diff --git a/src/main/services/agent-run-loop.ts b/src/main/services/agent-run-loop.ts
index 416f414e..f36a34eb 100644
--- a/src/main/services/agent-run-loop.ts
+++ b/src/main/services/agent-run-loop.ts
@@ -6,6 +6,7 @@ import { executeWorkspaceTool, isWorkspaceTool, WORKSPACE_TOOLS } from "./agent-
 import { canonicalMentionHandle } from "../../shared/mention-handles";
 import type { AgentTurnMessage, ToolDefinition } from "./provider-tool-turn";
 import { isComposioTool, executeComposioTool } from "./composio/composio-tool-bridge";
+import { compactToolHistory } from "./run-context-compaction";
 
 const MAX_ITERATIONS = 12;
 
@@ -50,6 +51,11 @@ export async function runAgentLoop(deps: AgentRunLoopDeps, input: AgentRunLoopIn
   let lastRequestId = "";
 
   for (let iteration = 1; iteration <= MAX_ITERATIONS; iteration += 1) {
+    const compaction = compactToolHistory(messages);
+    if (compaction.elided > 0) {
+      messages.splice(0, messages.length, ...compaction.messages);
+      console.info(`[run-loop] iteration ${iteration}: elided ${compaction.elided} earlier tool result(s)`);
+    }
     const turn = await deps.providers.runToolTurn({
       orgId: input.orgId,
       providerId: input.providerId,
diff --git a/src/main/services/run-context-compaction.ts b/src/main/services/run-context-compaction.ts
new file mode 100644
index 00000000..c343822d
--- /dev/null
+++ b/src/main/services/run-context-compaction.ts
@@ -0,0 +1,27 @@
+import type { AgentTurnMessage } from "./provider-tool-turn";
+
+const KEEP_RECENT_TOOL_TURNS = 3;
+const ELIDE_ABOVE_CHARS = 600;
+const PREVIEW_CHARS = 300;
+
+/** Older tool results shrink to a preview; the latest turns stay verbatim. */
+export function compactToolHistory(messages: AgentTurnMessage[]): { messages: AgentTurnMessage[]; elided: number } {
+  const toolTurnIndexes = messages.flatMap((message, index) => (message.role === "tool" ? [index] : []));
+  const compactBefore = toolTurnIndexes.length > KEEP_RECENT_TOOL_TURNS
+    ? toolTurnIndexes[toolTurnIndexes.length - KEEP_RECENT_TOOL_TURNS]
+    : 0;
+  let elided = 0;
+  const compacted = messages.map((message, index) => {
+    if (message.role !== "tool" || index >= compactBefore) return message;
+    const results = message.results.map((result) => {
+      if (result.output.length <= ELIDE_ABOVE_CHARS || result.output.startsWith("[Earlier result of ")) return result;
+      elided += 1;
+      return {
+        ...result,
+        output: `[Earlier result of ${result.toolName} elided to save context (${result.output.length} chars). It began: ${result.output.slice(0, PREVIEW_CHARS)}… Call ${result.toolName} again if you need the full result.]`,
+      };
+    });
+    return { ...message, results };
+  });
+  return { messages: compacted, elided };
+}
diff --git a/tests/unit/run-context-compaction.test.ts b/tests/unit/run-context-compaction.test.ts
new file mode 100644
index 00000000..2df589a0
--- /dev/null
+++ b/tests/unit/run-context-compaction.test.ts
@@ -0,0 +1,86 @@
+import { randomUUID } from "node:crypto";
+import { tmpdir } from "node:os";
+import { join } from "node:path";
+import { describe, expect, test } from "vitest";
+import { compactToolHistory } from "../../src/main/services/run-context-compaction";
+import { runAgentLoop } from "../../src/main/services/agent-run-loop";
+import { DatabaseConnection } from "../../src/main/database/connection";
+import { OrganizationService } from "../../src/main/services/organization-service";
+import { ChatService } from "../../src/main/services/chat-service";
+import { IntegrationKeyStore } from "../../src/main/services/integration-key-store";
+import type { AgentTurnMessage, AgentTurnResult } from "../../src/main/services/provider-tool-turn";
+
+function toolTurn(name: string, output: string): AgentTurnMessage[] {
+  const id = `c_${randomUUID()}`;
+  return [
