diff --git a/packages/plugin/src/server/provider.ts b/packages/plugin/src/server/provider.ts
index 64f66430aa..5b9511f1f7 100644
--- a/packages/plugin/src/server/provider.ts
+++ b/packages/plugin/src/server/provider.ts
@@ -129,9 +129,9 @@ export interface ProviderConfigChanges {
   mode?: string | null;
   thinkingOption?: string | null;
   /**
-   * The option keys to change on the running session. A key it cannot apply live is not in
-   * `controls`, and Paseo does not send it. `null` returns the key to the provider's own default.
-   * Apply the change or fail the request; the committed values come back in `session.config`.
+   * The option keys to change on the running session, with or without a control. Apply every key
+   * or fail the whole request, for a key you only read when a session opens. `null` returns the
+   * key to the provider's own default. The committed values come back in `session.config`.
    */
   providerOptions?: Readonly<Record<string, JsonValue>>;
   /** @deprecated Sent next to `providerOptions` to a provider that reports `settings`. */
diff --git a/packages/server/src/server/agent/plugin-provider.test.ts b/packages/server/src/server/agent/plugin-provider.test.ts
index 2772cd1030..986e65fbeb 100644
--- a/packages/server/src/server/agent/plugin-provider.test.ts
+++ b/packages/server/src/server/agent/plugin-provider.test.ts
@@ -1016,7 +1016,10 @@ describe("PluginAgentClientRegistry", () => {
       given: Record<string, boolean | string>,
       { refuseAfterChanging = false }: { refuseAfterChanging?: boolean } = {},
     ) {
-      const state = { voice: "direct", loud: false };
+      const state: { voice: string; loud: boolean; tokenBudget?: number } = {
+        voice: "direct",
+        loud: false,
+      };
       let openedSessionId = "";
       const reported = () =>
         shape === "controls"
@@ -1041,7 +1044,11 @@ describe("PluginAgentClientRegistry", () => {
                   defaultValue: false,
                 },
               ],
-              providerOptions: { voice: state.voice, loud: state.loud },
+              providerOptions: {
+                voice: state.voice,
+                loud: state.loud,
+                ...(state.tokenBudget === undefined ? {} : { token_budget: state.tokenBudget }),
+              },
             }
           : {
               settings: [
@@ -1089,8 +1096,18 @@ describe("PluginAgentClientRegistry", () => {
             return true;
           }
           if (input.type === "session.configure") {
-            const loud = input.changes.providerOptions?.loud;
+            const { loud, token_budget: tokenBudget } = input.changes.providerOptions ?? {};
+            // A plugin that takes `token_budget` live refuses the whole request on a bad value.
+            if (tokenBudget !== undefined && typeof tokenBudget !== "number") {
+              emit({
+                type: "request.failed",
+                requestId: input.requestId,
+                error: { message: "bad budget" },
+              });
+              return true;
+            }
             if (typeof loud === "boolean") state.loud = loud;
+            if (typeof tokenBudget === "number") state.tokenBudget = tokenBudget;
             emitConfig(emit, input.sessionId);
             emit(
               refuseAfterChanging
@@ -1201,24 +1218,47 @@ describe("PluginAgentClientRegistry", () => {
       await session.close();
     });
 
-    test("rejects a key the plugin does not report as a setting, and configures none of a mixed patch", async () => {
-      const { harness, session } = await openStubbornVoiceSession({ launch_key: "original" });
-      const configureBefore = lastConfigure(harness.inputs);
+    test.runIf(shape === "controls")(
+      "sends a live option that has no control, and the plugin's answer decides",
+      async () => {
+        const { harness, session, events } = await openStubbornVoiceSession({});
 
-      await expect(session.applyOptions?.({ loud: true, launch_key: "changed" })).rejects.toThrow(
-        /launch_key.*cannot change on a running session/,
-      );
+        await session.applyOptions?.({ token_budget: 2000 });
+        expect(lastConfigure(harness.inputs)).toMatchObject({
+          changes: { providerOptions: { token_budget: 2000 } },
+        });
 
