diff --git a/.agents/references/README.md b/.agents/references/README.md
index 790336f6..c2fc3f13 100644
--- a/.agents/references/README.md
+++ b/.agents/references/README.md
@@ -10,7 +10,7 @@ Use these references from both implementation-time and review-time skills. Treat
 - [react-use-effect.md](react-use-effect.md) — state ownership, `useEffect`, async lifecycle, subscriptions, memoization
 - [accessibility.md](accessibility.md) — interactive semantics, keyboard support, focus, labels, announced state
 - [low-level-apis.md](low-level-apis.md) — timers, measurement, observers, imperative DOM, browser coordination
-- [composite-field-controls.md](composite-field-controls.md) — field semantics, composite inputs, `Field` / `Form` bridging, proxy or hidden inputs, validation wiring, and alignment with nearby Base UI-backed control contracts
+- [composite-field-controls.md](composite-field-controls.md) — field semantics, composite inputs, `Field` / `Form` bridging, proxy or hidden inputs, validation wiring, the `Field.Control` self-wired list, and alignment with nearby Base UI-backed control contracts
 
 ## Inclusion Criteria
 
diff --git a/.agents/references/composite-field-controls.md b/.agents/references/composite-field-controls.md
index e39f230d..ee813024 100644
--- a/.agents/references/composite-field-controls.md
+++ b/.agents/references/composite-field-controls.md
@@ -37,6 +37,10 @@ Review for consistency around:
 
 Be skeptical when a composite field control invents a parallel API unless the underlying semantics truly differ.
 
+### Register as self-wired
+
+Every control that draws its own frame and connects to `Field.Root` by itself — composite or a thin Base UI wrapper — gets an entry in `selfWiredControls` in `components/field/field.tsx`, including compound members such as `.Async`. `Field.Control` uses that list to warn when the control is passed to its `render` prop, which draws a double frame. A control missing from the list fails silently: no warning, the same double frame.
+
 ### One semantic value across all input paths
 
