diff --git a/.github/workflows/seed-corpus.yml b/.github/workflows/seed-corpus.yml
index 8d2fcb64b..baaab25fa 100644
--- a/.github/workflows/seed-corpus.yml
+++ b/.github/workflows/seed-corpus.yml
@@ -264,24 +264,25 @@ jobs:
             --body "$(cat <<'EOF'
           ## Seed corpus update
 
-          Automated PR from the \`seed-corpus\` workflow (run [${{ github.run_number }}](${{ github.server_url }}/${{ github.repository }}/actions/runs/${{ github.run_id }})).
+          Automated PR from the `seed-corpus` workflow (run [${{ github.run_number }}](${{ github.server_url }}/${{ github.repository }}/actions/runs/${{ github.run_id }})).
 
           ### Bundles included
 
-          New or updated result bundles are committed under \`results-data/bundles/\`.
+          New or updated result bundles are committed under `results-data/bundles/`.
           Review the diff to confirm expected benchmark × platform × scale coverage.
 
           ### Trust label
 
-          All bundles in this PR carry the \`maintainer-run\` / \`public-curated\` trust label.
+          All bundles in this PR carry the `maintainer-run` / `public-curated` trust label.
 
           ### Merging
 
-          Merge triggers the \`docs\` workflow which rebuilds the read model and
-          redeploys the results explorer.
+          Merge into `develop` triggers `sync-results-data-to-published`, which
+          opens a draft PR mirroring these bundles onto the `published-results`
+          corpus branch.
           EOF
           )" \
-            --base main \
+            --base develop \
             --head "${{ steps.commit.outputs.branch }}"
 
       - name: No changes to commit
diff --git a/tests/unit/workflows/test_seed_corpus_pr_base.py b/tests/unit/workflows/test_seed_corpus_pr_base.py
new file mode 100644
index 000000000..1fd2f2c2b
--- /dev/null
+++ b/tests/unit/workflows/test_seed_corpus_pr_base.py
@@ -0,0 +1,87 @@
+"""Guardrails for the seed-corpus workflow's PR base branch.
+
+`seed-corpus.yml` is `workflow_dispatch`-only and `release-cut` curates it out
+of the release tree, so no CI job ever exercises its `gh pr create` call. These
+tests stand in for that missing coverage: they pin the base branch to `develop`
+and encode why the release-only branch can never be a valid target.
+"""
+
+from __future__ import annotations
+
+import re
+from pathlib import Path
+
+import pytest
+import yaml
+
+pytestmark = [
+    pytest.mark.unit,
+    pytest.mark.fast,
+]
+
+REPO_ROOT = Path(__file__).resolve().parents[3]
+WORKFLOW_PATH = REPO_ROOT / ".github" / "workflows" / "seed-corpus.yml"
+
+# Mirrors the head-branch gate on the release-only branch (`validate-main-pr.yml`,
+# renamed to `validate-release-pr.yml` by the main -> release rename). Duplicated
+# rather than parsed out of that workflow so this test does not break when the
+# rename lands. Only `vX.Y.Z` heads may merge into the release branch.
+RELEASE_HEAD_RE = re.compile(r"^v[0-9]+\.[0-9]+\.[0-9]+(-[A-Za-z0-9.+-]+)?$")
+
+
+def _create_pr_steps() -> dict[str, str]:
+    """Map step name -> `run` script for the workflow's `create-pr` job."""
+    workflow = yaml.safe_load(WORKFLOW_PATH.read_text(encoding="utf-8"))
+    steps = workflow["jobs"]["create-pr"]["steps"]
+    return {step["name"]: step.get("run", "") for step in steps if "name" in step}
+
+
+def _rendered_head_branch(commit_script: str) -> str:
+    """Render the `BRANCH=` template the commit step pushes as the PR head."""
+    match = re.search(r'BRANCH="([^"]+)"', commit_script)
+    assert match is not None, "could not find the BRANCH= assignment in the commit step"
+    branch = match.group(1)
+    branch = branch.replace("${{ github.run_number }}", "123")
+    return branch.replace("${DATE}", "20260710")
+
+
+def test_seed_corpus_pr_targets_develop() -> None:
+    """The seed corpus PR opens against `develop`, the default branch.
+
+    `main` is release-only and rejects non-`vX.Y.Z` heads; it also disappears
+    once the main -> release rename lands, which would hard-fail `gh pr create`.
+    """
+    run = _create_pr_steps()["Open pull request"]
+
+    assert "--base develop" in run
+    assert "--base main" not in run
+    assert "--base release" not in run
+
+
+def test_seed_corpus_head_branch_can_never_target_the_release_branch() -> None:
+    """The pushed head is a `chore/` branch, so the release branch would reject it."""
+    steps = _create_pr_steps()
+    head = _rendered_head_branch(steps["Create PR branch and commit"])
+
+    assert head.startswith("chore/seed-corpus-")
+    assert not RELEASE_HEAD_RE.match(head)
+
+
+def test_seed_corpus_pr_body_does_not_escape_backticks() -> None:
+    """The PR body heredoc is quoted (`<<'EOF'`), so nothing inside is expanded.
+
+    Backslash-escaping a backtick there is not protection, it is a literal
+    backslash in the rendered PR body.
+    """
+    run = _create_pr_steps()["Open pull request"]
+    body = run.split("<<'EOF'", 1)[1].split("\nEOF", 1)[0]
+
+    assert "`" in body, "sanity: the body is expected to contain backticks"
+    assert "\\`" not in body
+
+
+def test_release_head_regex_matches_real_release_branches() -> None:
+    """Guard the mirrored regex itself, so the test above cannot pass vacuously."""
+    assert RELEASE_HEAD_RE.match("v0.3.1")
+    assert RELEASE_HEAD_RE.match("v1.2.3-rc.1")
+    assert not RELEASE_HEAD_RE.match("chore/seed-corpus-20260710-123")