-      expect(lastConfigure(harness.inputs)).toBe(configureBefore);
+        // The plugin refuses the request as a whole, so the other key it was given is not applied.
+        await expect(session.applyOptions?.({ loud: true, token_budget: "lots" })).rejects.toThrow(
+          "bad budget",
+        );
+        expect(eventsOfType(events, "options_changed")).toEqual([]);
+        expect(await session.applyOptions?.({ token_budget: 3000 })).toEqual({});
+        await session.close();
+      },
+    );
 
-      // The value it opened with is not a change, so a whole profile can be applied.
-      await session.applyOptions?.({ loud: true, launch_key: "original" });
-      const configure = lastConfigure(harness.inputs) as {
-        changes: { providerOptions: object };
-      };
-      expect(Object.keys(configure.changes.providerOptions)).toEqual(["loud"]);
-      await session.close();
-    });
+    test.runIf(shape === "settings")(
+      "rejects a key the plugin does not report as a setting, and configures none of a mixed patch",
+      async () => {
+        const { harness, session } = await openStubbornVoiceSession({ launch_key: "original" });
+        const configureBefore = lastConfigure(harness.inputs);
+
+        await expect(session.applyOptions?.({ loud: true, launch_key: "changed" })).rejects.toThrow(
+          /launch_key.*cannot change on a running session/,
+        );
+
+        expect(lastConfigure(harness.inputs)).toBe(configureBefore);
+
+        // The value it opened with is not a change, so a whole profile can be applied.
+        await session.applyOptions?.({ loud: true, launch_key: "original" });
+        const configure = lastConfigure(harness.inputs) as {
+          changes: { providerOptions: object };
+        };
+        expect(Object.keys(configure.changes.providerOptions)).toEqual(["loud"]);
+        await session.close();
+      },
+    );
 
     test("applying options returns the settings that ended up different, and emits nothing", async () => {
       const { session, events } = await openStubbornVoiceSession({});
diff --git a/packages/server/src/server/agent/plugin-provider.ts b/packages/server/src/server/agent/plugin-provider.ts
index 8a0fe677b1..f06f70079b 100644
--- a/packages/server/src/server/agent/plugin-provider.ts
+++ b/packages/server/src/server/agent/plugin-provider.ts
@@ -1420,19 +1420,26 @@ class PluginAgentSession implements AgentSession {
     this.assertReplayComplete();
     const before = this.currentOptions();
     const { controls, legacySettings } = readPluginOptionState(this.bridge.config);
-    const live = controls.map((control) => control.key);
-    // A key the plugin has no control for is one it only reads when the session opens;
-    // a value equal to the one it opened with is not a change.
-    assertChangesAreLive({
-      provider: this.provider,
-      patch: options,
-      current: this.givenOptions,
-      live,
-    });
     const settings: Record<string, JsonValue> = {};
-    for (const [id, value] of Object.entries(options)) {
-      if (!live.includes(id)) continue;
-      settings[id] = toJsonValue(value, `option '${id}'`);
+    // COMPAT(plugin-provider-settings): added in v0.15.0, remove after 2027-05-01. A plugin
+    // reporting `settings` cannot refuse a key, so only its settings are sent and any other
+    // changed key is rejected here; a value equal to the one it opened with is not a change.
+    if (legacySettings) {
+      const live = controls.map((control) => control.key);
+      assertChangesAreLive({
+        provider: this.provider,
+        patch: options,
+        current: this.givenOptions,
+        live,
+      });
+      for (const [id, value] of Object.entries(options)) {
+        if (live.includes(id)) settings[id] = toJsonValue(value, `option '${id}'`);
+      }
+    } else {
+      // The plugin applies every key it is given or rejects the whole request.
+      for (const [id, value] of Object.entries(options)) {
+        settings[id] = toJsonValue(value, `option '${id}'`);
+      }
     }
     if (Object.keys(settings).length === 0) return {};
     this.applyingOptions = true;
diff --git a/public-docs/plugins/providers.md b/public-docs/plugins/providers.md
index 75c12abdd6..5495405bfd 100644
--- a/public-docs/plugins/providers.md
+++ b/public-docs/plugins/providers.md
@@ -275,9 +275,11 @@ at the default and values nobody set. The same controls appear in the New worksp
 tabs, and on running agents. Offer a control only for a key you can change on a running session.
 The provider may change its controls at runtime, including after a model change.
 
