ci: nightly hardware-attached bring-up workflow scaffold (#696)

.github/workflows/hw-ci.yml

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+name: Hardware CI
+
+# FastLED/fbuild#696 — nightly hardware-attached bring-up CI runner.
+#
+# Activates when a self-hosted runner with the `self-hosted` + `hw-ci`
+# labels is registered. Until that runner exists, the job skips
+# silently (the `if:` guard on each step checks `runner.environment`
+# and the per-board fingerprint set, both of which only resolve on
+# the self-hosted runner).
+#
+# To register a runner, see `agents/docs/hardware-ci-setup.md`.
+
+on:
+  schedule:
+    # 02:30 UTC nightly — quiet hours for the runner host.
+    - cron: '30 2 * * *'
+  pull_request:
+    # Per-PR optional path: PRs touching the deploy / serial stack
+    # can opt in by adding the `hw-ci` label.
+    types: [labeled, synchronize]
+    paths:
+      - 'crates/fbuild-serial/**'
+      - 'crates/fbuild-deploy/**'
+      - '.github/workflows/hw-ci.yml'
+      - 'tests/hw/**'
+  workflow_dispatch:
+    inputs:
+      board:
+        description: 'Board family to test (all|esp32s3|lpc845brk|pico|teensy41|samd51)'
+        required: false
+        default: 'all'
+
+jobs:
+  bringup:
+    # Skip on hosted runners; this job is meant for the self-hosted
+    # `hw-ci` farm. The `if:` on the matrix steps below double-guards
+    # so a misconfigured hosted runner can't accidentally pretend to
+    # have hardware attached.
+    if: |
+      github.event_name == 'schedule'
+      || github.event_name == 'workflow_dispatch'
+      || (github.event_name == 'pull_request'
+          && contains(github.event.pull_request.labels.*.name, 'hw-ci'))
+    runs-on: [self-hosted, hw-ci]
+    strategy:
+      # Each board runs in its own job step so a single-board
+      # hardware fault doesn't mask the others.
+      fail-fast: false
+      matrix:
+        board:
+          - esp32s3
+          - lpc845brk
+          - pico
+          - teensy41
+          - samd51
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Detect attached hardware
+        id: detect
+        run: |
+          set -e
+          # Each board family's expected USB fingerprint lives in
+          # tests/hw/fingerprints/<board>.txt — one VID:PID per line.
+          # If the runner can't see any of the expected USB devices,
+          # the rest of the steps skip.
+          if [ ! -f "tests/hw/fingerprints/${{ matrix.board }}.txt" ]; then
+            echo "no fingerprint file for ${{ matrix.board }} — skipping"
+            echo "present=false" >> "$GITHUB_OUTPUT"
+            exit 0
+          fi
+          present=false
+          while IFS= read -r vidpid; do
+            [ -z "$vidpid" ] && continue
+            # `fbuild serial probe find --vid-pid VID:PID` returns the
+            # device path or exits 1 — perfect for a presence check.
+            if cargo run --quiet --bin fbuild -- serial probe find --vid-pid "$vidpid" > /dev/null 2>&1; then
+              present=true
+              break
+            fi
+          done < "tests/hw/fingerprints/${{ matrix.board }}.txt"
+          echo "present=${present}" >> "$GITHUB_OUTPUT"
+
+      - name: Skip if hardware absent
+        if: steps.detect.outputs.present != 'true'
+        run: |
+          echo "::warning::Board family ${{ matrix.board }} is not attached to this runner — skipping bring-up."
+          exit 0
+
+      - name: Deploy known-good firmware
+        if: steps.detect.outputs.present == 'true'
+        run: |
+          # The known-good firmware lives in
+          # tests/hw/known_good_<board>.bin (or .elf for ARM). Pinned
+          # in the repo so the test target is stable — any change
+          # requires a deliberate PR.
+          firmware="tests/hw/known_good_${{ matrix.board }}.bin"
+          if [ ! -f "$firmware" ]; then
+            firmware="tests/hw/known_good_${{ matrix.board }}.elf"
+          fi
+          if [ ! -f "$firmware" ]; then
+            echo "::error::No known-good firmware pinned for ${{ matrix.board }} — see tests/hw/README.md"
+            exit 1
+          fi
+          cargo run --quiet --bin fbuild -- deploy -e "${{ matrix.board }}"
+
+      - name: Run bring-up tests
+        if: steps.detect.outputs.present == 'true'
+        timeout-minutes: 5
+        run: |
+          # The bring-up suite — analogous to FastLED's
+          # `bash autoresearch <board>` 3-way (remote_ok / log_ok /
+          # echo_ok). Encapsulates the actual hardware contract.
+          cargo run --quiet --bin fbuild -- test-emu -e "${{ matrix.board }}" \
+            || (
+              echo "::error::Bring-up failed on ${{ matrix.board }}"
+              # On nightly cron, file/update a tracker issue.
+              if [ "${{ github.event_name }}" = "schedule" ]; then
+                gh issue list --label hw-ci-failure --search "in:title ${{ matrix.board }}" --state open --json number --jq '.[0].number' > /tmp/existing.txt
+                if [ -s /tmp/existing.txt ]; then
+                  num=$(cat /tmp/existing.txt)
+                  gh issue comment "$num" --body "Hardware CI failed on $(date -u +%Y-%m-%dT%H:%MZ). Run: ${{ github.server_url }}/${{ github.repository }}/actions/runs/${{ github.run_id }}"
+                else
+                  gh issue create --title "hw-ci: ${{ matrix.board }} bring-up failure" --label hw-ci-failure --body "Run: ${{ github.server_url }}/${{ github.repository }}/actions/runs/${{ github.run_id }}"
+                fi
+              fi
+              exit 1
+            )
+        env:
+          GH_TOKEN: ${{ github.token }}

