diff --git a/module-ci-bitbucket/README.md b/module-ci-bitbucket/README.md
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+# Facets Module CI — Bitbucket Pipelines glue
+
+The Bitbucket counterpart of [`module-ci-action`](../module-ci-action/README.md) (GitHub) and
+[`module-ci-gitlab`](../module-ci-gitlab/README.md) (GitLab). It runs the **same** shared
+[`module-ci-core.sh`](../module-ci-core.sh) the other hosts run, so the three never drift — this
+is only the thin Bitbucket glue: resolve the mode, map Bitbucket's predefined variables to the
+generic `MC_*` contract, fetch + run the core, and post the pull-request preview comment.
+
+## Why a script, not an include
+
+GitLab consumes its template as a remote `include:`. **Bitbucket Pipelines has no remote
+include**, so a modules repo's `bitbucket-pipelines.yml` can't pull a hosted template. It instead
+`curl`s [`run.sh`](./run.sh) (pinned to a tag) and runs it — the control plane wires that in at
+bootstrap, the same way it wires `module-ci-action@v1` (GitHub) or the GitLab include. The glue is
+still centrally versioned here; only the thin fetch-and-run lives in the repo.
+
+```yaml
+# bitbucket-pipelines.yml (what the control plane pushes into the repo)
+script:
+  - curl -fsSL "https://raw.githubusercontent.com/Facets-cloud/github-actions/v1/module-ci-bitbucket/run.sh" -o /tmp/run.sh
+  - bash /tmp/run.sh
+```
+
+## Modes
+
+- **Preview (on pull request)**: creates each changed output type the control plane does not have
+  yet, validates each changed module, and registers an unpublishable feature-branch preview pinned
+  to the source commit. Posts a PR comment when `FACETS_PR_TOKEN` is set.
+- **Publish (on default-branch push)**: applies each changed output type, then uploads and
+  publishes each changed module (PREVIEW → PUBLISHED), declaring compatible-update vs
+  version-upgrade from what the registry already holds.
+
+Output types are always applied **before** any module — a module names its output type by
+reference, and the control plane refuses a module whose type it does not already hold.
+
+## Variables
+
+| Variable | Required | Meaning |
+|---|---|---|
+| `CONTROL_PLANE_URL` | yes | Facets Control Plane URL |
+| `FACETS_USERNAME` | yes | Facets username |
+| `FACETS_TOKEN` | yes | Facets API token |
+| `FACETS_PATH_PREFIX` | no | sub-path to `modules/` (default `""`: repo root) |
+| `FACETS_MODULE_CI_REF` | no | `github-actions` ref the core + glue are fetched from (default `v1`) |
+| `FACETS_PR_TOKEN` | no | a Bitbucket access token that can write PR comments; enables the preview comment |
+
+The control-plane bootstrap provisions the three required variables as secured pipeline variables.
+
+## Not yet supported
+
+**Cleanup-on-close.** Bitbucket runs no pipeline when a pull request is closed, so deleting a
+closed PR's preview needs a separate trigger (a webhook or a scheduled sweep). The core already
+implements `cleanup` (ownership-checked); only the Bitbucket trigger is missing. Tracked as a
+follow-up — the same gap GitLab has.
diff --git a/module-ci-bitbucket/run.sh b/module-ci-bitbucket/run.sh
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+#!/usr/bin/env bash
+# Facets Module CI — Bitbucket Pipelines glue.
+#
+# The Bitbucket counterpart of module-ci-action (GitHub) and module-ci-gitlab
+# (GitLab). It runs the SAME shared module-ci-core.sh the other hosts run, so the
+# three never drift — this file is only the thin Bitbucket glue: resolve the mode,
+# map Bitbucket's predefined variables to the generic MC_* contract, fetch + run
+# the core, and post the pull-request preview as a comment.
+#
+# Bitbucket Pipelines has no remote-include (unlike GitLab's `include: remote:`),
+# so the modules repo's bitbucket-pipelines.yml can't pull a hosted template. It
+# instead curls THIS script (pinned to a tag) and runs it — the control plane
+# wires that in at bootstrap, the same way it wires module-ci-action@v1 (GitHub)
+# or the GitLab include.
+#
+# Required repository variables (set by the control-plane bootstrap, masked):
+#   CONTROL_PLANE_URL, FACETS_USERNAME, FACETS_TOKEN
+# Optional:
+#   FACETS_PATH_PREFIX    sub-path to modules/ (default "": modules/ at repo root)
+#   FACETS_MODULE_CI_REF  github-actions ref the core is fetched from (default "v1")
+#   FACETS_PR_TOKEN       a Bitbucket access token that can write PR comments; when
+#                         set, the preview is posted as a PR comment (mirrors the
+#                         GitHub github_token / GitLab FACETS_MR_TOKEN)
+#
+# NOTE (v1 scope): preview (on pull request) and publish (on default-branch push)
+# are supported. Cleanup-on-close is not — Bitbucket runs no pipeline when a PR is
+# closed, so preview cleanup needs a separate trigger (a webhook or a scheduled
+# sweep); the core already implements `cleanup`, only the Bitbucket trigger is
+# missing. Tracked as a follow-up, same as GitLab.
