diff --git a/server/src/__tests__/agent-adapter-validation-routes.test.ts b/server/src/__tests__/agent-adapter-validation-routes.test.ts
index f17158ce37..ff1a00e9d8 100644
--- a/server/src/__tests__/agent-adapter-validation-routes.test.ts
+++ b/server/src/__tests__/agent-adapter-validation-routes.test.ts
@@ -11,6 +11,10 @@ const mockAgentService = vi.hoisted(() => ({
   update: vi.fn(),
 }));
 
+const mockAdapterPluginStore = vi.hoisted(() => ({
+  getDisabledAdapterTypes: vi.fn<() => string[]>(() => []),
+}));
+
 const mockAccessService = vi.hoisted(() => ({
   canUser: vi.fn(),
   decide: vi.fn(),
@@ -114,6 +118,18 @@ function registerModuleMocks() {
   vi.doMock("../services/secrets.js", () => ({
     secretService: () => mockSecretService,
   }));
+
+  // The adapter registry reads the disabled set from this store. Mock it so a
+  // test can declare an adapter disabled without writing to the real
+  // ~/.paperclip/adapter-settings.json.
+  vi.doMock("../services/adapter-plugin-store.js", () => ({
+    getDisabledAdapterTypes: mockAdapterPluginStore.getDisabledAdapterTypes,
+    isAdapterDisabled: (type: string) =>
+      mockAdapterPluginStore.getDisabledAdapterTypes().includes(type),
+    listAdapterPlugins: () => [],
+    getAdapterPluginByType: () => undefined,
+    setAdapterDisabled: vi.fn(),
+  }));
 }
 
 const externalAdapter: ServerAdapterModule = {
@@ -204,6 +220,7 @@ describe("agent routes adapter validation", () => {
     vi.doUnmock("../routes/agents.js");
     registerModuleMocks();
     vi.clearAllMocks();
+    mockAdapterPluginStore.getDisabledAdapterTypes.mockReturnValue([]);
     mockCompanySkillService.listRuntimeSkillEntries.mockResolvedValue([]);
     mockCompanySkillService.resolveRequestedSkillKeys.mockResolvedValue([]);
     mockAccessService.canUser.mockResolvedValue(true);
@@ -423,4 +440,77 @@ describe("agent routes adapter validation", () => {
     expect(res.status, JSON.stringify(res.body)).toBe(422);
     expect(String(res.body.error ?? res.body.message ?? "")).toContain(`Unknown adapter type: ${missingAdapterType}`);
   });
+
+  it("refuses to create an agent on an adapter the instance has disabled", async () => {
+    // A disabled adapter is one the instance cannot run (e.g. curated out of
+    // PAPERCLIP_ADAPTERS). Creating an agent on it "succeeds" and then every
+    // run of that agent dies at lease time with "not in the configured adapter
+    // registry", so the refusal belongs here, where it can name the choices.
+    const { registerServerAdapter } = await import("../adapters/index.js");
+    registerServerAdapter(externalAdapter);
+    mockAdapterPluginStore.getDisabledAdapterTypes.mockReturnValue(["external_test"]);
+
+    const app = await createApp();
+    const res = await requestApp(app, (baseUrl) =>
+      request(baseUrl)
+        .post("/api/companies/company-1/agents")
+        .send({ name: "Disabled Harness", adapterType: "external_test" }),
+    );
+
+    expect(res.status, JSON.stringify(res.body)).toBe(422);
+    const message = String(res.body.error ?? res.body.message ?? "");
+    expect(message).toContain('Adapter "external_test" is not available on this instance');
+    // The message must be actionable: it names what CAN be chosen.
+    expect(message).toMatch(/Available adapters?: .+/);
+    expect(mockAgentService.create).not.toHaveBeenCalled();
+  });
+
+  it("refuses to switch an existing agent onto a disabled adapter", async () => {
+    const { registerServerAdapter } = await import("../adapters/index.js");
+    registerServerAdapter(externalAdapter);
+    mockAdapterPluginStore.getDisabledAdapterTypes.mockReturnValue(["external_test"]);
+
+    const app = await createApp();
+    const res = await requestApp(app, (baseUrl) =>
+      request(baseUrl)
+        .patch("/api/agents/11111111-1111-4111-8111-111111111111")
+        .send({ adapterType: "external_test" }),
+    );
+
+    expect(res.status, JSON.stringify(res.body)).toBe(422);
+    expect(String(res.body.error ?? res.body.message ?? "")).toContain(
+      'Adapter "external_test" is not available on this instance',
+    );
+    expect(mockAgentService.update).not.toHaveBeenCalled();
+  });
+
+  it("still lets an agent already on a disabled adapter be edited", async () => {
+    // Disabling an adapter must not make the agents that already use it
+    // uneditable — only NEW selections of it are refused.
+    mockAdapterPluginStore.getDisabledAdapterTypes.mockReturnValue(["codex_local"]);
+
+    const app = await createApp();
+    const res = await requestApp(app, (baseUrl) =>
+      request(baseUrl)
+        .patch("/api/agents/11111111-1111-4111-8111-111111111111")
+        .send({ adapterType: "codex_local", adapterConfig: { model: "gpt-5.4" } }),
+    );
+
+    expect(res.status, JSON.stringify(res.body)).toBe(200);
+  });
+
+  it("still creates an agent on an adapter that is registered and enabled", async () => {
+    const { registerServerAdapter } = await import("../adapters/index.js");
+    registerServerAdapter(externalAdapter);
+    mockAdapterPluginStore.getDisabledAdapterTypes.mockReturnValue(["some_other_adapter"]);
+
+    const app = await createApp();
+    const res = await requestApp(app, (baseUrl) =>
+      request(baseUrl)
+        .post("/api/companies/company-1/agents")
+        .send({ name: "Enabled Harness", adapterType: "external_test" }),
+    );
+
+    expect(res.status, JSON.stringify(res.body)).toBe(201);
+  });
 });
diff --git a/server/src/routes/agents.ts b/server/src/routes/agents.ts
index 3dbdc4a7ed..7ff546cb9f 100644
--- a/server/src/routes/agents.ts
+++ b/server/src/routes/agents.ts
@@ -73,6 +73,7 @@ import type {
   AdapterEnvironmentTestResult,
   AdapterModelProfileDefinition,
 } from "@paperclipai/adapter-utils";
+import { getDisabledAdapterTypes } from "../services/adapter-plugin-store.js";
 import { skillVersionSelectionMap } from "../services/runtime-skill-selections.js";
 import { secretService } from "../services/secrets.js";
 import { authorizationDeniedDetails } from "../services/authorization.js";
@@ -80,6 +81,7 @@ import {
   detectAdapterModel,
   findActiveServerAdapter,
   findServerAdapter,
+  listServerAdapters,
   listAdapterModels,
   listAdapterModelProfiles,
   refreshAdapterModels,
@@ -1288,6 +1290,37 @@ export function agentRoutes(
     return adapterType;
   }
 
