diff --git a/src/cli/run/runner.test.ts b/src/cli/run/runner.test.ts
new file mode 100644
index 00000000..678a26ea
--- /dev/null
+++ b/src/cli/run/runner.test.ts
@@ -0,0 +1,70 @@
+import { describe, it, expect } from "bun:test"
+import type { OhMyOpenCodeConfig } from "../../config"
+import { resolveRunAgent } from "./runner"
+
+const createConfig = (overrides: Partial<OhMyOpenCodeConfig> = {}): OhMyOpenCodeConfig => ({
+  ...overrides,
+})
+
+describe("resolveRunAgent", () => {
+  it("uses CLI agent over env and config", () => {
+    // given
+    const config = createConfig({ default_run_agent: "prometheus" })
+    const env = { OPENCODE_DEFAULT_AGENT: "Atlas" }
+
+    // when
+    const agent = resolveRunAgent(
+      { message: "test", agent: "Hephaestus" },
+      config,
+      env
+    )
+
+    // then
+    expect(agent).toBe("hephaestus")
+  })
+
+  it("uses env agent over config", () => {
+    // given
+    const config = createConfig({ default_run_agent: "prometheus" })
+    const env = { OPENCODE_DEFAULT_AGENT: "Atlas" }
+
+    // when
+    const agent = resolveRunAgent({ message: "test" }, config, env)
+
+    // then
+    expect(agent).toBe("atlas")
+  })
+
+  it("uses config agent over default", () => {
+    // given
+    const config = createConfig({ default_run_agent: "Prometheus" })
+
+    // when
+    const agent = resolveRunAgent({ message: "test" }, config, {})
+
+    // then
+    expect(agent).toBe("prometheus")
+  })
+
+  it("falls back to sisyphus when none set", () => {
+    // given
+    const config = createConfig()
+
+    // when
+    const agent = resolveRunAgent({ message: "test" }, config, {})
+
+    // then
+    expect(agent).toBe("sisyphus")
+  })
+
+  it("skips disabled sisyphus for next available core agent", () => {
+    // given
+    const config = createConfig({ disabled_agents: ["sisyphus"] })
+
+    // when
+    const agent = resolveRunAgent({ message: "test" }, config, {})
+
+    // then
+    expect(agent).toBe("hephaestus")
+  })
+})