diff --git a/packages/cli/src/acp/acpClient.ts b/packages/cli/src/acp/acpClient.ts
index 2a8a524ff8..2e3a85b498 100644
--- a/packages/cli/src/acp/acpClient.ts
+++ b/packages/cli/src/acp/acpClient.ts
@@ -358,7 +358,10 @@ export class GeminiAgent {
       config.setFileSystemService(acpFileSystemService);
     }
 
-    const clientHistory = convertSessionToClientHistory(sessionData.messages);
+    const clientHistory = convertSessionToClientHistory(
+      sessionData.messages,
+      sessionData.lastCompressionIndex,
+    );
 
     const geminiClient = config.getGeminiClient();
     await geminiClient.initialize();
diff --git a/packages/cli/src/nonInteractiveCli.ts b/packages/cli/src/nonInteractiveCli.ts
index c2cab72353..8454a6b541 100644
--- a/packages/cli/src/nonInteractiveCli.ts
+++ b/packages/cli/src/nonInteractiveCli.ts
@@ -222,6 +222,7 @@ export async function runNonInteractive({
         await geminiClient.resumeChat(
           convertSessionToClientHistory(
             resumedSessionData.conversation.messages,
+            resumedSessionData.conversation.lastCompressionIndex,
           ),
           resumedSessionData,
         );
diff --git a/packages/cli/src/ui/hooks/useSessionBrowser.ts b/packages/cli/src/ui/hooks/useSessionBrowser.ts
index 9c6d05b322..0e6bf25f3f 100644
--- a/packages/cli/src/ui/hooks/useSessionBrowser.ts
+++ b/packages/cli/src/ui/hooks/useSessionBrowser.ts
@@ -76,12 +76,17 @@ export const useSessionBrowser = (
 