 Check whether these paths still converge on the same meaning when they exist:
diff --git a/.changeset/field-control-render-warning.md b/.changeset/field-control-render-warning.md
new file mode 100644
index 00000000..e9104146
--- /dev/null
+++ b/.changeset/field-control-render-warning.md
@@ -0,0 +1,5 @@
+---
+"@tailor-platform/app-shell": patch
+---
+
+`Field.Control` now logs a console warning when it is given an AppShell control that draws its own frame through `render`, such as `<Field.Control render={<Select />} />`. That composition renders a double border. The warning logs in every build, not only in development, because it only fires for UI that is already broken. `Select`, `Combobox`, `Autocomplete`, `Checkbox`, `Textarea`, `DateField`, `DatePicker`, and `DateRangePicker` go directly under `Field.Root` instead. The Form, Select, and form-modal docs now say which controls go where.
diff --git a/docs-manifest.json b/docs-manifest.json
index 0589330d..387f1956 100644
--- a/docs-manifest.json
+++ b/docs-manifest.json
@@ -699,9 +699,9 @@
       "symbols": ["Form", "FormProps"],
       "hashes": {
         "typeSurface": "7b374d45d53d4535",
-        "outline": "79c9b0f08ca38027",
+        "outline": "7fefd291a00de910",
         "snapshot": "5d7a7904c5256f29",
-        "outputMd": "91d901b17aed7781",
+        "outputMd": "e4a66f7b1ee4aa98",
         "examples": null
       }
     },
@@ -733,9 +733,9 @@
       "symbols": [],
       "hashes": {
         "typeSurface": null,
-        "outline": "3301b263f6802090",
+        "outline": "a39589955fe582c8",
         "snapshot": null,
-        "outputMd": "9d068e568c9f3bdc",
+        "outputMd": "be00d1109761b7f1",
         "examples": "7836309f2df327ee"
       }
     },
@@ -1209,9 +1209,9 @@
       "symbols": ["Select", "SelectAsyncFetcher"],
       "hashes": {
         "typeSurface": "429710973dfa912b",
-        "outline": "721e8995f53f0e8f",
+        "outline": "a8b7834a8817e0d5",
         "snapshot": "2ef5b7324018ff8f",
-        "outputMd": "ae287e2bb5abc1c6",
+        "outputMd": "b3dd3b9a58a9d290",
         "examples": "1ce89cec30045466"
       }
     },
@@ -1759,14 +1759,14 @@
     "packages/core/skills/app-shell-patterns/references/components/dialog.md": "ec6a0ac098d1d87a",
     "packages/core/skills/app-shell-patterns/references/components/document-progress-card.md": "d0fb940f685f8869",
     "packages/core/skills/app-shell-patterns/references/components/filter-rail.md": "c6a48c4d8e8b0078",
-    "packages/core/skills/app-shell-patterns/references/components/form.md": "91d901b17aed7781",
+    "packages/core/skills/app-shell-patterns/references/components/form.md": "e4a66f7b1ee4aa98",
     "packages/core/skills/app-shell-patterns/references/components/global-header-layout.md": "dd2b0da3702cf8d9",
     "packages/core/skills/app-shell-patterns/references/components/grid.md": "9051eb53dde4179f",
     "packages/core/skills/app-shell-patterns/references/components/input.md": "a3a6c9679af99d37",
     "packages/core/skills/app-shell-patterns/references/components/layout.md": "66696139a46fabb0",
     "packages/core/skills/app-shell-patterns/references/components/menu.md": "ceb4a05822538d20",
     "packages/core/skills/app-shell-patterns/references/components/metric-card.md": "5a1c557768c6590f",
-    "packages/core/skills/app-shell-patterns/references/components/select.md": "ae287e2bb5abc1c6",
+    "packages/core/skills/app-shell-patterns/references/components/select.md": "b3dd3b9a58a9d290",
     "packages/core/skills/app-shell-patterns/references/components/sheet.md": "1f81ebd562c50371",
     "packages/core/skills/app-shell-patterns/references/components/sidebar-group.md": "a36192df64f16adc",
     "packages/core/skills/app-shell-patterns/references/components/sidebar-item.md": "9236c03e53aa79f2",
@@ -1807,7 +1807,7 @@
     "packages/core/skills/app-shell-patterns/references/api/use-time-zone.md": "30c15545ab3c4954",
     "packages/core/skills/app-shell-patterns/references/api/use-toast.md": "30983a761bc61593",
     "packages/core/skills/app-shell-patterns/references/patterns/form-composer.md": "ed187ac3a0773d3d",
-    "packages/core/skills/app-shell-patterns/references/patterns/form-modal.md": "9d068e568c9f3bdc",
+    "packages/core/skills/app-shell-patterns/references/patterns/form-modal.md": "be00d1109761b7f1",
     "packages/core/skills/app-shell-patterns/references/patterns/form-sectioned.md": "d31cd3ae6ad0790c",
     "packages/core/skills/app-shell-patterns/references/patterns/form-single-page.md": "10a0f4d91a120752",
     "packages/core/skills/app-shell-patterns/references/patterns/form-wizard.md": "851afb4672da6673",
diff --git a/docs-src/components/form.docs.outline.md b/docs-src/components/form.docs.outline.md
index 08958cbd..7e6f81d8 100644
--- a/docs-src/components/form.docs.outline.md
+++ b/docs-src/components/form.docs.outline.md
@@ -102,14 +102,14 @@ A compound component that groups all parts of a form field and manages its valid
 
 ### Sub-components
 
-| Sub-component       | Description                                                                                   |
-| ------------------- | --------------------------------------------------------------------------------------------- |
-| `Field.Root`        | Context boundary for a single field. Manages validation state.                                |
-| `Field.Label`       | Accessible label; `htmlFor` is resolved automatically via context.                            |
-| `Field.Control`     | Styled `<input>`. Can be omitted when using a Base UI-backed AppShell component as the input. |
-| `Field.Description` | Supplementary help text; automatically linked via `aria-describedby`.                         |
-| `Field.Error`       | Validation error message. Use `match` to target specific validity states.                     |
-| `Field.Validity`    | Render-prop access to the field's `ValidityState` for fully custom validation UI.             |
+| Sub-component       | Description                                                                                                            |
+| ------------------- | ---------------------------------------------------------------------------------------------------------------------- |
+| `Field.Root`        | Context boundary for a single field. Manages validation state.                                                         |
+| `Field.Label`       | Accessible label; `htmlFor` is resolved automatically via context.                                                     |
+| `Field.Control`     | Styled text `<input>`. `Select`, `Combobox`, and the other self-wired controls go directly under `Field.Root` instead. |
+| `Field.Description` | Supplementary help text; automatically linked via `aria-describedby`.                                                  |
+| `Field.Error`       | Validation error message. Use `match` to target specific validity states.                                              |
+| `Field.Validity`    | Render-prop access to the field's `ValidityState` for fully custom validation UI.                                      |
 
