Update DIRAC docs

docs/merlin7/05-Software-Support/dirac.md

@@ -76,9 +76,21 @@ source ~/dirac_ui/diracos/diracosrc
 
 Install the DIRAC Python client:
 ```bash
-pip install DIRAC # Alternative DIRAC==$VERSION, e.g. DIRAC==8.0.74
+pip install DIRAC==8.0.74
 ```
 
+!!! warning
+    **Do not install the latest DIRAC release (v9 or newer).**
+
+    In particular, **do not run**:
+    ```bash
+    pip install DIRAC
+    ```
+    as this will automatically install the most recent DIRAC version.
+
+    ⚠️ **Mu3e is currently compatible only with DIRAC v8.**
+    Using DIRAC v9 or newer is known to cause incompatibilities and will result in a non-functional setup.
+
 ### Install Certificate Authorities (CAs)
 
 **DIRAC** requires trusted CA certificates to validate remote services. Merlin7 does not provide CA certificates
@@ -87,26 +99,34 @@ and users are responsible for managing and updating them.
 !!! warning
     Users are responsible to maintain the CAs up to date
 
-Download the required CA bundles:
+Download and install the CA bundles relevant to your GRID certificates:
+- **UK Science**: **required** for accessing Mu3e.org services.
+- **CERN**: optional, required only if you use a CERN-issued GRID certificate.
+- **Other CAs**: required if your GRID certificate was issued by a different certification authority.
+
 ```bash
 mkdir -p ~/Downloads
 cd ~/Downloads
 
+# UK Science
 wget https://repository.egi.eu/sw/production/cas/1/current/tgz/ca_UKeScienceCA-2B-1.138.tar.gz
 wget https://repository.egi.eu/sw/production/cas/1/current/tgz/ca_UKeScienceRoot-2007-1.138.tar.gz
+
+# CERN
+wget https://repository.egi.eu/sw/production/cas/1/current/tgz/ca_CERN-Root-2-1.138.tar.gz
+wget https://repository.egi.eu/sw/production/cas/1/current/tgz/ca_CERN-GridCA-1.138.tar.gz
 ```
 
 Install them into DIRACOS
 ```bash
 cd ~/dirac_ui
 
-tar xvzf ~/Downloads/ca_UKeScienceRoot-2007-1.138.tar.gz \
-  --strip-components=1 \
-  -C diracos/etc/grid-security/certificates/
-
-tar xvzf ~/Downloads/ca_UKeScienceCA-2B-1.138.tar.gz \
-  --strip-components=1 \
-  -C diracos/etc/grid-security/certificates/
+for ca_file in $(ls ~/Downloads/ca_*.tar.gz)
+do
+  tar xvzf ~/Downloads/$ca_file \
+    --strip-components=1 \
+    -C diracos/etc/grid-security/certificates/
+done
 ```
 
 ### Fetch Certificate Revocation Lists (CRLs)