feat(server): add hints for context files (#13444)

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

* **New Features**
* Attachments (files) are now included in the conversation context,
allowing users to reference files during chat sessions.
* Added a new "blobRead" tool enabling secure, permission-checked
reading of attachment content in chat sessions.

* **Improvements**
* Enhanced chat session preparation to always include relevant context
files.
* System messages now clearly display attached files and selected
content only when available, improving context clarity for users.
* Updated tool-calling guidelines to ensure user workspace is searched
even when attachment content suffices.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

packages/backend/server/src/plugins/copilot/providers/provider.ts

@@ -16,10 +16,12 @@ import { IndexerService } from '../../indexer';
 import { CopilotContextService } from '../context';
 import { PromptService } from '../prompt';
 import {
+  buildBlobContentGetter,
   buildContentGetter,
   buildDocContentGetter,
   buildDocKeywordSearchGetter,
   buildDocSearchGetter,
+  createBlobReadTool,
   createCodeArtifactTool,
   createConversationSummaryTool,
   createDocComposeTool,
@@ -156,6 +158,9 @@ export abstract class CopilotProvider<C = any> {
     if (options?.tools?.length) {
       this.logger.debug(`getTools: ${JSON.stringify(options.tools)}`);
       const ac = this.moduleRef.get(AccessController, { strict: false });
+      const context = this.moduleRef.get(CopilotContextService, {
+        strict: false,
+      });
       const docReader = this.moduleRef.get(DocReader, { strict: false });
       const models = this.moduleRef.get(Models, { strict: false });
       const prompt = this.moduleRef.get(PromptService, {
@@ -172,6 +177,16 @@ export abstract class CopilotProvider<C = any> {
           continue;
         }
         switch (tool) {
+          case 'blobRead': {
+            const docContext = options.session
+              ? await context.getBySessionId(options.session)
+              : null;
+            const getBlobContent = buildBlobContentGetter(ac, docContext);
+            tools.blob_read = createBlobReadTool(
+              getBlobContent.bind(null, options)
+            );
+            break;
+          }
           case 'codeArtifact': {
             tools.code_artifact = createCodeArtifactTool(prompt, this.factory);
             break;
@@ -194,9 +209,6 @@ export abstract class CopilotProvider<C = any> {
             break;
           }
           case 'docSemanticSearch': {
-            const context = this.moduleRef.get(CopilotContextService, {
-              strict: false,
-            });
             const docContext = options.session
               ? await context.getBySessionId(options.session)
               : null;