 ### Field.Root Props
 
@@ -136,7 +136,17 @@ A compound component that groups all parts of a form field and manages its valid
 
 ### Using Another AppShell Component as the Control
 
-`Field.Control` can be omitted when using a Base UI-backed AppShell component (e.g. `Select`, `Combobox`). The component registers itself with the `Field` context automatically, inheriting label association and validation state.
+`Field.Control` is a text input. It is the control for plain text-like fields, and you can pass it a native element such as `render={<textarea />}`. The controls in the last row of the table below go **directly under `Field.Root`**, as a sibling of `Field.Label`. Each one registers itself with the `Field` context, so it gets label association, `aria-describedby`, `disabled`, and validation state without `Field.Control`.
+
+| Control                                                                                                                         | Where it goes                                     |
+| ------------------------------------------------------------------------------------------------------------------------------- | ------------------------------------------------- |
+| Plain text, email, number, password, … input                                                                                    | `<Field.Control type="…" />`                      |
+| Native element (`<textarea>`, `<input type="…">`)                                                                               | `<Field.Control render={<textarea />} />`         |
+| `Select`, `Combobox`, `Autocomplete`, `Checkbox`, `Textarea`, `DateField`, `DatePicker`, `DateRangePicker` (and their `.Async`) | Directly under `Field.Root` — not `Field.Control` |
+
+`Input` is the exception. It is a plain `<input>` that does not connect to `Field.Root`, so inside a field use `<Field.Control />` in its place.
+
+Do not pass the self-wired controls to `Field.Control`'s `render` prop. They draw their own frame, so `<Field.Control render={<Select />} />` renders a second border around the select. `Field.Control` also passes them `<input>` props they don't take. `Field.Control` logs a console warning when it is given one of these controls directly as an element. A wrapper component or the function form of `render` is not detected.
 
 ```tsx
 const [country, setCountry] = React.useState<string | null>(null);
diff --git a/docs-src/components/select.docs.outline.md b/docs-src/components/select.docs.outline.md
index 1c89d19c..6e90e8fb 100644
--- a/docs-src/components/select.docs.outline.md
+++ b/docs-src/components/select.docs.outline.md
@@ -161,6 +161,16 @@ const { Root, Trigger, Value, Content, Item, Group, GroupLabel, Separator } = Se
 
 ## Form submission
 
+Inside a form, place `Select` directly under `Field.Root`, not inside `Field.Control`. `Select` draws
+its own trigger and registers with the field itself.
+
+```tsx
+<Field.Root name="country">
+  <Field.Label>Country</Field.Label>
+  <Select items={["Japan", "United States"]} placeholder="Select a country" />
+</Field.Root>
+```
+
 Inside a `Field.Root`, the field's `name` identifies the value and these props are unnecessary —
 see [Form](./form.md). They matter for **native** submission: a plain `<form>`, `new FormData(form)`,
 or a server action.
diff --git a/docs-src/patterns/form-modal.docs.outline.md b/docs-src/patterns/form-modal.docs.outline.md
index 7298de03..b1f76d24 100644
--- a/docs-src/patterns/form-modal.docs.outline.md
+++ b/docs-src/patterns/form-modal.docs.outline.md
@@ -67,7 +67,9 @@ placeholder.
   render_ — a submit gate, a dependent placeholder, a live character count. That state is
   load-bearing, not mirrored; see `form/composer`.
 - **`Field.Control` is already a styled input.** Write `<Field.Control />`, not
-  `<Field.Control render={<Input />} />`.
+  `<Field.Control render={<Input />} />`. Every other control — `Select`, `Combobox`,
+  `Autocomplete`, `Checkbox`, `Textarea`, `DateField`, `DatePicker` — goes directly under
+  `Field.Root`. Passing one to `Field.Control`'s `render` draws a second frame around it.
 - **Object items need `itemToStringValue`.** Items shaped `{ value, label }` submit `value`
   automatically; any other object submits as a JSON string unless you supply it.
 - **Server errors go through `Form`'s `errors` prop**, keyed by field `name` — not a toast or a
@@ -85,4 +87,5 @@ placeholder.
 - Registering the create path as a separate top-level route — that unmounts the parent list
 - Reaching for React Hook Form on a form this size — `onFormSubmit` already covers it
 - Holding a `Select`/`Combobox` value in `useState` just to submit it — `Field.Root` already does
+- Wrapping a `Select`/`Combobox` in `Field.Control` (`render={<Select />}`) — a double frame