+    { role: "assistant", text: "", toolCalls: [{ id, name, arguments: {} }] },
+    { role: "tool", results: [{ toolCallId: id, toolName: name, output }] },
+  ];
+}
+
+describe("tool history compaction", () => {
+  test("keeps the three latest tool turns verbatim and previews older long outputs", () => {
+    const big = (tag: string) => `${tag}:${"x".repeat(2000)}`;
+    const messages: AgentTurnMessage[] = [
+      { role: "user", text: "task" },
+      ...toolTurn("read_file", big("first")),
+      ...toolTurn("read_file", "short"),
+      ...toolTurn("fetch_url", big("third")),
+      ...toolTurn("read_file", big("fourth")),
+      ...toolTurn("read_file", big("fifth")),
+    ];
+    const { messages: compacted, elided } = compactToolHistory(messages);
+    expect(elided).toBe(1);
+    const outputs = compacted.flatMap((message) => (message.role === "tool" ? message.results.map((result) => result.output) : []));
+    expect(outputs[0]).toMatch(/^\[Earlier result of read_file elided to save context \(2006 chars\)\. It began: first:x+… Call read_file again/);
+    expect(outputs[1]).toBe("short");
+    expect(outputs[2]).toBe(big("third"));
+    expect(outputs[3]).toBe(big("fourth"));
+    expect(outputs[4]).toBe(big("fifth"));
+    expect(compactToolHistory(compacted).elided).toBe(0);
+  });
+
+  test("the run loop sends compacted history to the provider", async () => {
+    const connection = new DatabaseConnection(join(tmpdir(), `ac-compact-${randomUUID()}.db`));
+    const organization = new OrganizationService(connection.db);
+    let orgId = "";
+    let agentId = "";
+    connection.transaction(() => {
+      orgId = organization.createOrganization({ organizationName: "C", employeeName: "Y", mission: "m", goal: "g" });
+      agentId = organization.createAgent({
+        orgId, name: "Ana", role: "Analyst", department: "Operations",
+        modelProviderId: null, modelId: null, budgetCents: 1000, managerAgentId: null,
+      });
+    });
+    const chat = new ChatService(connection.db);
+    const general = connection.db.prepare("select id from chat_spaces where org_id = ? and name = 'general'").get(orgId) as { id: string };
+    chat.sendMessage({ orgId, spaceId: general.id, threadId: null, senderType: "agent", senderId: agentId, bodyMd: "y".repeat(3000), attachmentFileIds: [] });
+    const sent: AgentTurnMessage[][] = [];
+    let turn = 0;
+    const result = await runAgentLoop(
+      {
+        providers: {
+          integrationKeys: new IntegrationKeyStore(connection.db),
+          runToolTurn: async (input): Promise<AgentTurnResult & { requestId: string }> => {
+            sent.push(input.messages.map((message) => ({ ...message })));
+            turn += 1;
+            return turn <= 5
+              ? { text: "", toolCalls: [{ id: `c${turn}`, name: "read_messages", arguments: { channel: "general" } }], rawResponseJson: "{}", requestId: `r${turn}` }
+              : { text: "done", toolCalls: [], rawResponseJson: "{}", requestId: `r${turn}` };
+          },
+        },
+        tools: { db: connection.db, organization, chat },
+      },
+      {
+        orgId, providerId: "p", workspaceId: null, instructions: "i", initialUserTurn: "go",
+        toolContext: { orgId, agent: { id: agentId, modelProviderId: null, modelId: null }, taskProjectId: null, taskGoalId: null, taskId: null, sourceThreadId: null, workspace: null },
+      },
+    );
+    expect(result.finalText).toBe("done");
+    const outputs = sent[5].flatMap((message) => (message.role === "tool" ? message.results.map((item) => item.output) : []));
+    expect(outputs).toHaveLength(5);
+    expect(outputs.slice(0, 2).every((output) => output.startsWith("[Earlier result of read_messages elided"))).toBe(true);
+    expect(outputs.slice(2).every((output) => output.includes("y".repeat(3000)))).toBe(true);
+    connection.close();
+  });
+});