Fix: pip requirements handling for environment-marker dependencies

StabilityMatrix.Core/Processes/ProcessRunner.cs

@@ -651,8 +651,15 @@ public static Task<ProcessResult> RunBashCommand(
     /// </summary>
     public static string Quote(string argument)
     {
-        var inner = argument.Trim('"');
-        return inner.Contains(' ') ? $"\"{inner}\"" : argument;
+        var inner = argument.Length >= 2 && argument.StartsWith('"') && argument.EndsWith('"')
+            ? argument[1..^1]
+            : argument;
+
+        if (!inner.Contains(' ') && !inner.Contains('"'))
+            return argument;
+
+        var escaped = inner.Replace("\"", "\\\"");
+        return $"\"{escaped}\"";
     }
 
     /// <summary>

StabilityMatrix.Core/Python/PipInstallArgs.cs

@@ -54,7 +54,15 @@ public PipInstallArgs WithParsedFromRequirementsTxt(
             requirementsEntries = requirementsEntries.Where(s => !excludeRegex.IsMatch(s));
         }
 
-        return this.AddArgs(requirementsEntries.Select(Argument.Quoted).ToArray());
+        return this.AddArgs(requirementsEntries.Select(ToRequirementArgument).ToArray());
+    }
+
+    private static Argument ToRequirementArgument(string requirementEntry)
+    {
+        if (requirementEntry.StartsWith('-'))
+            return Argument.Quoted(requirementEntry);
+
+        return new Argument(requirementEntry);
     }
 
     /// <summary>

StabilityMatrix.Tests/Core/PipInstallArgsTests.cs

@@ -81,6 +81,26 @@ public void TestParsedFromRequirementsTxt()
         Assert.AreEqual("torch~=2.0.0 torchvision --extra-index-url https://example.org", args.ToString());
     }
 
+    [TestMethod]
+    public void TestParsedFromRequirementsTxt_KeepsEnvironmentMarkerRequirementAsSingleArgument()
+    {
+        const string requirements = """
+                                    onnxruntime-gpu==1.22.0; python_version < "3.11"
+                                    """;
+
+        var args = new PipInstallArgs().WithParsedFromRequirementsTxt(requirements).ToProcessArgs();
+
+        Assert.AreEqual(1, args.Count());
+        Assert.AreEqual(
+            "\"onnxruntime-gpu==1.22.0; python_version < \\\"3.11\\\"\"",
+            args.Single().GetQuotedValue()
+        );
+        Assert.AreEqual(
+            "\"onnxruntime-gpu==1.22.0; python_version < \\\"3.11\\\"\"",
+            args.ToString()
+        );
+    }
+
     [TestMethod]
     public void TestWithUserOverrides()
     {