 - Surfacing API validation failures in a toast or banner instead of routing them via `errors`
diff --git a/docs/components/form.md b/docs/components/form.md
index be7acb69..8825ce9f 100644
--- a/docs/components/form.md
+++ b/docs/components/form.md
@@ -100,14 +100,14 @@ A compound component that groups all parts of a form field and manages its valid
 
 ### Sub-components
 
-| Sub-component       | Description                                                                                   |
-| ------------------- | --------------------------------------------------------------------------------------------- |
-| `Field.Root`        | Context boundary for a single field. Manages validation state.                                |
-| `Field.Label`       | Accessible label; `htmlFor` is resolved automatically via context.                            |
-| `Field.Control`     | Styled `<input>`. Can be omitted when using a Base UI-backed AppShell component as the input. |
-| `Field.Description` | Supplementary help text; automatically linked via `aria-describedby`.                         |
-| `Field.Error`       | Validation error message. Use `match` to target specific validity states.                     |
-| `Field.Validity`    | Render-prop access to the field's `ValidityState` for fully custom validation UI.             |
+| Sub-component       | Description                                                                                                            |
+| ------------------- | ---------------------------------------------------------------------------------------------------------------------- |
+| `Field.Root`        | Context boundary for a single field. Manages validation state.                                                         |
+| `Field.Label`       | Accessible label; `htmlFor` is resolved automatically via context.                                                     |
+| `Field.Control`     | Styled text `<input>`. `Select`, `Combobox`, and the other self-wired controls go directly under `Field.Root` instead. |
+| `Field.Description` | Supplementary help text; automatically linked via `aria-describedby`.                                                  |
+| `Field.Error`       | Validation error message. Use `match` to target specific validity states.                                              |
+| `Field.Validity`    | Render-prop access to the field's `ValidityState` for fully custom validation UI.                                      |
 
 ### Field.Root Props
 
@@ -134,7 +134,17 @@ A compound component that groups all parts of a form field and manages its valid
 
 ### Using Another AppShell Component as the Control
 
-`Field.Control` can be omitted when using a Base UI-backed AppShell component (e.g. `Select`, `Combobox`). The component registers itself with the `Field` context automatically, inheriting label association and validation state.
+`Field.Control` is a text input. It is the control for plain text-like fields, and you can pass it a native element such as `render={<textarea />}`. The controls in the last row of the table below go **directly under `Field.Root`**, as a sibling of `Field.Label`. Each one registers itself with the `Field` context, so it gets label association, `aria-describedby`, `disabled`, and validation state without `Field.Control`.
+
+| Control                                                                                                                         | Where it goes                                     |
+| ------------------------------------------------------------------------------------------------------------------------------- | ------------------------------------------------- |
+| Plain text, email, number, password, … input                                                                                    | `<Field.Control type="…" />`                      |
+| Native element (`<textarea>`, `<input type="…">`)                                                                               | `<Field.Control render={<textarea />} />`         |
+| `Select`, `Combobox`, `Autocomplete`, `Checkbox`, `Textarea`, `DateField`, `DatePicker`, `DateRangePicker` (and their `.Async`) | Directly under `Field.Root` — not `Field.Control` |
+
+`Input` is the exception. It is a plain `<input>` that does not connect to `Field.Root`, so inside a field use `<Field.Control />` in its place.
+
+Do not pass the self-wired controls to `Field.Control`'s `render` prop. They draw their own frame, so `<Field.Control render={<Select />} />` renders a second border around the select. `Field.Control` also passes them `<input>` props they don't take. `Field.Control` logs a console warning when it is given one of these controls directly as an element. A wrapper component or the function form of `render` is not detected.
 
