diff --git a/tools/split-s00.sh b/tools/split-s00.sh
new file mode 100644
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--- /dev/null
+++ b/tools/split-s00.sh
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+#!/usr/bin/env bash
+#
+# split-s00.sh — one-off: split issue S-00 (#1) into sub-slices S-00-a..e per
+# CLAUDE.md §13. Creates the five sub-slice issues, then closes #1 with a
+# comment listing the replacements.
+#
+# Idempotent: sub-slices already present (matched by title) are skipped; the
+# closing comment is posted once (guarded by a marker); #1 is closed only if open.
+#
+# Usage:
+#   GITEA_TOKEN=<pat> bash tools/split-s00.sh
+#
+# Token scopes: write:issue.
+#
+set -euo pipefail
+
+: "${GITEA_TOKEN:?Set GITEA_TOKEN to a Gitea personal access token (scope: write:issue)}"
+
+BASE="https://git.labs.respellion.tech/api/v1"
+OWNER="eho"
+REPO="register-referentie"
+REPO_API="$BASE/repos/$OWNER/$REPO"
+PARENT=1                        # S-00 issue number
+MARKER="<!-- split-s00 -->"
+
+AUTH=(-H "Authorization: token $GITEA_TOKEN")
+JSON=(-H "Content-Type: application/json" -H "Accept: application/json")
+say() { printf '%s\n' "$*"; }
+
+code=$(curl -s -o /dev/null -w '%{http_code}' "${AUTH[@]}" "$REPO_API")
+[ "$code" = "200" ] || { say "ERROR: cannot access $OWNER/$REPO (HTTP $code)."; exit 1; }
+say "Authenticated against $REPO_API"
+
+labels_json=$(curl -s "${AUTH[@]}" "$REPO_API/labels?limit=100")
+milestones_json=$(curl -s "${AUTH[@]}" "$REPO_API/milestones?state=all&limit=100")
+existing_issues=$(curl -s "${AUTH[@]}" "$REPO_API/issues?state=all&type=issues&limit=100")
+
+MILESTONE="Iteration 0 — Foundations"
+
+DOD=$(cat <<'EOF'
+
+## Definition of Done
+
+- [ ] A linked Gitea issue exists (this one).
+- [ ] Failing test written and committed first.
+- [ ] Implementation makes the test pass.
+- [ ] Refactor commit follows if structure improved.
+- [ ] Conventional Commit messages referencing this issue (`refs #NN`).
+- [ ] All Gitea Actions CI jobs green.
+- [ ] `docker compose up` from a fresh clone reaches green health checks within 3 minutes.
+- [ ] Docs touched if behaviour, contracts, or operations changed.
+- [ ] ADR added in `docs/architecture/` if a non-obvious decision was made.
+- [ ] This issue closed by the merging PR (`closes #NN`).
+EOF
+)
+
+create_issue() {
+  local title="$1" labels_csv="$2" body="$3"
+  if echo "$existing_issues" | jq -e --arg t "$title" 'any(.[]; .title == $t)' >/dev/null; then
+    say "  skip   $title"
+    return
+  fi
+  local ms_id; ms_id=$(echo "$milestones_json" | jq -r --arg m "$MILESTONE" '.[] | select(.title == $m) | .id')
+  local want label_ids
+  want=$(printf '%s' "$labels_csv" | jq -R 'split(",")')
+  label_ids=$(echo "$labels_json" | jq -c --argjson want "$want" '[ .[] | select(.name as $n | $want | index($n)) | .id ]')
+  local payload
+  payload=$(jq -n --arg t "$title" --arg b "${body}${DOD}" --argjson ms "$ms_id" --argjson ls "$label_ids" \
+    '{title:$t, body:$b, milestone:$ms, labels:$ls}')
+  curl -s "${AUTH[@]}" "${JSON[@]}" -X POST "$REPO_API/issues" -d "$payload" >/dev/null
+  say "  create $title"
+}
+
+say ""
+say "== Sub-slice issues =="
+
+create_issue "S-00-a · Placeholder BFF + health endpoint" \
+  "type:slice,area:bff" "$(cat <<'EOF'
+**Outcome:** A minimal .NET BFF service exposing `GET /health` that returns a green (`Healthy`) status. Runnable with `dotnet run`.
+
+**Acceptance:**
+
+- A failing xUnit test asserts `GET /health` returns 200 with a `Healthy` payload (red commit first).
+- Implementation makes it pass; `dotnet run` then `curl /health` returns `Healthy`.
+- Project follows the §9 layering seed (minimal `Api` project; `Application`/`Domain` added as they earn their place).
+
+**Touches:** `services/bff/`, tests.
+
+**Out of scope:** Docker, CI, OIDC, any real endpoints.
+
+_Split from #1 (S-00) per CLAUDE.md §13._
+EOF
+)"
+
+create_issue "S-00-b · Dockerfile + compose skeleton + compose-up smoke" \
+  "type:slice,area:bff,area:infra" "$(cat <<'EOF'
+**Outcome:** The BFF is containerized and `infra/docker-compose.yml` brings it up; health goes green within 3 minutes from a fresh clone.
+
+**Acceptance:**
+
+- `docker build` of the BFF image succeeds.
