feat(config): add background task circuit breaker settings

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

src/config/schema/background-task-circuit-breaker.test.ts

@@ -0,0 +1,59 @@
+import { describe, expect, test } from "bun:test"
+import { ZodError } from "zod/v4"
+import { BackgroundTaskConfigSchema } from "./background-task"
+
+describe("BackgroundTaskConfigSchema.circuitBreaker", () => {
+  describe("#given valid circuit breaker settings", () => {
+    test("#when parsed #then returns nested config", () => {
+      const result = BackgroundTaskConfigSchema.parse({
+        circuitBreaker: {
+          maxToolCalls: 150,
+          windowSize: 10,
+          repetitionThresholdPercent: 70,
+        },
+      })
+
+      expect(result.circuitBreaker).toEqual({
+        maxToolCalls: 150,
+        windowSize: 10,
+        repetitionThresholdPercent: 70,
+      })
+    })
+  })
+
+  describe("#given windowSize below minimum", () => {
+    test("#when parsed #then throws ZodError", () => {
+      let thrownError: unknown
+
+      try {
+        BackgroundTaskConfigSchema.parse({
+          circuitBreaker: {
+            windowSize: 4,
+          },
+        })
+      } catch (error) {
+        thrownError = error
+      }
+
+      expect(thrownError).toBeInstanceOf(ZodError)
+    })
+  })
+
+  describe("#given repetitionThresholdPercent is zero", () => {
+    test("#when parsed #then throws ZodError", () => {
+      let thrownError: unknown
+
+      try {
+        BackgroundTaskConfigSchema.parse({
+          circuitBreaker: {
+            repetitionThresholdPercent: 0,
+          },
+        })
+      } catch (error) {
+        thrownError = error
+      }
+
+      expect(thrownError).toBeInstanceOf(ZodError)
+    })
+  })
+})