           // We've loaded it; tell the UI about it.
           setIsSessionBrowserOpen(false);
+          const compressionIndex = conversation.lastCompressionIndex;
           const historyData = convertSessionToHistoryFormats(
             conversation.messages,
+            compressionIndex,
           );
           await onLoadHistory(
             historyData.uiHistory,
-            convertSessionToClientHistory(conversation.messages),
+            convertSessionToClientHistory(
+              conversation.messages,
+              compressionIndex,
+            ),
             resumedSessionData,
           );
         } catch (error) {
diff --git a/packages/cli/src/ui/hooks/useSessionResume.ts b/packages/cli/src/ui/hooks/useSessionResume.ts
index 055686773b..affa2bcf7f 100644
--- a/packages/cli/src/ui/hooks/useSessionResume.ts
+++ b/packages/cli/src/ui/hooks/useSessionResume.ts
@@ -109,12 +109,18 @@ export function useSessionResume({
       !hasLoadedResumedSession.current
     ) {
       hasLoadedResumedSession.current = true;
+      const compressionIndex =
+        resumedSessionData.conversation.lastCompressionIndex;
       const historyData = convertSessionToHistoryFormats(
         resumedSessionData.conversation.messages,
+        compressionIndex,
       );
       void loadHistoryForResume(
         historyData.uiHistory,
-        convertSessionToClientHistory(resumedSessionData.conversation.messages),
+        convertSessionToClientHistory(
+          resumedSessionData.conversation.messages,
+          compressionIndex,
+        ),
         resumedSessionData,
       );
     }
diff --git a/packages/cli/src/utils/sessionUtils.test.ts b/packages/cli/src/utils/sessionUtils.test.ts
index bcf7c19dfe..92a1ba0ecd 100644
--- a/packages/cli/src/utils/sessionUtils.test.ts
+++ b/packages/cli/src/utils/sessionUtils.test.ts
@@ -10,10 +10,16 @@ import {
   extractFirstUserMessage,
   formatRelativeTime,
   hasUserOrAssistantMessage,
+  convertSessionToHistoryFormats,
   SessionError,
 } from './sessionUtils.js';
-import type { Config, MessageRecord } from '@google/gemini-cli-core';
+import type {
+  Config,
+  MessageRecord,
+  ConversationRecord,
+} from '@google/gemini-cli-core';
 import { SESSION_FILE_PREFIX } from '@google/gemini-cli-core';
+import { MessageType } from '../ui/types.js';
 import * as fs from 'node:fs/promises';
 import path from 'node:path';
 import { randomUUID } from 'node:crypto';
@@ -765,3 +771,80 @@ describe('formatRelativeTime', () => {
     expect(formatRelativeTime(thirtySecondsAgo.toISOString())).toBe('Just now');
   });
 });
+
+describe('convertSessionToHistoryFormats', () => {
+  const messages: ConversationRecord['messages'] = [
+    {
+      id: '1',
+      type: 'user',
+      timestamp: '2024-01-01T10:00:00Z',
+      content: 'First question',
+    },
+    {
+      id: '2',
+      type: 'gemini',
+      timestamp: '2024-01-01T10:01:00Z',
+      content: 'First answer',
+    },
+    {
+      id: '3',
+      type: 'user',
+      timestamp: '2024-01-01T10:02:00Z',
+      content: 'Second question',
+    },
+    {
+      id: '4',
+      type: 'gemini',
+      timestamp: '2024-01-01T10:03:00Z',
+      content: 'Second answer',
+    },
+  ];
+
+  it('should convert all messages when startIndex is undefined', () => {
+    const { uiHistory } = convertSessionToHistoryFormats(messages);
+
+    expect(uiHistory).toHaveLength(4);
+    expect(uiHistory[0]).toEqual({
+      type: MessageType.USER,
+      text: 'First question',
+    });
+    expect(uiHistory[1]).toEqual({
+      type: MessageType.GEMINI,
+      text: 'First answer',
+    });
+    expect(uiHistory[2]).toEqual({
+      type: MessageType.USER,
+      text: 'Second question',
+    });
+    expect(uiHistory[3]).toEqual({
+      type: MessageType.GEMINI,
+      text: 'Second answer',
+    });
+  });
+
+  it('should show only post-compression messages with a leading info message when startIndex is provided', () => {
+    const { uiHistory } = convertSessionToHistoryFormats(messages, 2);
+
+    // Should have: 1 info message + 2 remaining messages
+    expect(uiHistory).toHaveLength(3);
+
+    // First item is the compression info message
+    expect(uiHistory[0].type).toBe(MessageType.INFO);
+    expect((uiHistory[0] as { type: string; text: string }).text).toContain(
+      '2 messages',
+    );
+    expect((uiHistory[0] as { type: string; text: string }).text).toContain(
+      'compressed',
+    );
+
+    // Remaining items are the post-compression messages
+    expect(uiHistory[1]).toEqual({
+      type: MessageType.USER,
+      text: 'Second question',
+    });
+    expect(uiHistory[2]).toEqual({
+      type: MessageType.GEMINI,
+      text: 'Second answer',
+    });
+  });
+});
diff --git a/packages/cli/src/utils/sessionUtils.ts b/packages/cli/src/utils/sessionUtils.ts
index 3aa0131ac2..5d93e2568e 100644
--- a/packages/cli/src/utils/sessionUtils.ts
+++ b/packages/cli/src/utils/sessionUtils.ts
@@ -526,15 +526,31 @@ export class SessionSelector {
 
 /**
  * Converts session/conversation data into UI history format.
+ *
+ * @param messages - The full array of recorded messages.
+ * @param startIndex - If provided, only messages from this index onward are
+ *   converted.  A leading info item is added to indicate earlier history was
+ *   compressed away.
  */
 export function convertSessionToHistoryFormats(
   messages: ConversationRecord['messages'],
+  startIndex?: number,
 ): {
   uiHistory: HistoryItemWithoutId[];
 } {
   const uiHistory: HistoryItemWithoutId[] = [];
+  const hasCompressedHistory =
+    startIndex != null && startIndex > 0 && startIndex < messages.length;
+  const slice = hasCompressedHistory ? messages.slice(startIndex) : messages;
 
-  for (const msg of messages) {
+  if (hasCompressedHistory) {
+    uiHistory.push({
+      type: MessageType.INFO,
+      text: `ℹ️  Earlier history (${startIndex} messages) was compressed. Showing conversation from last compression point.`,
+    });
+  }
+
+  for (const msg of slice) {
     // Add thoughts if present
     if (msg.type === 'gemini' && msg.thoughts && msg.thoughts.length > 0) {
       for (const thought of msg.thoughts) {
diff --git a/packages/core/src/core/__snapshots__/prompts.test.ts.snap b/packages/core/src/core/__snapshots__/prompts.test.ts.snap
index 07ba92bafd..d3cd847f3c 100644
--- a/packages/core/src/core/__snapshots__/prompts.test.ts.snap
+++ b/packages/core/src/core/__snapshots__/prompts.test.ts.snap
@@ -408,6 +408,8 @@ Operate as a **strategic orchestrator**. Your own context window is your most pr
 
 When you delegate, the sub-agent's entire execution is consolidated into a single summary in your history, keeping your main loop lean.
 
