[APM] Add four decimal places float validation for transaction_sample…

…_rate (#188555)

Closes #183840 

## Summary

This PR adds four decimal places float validation for
`transaction_sample_rate` and keeps the three decimal places float
validation for all other fields


![image](https://github.com/user-attachments/assets/359136b8-6a3a-4a51-ab51-085cd03a0371)


## Testing 

- Open APM -> Settings -> Agent Configuration and go to the next time
where `transaction_sample_rate` and check the validation -> Up to 4
decimal places should be allowed:



https://github.com/user-attachments/assets/0c596277-11b2-40d3-991e-d04f97a4ac5f

x-pack/plugins/observability_solution/apm/common/agent_configuration/runtime_types/float_four_decimal_places_rt.test.ts

@@ -0,0 +1,39 @@
+/*
+ * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ * or more contributor license agreements. Licensed under the Elastic License
+ * 2.0; you may not use this file except in compliance with the Elastic License
+ * 2.0.
+ */
+
+import { floatFourDecimalPlacesRt } from './float_four_decimal_places_rt';
+import { isRight } from 'fp-ts/lib/Either';
+
+describe('floatFourDecimalPlacesRt', () => {
+  it('does not accept empty values', () => {
+    expect(isRight(floatFourDecimalPlacesRt.decode(undefined))).toBe(false);
+    expect(isRight(floatFourDecimalPlacesRt.decode(null))).toBe(false);
+    expect(isRight(floatFourDecimalPlacesRt.decode(''))).toBe(false);
+  });
+
+  it('should only accept stringified numbers', () => {
+    expect(isRight(floatFourDecimalPlacesRt.decode('0.5'))).toBe(true);
+    expect(isRight(floatFourDecimalPlacesRt.decode(0.5))).toBe(false);
+  });
+
+  it('checks if the number falls within 0, 1', () => {
+    expect(isRight(floatFourDecimalPlacesRt.decode('0'))).toBe(true);
+    expect(isRight(floatFourDecimalPlacesRt.decode('0.5'))).toBe(true);
+    expect(isRight(floatFourDecimalPlacesRt.decode('-0.1'))).toBe(false);
+    expect(isRight(floatFourDecimalPlacesRt.decode('1.1'))).toBe(false);
+    expect(isRight(floatFourDecimalPlacesRt.decode(NaN))).toBe(false);
+  });
+
+  it('checks whether the number of decimals is 4', () => {
+    expect(isRight(floatFourDecimalPlacesRt.decode('1'))).toBe(true);
+    expect(isRight(floatFourDecimalPlacesRt.decode('0.9'))).toBe(true);
+    expect(isRight(floatFourDecimalPlacesRt.decode('0.99'))).toBe(true);
+    expect(isRight(floatFourDecimalPlacesRt.decode('0.999'))).toBe(true);
+    expect(isRight(floatFourDecimalPlacesRt.decode('0.9999'))).toBe(true);
+    expect(isRight(floatFourDecimalPlacesRt.decode('0.99999'))).toBe(false);
+  });
+});

x-pack/plugins/observability_solution/apm/common/agent_configuration/runtime_types/float_four_decimal_places_rt.ts

@@ -0,0 +1,27 @@
+/*
+ * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ * or more contributor license agreements. Licensed under the Elastic License
+ * 2.0; you may not use this file except in compliance with the Elastic License
+ * 2.0.
+ */
+
+import * as t from 'io-ts';
+import { either } from 'fp-ts/lib/Either';
+
+export const floatFourDecimalPlacesRt = new t.Type<string, string, unknown>(
+  'floatFourDecimalPlacesRt',
+  t.string.is,
+  (input, context) => {
+    return either.chain(t.string.validate(input, context), (inputAsString) => {
+      const inputAsFloat = parseFloat(inputAsString);
+      const maxFourDecimals = parseFloat(inputAsFloat.toFixed(4)) === inputAsFloat;
+
+      const isValid = inputAsFloat >= 0 && inputAsFloat <= 1 && maxFourDecimals;
+
+      return isValid
+        ? t.success(inputAsString)
+        : t.failure(input, context, 'Must be a number between 0.0000 and 1');
+    });
+  },
+  t.identity
+);

x-pack/plugins/observability_solution/apm/common/agent_configuration/runtime_types/float_three_decimal_places_rt.test.ts

