core: simplify defaultAgent to single fallback path

Previously used 3-step fallback (primary -> visible -> build).
Now uses single check: find primary+visible OR hardcoded 'build'.
Same behavior, cleaner implementation.

Signed-off-by: assagman <[email protected]>

Author: assagman

packages/opencode/src/agent/agent.ts

@@ -256,13 +256,8 @@ export namespace Agent {
 
   export async function defaultAgent() {
     const agents = await list()
-    const primary = agents.find((a) => a.mode !== "subagent" && a.hidden !== true)
-    if (primary) return primary.name
-
-    const visible = agents.find((a) => a.hidden !== true)
-    if (visible) return visible.name
-
-    return "build"
+    const primaryVisible = agents.find((a) => a.mode !== "subagent" && a.hidden !== true)
+    return primaryVisible?.name || "build"
   }
 
   export async function generate(input: { description: string; model?: { providerID: string; modelID: string } }) {

packages/opencode/test/agent/agent.test.ts

@@ -513,8 +513,6 @@ test("explicit Truncate.DIR deny is respected", async () => {
   })
 })
 
-// Tests for Agent.defaultAgent()
-
 test("defaultAgent returns build when no default_agent config", async () => {
   await using tmp = await tmpdir()
   await Instance.provide({
@@ -627,3 +625,22 @@ test("defaultAgent returns plan when build is disabled and default_agent not set
     },
   })
 })
+
+test("defaultAgent returns first primary-capable agent when all natives are disabled", async () => {
+  await using tmp = await tmpdir({
+    config: {
+      agent: {
+        build: { disable: true },
+        plan: { disable: true },
+      },
+    },
+  })
+  await Instance.provide({
+    directory: tmp.path,
+    fn: async () => {
+      const agent = await Agent.defaultAgent()
+      // build and plan are disabled, so it should return general
+      expect(agent).toBe("build")
+    },
+  })
+})