diff --git a/hub/src/agent/runner.ts b/hub/src/agent/runner.ts
index 76f25f8..d9d962b 100644
--- a/hub/src/agent/runner.ts
+++ b/hub/src/agent/runner.ts
@@ -211,6 +211,12 @@ export async function runAgent(req: RunRequest): Promise<RunResult> {
       settings: {
         disableBundledSkills: true,
         todoFeatureEnabled: true,
+        // Sessions are resumed across runs (ADR-0017). Without auto-compact
+        // the SDK jsonl grows unboundedly — a long-lived project session hit
+        // 31 MB / 1995 lines, making every API call resend the entire history
+        // and inflating a "change a title" task to 22 minutes. Let the SDK
+        // compact automatically when the context window fills.
+        autoCompactEnabled: true,
       },
       ...(hasSkills && security.skillPluginRoot !== undefined
         ? { plugins: [{ type: "local" as const, path: security.skillPluginRoot, skipMcpDiscovery: true }] }
diff --git a/hub/test/unit/runner.test.ts b/hub/test/unit/runner.test.ts
index 71e6805..24d51d0 100644
--- a/hub/test/unit/runner.test.ts
+++ b/hub/test/unit/runner.test.ts
@@ -113,7 +113,7 @@ describe("runAgent", () => {
         permissionMode: "bypassPermissions",
         allowDangerouslySkipPermissions: true,
         settingSources: [],
-        settings: { disableBundledSkills: true, todoFeatureEnabled: true },
+        settings: { disableBundledSkills: true, todoFeatureEnabled: true, autoCompactEnabled: true },
         tools: expect.arrayContaining(["Read", "Write", "Edit", "Bash", "Glob", "Grep", "TodoWrite"]),
         allowedTools: expect.arrayContaining(["TodoWrite", "mcp__cph_hub__todo_write"]),
         disallowedTools: expect.arrayContaining(["Agent", "SendMessage", "Task", "TeamCreate", "ScheduleWakeup"]),