fix(config): prevent plan agent from inheriting prometheus prompt on demote

Plan agent demote now only sets mode to 'subagent' without spreading
prometheus config. This ensures plan agent uses OpenCode's default
prompt instead of inheriting prometheus prompt.

src/plugin-handlers/config-handler.test.ts

@@ -145,8 +145,8 @@ describe("Plan agent demote behavior", () => {
     expect(ordered).toEqual(coreAgents)
   })
 
-  test("plan agent should be demoted to subagent mode when replacePlan is true", async () => {
-    // given
+  test("plan agent should be demoted to subagent without inheriting prometheus prompt", async () => {
+    // #given
     const pluginConfig: OhMyOpenCodeConfig = {
       sisyphus_agent: {
         planner_enabled: true,
@@ -172,62 +172,22 @@ describe("Plan agent demote behavior", () => {
       },
     })
 
-    // when
+    // #when
     await handler(config)
 
-    // then
+    // #then - plan is demoted to subagent but does NOT inherit prometheus prompt
     const agents = config.agent as Record<string, { mode?: string; name?: string; prompt?: string }>
     expect(agents.plan).toBeDefined()
     expect(agents.plan.mode).toBe("subagent")
-    expect(agents.plan.name).toBe("plan")
-    expect(agents.plan.prompt).toBe("original plan prompt")
-    expect(agents.plan.prompt).not.toBe(agents.prometheus?.prompt)
+    expect(agents.plan.prompt).toBeUndefined()
+    expect(agents.prometheus?.prompt).toBeDefined()
   })
 
-  test("plan agent should not be demoted when replacePlan is false", async () => {
-    // given
-    const pluginConfig: OhMyOpenCodeConfig = {
-      sisyphus_agent: {
-        planner_enabled: true,
-        replace_plan: false,
-      },
-    }
-    const config: Record<string, unknown> = {
-      model: "anthropic/claude-opus-4-5",
-      agent: {
-        plan: {
-          name: "plan",
-          mode: "primary",
-          prompt: "original plan prompt",
-        },
-      },
-    }
-    const handler = createConfigHandler({
-      ctx: { directory: "/tmp" },
-      pluginConfig,
-      modelCacheState: {
-        anthropicContext1MEnabled: false,
-        modelContextLimitsCache: new Map(),
-      },
-    })
-
-    // when
-    await handler(config)
-
-    // then
-    const agents = config.agent as Record<string, { mode?: string; name?: string; prompt?: string }>
-    expect(agents.plan).toBeDefined()
-    expect(agents.plan.mode).toBe("primary")
-    expect(agents.plan.name).toBe("plan")
-    expect(agents.plan.prompt).toBe("original plan prompt")
-  })
-
-  test("plan agent should not be demoted when planner is disabled", async () => {
-    // given
+  test("plan agent remains unchanged when planner is disabled", async () => {
+    // #given
     const pluginConfig: OhMyOpenCodeConfig = {
       sisyphus_agent: {
         planner_enabled: false,
-        replace_plan: true,
       },
     }
     const config: Record<string, unknown> = {
@@ -249,50 +209,15 @@ describe("Plan agent demote behavior", () => {
       },
     })
 
-    // when
+    // #when
     await handler(config)
 
-    // then
+    // #then - plan is not touched, prometheus is not created
     const agents = config.agent as Record<string, { mode?: string; name?: string; prompt?: string }>
     expect(agents.prometheus).toBeUndefined()
     expect(agents.plan).toBeDefined()
     expect(agents.plan.mode).toBe("primary")
-  })
-
-  test("preserves empty plan prompt when demoting", async () => {
-    // given
-    const pluginConfig: OhMyOpenCodeConfig = {
-      sisyphus_agent: {
-        planner_enabled: true,
-        replace_plan: true,
-      },
-    }
-    const config: Record<string, unknown> = {
-      model: "anthropic/claude-opus-4-5",
-      agent: {
-        plan: {
-          name: "plan",
-          mode: "primary",
-          prompt: "",
-        },
-      },
-    }
-    const handler = createConfigHandler({
-      ctx: { directory: "/tmp" },
-      pluginConfig,
-      modelCacheState: {
-        anthropicContext1MEnabled: false,
-        modelContextLimitsCache: new Map(),
-      },
-    })
-
-    // when
-    await handler(config)
-
-    // then
-    const agents = config.agent as Record<string, { prompt?: string }>
-    expect(agents.plan).toBeDefined()
-    expect(agents.plan.prompt).toBe("")
+    expect(agents.plan.prompt).toBe("original plan prompt")
   })
 
   test("prometheus should have mode 'all' to be callable via delegate_task", async () => {