ci: CI-resolve mempalace-toolkit to a pinned SHA

mempalace-toolkit is the only dependency cloned in Dockerfile.base (all
others live in the variant), so it bypassed the resolve-versions ->
build-arg plumbing and its ref stayed a literal `main`. Because the base
only rebuilds on a content hash, a toolkit-only fix would silently fail to
land unless Dockerfile.base itself changed.

Mirrors pi-devbox commit 4744f05, adapted to this repo:
- resolve-versions: new mempalace_toolkit_ref output via the gitea commits
  API (first gitea call in this repo's CI; works unauthenticated, no secret).
- base-decide: needs resolve-versions; fold the SHA into the base-tag hash
  so a moved toolkit forces a base rebuild (they no longer run in parallel).
- build-base: needs resolve-versions; pass --build-arg MEMPALACE_TOOLKIT_REF.
- Dockerfile.base: clone switched to SHA-capable git fetch + checkout
  FETCH_HEAD (git clone --branch <SHA> would fail).
- docs lockstep: .gitea/README.md Step 1 (no longer "in parallel"), AGENTS.md
  Critical conventions, CHANGELOG Unreleased.

base_tag now reflects a live gitea lookup; on API blip it falls back to
`main`, triggering one extra rebuild, never a missed one. No new tag —
lands on the next release or workflow_dispatch.

.gitea/workflows/docker-publish-split.yml

@@ -48,6 +48,7 @@ env:
 jobs:
   # ── Phase 1: decide whether base needs rebuilding ──────────────────
   base-decide:
+    needs: [resolve-versions]
     runs-on: ubuntu-latest
     container:
       image: catthehacker/ubuntu:act-latest
@@ -77,6 +78,10 @@ jobs:
                 ! -name '._*' \
                 -print0 2>/dev/null | sort -z | xargs -0 cat 2>/dev/null
               cat entrypoint.sh entrypoint-user.sh
+              # mempalace-toolkit is cloned in Dockerfile.base at a ref CI
+              # resolves to a SHA; fold it in so base_tag changes when the
+              # toolkit moves (otherwise a toolkit-only fix never lands).
+              echo "${{ needs.resolve-versions.outputs.mempalace_toolkit_ref }}"
             } | sha256sum | cut -c1-12
           )
           BASE_TAG="base-${HASH}"
@@ -121,6 +126,7 @@ jobs:
       image: catthehacker/ubuntu:act-latest
     outputs:
       omos_version: ${{ steps.resolve.outputs.omos_version }}
+      mempalace_toolkit_ref: ${{ steps.resolve.outputs.mempalace_toolkit_ref }}
     steps:
       - name: Resolve omos version from npm registry
         id: resolve
@@ -134,10 +140,24 @@ jobs:
           OMOS_VERSION=$(curl -sf "https://registry.npmjs.org/oh-my-opencode-slim/latest" | jq -r '.version')
           echo "omos_version=${OMOS_VERSION}" >> "$GITHUB_OUTPUT"
           echo "Resolved OMOS_VERSION=${OMOS_VERSION}"
+          # Resolve mempalace-toolkit main HEAD to a commit SHA. Unlike omos
+          # (an npm pkg baked into the VARIANT), mempalace-toolkit is cloned
+          # in Dockerfile.base, so this SHA is ALSO folded into the
+          # base-decide hash to force a base rebuild when the toolkit moves
+          # (without it, a toolkit-only fix silently fails to land unless
+          # Dockerfile.base itself changes). gitea allows unauthenticated
+          # public-repo commit listing; the token header is harmless if the
+          # env vars are unset (degrades to anon, still HTTP 200).
+          MEMPALACE_TOOLKIT_REF=$(curl -sf -H "Authorization: token ${GITEA_BUILD_TOKEN:-${GITHUB_TOKEN:-}}" \
+            "https://gitea.jordbo.se/api/v1/repos/joakimp/mempalace-toolkit/commits?limit=1&sha=main" \
+            | jq -r '.[0].sha // "main"' 2>/dev/null || echo "main")
+          [ -n "$MEMPALACE_TOOLKIT_REF" ] || MEMPALACE_TOOLKIT_REF=main
+          echo "mempalace_toolkit_ref=${MEMPALACE_TOOLKIT_REF}" >> "$GITHUB_OUTPUT"
+          echo "Resolved MEMPALACE_TOOLKIT_REF=${MEMPALACE_TOOLKIT_REF}"
 
   # ── Phase 2: build & push base (multi-arch), only when needed ──────
   build-base:
-    needs: [base-decide]
+    needs: [base-decide, resolve-versions]
     if: needs.base-decide.outputs.need_build == 'true'
     runs-on: ubuntu-latest
     container:
@@ -185,6 +205,7 @@ jobs:
         shell: bash
         env:
           BASE_TAG_FULL: ${{ env.IMAGE }}:${{ needs.base-decide.outputs.base_tag }}
+          MEMPALACE_TOOLKIT_REF: ${{ needs.resolve-versions.outputs.mempalace_toolkit_ref }}
         run: |
           set -euo pipefail
           # 3-attempt retry around `docker buildx build --push` for transient
@@ -205,6 +226,7 @@ jobs:
             if docker buildx build \
                 --platform linux/amd64,linux/arm64 \
                 --file Dockerfile.base \
+                --build-arg MEMPALACE_TOOLKIT_REF="${MEMPALACE_TOOLKIT_REF}" \
                 --push \
                 --tag "${BASE_TAG_FULL}" \
                 .; then