ci(promote-latest): workflow_dispatch to retag :staging-<sha> → :latest

Escape hatch for the initial rollout window (canary fleet not yet
provisioned, so canary-verify.yml's automatic promotion doesn't fire)
AND for manual rollback scenarios.

Uses the default GITHUB_TOKEN which carries write:packages on repo-
owned GHCR images, so no new secrets are needed. crane handles the
remote retag without pulling or pushing layers.

Validates the src tag exists before retagging + verifies the :latest
digest post-retag so a typo can't silently promote the wrong image.

Trigger from Actions → promote-latest → Run workflow → enter the
short sha (e.g. "4c1d56e").

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

.github/workflows/promote-latest.yml

@@ -0,0 +1,88 @@
+name: promote-latest
+
+# Manually retag ghcr.io/molecule-ai/platform:staging-<sha> →  :latest
+# (and the same for the tenant image). Use this to:
+#
+#   1. Promote a :staging-<sha> to prod before the canary fleet is live
+#      (one-off during the initial rollout).
+#   2. Roll back :latest to a prior known-good digest after a bad
+#      promotion slipped past canary (use scripts/rollback-latest.sh
+#      for a local / emergency path; this workflow is for scheduled
+#      or from-browser promotions).
+#
+# Running this workflow needs no extra secrets — GitHub's default
+# GITHUB_TOKEN has write:packages for repo-owned GHCR images, which
+# is all we need for a remote retag via `crane tag`.
+
+on:
+  workflow_dispatch:
+    inputs:
+      sha:
+        description: 'Short sha to promote (e.g. 4c1d56e). Must match an existing :staging-<sha> tag.'
+        required: true
+        type: string
+
+permissions:
+  contents: read
+  packages: write
+
+env:
+  IMAGE_NAME: ghcr.io/molecule-ai/platform
+  TENANT_IMAGE_NAME: ghcr.io/molecule-ai/platform-tenant
+
+jobs:
+  promote:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Install crane
+        run: |
+          curl -fsSL https://github.com/google/go-containerregistry/releases/download/v0.20.2/go-containerregistry_Linux_x86_64.tar.gz \
+            | tar xz -C /usr/local/bin crane
+
+      - name: GHCR login
+        run: |
+          echo "${{ secrets.GITHUB_TOKEN }}" \
+            | crane auth login ghcr.io -u "${{ github.actor }}" --password-stdin
+
+      - name: Retag platform image
+        run: |
+          set -eu
+          SRC="${IMAGE_NAME}:staging-${{ inputs.sha }}"
+          if ! crane digest "$SRC" >/dev/null 2>&1; then
+            echo "::error::$SRC not found in registry — double-check the sha."
+            exit 1
+          fi
+          EXPECTED=$(crane digest "$SRC")
+          crane tag "$SRC" latest
+          ACTUAL=$(crane digest "${IMAGE_NAME}:latest")
+          if [ "$ACTUAL" != "$EXPECTED" ]; then
+            echo "::error::retag digest mismatch (expected $EXPECTED, got $ACTUAL)"
+            exit 1
+          fi
+          echo "OK  ${IMAGE_NAME}:latest → $ACTUAL"
+
+      - name: Retag tenant image
+        run: |
+          set -eu
+          SRC="${TENANT_IMAGE_NAME}:staging-${{ inputs.sha }}"
+          if ! crane digest "$SRC" >/dev/null 2>&1; then
+            echo "::error::$SRC not found — tenant image may not have built for this sha."
+            exit 1
+          fi
+          EXPECTED=$(crane digest "$SRC")
+          crane tag "$SRC" latest
+          ACTUAL=$(crane digest "${TENANT_IMAGE_NAME}:latest")
+          if [ "$ACTUAL" != "$EXPECTED" ]; then
+            echo "::error::tenant retag digest mismatch"
+            exit 1
+          fi
+          echo "OK  ${TENANT_IMAGE_NAME}:latest → $ACTUAL"
+
+      - name: Summary
+        run: |
+          {
+            echo "## :latest promoted to staging-${{ inputs.sha }}"
+            echo
+            echo "Both platform + tenant images retagged. Prod tenants"
+            echo "will auto-pull within their 5-min update cycle."
+          } >> "$GITHUB_STEP_SUMMARY"