[9.0] Pass system message to inferenceCliente.chatComplete (elastic#2…

…11263) (elastic#211360)

# Backport

This will backport the following commits from `main` to `9.0`:
- [Pass system message to inferenceCliente.chatComplete
(elastic#211263)](elastic#211263)

<!--- Backport version: 9.4.3 -->

### Questions ?
Please refer to the [Backport tool
documentation](https://github.com/sqren/backport)

<!--BACKPORT [{"author":{"name":"Arturo
Lidueña","email":"arturo.liduena@elastic.co"},"sourceCommit":{"committedDate":"2025-02-16T08:43:50Z","message":"Pass
system message to inferenceCliente.chatComplete (elastic#211263)\n\nCloses
elastic#211257 \r\n\r\n## Summary\r\n\r\nRegression introduced in
8.18\r\n(https://github.com/elastic/kibana/pull/199286)\r\n\r\nWe no
longer pass the `system` message to the inference plugin, and\r\nthereby
the LLM. This means that we are only passing user messages to\r\nthe
LLM. The system message is important in steering the
conversation,\r\nand providing guardrails to the
LLM.","sha":"117802cbb2ba73df14f82a2ee1caee1bfe5b1ced","branchLabelMapping":{"^v9.1.0$":"main","^v8.19.0$":"8.x","^v(\\d+).(\\d+).\\d+$":"$1.$2"}},"sourcePullRequest":{"labels":["release_note:fix","v9.0.0","Team:Obs
AI
Assistant","backport:version","v8.18.0","v9.1.0","v8.19.0"],"title":"Pass
system message to
inferenceCliente.chatComplete","number":211263,"url":"https://github.com/elastic/kibana/pull/211263","mergeCommit":{"message":"Pass
system message to inferenceCliente.chatComplete (elastic#211263)\n\nCloses
elastic#211257 \r\n\r\n## Summary\r\n\r\nRegression introduced in
8.18\r\n(https://github.com/elastic/kibana/pull/199286)\r\n\r\nWe no
longer pass the `system` message to the inference plugin, and\r\nthereby
the LLM. This means that we are only passing user messages to\r\nthe
LLM. The system message is important in steering the
conversation,\r\nand providing guardrails to the
LLM.","sha":"117802cbb2ba73df14f82a2ee1caee1bfe5b1ced"}},"sourceBranch":"main","suggestedTargetBranches":["9.0","8.18","8.x"],"targetPullRequestStates":[{"branch":"9.0","label":"v9.0.0","branchLabelMappingKey":"^v(\\d+).(\\d+).\\d+$","isSourceBranch":false,"state":"NOT_CREATED"},{"branch":"8.18","label":"v8.18.0","branchLabelMappingKey":"^v(\\d+).(\\d+).\\d+$","isSourceBranch":false,"state":"NOT_CREATED"},{"branch":"main","label":"v9.1.0","branchLabelMappingKey":"^v9.1.0$","isSourceBranch":true,"state":"MERGED","url":"https://github.com/elastic/kibana/pull/211263","number":211263,"mergeCommit":{"message":"Pass
system message to inferenceCliente.chatComplete (elastic#211263)\n\nCloses
elastic#211257 \r\n\r\n## Summary\r\n\r\nRegression introduced in
8.18\r\n(https://github.com/elastic/kibana/pull/199286)\r\n\r\nWe no
longer pass the `system` message to the inference plugin, and\r\nthereby
the LLM. This means that we are only passing user messages to\r\nthe
LLM. The system message is important in steering the
conversation,\r\nand providing guardrails to the
LLM.","sha":"117802cbb2ba73df14f82a2ee1caee1bfe5b1ced"}},{"branch":"8.x","label":"v8.19.0","branchLabelMappingKey":"^v8.19.0$","isSourceBranch":false,"state":"NOT_CREATED"}]}]
BACKPORT-->

Co-authored-by: Arturo Lidueña <arturo.liduena@elastic.co>

x-pack/platform/plugins/shared/observability_ai_assistant/server/service/client/index.test.ts

@@ -346,6 +346,7 @@ describe('Observability AI Assistant client', () => {
           {
             connectorId: 'foo',
             stream: true,
+            system: EXPECTED_STORED_SYSTEM_MESSAGE,
             messages: expect.arrayContaining([
               { role: 'user', content: 'How many alerts do I have?' },
             ]),
@@ -916,6 +917,7 @@ describe('Observability AI Assistant client', () => {
           {
             connectorId: 'foo',
             stream: true,
+            system: EXPECTED_STORED_SYSTEM_MESSAGE,
             messages: expect.arrayContaining([
               { role: 'user', content: 'How many alerts do I have?' },
             ]),
@@ -1077,6 +1079,7 @@ describe('Observability AI Assistant client', () => {
           {
             connectorId: 'foo',
             stream: true,
+            system: EXPECTED_STORED_SYSTEM_MESSAGE,
             messages: expect.arrayContaining([
               { role: 'user', content: 'How many alerts do I have?' },
             ]),

x-pack/platform/plugins/shared/observability_ai_assistant/server/service/client/index.ts

@@ -508,6 +508,8 @@ export class ObservabilityAIAssistantClient {
 
     const options = {
       connectorId,
+      system: messages.find((message) => message.message.role === MessageRole.System)?.message
+        .content,
       messages: convertMessagesForInference(
         messages.filter((message) => message.message.role !== MessageRole.System)
       ),