+  /**
+   * Adapter validation for the paths that CHOOSE a harness for a new agent
+   * (hire + create), as opposed to the paths that operate on an existing one.
+   *
+   * A disabled adapter is one this instance cannot run — most often because a
+   * declarative registry (PAPERCLIP_ADAPTERS) curated it out, which
+   * reconcileAdapterAvailability turns into a disabled type at boot. Registered
+   * but disabled still passes assertKnownAdapterType, so an agent could be
+   * created on it and then fail EVERY run at lease time with
+   * `Adapter "..." is not in the configured adapter registry` — an error that
+   * arrives minutes later, in a run log, with no way back to the choice that
+   * caused it. Refuse at selection time instead, and name what can be chosen.
+   *
+   * Existing agents on a now-disabled adapter are deliberately untouched
+   * (listEnabledServerAdapters documents the same rule: hidden from selection,
+   * still functional for agents that already use them).
+   */
+  function assertSelectableAdapterType(type: string | null | undefined): string {
+    const adapterType = assertKnownAdapterType(type);
+    const disabled = new Set(getDisabledAdapterTypes());
+    if (!disabled.has(adapterType)) return adapterType;
+    const available = listServerAdapters()
+      .map((a) => a.type)
+      .filter((t) => !disabled.has(t))
+      .sort();
+    throw unprocessable(
+      `Adapter "${adapterType}" is not available on this instance. `
+      + `Available adapters: ${available.length > 0 ? available.join(", ") : "(none configured)"}`,
+    );
+  }
+
   async function assertAgentDefaultEnvironmentSelection(
     companyId: string,
     environmentId: string | null | undefined,
@@ -2945,7 +2978,7 @@ export function agentRoutes(
       sourceIssueIds: _sourceIssueIds,
       ...hireInput
     } = req.body;
-    hireInput.adapterType = assertKnownAdapterType(hireInput.adapterType);
+    hireInput.adapterType = assertSelectableAdapterType(hireInput.adapterType);
     const rawHireAdapterConfig = (hireInput.adapterConfig ?? {}) as Record<string, unknown>;
     assertNoNewAgentLegacyPromptTemplate(
       hireInput.adapterType,
@@ -3141,7 +3174,7 @@ export function agentRoutes(
       instructionsBundle,
       ...createInput
     } = req.body;
-    createInput.adapterType = assertKnownAdapterType(createInput.adapterType);
+    createInput.adapterType = assertSelectableAdapterType(createInput.adapterType);
     const rawCreateAdapterConfig = (createInput.adapterConfig ?? {}) as Record<string, unknown>;
     assertNoNewAgentLegacyPromptTemplate(
       createInput.adapterType,
@@ -3553,8 +3586,15 @@ export function agentRoutes(
       patchData.adapterConfig = adapterConfig;
     }
 
+    // Switching an existing agent ONTO another adapter is a new selection, so
+    // it gets the selectable check; keeping the agent's current adapter (even
+    // one since disabled) stays allowed, so a disabled harness does not make an
+    // existing agent uneditable.
     const requestedAdapterType = hasOwn(patchData, "adapterType")
-      ? assertKnownAdapterType(patchData.adapterType as string | null | undefined)
+      ? (() => {
+        const next = assertKnownAdapterType(patchData.adapterType as string | null | undefined);
+        return next === existing.adapterType ? next : assertSelectableAdapterType(next);
+      })()
       : existing.adapterType;
     let requestedRuntimeConfig: Record<string, unknown> | null = null;
     if (hasOwn(patchData, "runtimeConfig")) {