diff --git a/.github/workflows/codeql-analysis.yml b/.github/workflows/codeql-analysis.yml
index 71db85b70..c613ade92 100644
--- a/.github/workflows/codeql-analysis.yml
+++ b/.github/workflows/codeql-analysis.yml
@@ -32,6 +32,21 @@ on:
   schedule:
     - cron: '17 9 * * 5'
 
+# Avoid duplicate runs for the same source branch and repository.
+# For pull_request events, uses the source repo name from
+# github.event.pull_request.head.repo.full_name; otherwise uses github.repository.
+# For push events, uses the branch name from github.ref_name.
+# For pull_request events, uses the source branch name from github.head_ref.
+# This ensures events for the same repo and branch share the same group,
+# and avoids cross-fork collisions when branch names are reused.
+# Schedule events are not cancelled to ensure weekly scans complete.
+concurrency:
+  group: >-
+    ${{ github.workflow }}-${{
+      github.event.pull_request.head.repo.full_name || github.repository
+    }}-${{ github.head_ref || github.ref_name }}
+  cancel-in-progress: ${{ github.event_name != 'schedule' }}
+
 jobs:
   analyze:
     name: Analyze
diff --git a/.github/workflows/lint.yml b/.github/workflows/lint.yml
index 7d88abf11..383158175 100644
--- a/.github/workflows/lint.yml
+++ b/.github/workflows/lint.yml
@@ -24,6 +24,20 @@ on:
       - '**.yml'
       - 'docs/**'
 
+# Avoid duplicate runs for the same source branch and repository.
+# For pull_request events, uses the source repo name from
+# github.event.pull_request.head.repo.full_name; otherwise uses github.repository.
+# For push events, uses the branch name from github.ref_name.
+# For pull_request events, uses the source branch name from github.head_ref.
+# This ensures events for the same repo and branch share the same group,
+# and avoids cross-fork collisions when branch names are reused.
+concurrency:
+  group: >-
+    ${{ github.workflow }}-${{
+      github.event.pull_request.head.repo.full_name || github.repository
+    }}-${{ github.head_ref || github.ref_name }}
+  cancel-in-progress: true
+
 jobs:
   ruff:
     runs-on: ubuntu-latest
diff --git a/.github/workflows/pypi-publish.yml b/.github/workflows/pypi-publish.yml
index f3158dec1..de1461fe4 100644
--- a/.github/workflows/pypi-publish.yml
+++ b/.github/workflows/pypi-publish.yml
@@ -15,6 +15,21 @@ on:
     types: [published]  # "Publish release" button
   workflow_dispatch:    # Manual trigger to test wheel build
 
+# Avoid duplicate runs for the same source branch and repository.
+# For pull_request events, uses the source repo name from
+# github.event.pull_request.head.repo.full_name; otherwise uses github.repository.
+# For push events, uses the branch name from github.ref_name.
+# For pull_request events, uses the source branch name from github.head_ref.
+# This ensures events for the same repo and branch share the same group,
+# and avoids cross-fork collisions when branch names are reused.
+# Also applies to release (uses tag name) and workflow_dispatch (uses branch/tag name).
+concurrency:
+  group: >-
+    ${{ github.workflow }}-${{
+      github.event.pull_request.head.repo.full_name || github.repository
+    }}-${{ github.head_ref || github.ref_name }}
+  cancel-in-progress: true
+
 jobs:
   echo_github_env:
     name: Echo env variables
diff --git a/.github/workflows/unittest.yml b/.github/workflows/unittest.yml
index 7e2a85328..b1b9f3ad5 100644
--- a/.github/workflows/unittest.yml
+++ b/.github/workflows/unittest.yml
@@ -27,6 +27,20 @@ on:
       - "MANIFEST.in"
       - "pyproject.toml"
 
+# Avoid duplicate runs for the same source branch and repository.
+# For pull_request events, uses the source repo name from
+# github.event.pull_request.head.repo.full_name; otherwise uses github.repository.
+# For push events, uses the branch name from github.ref_name.
+# For pull_request events, uses the source branch name from github.head_ref.
+# This ensures events for the same repo and branch share the same group,
+# and avoids cross-fork collisions when branch names are reused.
+concurrency:
+  group: >-
+    ${{ github.workflow }}-${{
+      github.event.pull_request.head.repo.full_name || github.repository
+    }}-${{ github.head_ref || github.ref_name }}
+  cancel-in-progress: true
+
 jobs:
   unittest:
     strategy: