diff --git a/.github/workflows/php-security.yml b/.github/workflows/php-security.yml
index 6dae3b1..72d14df 100644
--- a/.github/workflows/php-security.yml
+++ b/.github/workflows/php-security.yml
@@ -1,6 +1,15 @@
 # SPDX-License-Identifier: MPL-2.0-or-later
 name: PHP Security Check
-on: [push, pull_request]
+on:
+  push:
+    branches: [main, master]
+  pull_request:
+
+# Estate guardrail: scope push to default branches so a PR fires once (not
+# push+PR), and cancel superseded runs. Safe — read-only PR-triggered check.
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
 
 permissions:
   contents: read
diff --git a/.github/workflows/rescript-deno-ci.yml b/.github/workflows/rescript-deno-ci.yml
index 540b2e6..674d5d9 100644
--- a/.github/workflows/rescript-deno-ci.yml
+++ b/.github/workflows/rescript-deno-ci.yml
@@ -1,6 +1,15 @@
 # SPDX-License-Identifier: MPL-2.0-or-later
 name: ReScript/Deno CI
-on: [push, pull_request]
+on:
+  push:
+    branches: [main, master]
+  pull_request:
+
+# Estate guardrail: scope push to default branches so a PR fires once (not
+# push+PR), and cancel superseded runs. Safe — read-only PR-triggered check.
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
 
 permissions:
   contents: read