 ```tsx
 const [country, setCountry] = React.useState<string | null>(null);
diff --git a/docs/components/select.md b/docs/components/select.md
index c141ab87..df4e7e7c 100644
--- a/docs/components/select.md
+++ b/docs/components/select.md
@@ -171,6 +171,16 @@ const { Root, Trigger, Value, Content, Item, Group, GroupLabel, Separator } = Se
 
 ## Form submission
 
+Inside a form, place `Select` directly under `Field.Root`, not inside `Field.Control`. `Select` draws
+its own trigger and registers with the field itself.
+
+```tsx
+<Field.Root name="country">
+  <Field.Label>Country</Field.Label>
+  <Select items={["Japan", "United States"]} placeholder="Select a country" />
+</Field.Root>
+```
+
 Inside a `Field.Root`, the field's `name` identifies the value and these props are unnecessary —
 see [Form](./form.md). They matter for **native** submission: a plain `<form>`, `new FormData(form)`,
 or a server action.
diff --git a/docs/patterns/form-modal.md b/docs/patterns/form-modal.md
index 4b2e471f..e436d6e3 100644
--- a/docs/patterns/form-modal.md
+++ b/docs/patterns/form-modal.md
@@ -147,7 +147,9 @@ placeholder.
   render_ — a submit gate, a dependent placeholder, a live character count. That state is
   load-bearing, not mirrored; see `form/composer`.
 - **`Field.Control` is already a styled input.** Write `<Field.Control />`, not
-  `<Field.Control render={<Input />} />`.
+  `<Field.Control render={<Input />} />`. Every other control — `Select`, `Combobox`,
+  `Autocomplete`, `Checkbox`, `Textarea`, `DateField`, `DatePicker` — goes directly under
+  `Field.Root`. Passing one to `Field.Control`'s `render` draws a second frame around it.
 - **Object items need `itemToStringValue`.** Items shaped `{ value, label }` submit `value`
   automatically; any other object submits as a JSON string unless you supply it.
 - **Server errors go through `Form`'s `errors` prop**, keyed by field `name` — not a toast or a
@@ -165,4 +167,5 @@ placeholder.
 - Registering the create path as a separate top-level route — that unmounts the parent list
 - Reaching for React Hook Form on a form this size — `onFormSubmit` already covers it
 - Holding a `Select`/`Combobox` value in `useState` just to submit it — `Field.Root` already does
+- Wrapping a `Select`/`Combobox` in `Field.Control` (`render={<Select />}`) — a double frame
 - Surfacing API validation failures in a toast or banner instead of routing them via `errors`
diff --git a/packages/core/src/components/ai-chat/ai-chat.tsx b/packages/core/src/components/ai-chat/ai-chat.tsx
index 2dae9973..c280def4 100644
--- a/packages/core/src/components/ai-chat/ai-chat.tsx
+++ b/packages/core/src/components/ai-chat/ai-chat.tsx
@@ -1,15 +1,14 @@
 import {
   Children,
   isValidElement,
-  useEffect,
   useMemo,
-  useRef,
   type ComponentProps,
   type ReactElement,
   type ReactNode,
 } from "react";
 
