diff --git a/.github/workflows/guix-nix-policy.yml b/.github/workflows/guix-nix-policy.yml
index d3b1f2b..6015d0c 100644
--- a/.github/workflows/guix-nix-policy.yml
+++ b/.github/workflows/guix-nix-policy.yml
@@ -1,6 +1,15 @@
 # SPDX-License-Identifier: MPL-2.0
 name: Guix/Nix Package Policy
-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+# push+PR), and cancel superseded runs.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/npm-bun-blocker.yml b/.github/workflows/npm-bun-blocker.yml
index 2fd984f..0ae6839 100644
--- a/.github/workflows/npm-bun-blocker.yml
+++ b/.github/workflows/npm-bun-blocker.yml
@@ -1,6 +1,15 @@
 # SPDX-License-Identifier: MPL-2.0
 name: NPM/Bun Blocker
-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+# push+PR), and cancel superseded runs.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/quality.yml b/.github/workflows/quality.yml
index b1de134..1afc9a2 100644
--- a/.github/workflows/quality.yml
+++ b/.github/workflows/quality.yml
@@ -1,6 +1,15 @@
 # SPDX-License-Identifier: MPL-2.0
 name: Code Quality
-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+# push+PR), and cancel superseded runs.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:
diff --git a/.github/workflows/security-policy.yml b/.github/workflows/security-policy.yml
index 6f07f86..2964da6 100644
--- a/.github/workflows/security-policy.yml
+++ b/.github/workflows/security-policy.yml
@@ -1,6 +1,15 @@
 # SPDX-License-Identifier: MPL-2.0
 name: Security Policy
-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+# push+PR), and cancel superseded runs.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/ts-blocker.yml b/.github/workflows/ts-blocker.yml
index 432a88f..8dd25ee 100644
--- a/.github/workflows/ts-blocker.yml
+++ b/.github/workflows/ts-blocker.yml
@@ -1,6 +1,15 @@
 # SPDX-License-Identifier: MPL-2.0
 name: TypeScript/JavaScript Blocker
-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/zig-ffi.yml b/.github/workflows/zig-ffi.yml
index d2a2434..57eb309 100644
--- a/.github/workflows/zig-ffi.yml
+++ b/.github/workflows/zig-ffi.yml
@@ -6,7 +6,16 @@
 # ffi/zig/src/main.zig (the grep-based E2E job only checks source strings).
 name: Zig FFI
 
-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