diff --git a/src/domain/desktop/appTask.ts b/src/domain/desktop/appTask.ts
index 64da7ef204..a3d069de9e 100644
--- a/src/domain/desktop/appTask.ts
+++ b/src/domain/desktop/appTask.ts
@@ -1,6 +1,7 @@
 import { isPortableBundleName } from "../portableBundleName.js";
 import { z } from "zod";
 
+import { jsonRecordSchema } from "../jsonRecord.js";
 import { jsonValueSchema, type JsonValue } from "../jsonValue.js";
 import { err, ok, type Result } from "../result.js";
 import { describeValidationFailure } from "../validationFailure.js";
@@ -15,12 +16,10 @@ const line = z
   .refine((value) => !value.includes("\n"), "a line cannot hold a line break");
 const lines = z.array(line).min(1).max(100);
 const count = z.int().min(0);
-const where = z
-  .record(z.string().min(1), jsonValueSchema)
-  .refine(
-    (columns) => Object.keys(columns).length > 0,
-    "name at least one column",
-  );
+const where = jsonRecordSchema(jsonValueSchema, z.string().min(1)).refine(
+  (columns) => Object.keys(columns).length > 0,
+  "name at least one column",
+);
 const comparison = {
   equals: count.optional(),
   at_least: count.optional(),
diff --git a/src/domain/desktop/appTaskOwnKeys.test.ts b/src/domain/desktop/appTaskOwnKeys.test.ts
new file mode 100644
index 0000000000..a580256f7b
--- /dev/null
+++ b/src/domain/desktop/appTaskOwnKeys.test.ts
@@ -0,0 +1,66 @@
+import { expect, it } from "vitest";
+import { parseDesktopTask } from "./appTask.js";
+import { evaluateTaskChecks } from "./appTaskChecks.js";
+
+it.each(["__proto__", "constructor", "ordinary"])(
+  "retains the own row condition %s while grading every selected column",
+  (column) => {
+    const where = Object.fromEntries([
+      ["id", 1],
+      [column, "wanted"],
+    ]);
+    const common = { file: "db.sqlite", table: "rows", where };
+    const parsed = parseDesktopTask({
+      name: "find-row",
+      prompt: "Find the row matching every selected column.",
+      checks: [
+        { kind: "row_present", ...common },
+        { kind: "row_absent", ...common },
+        { kind: "row_count", ...common, equals: 0 },
+      ],
+    });
+    if (!parsed.ok) throw new Error(parsed.error);
+    const first = parsed.value.checks[0];
+    if (first?.kind !== "row_present") throw new Error("Expected a row check");
+    expect(Object.keys(first.where)).toEqual(["id", column]);
+    const views = new Map([
+      [
+        "db.sqlite",
+        {
+          format: "sqlite",
+          view: {
+            tables: {
+              rows: {
+                columns: ["id", column],
+                primary_key: ["id"],
+                rows: [[1, "other"]],
+                truncated: false,
+              },
+            },
+            tables_truncated: false,
+          },
+        },
+      ],
+    ]);
+    expect(
+      evaluateTaskChecks(parsed.value.checks, views).map(
+        ({ passed }) => passed,
+      ),
+    ).toEqual([false, true, true]);
+    expect(Object.keys(where)).toEqual(["id", column]);
+  },
+);
+
+it("accepts an own __proto__ condition as a nonempty row predicate", () => {
+  const where = JSON.parse('{"__proto__":"wanted"}');
+  const parsed = parseDesktopTask({
+    name: "find-row",
+    prompt: "Find the selected row.",
+    checks: [{ kind: "row_present", file: "db.sqlite", table: "rows", where }],
+  });
+  if (!parsed.ok) throw new Error(parsed.error);
+  const check = parsed.value.checks[0];
+  if (check?.kind !== "row_present") throw new Error("Expected a row check");
+  expect(Object.keys(check.where)).toEqual(["__proto__"]);
+  expect(check.where["__proto__"]).toBe("wanted");
+});
diff --git a/src/domain/desktop/buildWitness.test.ts b/src/domain/desktop/buildWitness.test.ts
index 6fa138ce3d..e1b32477e5 100644
--- a/src/domain/desktop/buildWitness.test.ts
+++ b/src/domain/desktop/buildWitness.test.ts
@@ -8,6 +8,8 @@ import {
   type WitnessStageRecord,
 } from "./buildWitness.js";
 import type { ComputerAction } from "./computerActions.js";
+import { parseDesktopTask } from "./appTask.js";
+import { evaluateTaskChecks } from "./appTaskChecks.js";
 
