diff --git a/src/server/management/agent-settings-routes.ts b/src/server/management/agent-settings-routes.ts
index d7617c5884..d9757d5b11 100644
--- a/src/server/management/agent-settings-routes.ts
+++ b/src/server/management/agent-settings-routes.ts
@@ -948,10 +948,16 @@ export async function handleAgentSettingsRoutes(ctx: ManagementContext): Promise
       const { parseDesktopProfile, reconcileDesktopProfile } = await import("../../claude/desktop-profile");
       const parsed = parseDesktopProfile(body.profile);
       const current = await buildClaudeDesktopState(config);
+      const availableRoutes = new Set(current.models.filter(item => item.available).map(item => item.route));
+      for (const route of Object.keys(parsed.assignments)) {
+        if (!current.profile.assignments[route] && !availableRoutes.has(route)) {
+          throw new Error(`현재 사용할 수 없는 모델은 추가할 수 없습니다: ${route}`);
+        }
+      }
       for (const model of current.models.filter(item => !item.available)) {
         const before = current.profile.assignments[model.route];
         const after = parsed.assignments[model.route];
-        if (JSON.stringify(before) !== JSON.stringify(after)) {
+        if (after !== undefined && JSON.stringify(before) !== JSON.stringify(after)) {
           throw new Error(`현재 사용할 수 없는 모델은 옮길 수 없습니다: ${model.route}`);
         }
       }
diff --git a/tests/claude-integration/claude-management-api.test.ts b/tests/claude-integration/claude-management-api.test.ts
index fa99f3c14f..60bc012fa2 100644
--- a/tests/claude-integration/claude-management-api.test.ts
+++ b/tests/claude-integration/claude-management-api.test.ts
@@ -895,3 +895,64 @@ test("Claude Desktop PUT retains but cannot move an unavailable route", async ()
     await server.stop(true);
   }
 });
+
+test("Claude Desktop PUT allows deleting an unavailable route, but rejects modifying or adding one", async () => {
+  const seeded = loadConfig();
+  seeded.claudeCode = {
+    desktopProfile: {
+      version: 1,
+      assignments: {
+        "missing/old-model": { family: "opus", alias: "claude-opus-4-8-20260101" },
+      },
+      defaults: { opus: "missing/old-model", fable: null, sonnet: null, haiku: null },
+    },
+  };
+  saveConfig(seeded);
+  const server = startServer(0);
+  try {
+    const state = await fetch(new URL("/api/claude-desktop", server.url)).then(r => r.json()) as Record<string, any>;
+    expect(state.models.find((model: { route: string }) => model.route === "missing/old-model")?.available).toBe(false);
+
+    // Modifying an existing unavailable assignment (e.g. changing alias) is rejected with 400.
+    const modifyEdit = structuredClone(state.profile);
+    modifyEdit.assignments["missing/old-model"].alias = "claude-opus-4-8-20260202";
+    const putModify = await fetch(new URL("/api/claude-desktop", server.url), {
+      method: "PUT",
+      headers: { "Content-Type": "application/json" },
+      body: JSON.stringify({ profile: modifyEdit }),
+    });
+    expect(putModify.status).toBe(400);
+    expect((await putModify.json() as { error: string }).error).toContain("현재 사용할 수 없는 모델은 옮길 수 없습니다: missing/old-model");
+    expect(loadConfig().claudeCode?.desktopProfile?.assignments["missing/old-model"]?.alias).toBe("claude-opus-4-8-20260101");
+
+    // Deleting an existing unavailable assignment succeeds with 200.
+    const deleteEdit = structuredClone(state.profile);
+    delete deleteEdit.assignments["missing/old-model"];
+    deleteEdit.defaults.opus = Object.keys(deleteEdit.assignments).filter(route => deleteEdit.assignments[route].family === "opus").sort()[0] ?? null;
+
+    const putDelete = await fetch(new URL("/api/claude-desktop", server.url), {
+      method: "PUT",
+      headers: { "Content-Type": "application/json" },
+      body: JSON.stringify({ profile: deleteEdit }),
+    });
+    expect(putDelete.status).toBe(200);
+    const deleteResult = await putDelete.json() as Record<string, any>;
+    expect(deleteResult.models.some((model: { route: string }) => model.route === "missing/old-model")).toBe(false);
+    expect(deleteResult.profile.assignments["missing/old-model"]).toBeUndefined();
+    expect(loadConfig().claudeCode?.desktopProfile?.assignments["missing/old-model"]).toBeUndefined();
+
+    // Adding a newly unavailable assignment is rejected with 400.
+    const addEdit = structuredClone(deleteResult.profile);
+    addEdit.assignments["missing/new-model"] = { family: "fable", alias: "claude-opus-4-8-20260102" };
+    addEdit.defaults.fable = "missing/new-model";
+    const putAdd = await fetch(new URL("/api/claude-desktop", server.url), {
+      method: "PUT",
+      headers: { "Content-Type": "application/json" },
+      body: JSON.stringify({ profile: addEdit }),
+    });
+    expect(putAdd.status).toBe(400);
+    expect((await putAdd.json() as { error: string }).error).toContain("현재 사용할 수 없는 모델은 추가할 수 없습니다: missing/new-model");
+  } finally {
+    await server.stop(true);
+  }
+});