diff --git a/.github/workflows/catalog-drift.yml b/.github/workflows/catalog-drift.yml
index ec856a98c5..c57f02ab12 100644
--- a/.github/workflows/catalog-drift.yml
+++ b/.github/workflows/catalog-drift.yml
@@ -26,7 +26,6 @@ name: Catalog Drift Check
 
 on:
   pull_request:
-    branches: [ main ]
     paths:
       - 'MyIA.AI.Notebooks/**/*.ipynb'
       - 'MyIA.AI.Notebooks/**/README.md'
diff --git a/.github/workflows/cell-order-gate.yml b/.github/workflows/cell-order-gate.yml
index b8c5a7a877..5a85a6ce8c 100644
--- a/.github/workflows/cell-order-gate.yml
+++ b/.github/workflows/cell-order-gate.yml
@@ -14,7 +14,6 @@ name: Cell-order gate
 
 on:
   pull_request:
-    branches: [ main ]
     paths:
       - 'MyIA.AI.Notebooks/**/*.ipynb'
       - 'scripts/notebook_tools/scan_cell_ordering.py'
diff --git a/.github/workflows/notebook-validation.yml b/.github/workflows/notebook-validation.yml
index 429330a0d7..702db85ab3 100644
--- a/.github/workflows/notebook-validation.yml
+++ b/.github/workflows/notebook-validation.yml
@@ -6,7 +6,6 @@ on:
     paths:
       - '**.ipynb'
   pull_request:
-    branches: [ main ]
     paths:
       - '**.ipynb'
   # Manual revalidate after a merge batch (issue #13861):
diff --git a/.github/workflows/solution-leak-guard.yml b/.github/workflows/solution-leak-guard.yml
index c0b28ea3d1..282781ce36 100644
--- a/.github/workflows/solution-leak-guard.yml
+++ b/.github/workflows/solution-leak-guard.yml
@@ -44,7 +44,6 @@ name: solution-leak-guard
 
 on:
   pull_request:
-    branches: [ main ]
     paths:
       - '**.ipynb'
       - 'scripts/notebook_tools/audit_solution_leaks.py'
diff --git a/.github/workflows/source-output-ratchet.yml b/.github/workflows/source-output-ratchet.yml
index 93559dfcc1..da374ac132 100644
--- a/.github/workflows/source-output-ratchet.yml
+++ b/.github/workflows/source-output-ratchet.yml
@@ -33,7 +33,6 @@ name: Source-Output Ratchet
 
 on:
   pull_request:
-    branches: [ main ]
     # #10600 tranche 2: the ratchet only has something to diff when a
     # notebook changed -- a PR without .ipynb made it pay a full-history
     # checkout + python setup to render "no changed notebooks". Script and
@@ -44,6 +43,12 @@ on:
       - '.github/workflows/source-output-ratchet.yml'
   workflow_dispatch:
 
+# Condition jointe a l'arbitrage #19426 (c.6300191475) : tout workflow
+# touche sans bloc concurrency en recoit un, cle sur la PR.
+concurrency:
+  group: source-output-ratchet-${{ github.event.pull_request.number || github.ref }}
+  cancel-in-progress: ${{ github.event_name == 'pull_request' }}
+
 permissions:
   contents: read
 
diff --git a/.github/workflows/translation-guard.yml b/.github/workflows/translation-guard.yml
index 4c1a397b81..4d92250050 100644
--- a/.github/workflows/translation-guard.yml
+++ b/.github/workflows/translation-guard.yml
@@ -27,7 +27,6 @@ name: Translation Guard
 
 on:
   pull_request:
-    branches: [ main ]
     # #12773 tranche 1b + amend. #13196 Hermes : paths-filter pour limiter
     # les declenchements aux PR touchant la surface reelle du garde
     # (`translation_override_required.py` qui interroge l'API `gh pr`). La
diff --git a/.github/workflows/twin-parity.yml b/.github/workflows/twin-parity.yml
index 2972c4feae..8c1a69c36d 100644
--- a/.github/workflows/twin-parity.yml
+++ b/.github/workflows/twin-parity.yml
@@ -43,7 +43,6 @@ name: Twin Parity Check
 
 on:
   pull_request:
-    branches: [ main ]
     paths:
       - 'scripts/notebook_tools/twin_pairs.d/**'
       - 'scripts/notebook_tools/check_twin_parity.py'