+**Concurrency Safety and Mandate:** You should NEVER run multiple subagents in a single turn if their abilities mutate the same files or resources. This is to prevent race conditions and ensure that the workspace is in a consistent state. Only run multiple subagents in parallel when their tasks are independent (e.g., multiple concurrent research or read-only tasks) or if parallel execution is explicitly requested by the user.
+
 **High-Impact Delegation Candidates:**
 - **Repetitive Batch Tasks:** Tasks involving more than 3 files or repeated steps (e.g., "Add license headers to all files in src/", "Fix all lint errors in the project").
 - **High-Volume Output:** Commands or tools expected to return large amounts of data (e.g., verbose builds, exhaustive file searches).
@@ -1143,6 +1145,8 @@ Operate as a **strategic orchestrator**. Your own context window is your most pr
 
 When you delegate, the sub-agent's entire execution is consolidated into a single summary in your history, keeping your main loop lean.
 
+**Concurrency Safety and Mandate:** You should NEVER run multiple subagents in a single turn if their abilities mutate the same files or resources. This is to prevent race conditions and ensure that the workspace is in a consistent state. Only run multiple subagents in parallel when their tasks are independent (e.g., multiple concurrent research or read-only tasks) or if parallel execution is explicitly requested by the user.
+
 **High-Impact Delegation Candidates:**
 - **Repetitive Batch Tasks:** Tasks involving more than 3 files or repeated steps (e.g., "Add license headers to all files in src/", "Fix all lint errors in the project").
 - **High-Volume Output:** Commands or tools expected to return large amounts of data (e.g., verbose builds, exhaustive file searches).
@@ -1294,6 +1298,8 @@ Operate as a **strategic orchestrator**. Your own context window is your most pr
 
 When you delegate, the sub-agent's entire execution is consolidated into a single summary in your history, keeping your main loop lean.
 
+**Concurrency Safety and Mandate:** You should NEVER run multiple subagents in a single turn if their abilities mutate the same files or resources. This is to prevent race conditions and ensure that the workspace is in a consistent state. Only run multiple subagents in parallel when their tasks are independent (e.g., multiple concurrent research or read-only tasks) or if parallel execution is explicitly requested by the user.
+
 **High-Impact Delegation Candidates:**
 - **Repetitive Batch Tasks:** Tasks involving more than 3 files or repeated steps (e.g., "Add license headers to all files in src/", "Fix all lint errors in the project").
 - **High-Volume Output:** Commands or tools expected to return large amounts of data (e.g., verbose builds, exhaustive file searches).
@@ -1464,6 +1470,8 @@ Operate as a **strategic orchestrator**. Your own context window is your most pr
 
 When you delegate, the sub-agent's entire execution is consolidated into a single summary in your history, keeping your main loop lean.
 
+**Concurrency Safety and Mandate:** You should NEVER run multiple subagents in a single turn if their abilities mutate the same files or resources. This is to prevent race conditions and ensure that the workspace is in a consistent state. Only run multiple subagents in parallel when their tasks are independent (e.g., multiple concurrent research or read-only tasks) or if parallel execution is explicitly requested by the user.
+
 **High-Impact Delegation Candidates:**
 - **Repetitive Batch Tasks:** Tasks involving more than 3 files or repeated steps (e.g., "Add license headers to all files in src/", "Fix all lint errors in the project").
 - **High-Volume Output:** Commands or tools expected to return large amounts of data (e.g., verbose builds, exhaustive file searches).
@@ -1608,6 +1616,8 @@ Operate as a **strategic orchestrator**. Your own context window is your most pr
 
 When you delegate, the sub-agent's entire execution is consolidated into a single summary in your history, keeping your main loop lean.
 
