The `build` job runs untrusted PR code (uv sync + mkdocs/mkdocstrings importing the PR's `src/mcp`) under `pull_request_target` with `setup-uv` `enable-cache: true`, so any cache it saves lands in the base-branch (main) Actions cache scope where trusted workflows (shared.yml, conformance.yml, deploy-docs.yml) can restore it — a cache-poisoning vector the artifact-handoff isolation doesn't cover. Set `enable-cache: false` in this job (as publish-pypi.yml already does) or use a `cache-suffix` name

Because this workflow triggers on every `issue_comment: created` and the workflow-level concurrency group resolves to `docs-preview-pr-<N>` for both `pull_request_target` and `issue_comment` events with `cancel-in-progress: true`, any ordinary comment posted on PR N while a preview build/deploy is in flight cancels that run — the new run then skips every job (the `authorize` job filters out non-`/preview-docs` comments), so the preview is silently lost and the sticky comment is never updated. Co