diff --git a/.github/workflows/accelerate-examples.yml b/.github/workflows/accelerate-examples.yml
index bc43d2208..728cae943 100644
--- a/.github/workflows/accelerate-examples.yml
+++ b/.github/workflows/accelerate-examples.yml
@@ -10,12 +10,16 @@
 name: accelerate-examples
 
 concurrency:
-  # schedule runs serialize; each manual run gets its own group so a
-  # dispatch is never blocked behind a scheduled run.
-  group: ${{ github.event_name == 'schedule' && 'accelerate-examples-schedule' || format('manual-{0}', github.run_id) }}
-  # false: a run cancelled mid-way loses its outcome writeback, and the
-  # outcome is what drives the next cycle's retry.
-  cancel-in-progress: false
+  # Three groups: schedule runs serialize (a run cancelled mid-way
+  # loses its outcome writeback, and the outcome drives the next
+  # cycle's retry); each PR serializes per number so a new push
+  # cancels the stale run instead of queueing another matrix on the
+  # NPU runners; each manual run stands alone. Group names are
+  # repository-wide, so the PR group carries the workflow name.
+  group: ${{ github.event_name == 'schedule' && 'accelerate-examples-schedule' || (github.event_name == 'pull_request' && format('accelerate-examples-pr-{0}', github.event.pull_request.number)) || format('manual-{0}', github.run_id) }}
+  # true on PR runs only: a stale push's matrix should be cancelled,
+  # but a schedule run cancelled mid-way loses its outcome writeback.
+  cancel-in-progress: ${{ github.event_name == 'pull_request' }}
 
 on:
   # Daily at 02:00 Beijing time (UTC 18:00).
@@ -28,6 +32,18 @@ on:
         required: false
         default: ''
         type: string
+  # PR runs need no merge: GitHub executes the workflow files from the
+  # PR merge ref, so a newly added trigger and engine run on the PR
+  # that adds them. `pull_request`, not `pull_request_target`: the
+  # declared read permissions are all the engine needs. paths lists
+  # only this project's files, so a PR that touches only the shared
+  # engine, scripts or schema starts no project's matrix.
+  pull_request:
+    branches: [main]
+    types: [opened, synchronize, reopened]
+    paths:
+      - 'examples-guards/accelerate/**'
+      - '.github/workflows/accelerate-examples.yml'
 
 # Engine jobs query the GitHub Job API (validate-results); called
 # workflows run with the caller's GITHUB_TOKEN permissions.