diff --git a/.github/workflows/drupal-contrib-integration-test.yml b/.github/workflows/drupal-contrib-integration-test.yml
index 052a977..7718e2d 100644
--- a/.github/workflows/drupal-contrib-integration-test.yml
+++ b/.github/workflows/drupal-contrib-integration-test.yml
@@ -479,7 +479,7 @@ jobs:
       run:
         shell: bash -euo pipefail {0}
     env:
-      WORKSPACE_NAME: gc-${{ matrix.project }}-d${{ matrix.drupal_version }}-${{ github.run_number }}-${{ github.run_attempt }}
+      WORKSPACE_NAME: gc-${{ matrix.project }}-d${{ matrix.drupal_version }}-${{ github.event.pull_request.number && format('pr{0}', github.event.pull_request.number) || github.ref_name == 'main' && 'main' || format('x{0}', github.run_number) }}-${{ github.run_number }}-${{ github.run_attempt }}
       CI: "true"
       DDEV_NONINTERACTIVE: "true"
       NO_COLOR: "1"
@@ -512,7 +512,7 @@ jobs:
             --variable github_token=${{ secrets.GITHUB_TOKEN }}
 
       - name: Reap predecessor workspaces (cancelled prior runs of this cell)
-        run: ./scripts/ci-reap-family.sh "gc-${{ matrix.project }}-d${{ matrix.drupal_version }}-" "${{ env.WORKSPACE_NAME }}"
+        run: ./scripts/ci-reap-family.sh "${WORKSPACE_NAME%-*-*}-" "$WORKSPACE_NAME"
 
       - name: Acquire staging box lock
         run: ./scripts/ci-acquire-staging-lock.sh
@@ -696,7 +696,7 @@ jobs:
       run:
         shell: bash -euo pipefail {0}
     env:
-      WORKSPACE_NAME: gc-fork-${{ github.run_number }}-${{ github.run_attempt }}
+      WORKSPACE_NAME: gc-fork-${{ github.event.pull_request.number && format('pr{0}', github.event.pull_request.number) || github.ref_name == 'main' && 'main' || format('x{0}', github.run_number) }}-${{ github.run_number }}-${{ github.run_attempt }}
       CI: "true"
       DDEV_NONINTERACTIVE: "true"
       NO_COLOR: "1"
@@ -765,7 +765,7 @@ jobs:
             --variable github_token=${{ secrets.GITHUB_TOKEN }}
 
       - name: Reap predecessor workspaces (cancelled prior runs of this cell)
-        run: ./scripts/ci-reap-family.sh "gc-fork-" "${{ env.WORKSPACE_NAME }}"
+        run: ./scripts/ci-reap-family.sh "${WORKSPACE_NAME%-*-*}-" "$WORKSPACE_NAME"
 
       - name: Acquire staging box lock
         run: ./scripts/ci-acquire-staging-lock.sh
@@ -906,7 +906,7 @@ jobs:
       run:
         shell: bash -euo pipefail {0}
     env:
-      WORKSPACE_NAME: gc-glfork-${{ github.run_number }}-${{ github.run_attempt }}
+      WORKSPACE_NAME: gc-glfork-${{ github.event.pull_request.number && format('pr{0}', github.event.pull_request.number) || github.ref_name == 'main' && 'main' || format('x{0}', github.run_number) }}-${{ github.run_number }}-${{ github.run_attempt }}
       CI: "true"
       DDEV_NONINTERACTIVE: "true"
       NO_COLOR: "1"
@@ -975,7 +975,7 @@ jobs:
             --variable github_token=${{ secrets.GITHUB_TOKEN }}
 
       - name: Reap predecessor workspaces (cancelled prior runs of this cell)
-        run: ./scripts/ci-reap-family.sh "gc-glfork-" "${{ env.WORKSPACE_NAME }}"
+        run: ./scripts/ci-reap-family.sh "${WORKSPACE_NAME%-*-*}-" "$WORKSPACE_NAME"
 
       - name: Acquire staging box lock
         run: ./scripts/ci-acquire-staging-lock.sh
diff --git a/.github/workflows/drupal-integration-test.yml b/.github/workflows/drupal-integration-test.yml
index 6aad51f..3ace2fb 100644
--- a/.github/workflows/drupal-integration-test.yml
+++ b/.github/workflows/drupal-integration-test.yml
@@ -256,7 +256,7 @@ jobs:
       run:
         shell: bash -euo pipefail {0}
     env:
-      WORKSPACE_NAME: gd-${{ matrix.drupal_version }}-${{ github.run_number }}-${{ github.run_attempt }}
+      WORKSPACE_NAME: gd-${{ matrix.drupal_version }}-${{ github.event.pull_request.number && format('pr{0}', github.event.pull_request.number) || github.ref_name == 'main' && 'main' || format('x{0}', github.run_number) }}-${{ github.run_number }}-${{ github.run_attempt }}
       CI: "true"
       DDEV_NONINTERACTIVE: "true"
       NO_COLOR: "1"
@@ -290,7 +290,7 @@ jobs:
             --variable github_token=${{ secrets.GITHUB_TOKEN }}
 
