fix(validation): stop unrecognised boolean strings coercing to a silent false

checkField in packages/validation/src/index.ts (and its browser mirror in
runtime.ts) treated any string other than "true"/"on" as false with no
error, so typos like "treu" or values like "yes"/"1"/"TRUE" silently
passed as false.

Now:
- true/false booleans pass through unchanged
- recognised true strings (case-insensitive, trimmed): true, on, 1, yes
- recognised false strings: false, off, 0, no
- numeric 1/0 coerce (JSON payloads)
- undefined/null/"" still coerce to false (unchecked-checkbox semantics)
- anything else is now a type error (desc.typeMessage or "Must be true or
  false") instead of a silent false

Locked-in behaviours preserved: a required boolean given false still
errors, and parseEnv DEBUG: "true" coercion still works.

Added coverage for recognised strings, numeric 1/0, the type-error
regression guard, absent/empty handling, the required+false case, and a
client/server parity test driving both checkField and the browser runtime
through the same inputs.

Blast radius: searched packages/, examples/, services/ for v.boolean()
usage; all existing call sites (auth consent/rememberDevice, db 'active'
default, example consent checkboxes) feed true/false/'on'/absent values,
none of which change behavior.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

packages/validation/src/index.ts

@@ -114,7 +114,28 @@ export function checkField(
   }
 
   if (desc.type === "boolean") {
-    const value = raw === true || raw === "true" || raw === "on";
+    const empty = raw === undefined || raw === null || raw === "";
+    let value: boolean;
+    if (typeof raw === "boolean") {
+      value = raw;
+    } else if (empty) {
+      value = false;
+    } else if (raw === 1) {
+      value = true;
+    } else if (raw === 0) {
+      value = false;
+    } else if (typeof raw === "string") {
+      const norm = raw.trim().toLowerCase();
+      if (norm === "true" || norm === "on" || norm === "1" || norm === "yes") {
+        value = true;
+      } else if (norm === "false" || norm === "off" || norm === "0" || norm === "no") {
+        value = false;
+      } else {
+        return { value: raw, error: desc.typeMessage ?? "Must be true or false" };
+      }
+    } else {
+      return { value: raw, error: desc.typeMessage ?? "Must be true or false" };
+    }
     if (!desc.optional && !value) {
       return { value, error: desc.requiredMessage || "Required" };
     }

packages/validation/src/runtime.ts

@@ -45,7 +45,28 @@ export const VALIDATE_RUNTIME = String.raw`
       return (missing && !desc.optional) ? (desc.requiredMessage || "Required") : null;
     }
     if (desc.type === "boolean") {
-      var b = raw === true || raw === "true" || raw === "on";
+      var bEmpty = raw === undefined || raw === null || raw === "";
+      var b;
+      if (typeof raw === "boolean") {
+        b = raw;
+      } else if (bEmpty) {
+        b = false;
+      } else if (raw === 1) {
+        b = true;
+      } else if (raw === 0) {
+        b = false;
+      } else if (typeof raw === "string") {
+        var bNorm = raw.trim().toLowerCase();
+        if (bNorm === "true" || bNorm === "on" || bNorm === "1" || bNorm === "yes") {
+          b = true;
+        } else if (bNorm === "false" || bNorm === "off" || bNorm === "0" || bNorm === "no") {
+          b = false;
+        } else {
+          return desc.typeMessage || "Must be true or false";
+        }
+      } else {
+        return desc.typeMessage || "Must be true or false";
+      }
       return (!desc.optional && !b) ? (desc.requiredMessage || "Required") : null;
     }
     var pre = desc.trim && typeof raw === "string" ? raw.trim() : raw;

packages/validation/test/validation.test.ts

@@ -114,6 +114,140 @@ test("checkField coerces and applies rules", () => {
   ).toBe("Email is required");
 });
 