 import type { AIChatStatus } from "@/ai/use-ai-chat";
+import { useOnceWarnings } from "@/hooks/use-once-warnings";
 import { cn } from "@/lib/utils";
 import { Action, Actions } from "./actions";
 import { AIChatContext } from "./ai-chat-context";
@@ -79,27 +78,6 @@ type AIChatProps = Omit<ComponentProps<"div">, "children"> & {
  * </Card.Root>
  * ```
  */
-/**
- * Emits each distinct message once per mounted root.
- *
- * The root re-renders on every streamed token, so warning inline during
- * render would repeat the same line hundreds of times in a single response —
- * and twice per render again under StrictMode. Deliberately not gated on
- * `process.env.NODE_ENV`: this package has no other reference to `process`,
- * and adding one would break consumers whose bundler does not shim it.
- */
-function useOnceWarnings(warnings: readonly string[]) {
-  const seen = useRef<Set<string>>(new Set());
-
-  useEffect(() => {
-    for (const warning of warnings) {
-      if (seen.current.has(warning)) continue;
-      seen.current.add(warning);
-      console.warn(warning);
-    }
-  });
-}
-
 type Regions = {
   header?: ReactElement;
   conversation?: ReactElement;
diff --git a/packages/core/src/components/field/field.test.tsx b/packages/core/src/components/field/field.test.tsx
index e3ce5aac..ce42e221 100644
--- a/packages/core/src/components/field/field.test.tsx
+++ b/packages/core/src/components/field/field.test.tsx
@@ -2,6 +2,8 @@ import { afterEach, describe, expect, it, vi } from "vitest";
 import { cleanup, render, screen, waitFor } from "@testing-library/react";
 import userEvent from "@testing-library/user-event";
 import { renderRHFForm } from "../../../tests/rhf-test-utils";
+import { Checkbox } from "../checkbox";
+import { Select } from "../select";
 import { Field } from "./field";
 
 afterEach(() => {
@@ -202,4 +204,50 @@ describe("Field", () => {
       expect(screen.getByText("Something went wrong")).toBeDefined();
     });
   });
+
+  describe("render misuse warning", () => {
+    it("warns when a self-wired control is passed to render", () => {
+      const warn = vi.spyOn(console, "warn").mockImplementation(() => {});
+      render(
+        <Field.Root name="country">
+          <Field.Control render={<Select items={["Japan"]} />} />
+        </Field.Root>,
+      );
+      expect(warn).toHaveBeenCalledTimes(1);
+      expect(warn.mock.calls[0][0]).toContain("render={<Select />}");
+      expect(warn.mock.calls[0][0]).toContain("directly under <Field.Root>");
+      warn.mockRestore();
+    });
+
+    it("names the compound member", () => {
+      const warn = vi.spyOn(console, "warn").mockImplementation(() => {});
+      render(
+        <Field.Root name="country">
+          <Field.Control render={<Select.Async fetcher={async () => []} />} />
+        </Field.Root>,
+      );
+      expect(warn.mock.calls[0][0]).toContain("render={<Select.Async />}");
+      warn.mockRestore();
+    });
+
+    it("warns once across re-renders", () => {
+      const warn = vi.spyOn(console, "warn").mockImplementation(() => {});
+      const { rerender } = render(<Field.Control render={<Checkbox />} />);
+      rerender(<Field.Control render={<Checkbox />} />);
+      expect(warn).toHaveBeenCalledTimes(1);
+      warn.mockRestore();
+    });
+
+    it("stays silent for a plain control or a native element", () => {
+      const warn = vi.spyOn(console, "warn").mockImplementation(() => {});
+      render(
+        <Field.Root name="bio">
+          <Field.Control />
+          <Field.Control render={<textarea />} />
+        </Field.Root>,
+      );
+      expect(warn).not.toHaveBeenCalled();
+      warn.mockRestore();
+    });
+  });
 });
diff --git a/packages/core/src/components/field/field.tsx b/packages/core/src/components/field/field.tsx
index c7c53c00..c74e36b8 100644
--- a/packages/core/src/components/field/field.tsx
+++ b/packages/core/src/components/field/field.tsx
@@ -1,9 +1,16 @@
 import * as React from "react";
 import { Field as BaseField } from "@base-ui/react/field";
 
+import { useOnceWarnings } from "@/hooks/use-once-warnings";
 import { cn } from "@/lib/utils";
 import { inputBaseClasses } from "@/lib/input-classes";
 import { Text } from "../text";
+import { Autocomplete } from "../autocomplete";
+import { Checkbox } from "../checkbox";
+import { Combobox } from "../combobox";
+import { DateField, DatePicker, DateRangePicker } from "../date-field";
+import { Select } from "../select";
+import { Textarea } from "../textarea";
 
 // Only the props relevant to the Field abstraction are picked from BaseField.Root.