@@ -0,0 +1,38 @@
+/*
+ * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ * or more contributor license agreements. Licensed under the Elastic License
+ * 2.0; you may not use this file except in compliance with the Elastic License
+ * 2.0.
+ */
+
+import { floatThreeDecimalPlacesRt } from './float_three_decimal_places_rt';
+import { isRight } from 'fp-ts/lib/Either';
+
+describe('floatThreeDecimalPlacesRt', () => {
+  it('does not accept empty values', () => {
+    expect(isRight(floatThreeDecimalPlacesRt.decode(undefined))).toBe(false);
+    expect(isRight(floatThreeDecimalPlacesRt.decode(null))).toBe(false);
+    expect(isRight(floatThreeDecimalPlacesRt.decode(''))).toBe(false);
+  });
+
+  it('should only accept stringified numbers', () => {
+    expect(isRight(floatThreeDecimalPlacesRt.decode('0.5'))).toBe(true);
+    expect(isRight(floatThreeDecimalPlacesRt.decode(0.5))).toBe(false);
+  });
+
+  it('checks if the number falls within 0, 1', () => {
+    expect(isRight(floatThreeDecimalPlacesRt.decode('0'))).toBe(true);
+    expect(isRight(floatThreeDecimalPlacesRt.decode('0.5'))).toBe(true);
+    expect(isRight(floatThreeDecimalPlacesRt.decode('-0.1'))).toBe(false);
+    expect(isRight(floatThreeDecimalPlacesRt.decode('1.1'))).toBe(false);
+    expect(isRight(floatThreeDecimalPlacesRt.decode(NaN))).toBe(false);
+  });
+
+  it('checks whether the number of decimals is 3', () => {
+    expect(isRight(floatThreeDecimalPlacesRt.decode('1'))).toBe(true);
+    expect(isRight(floatThreeDecimalPlacesRt.decode('0.9'))).toBe(true);
+    expect(isRight(floatThreeDecimalPlacesRt.decode('0.99'))).toBe(true);
+    expect(isRight(floatThreeDecimalPlacesRt.decode('0.999'))).toBe(true);
+    expect(isRight(floatThreeDecimalPlacesRt.decode('0.9999'))).toBe(false);
+  });
+});

x-pack/plugins/observability_solution/apm/common/agent_configuration/runtime_types/float_rt.ts → x-pack/plugins/observability_solution/apm/common/agent_configuration/runtime_types/float_three_decimal_places_rt.ts

@@ -8,8 +8,8 @@
 import * as t from 'io-ts';
 import { either } from 'fp-ts/lib/Either';
 
-export const floatRt = new t.Type<string, string, unknown>(
-  'floatRt',
+export const floatThreeDecimalPlacesRt = new t.Type<string, string, unknown>(
+  'floatThreeDecimalPlacesRt',
   t.string.is,
   (input, context) => {
     return either.chain(t.string.validate(input, context), (inputAsString) => {

x-pack/plugins/observability_solution/apm/common/agent_configuration/setting_definitions/index.ts

@@ -13,7 +13,8 @@ import { AgentName } from '../../../typings/es_schemas/ui/fields/agent';
 import { booleanRt } from '../runtime_types/boolean_rt';
 import { getIntegerRt } from '../runtime_types/integer_rt';
 import { isRumOrMobileAgentName } from '../../agent_name';
-import { floatRt } from '../runtime_types/float_rt';
+import { floatThreeDecimalPlacesRt } from '../runtime_types/float_three_decimal_places_rt';
+import { floatFourDecimalPlacesRt } from '../runtime_types/float_four_decimal_places_rt';
 import { RawSettingDefinition, SettingDefinition } from './types';
 import { generalSettings } from './general_settings';
 import { javaSettings } from './java_settings';
@@ -45,8 +46,14 @@ function getSettingDefaults(setting: RawSettingDefinition): SettingDefinition {
     }
 
     case 'float': {
+      if (setting.key === 'transaction_sample_rate') {
+        return {
+          validation: floatFourDecimalPlacesRt,
+          ...setting,
+        };
+      }
       return {
-        validation: floatRt,
+        validation: floatThreeDecimalPlacesRt,
         ...setting,
       };
     }