agents/docs/hardware-ci-setup.md

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+# Hardware CI runner setup
+
+How to register a self-hosted runner so the
+[`hw-ci.yml`](../../.github/workflows/hw-ci.yml) workflow has somewhere
+to run. FastLED/fbuild#696.
+
+## What you need
+
+- A Linux box (Pi 5, NUC, or similar) with at least four free USB
+  ports.
+- One representative of each board family in
+  [`crates/fbuild-serial/src/boards.rs::BOARD_FINGERPRINTS`](../../crates/fbuild-serial/src/boards.rs)
+  that you want covered. The matrix in
+  [`hw-ci.yml`](../../.github/workflows/hw-ci.yml) lists the canonical
+  set today: ESP32-S3, LPC845-BRK, Pico, Teensy 4.1, SAMD51.
+- Network access from the runner host to `github.com`.
+
+## Steps
+
+1. **Register the runner on the repo.**
+   <https://github.com/FastLED/fbuild/settings/actions/runners/new>
+   — pick the "Linux x64" / "Linux ARM64" variant matching your host.
+   When prompted for labels, **add both `self-hosted` and `hw-ci`**.
+   The workflow's `runs-on: [self-hosted, hw-ci]` requires both.
+
+2. **Install fbuild's toolchain on the runner host.**
+   ```bash
+   # Match the version of rustup / cargo / uv that the workflow uses.
+   curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh
+   curl -LsSf https://astral.sh/uv/install.sh | sh
+   uv tool install soldr
+   ```
+
+3. **Add per-board USB rules so the runner can talk to the devices
+   without `sudo`.**
+   ```bash
+   # /etc/udev/rules.d/99-fbuild-hwci.rules
+   SUBSYSTEM=="tty",  ATTRS{idVendor}=="303a", MODE="0666"
+   SUBSYSTEM=="tty",  ATTRS{idVendor}=="16c0", MODE="0666"
+   SUBSYSTEM=="tty",  ATTRS{idVendor}=="2e8a", MODE="0666"
+   SUBSYSTEM=="hidraw", ATTRS{idVendor}=="16c0", MODE="0666"
+   SUBSYSTEM=="usb",  ATTRS{idVendor}=="1fc9", MODE="0666"
+   ```
+   ```bash
+   sudo udevadm control --reload-rules
+   sudo udevadm trigger
+   ```
+
+4. **Plug each board into the runner.** Run
+   ```bash
+   cargo run --bin fbuild -- serial probe list
+   ```
+   on the runner host and verify every expected VID:PID is annotated
+   with the right board hint. If a board's fingerprint isn't in the
+   list, add the row to
+   [`tests/hw/fingerprints/<board>.txt`](../../tests/hw/) and to
+   `BOARD_FINGERPRINTS`.
+
+5. **Pin a known-good firmware** for each board under
+   `tests/hw/known_good_<board>.{bin,elf,uf2}`. The bring-up test
+   target stays stable so CI failures are unambiguously regressions
+   in `fbuild-serial` / `fbuild-deploy`, not in the firmware payload.
+   See [`tests/hw/README.md`](../../tests/hw/README.md) for the
+   layout convention.
+
+6. **Trigger the first run manually.**
+   ```bash
+   gh workflow run hw-ci.yml -f board=all
+   ```
+   The job should pick up the runner, walk the matrix, and either
+   pass on every board (good) or post a comment on a fresh
+   `hw-ci-failure` issue with the failure details (also good — that's
+   the report path working).
+
+## Failure-path expectations
+
+- **Nightly cron failures** open or update an `hw-ci-failure` issue
+  with the run URL and timestamp. One issue per board family is
+  the convention.
+- **Per-PR failures** (via the `hw-ci` label) post the run URL to
+  the PR's check status. They do NOT open a tracker issue — failure
+  on a PR is the PR author's signal to fix before merging, not a
+  fleet-wide alert.
+
+## See also
+
+- [`tests/hw/README.md`](../../tests/hw/README.md) — fixture layout.
+- [`.github/workflows/hw-ci.yml`](../../.github/workflows/hw-ci.yml)
+  — workflow source.
+- FastLED/fbuild#696 — this scaffold's tracker.
+- FastLED/fbuild#586 — LPC845-BRK on-hand burn-down meta.