+test("checkField coerces recognised true/false boolean strings, case-insensitively and trimmed", () => {
+  const desc = { type: "boolean" as const, optional: true, rules: [] };
+  for (const raw of [
+    "true",
+    "TRUE",
+    " True ",
+    "on",
+    "ON",
+    " on ",
+    "1",
+    " 1 ",
+    "yes",
+    "YES",
+    " Yes ",
+  ]) {
+    expect(checkField(desc, raw)).toEqual({ value: true, error: null });
+  }
+  for (const raw of [
+    "false",
+    "FALSE",
+    " False ",
+    "off",
+    "OFF",
+    " off ",
+    "0",
+    " 0 ",
+    "no",
+    "NO",
+    " No ",
+  ]) {
+    expect(checkField(desc, raw)).toEqual({ value: false, error: null });
+  }
+});
+
+test("checkField coerces numeric 1/0 booleans (common in JSON payloads)", () => {
+  const desc = { type: "boolean" as const, optional: true, rules: [] };
+  expect(checkField(desc, 1)).toEqual({ value: true, error: null });
+  expect(checkField(desc, 0)).toEqual({ value: false, error: null });
+  expect(checkField(desc, true)).toEqual({ value: true, error: null });
+  expect(checkField(desc, false)).toEqual({ value: false, error: null });
+});
+
+test("checkField rejects unrecognised boolean strings/values as a type error, not a silent false", () => {
+  const desc = { type: "boolean" as const, optional: true, rules: [] };
+  for (const raw of ["yes please", "maybe", "treu", "TRUE!", "2", { a: 1 }, [1, 2]]) {
+    const result = checkField(desc, raw);
+    expect(result.error).toBe("Must be true or false");
+  }
+  const custom = checkField(
+    { type: "boolean" as const, optional: true, typeMessage: "Pick yes or no", rules: [] },
+    "maybe",
+  );
+  expect(custom.error).toBe("Pick yes or no");
+});
+
+test("checkField treats absent/empty boolean input as false, erroring only when required", () => {
+  const optionalDesc = { type: "boolean" as const, optional: true, rules: [] };
+  expect(checkField(optionalDesc, undefined)).toEqual({ value: false, error: null });
+  expect(checkField(optionalDesc, null)).toEqual({ value: false, error: null });
+  expect(checkField(optionalDesc, "")).toEqual({ value: false, error: null });
+
+  const requiredDesc = {
+    type: "boolean" as const,
+    requiredMessage: "Required",
+    rules: [],
+  };
+  expect(checkField(requiredDesc, undefined).error).toBe("Required");
+  expect(checkField(requiredDesc, "").error).toBe("Required");
+});
+
+test("checkField still errors when a required boolean is explicitly false (checkbox semantics locked in)", () => {
+  expect(
+    checkField(
+      { type: "boolean" as const, requiredMessage: "Accept the terms to continue", rules: [] },
+      false,
+    ),
+  ).toEqual({ value: false, error: "Accept the terms to continue" });
+});
+
+test("client/server boolean parity: checkField and the browser runtime agree on every case", () => {
+  const win = new Window() as unknown as Window & Record<string, unknown>;
+  win.document.body.innerHTML = `
+    <form data-schema="parity">
+      <input name="field">
+      <span data-error="field"></span>
+    </form>`;
+  const schema = v.object({ field: v.boolean().optional() }).describe();
+  win.__wrnSchemas = { parity: schema };
+  (globalThis as Record<string, unknown>).window = win;
+  (globalThis as Record<string, unknown>).document = win.document;
+
+  try {
+    (0, eval)(VALIDATE_RUNTIME);
+    const runtime = win.__wrnValidate as { init(root: Document): void };
+    runtime.init(win.document as unknown as Document);
+    const input = win.document.querySelector("input") as HappyDOMHTMLInputElement;
+    const error = win.document.querySelector("[data-error=field]") as HappyDOMHTMLElement;
+
+    const cases = [
+      "true",
+      "TRUE",
+      " True ",
+      "on",
+      "ON",
+      "1",
+      " 1 ",
+      "yes",
+      "YES",
+      "false",
+      "FALSE",
+      "off",
+      "OFF",
+      "0",
+      "no",
+      "NO",
+      "",
+      "yes please",
+      "maybe",
+      "treu",
+    ];
+
+    for (const raw of cases) {
+      const serverResult = checkField(schema.fields.field, raw);
+      input.value = raw;
+      input.dispatchEvent(windowEvent(win, "blur", { bubbles: true }));
+      const clientRejected = error.textContent !== "";
+      expect(clientRejected).toBe(serverResult.error !== null);
+    }
+  } finally {
+    delete (globalThis as Record<string, unknown>).window;
+    delete (globalThis as Record<string, unknown>).document;
+  }
+});
+
 test("invalid() returns a 400 with errors", async () => {
   const res = invalid({ email: "bad" });
   expect(res.status).toBe(400);