+**Concurrency Safety and Mandate:** You should NEVER run multiple subagents in a single turn if their abilities mutate the same files or resources. This is to prevent race conditions and ensure that the workspace is in a consistent state. Only run multiple subagents in parallel when their tasks are independent (e.g., multiple concurrent research or read-only tasks) or if parallel execution is explicitly requested by the user.
+
 **High-Impact Delegation Candidates:**
 - **Repetitive Batch Tasks:** Tasks involving more than 3 files or repeated steps (e.g., "Add license headers to all files in src/", "Fix all lint errors in the project").
 - **High-Volume Output:** Commands or tools expected to return large amounts of data (e.g., verbose builds, exhaustive file searches).
@@ -3171,6 +3181,8 @@ Operate as a **strategic orchestrator**. Your own context window is your most pr
 
 When you delegate, the sub-agent's entire execution is consolidated into a single summary in your history, keeping your main loop lean.
 
+**Concurrency Safety and Mandate:** You should NEVER run multiple subagents in a single turn if their abilities mutate the same files or resources. This is to prevent race conditions and ensure that the workspace is in a consistent state. Only run multiple subagents in parallel when their tasks are independent (e.g., multiple concurrent research or read-only tasks) or if parallel execution is explicitly requested by the user.
+
 **High-Impact Delegation Candidates:**
 - **Repetitive Batch Tasks:** Tasks involving more than 3 files or repeated steps (e.g., "Add license headers to all files in src/", "Fix all lint errors in the project").
 - **High-Volume Output:** Commands or tools expected to return large amounts of data (e.g., verbose builds, exhaustive file searches).
@@ -3323,6 +3335,8 @@ Operate as a **strategic orchestrator**. Your own context window is your most pr
 
 When you delegate, the sub-agent's entire execution is consolidated into a single summary in your history, keeping your main loop lean.
 
+**Concurrency Safety and Mandate:** You should NEVER run multiple subagents in a single turn if their abilities mutate the same files or resources. This is to prevent race conditions and ensure that the workspace is in a consistent state. Only run multiple subagents in parallel when their tasks are independent (e.g., multiple concurrent research or read-only tasks) or if parallel execution is explicitly requested by the user.
+
 **High-Impact Delegation Candidates:**
 - **Repetitive Batch Tasks:** Tasks involving more than 3 files or repeated steps (e.g., "Add license headers to all files in src/", "Fix all lint errors in the project").
 - **High-Volume Output:** Commands or tools expected to return large amounts of data (e.g., verbose builds, exhaustive file searches).
@@ -3795,6 +3809,8 @@ Operate as a **strategic orchestrator**. Your own context window is your most pr
 
 When you delegate, the sub-agent's entire execution is consolidated into a single summary in your history, keeping your main loop lean.
 
+**Concurrency Safety and Mandate:** You should NEVER run multiple subagents in a single turn if their abilities mutate the same files or resources. This is to prevent race conditions and ensure that the workspace is in a consistent state. Only run multiple subagents in parallel when their tasks are independent (e.g., multiple concurrent research or read-only tasks) or if parallel execution is explicitly requested by the user.
+
 **High-Impact Delegation Candidates:**
 - **Repetitive Batch Tasks:** Tasks involving more than 3 files or repeated steps (e.g., "Add license headers to all files in src/", "Fix all lint errors in the project").
 - **High-Volume Output:** Commands or tools expected to return large amounts of data (e.g., verbose builds, exhaustive file searches).
diff --git a/packages/core/src/core/client.test.ts b/packages/core/src/core/client.test.ts
index b9e8b11b8a..d34009392c 100644
--- a/packages/core/src/core/client.test.ts
+++ b/packages/core/src/core/client.test.ts
@@ -415,6 +415,7 @@ describe('Gemini Client (client.ts)', () => {
         getChatRecordingService: vi.fn().mockReturnValue({
           getConversation: vi.fn().mockReturnValue(null),
           getConversationFilePath: vi.fn().mockReturnValue(null),
+          recordCompressionPoint: vi.fn(),
         }),
       };
       client['chat'] = mockOriginalChat as GeminiChat;
@@ -649,6 +650,7 @@ describe('Gemini Client (client.ts)', () => {
       const mockRecordingService = {
         getConversation: vi.fn().mockReturnValue(mockConversation),
         getConversationFilePath: vi.fn().mockReturnValue(mockFilePath),
+        recordCompressionPoint: vi.fn(),
       };
       vi.mocked(mockOriginalChat.getChatRecordingService!).mockReturnValue(
         mockRecordingService as unknown as ChatRecordingService,
@@ -1552,6 +1554,7 @@ ${JSON.stringify(
         getChatRecordingService: vi.fn().mockReturnValue({
           getConversation: vi.fn(),
           getConversationFilePath: vi.fn(),
+          recordCompressionPoint: vi.fn(),
         }),
       } as unknown as GeminiChat;
 