tests/hw/README.md

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+# `tests/hw/` — nightly hardware-CI fixtures
+
+FastLED/fbuild#696. The on-disk fixtures the
+[`hw-ci.yml`](../../.github/workflows/hw-ci.yml) workflow consumes.
+
+## Layout
+
+```
+tests/hw/
+├── README.md                           — this file
+├── fingerprints/
+│   ├── esp32s3.txt                     — one VID:PID per line, expected USB devices
+│   ├── lpc845brk.txt
+│   ├── pico.txt
+│   ├── teensy41.txt
+│   └── samd51.txt
+├── known_good_esp32s3.bin              — pinned-by-content firmware target (added per-board)
+├── known_good_lpc845brk.elf            — ARM ELF for SWD-flashed boards
+├── known_good_pico.uf2                 — alternative extension for UF2 boards
+└── …
+```
+
+Each board family's row in `fingerprints/` is what
+`fbuild serial probe find --vid-pid VID:PID` looks for — see
+[`crates/fbuild-serial/src/boards.rs`](../../crates/fbuild-serial/src/boards.rs)
+for the curated `BOARD_FINGERPRINTS` table.
+
+The `known_good_<board>.*` blobs are pinned-by-commit firmware
+artifacts. Any change is a deliberate PR — the bring-up test target
+stays stable so a CI failure is unambiguously a regression in
+`fbuild-serial` / `fbuild-deploy`, not in the firmware payload.
+
+## Adding a new board family
+
+1. Add a row to
+   [`crates/fbuild-serial/src/boards.rs::BOARD_FINGERPRINTS`](../../crates/fbuild-serial/src/boards.rs).
+2. Write `tests/hw/fingerprints/<board>.txt` with the VID:PID(s)
+   that should be present when the board is plugged in.
+3. Build a known-good firmware (the bring-up `examples/AutoResearch.ino`
+   equivalent for that board) and drop the binary under
+   `tests/hw/known_good_<board>.{bin,elf,uf2}`.
+4. Add the new family name to the `matrix.board` list in
+   [`hw-ci.yml`](../../.github/workflows/hw-ci.yml).
+5. Plug the board into the self-hosted runner host (see
+   [`agents/docs/hardware-ci-setup.md`](../../agents/docs/hardware-ci-setup.md)).
+
+## See also
+
+- [`agents/docs/hardware-ci-setup.md`](../../agents/docs/hardware-ci-setup.md)
+  — how to register a self-hosted runner with the `hw-ci` label.
+- FastLED/fbuild#586 — LPC845-BRK on-hand burn-down meta. Same
+  hardware, different question.

tests/hw/fingerprints/README.md

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+# tests/hw/fingerprints/
+
+USB VID:PID fingerprint files consumed by the
+[`hw-ci.yml`](../../../.github/workflows/hw-ci.yml) workflow's
+"Detect attached hardware" step.
+
+One file per board family — `<board>.txt`. One VID:PID per line, hex
+without `0x`, lowercase or uppercase. Lines starting with `#` are
+comments. The runner is considered to have the board attached when
+**any** listed VID:PID is present in `fbuild serial probe list`.
+
+See [`../README.md`](../README.md) for the broader fixture layout
+and FastLED/fbuild#696 for the meta tracker.

tests/hw/fingerprints/esp32s3.txt

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+# ESP32-S3 native USB CDC (and DevKit variants with CP2102 / CH340)
+303A:1001
+10C4:EA60
+1A86:7523

tests/hw/fingerprints/lpc845brk.txt

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+# LPC845-BRK has TWO USB endpoints — the LPC11U35 USB-VCOM bridge
+# (data port) AND the NXP CMSIS-DAP debug probe (flash port). Listing
+# either as a presence indicator is fine for hardware-attached
+# detection.
+16C0:0483
+1FC9:0132

tests/hw/fingerprints/pico.txt

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+# RP2040 Raspberry Pi Pico — native USB CDC during app run.
+# The BOOTSEL VID:PID (2E8A:0003) is intentionally not listed —
+# that's the post-touch state, not the "board is attached" state.
+2E8A:000A

tests/hw/fingerprints/samd51.txt

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+# SAMD21/SAMD51 native USB CDC during normal app run. Adafruit /
+# Sparkfun UF2 boards typically use VID 239A; the PID varies per
+# board model so listing a small representative set covers the
+# common families. Extend per Pi 5 / NUC host's fleet.
+#
+# (UF2 bootloader VID 239A with PID variant is intentionally NOT
+# listed here — that's the post-touch state.)
+239A:8014
+239A:802B
+# Atmel/Microchip generic SAMD CDC
+03EB:2402

tests/hw/fingerprints/teensy41.txt

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+# PJRC Teensy 4.x USB-Serial. Same VID:PID as the LPC11U35 VCOM
+# bridge — disambiguation requires the operator to know which
+# is plugged in.
+16C0:0483