-A user change arrives as `session.configure` with `changes.providerOptions` holding only the keys
-that changed. Apply the change and publish the committed `session.config` before
-`request.completed`, or fail the request with `request.failed` and leave every key as it was. A
+A change arrives as `session.configure` with `changes.providerOptions` holding only the keys
+that changed, whether or not they have a control. Apply every key and publish the committed
+`session.config` before `request.completed`. Fail the request with `request.failed` and leave
+every key as it was when you cannot apply one, for example a key you read only when a session
+opens. A
 value of `null` returns that key to the provider's default. Publish what the session ended up
 with, not a copy of the request: Paseo stores your published values so the stored options match
 what runs.
@@ -286,8 +288,10 @@ If the provider changes an option on its own, for example a model switch turns F
 a new `session.config` with the new values. Paseo stores them and does not set the old ones
 back.
 
-Keys without a control are still delivered in `session.open` and stored. A provider-specific
-token budget, for example, belongs in `providerOptions` and is not a dedicated prompt field.
+Not every option needs a control. A provider-specific token budget, for example, belongs in
+`providerOptions` and is not a dedicated prompt field. It is delivered in `session.open`, a caller
+can change it on a running agent, and your `session.configure` handler decides whether it can
+apply it live. Report it in `providerOptions` so Paseo stores what runs.
 
 ## Add persistence and replay
 
diff --git a/public-docs/plugins/providers.zh-CN.md b/public-docs/plugins/providers.zh-CN.md
index 5f9b4a5a06..e917ba0538 100644
--- a/public-docs/plugins/providers.zh-CN.md
+++ b/public-docs/plugins/providers.zh-CN.md
@@ -244,11 +244,11 @@ emit({
 
 `icon` 是 Lucide 图标名称。`defaultValue` 是控件在键没有值时显示的值。会话打开或应用修改时，你报告的每个值（包括处于默认值的值和无人设置过的值）Paseo 都会保存。相同的控件会出现在“新建工作区”界面、草稿标签页和运行中的 Agent 上。只为你能在运行中的会话里修改的键提供控件。Provider 可以在运行时改变控件，包括在模型变化之后。
 
-用户的修改会以 `session.configure` 的形式到达，`changes.providerOptions` 只包含发生变化的键。应用它，并在 `request.completed` 之前发布已确定的 `session.config`；或者用 `request.failed` 使请求失败，并让每个键保持原样。值为 `null` 表示把该键恢复为 Provider 的默认值。请发布会话最终实际使用的值，而不是请求的副本：Paseo 会保存你发布的值，使保存的选项与实际运行的一致。
+修改会以 `session.configure` 的形式到达，`changes.providerOptions` 只包含发生变化的键，无论这些键是否有控件。应用每一个键，并在 `request.completed` 之前发布已确定的 `session.config`。如果无法应用其中某个键（例如只在会话打开时读取的键），用 `request.failed` 使请求失败，并让每个键保持原样。值为 `null` 表示把该键恢复为 Provider 的默认值。请发布会话最终实际使用的值，而不是请求的副本：Paseo 会保存你发布的值，使保存的选项与实际运行的一致。
 
 如果 Provider 自行改变了某个选项（例如切换模型后关闭了 Fast），请发布带有新值的 `session.config`。Paseo 会保存它们，不会把旧值设置回去。
 
-没有控件的键仍会在 `session.open` 中交付并被保存。例如 Provider 专属的 token 预算应放在 `providerOptions` 中，它不是一个专门的提示词字段。
+并非每个选项都需要控件。例如 Provider 专属的 token 预算应放在 `providerOptions` 中，它不是一个专门的提示词字段。它会在 `session.open` 中交付，调用方可以在运行中的 Agent 上修改它，由你的 `session.configure` 处理程序决定能否实时应用。请在 `providerOptions` 中报告它，使 Paseo 保存实际运行的值。
 
 ## 添加持久化与重放 {#add-persistence-and-replay}