@@ -1565,6 +1568,7 @@ ${JSON.stringify(
         getChatRecordingService: vi.fn().mockReturnValue({
           getConversation: vi.fn(),
           getConversationFilePath: vi.fn(),
+          recordCompressionPoint: vi.fn(),
         }),
       } as unknown as GeminiChat;
 
diff --git a/packages/core/src/core/client.ts b/packages/core/src/core/client.ts
index 123b80ff2c..834aa00b6d 100644
--- a/packages/core/src/core/client.ts
+++ b/packages/core/src/core/client.ts
@@ -1222,6 +1222,11 @@ Do not wait for a reflection cycle if the information is critical for future tur
         // capture current session data before resetting
         const currentRecordingService =
           this.getChat().getChatRecordingService();
+
+        // Mark this point in the recording so resume only loads
+        // messages from here onward (everything before was compressed).
+        currentRecordingService.recordCompressionPoint();
+
         const conversation = currentRecordingService.getConversation();
         const filePath = currentRecordingService.getConversationFilePath();
 
diff --git a/packages/core/src/prompts/promptProvider.ts b/packages/core/src/prompts/promptProvider.ts
index da165e3375..a39750ca09 100644
--- a/packages/core/src/prompts/promptProvider.ts
+++ b/packages/core/src/prompts/promptProvider.ts
@@ -178,6 +178,7 @@ export class PromptProvider {
                 approvedPlan: approvedPlanPath
                   ? { path: approvedPlanPath }
                   : undefined,
+                taskTracker: config.isTrackerEnabled(),
               }),
               !isPlanMode,
             ),
@@ -189,6 +190,7 @@ export class PromptProvider {
                   planModeToolsList,
                   plansDir: config.storage.getPlansDir(),
                   approvedPlanPath: config.getApprovedPlanPath(),
+                  taskTracker: config.isTrackerEnabled(),
                 }),
                 isPlanMode,
               )
@@ -200,48 +202,7 @@ export class PromptProvider {
               enableShellEfficiency: config.getEnableShellOutputEfficiency(),
               interactiveShellEnabled: config.isInteractiveShellEnabled(),
             })),
-          skills.length > 0,
-        ),
-        hookContext: isSectionEnabled('hookContext') || undefined,
-        primaryWorkflows: this.withSection(
-          'primaryWorkflows',
-          () => ({
-            interactive: interactiveMode,
-            enableCodebaseInvestigator: enabledToolNames.has(
-              CodebaseInvestigatorAgent.name,
-            ),
-            enableWriteTodosTool: enabledToolNames.has(WRITE_TODOS_TOOL_NAME),
-            enableEnterPlanModeTool: enabledToolNames.has(
-              ENTER_PLAN_MODE_TOOL_NAME,
-            ),
-            enableGrep: enabledToolNames.has(GREP_TOOL_NAME),
-            enableGlob: enabledToolNames.has(GLOB_TOOL_NAME),
-            approvedPlan: approvedPlanPath
-              ? { path: approvedPlanPath }
-              : undefined,
-            taskTracker: config.isTrackerEnabled(),
-          }),
-          !isPlanMode,
-        ),
-        planningWorkflow: this.withSection(
-          'planningWorkflow',
-          () => ({
-            planModeToolsList,
-            plansDir: config.storage.getPlansDir(),
-            approvedPlanPath: config.getApprovedPlanPath(),
-            taskTracker: config.isTrackerEnabled(),
-          }),
-          isPlanMode,
-        ),
         taskTracker: config.isTrackerEnabled(),
-        operationalGuidelines: this.withSection(
-          'operationalGuidelines',
-          () => ({
-            interactive: interactiveMode,
-            enableShellEfficiency: config.getEnableShellOutputEfficiency(),
-            interactiveShellEnabled: config.isInteractiveShellEnabled(),
-          }),
-        ),
         sandbox: this.withSection('sandbox', () => getSandboxMode()),
         interactiveYoloMode: this.withSection(
           'interactiveYoloMode',
diff --git a/packages/core/src/prompts/snippets.ts b/packages/core/src/prompts/snippets.ts
index 7219bd35f1..245700256e 100644
--- a/packages/core/src/prompts/snippets.ts
+++ b/packages/core/src/prompts/snippets.ts
@@ -138,6 +138,7 @@ export function getCoreSystemPrompt(options: SystemPromptOptions): string {
     options.planningWorkflow
       ? renderPlanningWorkflow(options.planningWorkflow)
       : renderPrimaryWorkflows(options.primaryWorkflows),
+    options.taskTracker ? renderTaskTracker() : '',
     renderOperationalGuidelines(options.operationalGuidelines),
     renderInteractiveYoloMode(options.interactiveYoloMode),
     renderSandbox(options.sandbox),
@@ -151,18 +152,6 @@ export function getCoreSystemPrompt(options: SystemPromptOptions): string {
     .trim();
 }
 