 // Base UI-internal props (e.g. actionsRef) are intentionally excluded
@@ -128,14 +135,45 @@ function Label({ className, ...props }: React.ComponentProps<typeof BaseField.La
 }
 Label.displayName = "Field.Label";
 
+// Controls that draw their own frame and connect to `Field.Root` themselves.
+// Passed to `Field.Control`'s `render`, they get a second frame plus `<input>`
+// props they don't take (platform-planning#1977).
+const selfWiredControls = new Map<unknown, string>([
+  [Select, "Select"],
+  [Select.Async, "Select.Async"],
+  [Combobox, "Combobox"],
+  [Combobox.Async, "Combobox.Async"],
+  [Autocomplete, "Autocomplete"],
+  [Autocomplete.Async, "Autocomplete.Async"],
+  [Checkbox, "Checkbox"],
+  [Textarea, "Textarea"],
+  [DateField, "DateField"],
+  [DatePicker, "DatePicker"],
+  [DateRangePicker, "DateRangePicker"],
+]);
+
+function renderMisuseWarnings(render: unknown): string[] {
+  if (!React.isValidElement(render)) return [];
+  const name = selfWiredControls.get(render.type);
+  if (!name) return [];
+  return [
+    `Field.Control: \`render={<${name} />}\` draws a second frame around ${name}. ${name} connects to Field.Root by itself — place it directly under <Field.Root> instead of inside Field.Control.`,
+  ];
+}
+
 /**
- * A styled input control for the field.
+ * A styled text input for the field.
  *
- * Can be omitted when using another Base UI-backed AppShell input component
- * (e.g. Select, Combobox, Autocomplete) as a sibling — those components
- * register themselves with the Field context automatically.
+ * Use it for plain text-like inputs, or pass a native element to `render`
+ * (e.g. `render={<textarea />}`). `Select`, `Combobox`, `Autocomplete`,
+ * `Checkbox`, `Textarea`, `DateField`, `DatePicker` and `DateRangePicker` go
+ * directly under `Field.Root` instead: each draws its own frame and registers
+ * with the Field context itself. Passing one to `render` draws a second frame
+ * and logs a warning. `Input` does not connect to `Field.Root` — use
+ * `Field.Control` in its place inside a field.
  */
 function Control({ className, ...props }: React.ComponentProps<typeof BaseField.Control>) {
+  useOnceWarnings(renderMisuseWarnings(props.render));
   return (
     <BaseField.Control
       data-slot="field-control"
diff --git a/packages/core/src/components/filter-rail/filter-rail.tsx b/packages/core/src/components/filter-rail/filter-rail.tsx
index 97bca34c..87496282 100644
--- a/packages/core/src/components/filter-rail/filter-rail.tsx
+++ b/packages/core/src/components/filter-rail/filter-rail.tsx
@@ -1,4 +1,5 @@
-import { useCallback, useEffect, useMemo, useRef, useState, type ReactNode } from "react";
+import { useCallback, useMemo, useRef, useState, type ReactNode } from "react";
+import { useOnceWarnings } from "@/hooks/use-once-warnings";
 import { cn } from "@/lib/utils";
 import type { CollectionControl, Filter } from "@/types/collection";
 import { Sheet } from "../sheet";
@@ -51,14 +52,7 @@ function Provider<TField extends string = string, TSectionField extends TField =
   onChangeRef.current = onFilterChange;
 
   // Dev guard: two sections on one field silently overwrite each other.
-  const warned = useRef(new Set<string>());
-  useEffect(() => {
-    for (const problem of findRailProblems(anySections)) {
-      if (warned.current.has(problem)) continue;
-      warned.current.add(problem);
-      console.warn(problem);
-    }
-  }, [anySections]);
+  useOnceWarnings(useMemo(() => findRailProblems(anySections), [anySections]));
 
   const owned = useMemo(() => railFields(anySections), [anySections]);
   const filters = anyControl.filters;
diff --git a/packages/core/src/hooks/use-once-warnings.ts b/packages/core/src/hooks/use-once-warnings.ts
new file mode 100644
index 00000000..6fa6afdb
--- /dev/null
+++ b/packages/core/src/hooks/use-once-warnings.ts
@@ -0,0 +1,22 @@
+import { useEffect, useRef } from "react";
+
+/**
+ * Dev guard: logs each distinct warning once per mounted component.
+ *
+ * Runs in an effect rather than inline so a component that re-renders often
+ * (or twice under StrictMode) doesn't repeat the same line. Deliberately not
+ * gated on `process.env.NODE_ENV`: this package has no other reference to
+ * `process`, and adding one would break consumers whose bundler does not
+ * shim it.
+ */
+export function useOnceWarnings(warnings: readonly string[]) {
+  const seen = useRef<Set<string>>(new Set());
+
+  useEffect(() => {
+    for (const warning of warnings) {
+      if (seen.current.has(warning)) continue;
+      seen.current.add(warning);
+      console.warn(warning);
+    }
+  });
+}