       - name: Reap predecessor workspaces (cancelled prior runs of this cell)
-        run: ./scripts/ci-reap-family.sh "gd-${{ matrix.drupal_version }}-" "${{ env.WORKSPACE_NAME }}"
+        run: ./scripts/ci-reap-family.sh "${WORKSPACE_NAME%-*-*}-" "$WORKSPACE_NAME"
 
       - name: Acquire staging box lock
         run: ./scripts/ci-acquire-staging-lock.sh
@@ -568,7 +568,7 @@ jobs:
       run:
         shell: bash -euo pipefail {0}
     env:
-      WORKSPACE_NAME: gd-fork-${{ github.run_number }}-${{ github.run_attempt }}
+      WORKSPACE_NAME: gd-fork-${{ github.event.pull_request.number && format('pr{0}', github.event.pull_request.number) || github.ref_name == 'main' && 'main' || format('x{0}', github.run_number) }}-${{ github.run_number }}-${{ github.run_attempt }}
       CI: "true"
       DDEV_NONINTERACTIVE: "true"
       NO_COLOR: "1"
@@ -621,7 +621,7 @@ jobs:
             --variable github_token=${{ secrets.GITHUB_TOKEN }}
 
       - name: Reap predecessor workspaces (cancelled prior runs of this cell)
-        run: ./scripts/ci-reap-family.sh "gd-fork-" "${{ env.WORKSPACE_NAME }}"
+        run: ./scripts/ci-reap-family.sh "${WORKSPACE_NAME%-*-*}-" "$WORKSPACE_NAME"
 
       - name: Acquire staging box lock
         run: ./scripts/ci-acquire-staging-lock.sh
diff --git a/.github/workflows/integration-test.yml b/.github/workflows/integration-test.yml
index bcc13ff..b072c83 100644
--- a/.github/workflows/integration-test.yml
+++ b/.github/workflows/integration-test.yml
@@ -323,7 +323,7 @@ jobs:
         shell: bash -euo pipefail {0}
     env:
       CI_TAG: ${{ github.run_number }}-${{ github.run_attempt }}
-      WORKSPACE_NAME: gh-${{ matrix.ws_name }}-${{ github.run_number }}-${{ github.run_attempt }}
+      WORKSPACE_NAME: gh-${{ matrix.ws_name }}-${{ github.event.pull_request.number && format('pr{0}', github.event.pull_request.number) || github.ref_name == 'main' && 'main' || format('x{0}', github.run_number) }}-${{ github.run_number }}-${{ github.run_attempt }}
       CI: "true"
       DDEV_NONINTERACTIVE: "true"
       NO_COLOR: "1"
@@ -363,7 +363,7 @@ jobs:
             ${{ matrix.extra_vars }}
 
       - name: Reap predecessor workspaces (cancelled prior runs of this cell)
-        run: ./scripts/ci-reap-family.sh "gh-${{ matrix.ws_name }}-" "${{ env.WORKSPACE_NAME }}"
+        run: ./scripts/ci-reap-family.sh "${WORKSPACE_NAME%-*-*}-" "$WORKSPACE_NAME"
 
       - name: Acquire staging box lock
         run: ./scripts/ci-acquire-staging-lock.sh
diff --git a/scripts/ci-reap-family.sh b/scripts/ci-reap-family.sh
index fdb7e5d..41cef78 100755
--- a/scripts/ci-reap-family.sh
+++ b/scripts/ci-reap-family.sh
@@ -10,9 +10,17 @@
 #   its own family and can delete any older sibling before creating its own.
 #
 #   Workspace names are <family>-<run_number>-<run_attempt> (e.g.
-#   gc-pathauto-d11-152-1). The family is the stable part shared across runs of
-#   the same matrix cell. Passing the family prefix here deletes every ci-bot
-#   workspace that starts with it EXCEPT the one this run is about to create.
+#   gc-pathauto-d11-pr212-152-1). The family is the stable part shared across
+#   runs of the same matrix cell ON THE SAME REF. Passing the family prefix here
+#   deletes every ci-bot workspace that starts with it EXCEPT the one this run
+#   is about to create.
+#
+#   The family MUST include a ref tag (pr<N> for pull requests, main for
+#   push/schedule/dispatch on main, x<run_number> elsewhere). Runs on different
+#   refs are in different concurrency groups and legitimately overlap; without
+#   the ref tag, a PR run's reap would delete main's in-flight workspace (this
+#   happened on main run 407, deleted by PR run 408). Callers derive the family
+#   from WORKSPACE_NAME as "${WORKSPACE_NAME%-*-*}-" so the two cannot drift.
 #
 # Usage:
 #   ci-reap-family.sh <family-prefix> [keep-name]