-${options.taskTracker ? renderTaskTracker() : ''}
-
-${renderOperationalGuidelines(options.operationalGuidelines)}
-
-${renderInteractiveYoloMode(options.interactiveYoloMode)}
-
-${renderSandbox(options.sandbox)}
-
-${renderGitRepo(options.gitRepo)}
-`.trim();
-}
-
 /**
  * Wraps the base prompt with user memory and approval mode plans.
  */
diff --git a/packages/core/src/services/chatRecordingService.test.ts b/packages/core/src/services/chatRecordingService.test.ts
index 2b8e8f1977..3317dce432 100644
--- a/packages/core/src/services/chatRecordingService.test.ts
+++ b/packages/core/src/services/chatRecordingService.test.ts
@@ -532,6 +532,60 @@ describe('ChatRecordingService', () => {
     });
   });
 
+  describe('recordCompressionPoint', () => {
+    it('should set lastCompressionIndex to the current message count and update on subsequent calls', () => {
+      chatRecordingService.initialize();
+
+      // Record a few messages
+      chatRecordingService.recordMessage({
+        type: 'user',
+        content: 'msg1',
+        model: 'm',
+      });
+      chatRecordingService.recordMessage({
+        type: 'gemini',
+        content: 'response1',
+        model: 'm',
+      });
+      chatRecordingService.recordMessage({
+        type: 'user',
+        content: 'msg2',
+        model: 'm',
+      });
+
+      // Record compression point
+      chatRecordingService.recordCompressionPoint();
+
+      const sessionFile = chatRecordingService.getConversationFilePath()!;
+      let conversation = JSON.parse(
+        fs.readFileSync(sessionFile, 'utf8'),
+      ) as ConversationRecord;
+
+      expect(conversation.lastCompressionIndex).toBe(3);
+
+      // Record more messages
+      chatRecordingService.recordMessage({
+        type: 'gemini',
+        content: 'response2',
+        model: 'm',
+      });
+      chatRecordingService.recordMessage({
+        type: 'user',
+        content: 'msg3',
+        model: 'm',
+      });
+
+      // Record compression point again
+      chatRecordingService.recordCompressionPoint();
+
+      conversation = JSON.parse(
+        fs.readFileSync(sessionFile, 'utf8'),
+      ) as ConversationRecord;
+
+      expect(conversation.lastCompressionIndex).toBe(5);
+    });
+  });
+
   describe('ENOSPC (disk full) graceful degradation - issue #16266', () => {
     it('should disable recording and not throw when ENOSPC occurs during initialize', () => {
       const enospcError = new Error('ENOSPC: no space left on device');
diff --git a/packages/core/src/services/chatRecordingService.ts b/packages/core/src/services/chatRecordingService.ts
index cd8d1e53c1..64d7056b6d 100644
--- a/packages/core/src/services/chatRecordingService.ts
+++ b/packages/core/src/services/chatRecordingService.ts
@@ -104,6 +104,13 @@ export interface ConversationRecord {
   directories?: string[];
   /** The kind of conversation (main agent or subagent) */
   kind?: 'main' | 'subagent';
+  /**
+   * The index into `messages` at which the last compression occurred.
+   * On resume, only messages from this index onward need to be loaded
+   * into the client history / UI — earlier messages were already
+   * summarised and folded into the compressed context.
+   */
+  lastCompressionIndex?: number;
 }
 
 /**
@@ -532,6 +539,25 @@ export class ChatRecordingService {
     this.writeConversation(conversation);
   }
 
