chore: add auto-import of GPG public key in devcontainer setup

.devcontainer/README.md

@@ -88,6 +88,32 @@ git commit -S -m "your message"   # -S optional if commit.gpgsign is true
 git push
 ```
 
+### Easiest rebuild-safe import flow
+
+This devcontainer auto-imports a public key from `.git/signing.pub` on start.
+If present, it runs `gpg --import .git/signing.pub` and removes the file after a
+successful import.
+
+So the easiest setup is:
+
+```bash
+# on the HOST, from repo root (auto-uses git user.signingkey)
+./.devcontainer/export-signing-key.sh
+
+# or pass a key explicitly
+./.devcontainer/export-signing-key.sh <YOUR_KEY_ID>
+```
+
+The helper auto-selects `gpg2`/`gpg` based on where your key is visible, which
+avoids host setups where the two binaries use different keyrings.
+
+After **Rebuild Container** (or next container start), verify in the container:
+
+```bash
+gpg --list-secret-keys --keyid-format=long
+git commit -S -m "test signed commit"
+```
+
 ### Manually importing your public key
 
 If `git commit -S` fails with `gpg: signing failed: No secret key`, the forwarded

.devcontainer/devcontainer.json

@@ -55,5 +55,7 @@
 
   "postCreateCommand": "pnpm install --frozen-lockfile",
 
+  "postStartCommand": "if [ -f .git/signing.pub ]; then gpg --import .git/signing.pub && rm .git/signing.pub; fi",
+
   "runArgs": ["--cap-drop=ALL", "--security-opt=no-new-privileges:true", "--pids-limit=512"]
 }

.devcontainer/export-signing-key.sh

@@ -0,0 +1,81 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+# Export your GPG public key to .git/signing.pub so the devcontainer can auto-import it.
+# Usage:
+#   ./.devcontainer/export-signing-key.sh
+#   ./.devcontainer/export-signing-key.sh <KEY_ID>
+
+SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+REPO_ROOT="$(cd "${SCRIPT_DIR}/.." && pwd)"
+OUTPUT_FILE="${REPO_ROOT}/.git/signing.pub"
+
+KEY_ID="${1:-$(git config --global user.signingkey || true)}"
+if [[ -z "${KEY_ID}" ]]; then
+  echo "No key ID provided and git user.signingkey is not set."
+  echo "Set it with: git config --global user.signingkey <YOUR_KEY_ID>"
+  echo "Or run: ./.devcontainer/export-signing-key.sh <YOUR_KEY_ID>"
+  exit 1
+fi
+
+available_bins=()
+for candidate in gpg2 gpg; do
+  if command -v "${candidate}" >/dev/null 2>&1; then
+    available_bins+=("${candidate}")
+  fi
+done
+
+if [[ ${#available_bins[@]} -eq 0 ]]; then
+  echo "Neither gpg nor gpg2 is available on PATH."
+  exit 1
+fi
+
+has_secret_key() {
+  local bin="$1"
+  "${bin}" --list-secret-keys --with-colons "${KEY_ID}" 2>/dev/null | grep -q '^sec'
+}
+
+try_export() {
+  local bin="$1"
+  "${bin}" --armor --export "${KEY_ID}" > "${OUTPUT_FILE}"
+  [[ -s "${OUTPUT_FILE}" ]]
+}
+
+selected_bin=""
+for bin in "${available_bins[@]}"; do
+  if has_secret_key "${bin}"; then
+    selected_bin="${bin}"
+    break
+  fi
+done
+
+if [[ -z "${selected_bin}" ]]; then
+  selected_bin="${available_bins[0]}"
+fi
+
+rm -f "${OUTPUT_FILE}"
+if ! try_export "${selected_bin}"; then
+  for bin in "${available_bins[@]}"; do
+    if [[ "${bin}" == "${selected_bin}" ]]; then
+      continue
+    fi
+    if try_export "${bin}"; then
+      selected_bin="${bin}"
+      break
+    fi
+  done
+fi
+
+if [[ ! -s "${OUTPUT_FILE}" ]]; then
+  rm -f "${OUTPUT_FILE}"
+  echo "Failed to export public key for ${KEY_ID}."
+  echo "Tried binaries: ${available_bins[*]}"
+  echo "Check key visibility with:"
+  echo "  gpg --list-secret-keys --keyid-format=long"
+  echo "  gpg2 --list-secret-keys --keyid-format=long"
+  exit 1
+fi
+
+echo "Exported public key ${KEY_ID} to ${OUTPUT_FILE}"
+echo "Using: ${selected_bin}"
+echo "Rebuild/start the devcontainer to auto-import it."