add ci.sh: run the flake-check.yml steps locally

CLAUDE.md

@@ -95,7 +95,8 @@ is the hardening knob). — full detail: `docs/src/security/threat-model.md`.
   checks (`bash -n`, the `host.sh` dry-run recipe, and — on a Nix+KVM box — `nix flake check` /
   `bash tests/boot.sh` / a `--shell` pass for TTY changes); if green, commit without stopping to ask
   per item. Surface anything only verifiable on a Nix+KVM box so it gets checked before being
-  claimed done.
+  claimed done. `./ci.sh` runs the exact `flake-check.yml` steps locally (it reads their `run:`
+  scripts straight from the workflow) — the fastest way to reproduce CI before a commit.
 - **Definition of done for a behaviour change:** `nix flake check` green **and** a stub-package boot
   test asserting the new behaviour under `tcg`/`q35` — plus a human `--shell` pass if it touches the
   TTY. Full loop + the fast stub-`claude` pattern: `docs/src/developing/build-test-debug.md`.

ci.sh

@@ -0,0 +1,43 @@
+#!/usr/bin/env bash
+# Local CI — runs the SAME checks as .github/workflows/flake-check.yml by pulling
+# each step's `run:` script straight from that workflow, so the command list lives
+# in exactly one place. Run before every commit.
+#
+# Safety: these `run:` scripts execute as your user with NO sandbox. If the workflow
+# differs from origin/main (an unreviewed/unexpected change), the commands are shown
+# and confirmation is required first — a silent edit to .github can't run behind your
+# back. (A compromised origin/main is out of scope: it auto-deploys the docs site to
+# GitHub Pages anyway.)
+#
+# `--inputs-from .` resolves every `nixpkgs#tool` against this flake's locked
+# nixpkgs, so the tools are hash-pinned to flake.lock (no unpinned registry fetch).
+set -euo pipefail
+cd "$(dirname "${BASH_SOURCE[0]}")"
+
+workflow=.github/workflows/flake-check.yml
+
+steps=$(nix run --inputs-from . nixpkgs#yq -- -r \
+  '.jobs.check.steps[] | select(.run) | "echo; echo \"» \(.name)\"\n\(.run)"' \
+  "$workflow")
+
+# Gate: if the workflow deviates from the trusted remote, show what runs and confirm.
+ref=origin/main
+if git rev-parse --verify --quiet "$ref" >/dev/null &&
+  ! git diff --quiet "$ref" -- "$workflow"; then
+  echo "⚠  $workflow differs from $ref — these commands will run as $(whoami):"
+  printf '%s\n' "----------------------------------------" "$steps" "----------------------------------------"
+  [ -t 0 ] || {
+    echo "refusing to auto-run a modified workflow non-interactively."
+    exit 1
+  }
+  read -rp "Proceed? [y/N] " reply
+  [ "$reply" = y ] || [ "$reply" = Y ] || {
+    echo "aborted."
+    exit 1
+  }
+fi
+
+bash -euo pipefail <<<"$steps"
+
+echo
+echo "✓ local CI passed"