+  /**
+   * Marks the current end of the messages array as the compression point.
+   * On resume, only messages from this index onward will be loaded.
+   */
+  recordCompressionPoint(): void {
+    if (!this.conversationFile) return;
+
+    try {
+      this.updateConversation((conversation) => {
+        conversation.lastCompressionIndex = conversation.messages.length;
+      });
+    } catch (error) {
+      debugLogger.error(
+        'Error recording compression point in chat history.',
+        error,
+      );
+    }
+  }
+
   /**
    * Saves a summary for the current session.
    */
diff --git a/packages/core/src/utils/sessionUtils.test.ts b/packages/core/src/utils/sessionUtils.test.ts
index d132087ee8..c2b778f7a2 100644
--- a/packages/core/src/utils/sessionUtils.test.ts
+++ b/packages/core/src/utils/sessionUtils.test.ts
@@ -182,4 +182,70 @@ describe('convertSessionToClientHistory', () => {
       },
     ]);
   });
+
+  describe('startIndex parameter', () => {
+    const messages: ConversationRecord['messages'] = [
+      {
+        id: '1',
+        type: 'user',
+        timestamp: '2024-01-01T10:00:00Z',
+        content: 'First message',
+      },
+      {
+        id: '2',
+        type: 'gemini',
+        timestamp: '2024-01-01T10:01:00Z',
+        content: 'First response',
+      },
+      {
+        id: '3',
+        type: 'user',
+        timestamp: '2024-01-01T10:02:00Z',
+        content: 'Second message',
+      },
+      {
+        id: '4',
+        type: 'gemini',
+        timestamp: '2024-01-01T10:03:00Z',
+        content: 'Second response',
+      },
+    ];
+
+    it('should only convert messages from startIndex onward', () => {
+      const history = convertSessionToClientHistory(messages, 2);
+
+      expect(history).toEqual([
+        { role: 'user', parts: [{ text: 'Second message' }] },
+        { role: 'model', parts: [{ text: 'Second response' }] },
+      ]);
+    });
+
+    it('should convert all messages when startIndex is 0', () => {
+      const history = convertSessionToClientHistory(messages, 0);
+
+      expect(history).toEqual([
+        { role: 'user', parts: [{ text: 'First message' }] },
+        { role: 'model', parts: [{ text: 'First response' }] },
+        { role: 'user', parts: [{ text: 'Second message' }] },
+        { role: 'model', parts: [{ text: 'Second response' }] },
+      ]);
+    });
+
+    it('should convert all messages when startIndex is undefined', () => {
+      const history = convertSessionToClientHistory(messages, undefined);
+
+      expect(history).toEqual([
+        { role: 'user', parts: [{ text: 'First message' }] },
+        { role: 'model', parts: [{ text: 'First response' }] },
+        { role: 'user', parts: [{ text: 'Second message' }] },
+        { role: 'model', parts: [{ text: 'Second response' }] },
+      ]);
+    });
+
+    it('should return empty array when startIndex exceeds messages length', () => {
+      const history = convertSessionToClientHistory(messages, 100);
+
+      expect(history).toEqual([]);
+    });
+  });
 });
diff --git a/packages/core/src/utils/sessionUtils.ts b/packages/core/src/utils/sessionUtils.ts
index 4803dd4f07..488f1dbbbf 100644
--- a/packages/core/src/utils/sessionUtils.ts
+++ b/packages/core/src/utils/sessionUtils.ts
@@ -26,13 +26,22 @@ function ensurePartArray(content: PartListUnion): Part[] {
 
 /**
  * Converts session/conversation data into Gemini client history formats.
+ *
+ * @param messages - The full array of recorded messages.
+ * @param startIndex - If provided, only messages from this index onward are
+ *   converted.  Used on resume to skip pre-compression history.
  */
 export function convertSessionToClientHistory(
   messages: ConversationRecord['messages'],
+  startIndex?: number,
 ): Array<{ role: 'user' | 'model'; parts: Part[] }> {
   const clientHistory: Array<{ role: 'user' | 'model'; parts: Part[] }> = [];
+  const slice =
+    startIndex != null && startIndex > 0
+      ? messages.slice(startIndex)
+      : messages;
 
-  for (const msg of messages) {
+  for (const msg of slice) {
     if (msg.type === 'info' || msg.type === 'error' || msg.type === 'warning') {
       continue;
     }