+- `docker compose up` brings the BFF to a healthy state; a compose-up smoke script curls `/health` and passes.
+- README documents the `docker compose up` path.
+
+**Touches:** `services/bff/Dockerfile`, `infra/docker-compose.yml`, smoke script.
+
+**Out of scope:** other services; CI wiring (S-00-c).
+
+_Split from #1 (S-00) per CLAUDE.md §13._
+EOF
+)"
+
+create_issue "S-00-c · Gitea Actions CI (lint, build, unit, compose-up smoke)" \
+  "type:slice,area:infra" "$(cat <<'EOF'
+**Outcome:** `.gitea/workflows/ci.yaml` runs on PRs and `main` with lint, build, unit tests, and the compose-up smoke test — all green.
+
+**Acceptance:**
+
+- Pipeline green on the branch.
+- Jobs: lint, build, unit, compose-up smoke. `uses:` references are absolute URLs pinned to a tag (CLAUDE.md §8.7 / §15).
+- Self-hosted runner label documented in `docs/runbooks/ci.md`.
+
+**Touches:** `.gitea/workflows/ci.yaml`, `docs/runbooks/ci.md`.
+
+**Out of scope:** mutation, e2e, container build + push (later slices).
+
+_Split from #1 (S-00) per CLAUDE.md §13._
+EOF
+)"
+
+create_issue "S-00-d · Contributor workflow: issue/PR templates, git-cliff, CHANGELOG" \
+  "type:slice,area:docs,area:infra" "$(cat <<'EOF'
+**Outcome:** Issue templates (`slice`/`bug`/`adr-proposal`), a PR template enforcing the DoD checklist, a `git-cliff` config producing an (empty) `CHANGELOG.md`, and `docs/gitea-workflow.md`.
+
+**Acceptance:**
+
+- `.gitea/ISSUE_TEMPLATE/{slice,bug,adr-proposal}.md` and `.gitea/PULL_REQUEST_TEMPLATE.md` present; opening a new issue offers the templates.
+- `cliff.toml` present; `git-cliff` generates `CHANGELOG.md`.
+- `docs/gitea-workflow.md` documents the issue → milestone → PR flow.
+
+**Touches:** `.gitea/ISSUE_TEMPLATE/`, `.gitea/PULL_REQUEST_TEMPLATE.md`, `cliff.toml`, `CHANGELOG.md`, `docs/gitea-workflow.md`.
+
+**Out of scope:** app code.
+
+_Split from #1 (S-00) per CLAUDE.md §13._
+EOF
+)"
+
+create_issue "S-00-e · Docs scaffold: MkDocs + ADR-0001 + README quickstart" \
+  "type:slice,area:docs" "$(cat <<'EOF'
+**Outcome:** MkDocs Material builds the `docs/` site; `docs/architecture/adr-0001-loose-coupling.md` exists as the ADR template; README gains a sub-10-minute quickstart.
+
+**Acceptance:**
+
+- `mkdocs build` succeeds (`mkdocs.yml` + nav).
+- `adr-0001-loose-coupling.md` present, Nygard template.
+- A new developer following `README.md` reaches a green local environment in under 10 minutes.
+
+**Touches:** `mkdocs.yml`, `docs/` nav, `docs/architecture/adr-0001-loose-coupling.md`, `README.md`.
+
+**Out of scope:** Gitea Pages publish workflow (later).
+
+_Split from #1 (S-00) per CLAUDE.md §13._
+EOF
+)"
+
+# --- Close #1 with a comment listing the replacements -----------------------
+say ""
+say "== Close parent #1 =="
+
+# Resolve the numbers of the sub-slices we now have.
+all_issues=$(curl -s "${AUTH[@]}" "$REPO_API/issues?state=all&type=issues&limit=100")
+refs=$(echo "$all_issues" | jq -r '
+  [ .[] | select(.title | startswith("S-00-")) ]
+  | sort_by(.title)
+  | map("- #\(.number) — \(.title)")
+  | join("\n")')
+
+comments=$(curl -s "${AUTH[@]}" "$REPO_API/issues/$PARENT/comments?limit=100")
+if echo "$comments" | jq -e --arg m "$MARKER" 'any(.[]; .body | contains($m))' >/dev/null; then
+  say "  skip   split comment (already posted)"
+else
+  body="$MARKER
+Split into sub-slices per CLAUDE.md §13. Replacement issues:
+
+$refs"
+  curl -s "${AUTH[@]}" "${JSON[@]}" -X POST "$REPO_API/issues/$PARENT/comments" \
+    -d "$(jq -n --arg b "$body" '{body:$b}')" >/dev/null
+  say "  create split comment on #$PARENT"
+fi
+
+state=$(echo "$all_issues" | jq -r --argjson n "$PARENT" '.[] | select(.number == $n) | .state')
+if [ "$state" = "closed" ]; then
+  say "  skip   #$PARENT already closed"
+else
+  curl -s "${AUTH[@]}" "${JSON[@]}" -X PATCH "$REPO_API/issues/$PARENT" \
+    -d "$(jq -n '{state:"closed"}')" >/dev/null
+  say "  closed #$PARENT"
+fi
+
+say ""
+say "Done."