+set -euo pipefail
+
+FACETS_MODULE_CI_REF="${FACETS_MODULE_CI_REF:-v1}"
+export PATH_PREFIX="${FACETS_PATH_PREFIX:-}"
+export MC_COMMENT_DIR="${BITBUCKET_CLONE_DIR:-$PWD}/.facets-mci"
+mkdir -p "$MC_COMMENT_DIR"
+
+if [ -n "${BITBUCKET_PR_ID:-}" ]; then
+  # Pull-request build: Bitbucket checks out the source branch, so HEAD is the
+  # source head. Diff against the merge base with the destination branch.
+  export MODE="preview"
+  export MC_HEAD_SHA="${BITBUCKET_COMMIT}"
+  dest="${BITBUCKET_PR_DESTINATION_BRANCH}"
+  git fetch -q origin "$dest" || true
+  base="$(git merge-base "origin/${dest}" HEAD 2>/dev/null || true)"
+  # Empty base (unreachable) => core falls back to the pushed commit's own tree.
+  export MC_DIFF_RANGE="${base:+${base}..${BITBUCKET_COMMIT}}"
+else
+  # Default-branch push: publish. Bitbucket exposes no "previous commit" variable
+  # like GitLab's CI_COMMIT_BEFORE_SHA, so diff the single merge commit.
+  # ponytail: HEAD~1..HEAD assumes a squash/merge lands one commit (the Facets
+  # squash-merge workflow). A multi-commit fast-forward would only CI the tip's
+  # changes; widen the range here if that workflow is ever adopted.
+  export MODE="publish"
+  if git rev-parse --verify --quiet "HEAD~1^{commit}" >/dev/null 2>&1; then
+    export MC_DIFF_RANGE="HEAD~1..HEAD"
+  else
+    export MC_DIFF_RANGE=""
+  fi
+fi
+
+curl -fsSL "https://raw.githubusercontent.com/Facets-cloud/github-actions/${FACETS_MODULE_CI_REF}/module-ci-core.sh" -o /tmp/module-ci-core.sh
+
+# after_script equivalent: post the preview comment even when the core gates on a
+# bad module (mirrors the GitHub comment's if: always() and GitLab's after_script).
+post_preview_comment() {
+  [ "${MODE}" = "preview" ] || return 0
+  if [ -z "${FACETS_PR_TOKEN:-}" ]; then
+    echo "FACETS_PR_TOKEN not set; skipping PR preview comment."
+    return 0
+  fi
+  local body_file api existing marker="<!-- facets-module-ci:preview -->"
+  body_file="$(mktemp)"
+  printf '%s\n' "$marker" > "$body_file"
+  [ -f "${MC_COMMENT_DIR}/preview_outputs.md" ] && { cat "${MC_COMMENT_DIR}/preview_outputs.md" >> "$body_file"; echo "" >> "$body_file"; }
+  [ -f "${MC_COMMENT_DIR}/preview_modules.md" ] && cat "${MC_COMMENT_DIR}/preview_modules.md" >> "$body_file"
+  if [ ! -s "${MC_COMMENT_DIR}/preview_outputs.md" ] && [ ! -s "${MC_COMMENT_DIR}/preview_modules.md" ]; then
+    echo "No preview comment body; nothing to post."
+    return 0
+  fi
+  api="https://api.bitbucket.org/2.0/repositories/${BITBUCKET_WORKSPACE}/${BITBUCKET_REPO_SLUG}/pullrequests/${BITBUCKET_PR_ID}/comments"
+  # Upsert: find an existing bot comment carrying our marker, else create one.
+  existing="$(curl -fsS -H "Authorization: Bearer ${FACETS_PR_TOKEN}" "${api}?pagelen=100" \
+    | jq -r --arg m "$marker" '.values[] | select(.content.raw | contains($m)) | .id' | head -n1 || true)"
+  local payload
+  payload="$(jq -Rs '{content:{raw:.}}' < "$body_file")"
+  if [ -n "$existing" ]; then
+    curl -fsS -X PUT -H "Authorization: Bearer ${FACETS_PR_TOKEN}" -H "Content-Type: application/json" \
+      -d "$payload" "${api}/${existing}" >/dev/null && echo "Updated PR preview comment ${existing}."
+  else
+    curl -fsS -X POST -H "Authorization: Bearer ${FACETS_PR_TOKEN}" -H "Content-Type: application/json" \
+      -d "$payload" "${api}" >/dev/null && echo "Posted PR preview comment."
+  fi
+}
+trap post_preview_comment EXIT
+
+bash /tmp/module-ci-core.sh