to write `base.py` via `write_stdin`, was told `Unknown process id 45`, and answered by
+incrementing the id — 46, 47, 48 — for **27 attempts over nine minutes** until a human killed it.
+
+⚠ **Emit tool calls as the API's JSON arguments only.** If you find yourself writing markup like
+`<parameter=...>` inside a string argument, you are mixing in a different tool-calling format and the
+call will not do what you mean. That is what the loop above degenerated into.
 
 ## Constraints