 type Logged = {
   readonly action: ComputerAction;
@@ -351,6 +353,60 @@ describe("build witness over a long session", () => {
 });
 
 describe("build witness state views", () => {
+  it.each(["__proto__", "constructor", "ordinary"])(
+    "grades the exact own state path %s instead of treating it as absent",
+    (path) => {
+      const view = JSON.parse('{"count":7,"__proto__":"retained value"}');
+      const parts = [
+        {
+          kind: "data",
+          data: {
+            state: Object.fromEntries([[path, { format: "json", view }]]),
+          },
+        },
+      ];
+      const task = parseDesktopTask({
+        name: "check-state",
+        prompt: "Check the selected file and its value.",
+        checks: [
+          { kind: "file_present", file: path },
+          { kind: "file_absent", file: path },
+          { kind: "value_equals", file: path, pointer: "/count", value: 7 },
+        ],
+      });
+      const parsed = appStateViews(parts);
+      if (!task.ok) throw new Error(task.error);
+      if (!parsed.ok) throw new Error(parsed.error);
+      expect([...parsed.value.keys()]).toEqual([path]);
+      expect(parsed.value.get(path)).toEqual({
+        format: "json",
+        view,
+        error: null,
+      });
+      expect(
+        evaluateTaskChecks(task.value.checks, parsed.value).map(
+          ({ passed }) => passed,
+        ),
+      ).toEqual([true, false, true]);
+      expect(Object.hasOwn(parts[0]!.data.state, path)).toBe(true);
+      expect(Object.hasOwn(view, "__proto__")).toBe(true);
+    },
+  );
+
+  it.each(
+    ["__proto__", "ordinary"].flatMap((path) => [
+      { path, entry: { format: 7, view: null } },
+      { path, entry: { format: "json" } },
+      { path, entry: { format: null, view: null, error: 7 } },
+    ]),
+  )("rejects a malformed view under $path: $entry", ({ path, entry }) => {
+    expect(
+      appStateViews([
+        { kind: "data", data: { state: Object.fromEntries([[path, entry]]) } },
+      ]),
+    ).toMatchObject({ ok: false });
+  });
+
   it("reads the app's data/get state into the views the checks read, keeping each file's error", () => {
     expect(
       appStateViews([
diff --git a/src/domain/desktop/buildWitness.ts b/src/domain/desktop/buildWitness.ts
index 9efbc5ac90..f729ec4db6 100644
--- a/src/domain/desktop/buildWitness.ts
+++ b/src/domain/desktop/buildWitness.ts
@@ -1,6 +1,7 @@
 import { z } from "zod";
 
 import { jsonValueSchema } from "../jsonValue.js";
+import { jsonRecordSchema } from "../jsonRecord.js";
 import { err, ok, type Result } from "../result.js";
 import type { TaskCheckOutcome, TaskFileView } from "./appTaskChecks.js";
 import type { ComputerAction } from "./computerActions.js";
@@ -221,14 +222,17 @@ export const admitWitnessStage = (
   return ok(log.total);
 };
 
-const fileViewSchema = z.looseObject({
+const fileViewSchema = z.object({
   format: z.string().nullable(),
   view: jsonValueSchema.nullable(),
-  error: z.string().nullish(),
+  error: z
+    .string()
+    .nullish()
+    .transform((error) => error ?? null),
 });
 const statePartSchema = z.looseObject({
   kind: z.literal("data"),
-  data: z.looseObject({ state: z.record(z.string(), fileViewSchema) }),
+  data: z.looseObject({ state: jsonRecordSchema(fileViewSchema) }),
 });
 
 /**
@@ -241,18 +245,7 @@ export const appStateViews = (
   for (const part of parts) {
     const parsed = statePartSchema.safeParse(part);
     if (parsed.success)
-      return ok(
-        new Map(
-          Object.entries(parsed.data.data.state).map(([path, entry]) => [
-            path,
-            {
-              format: entry.format,
-              view: entry.view,
-              error: entry.error ?? null,
-            },
-          ]),
-        ),
-      );
+      return ok(new Map(Object.entries(parsed.data.data.state)));
   }
   return err(
     "The app's data/get returned no state views; witness a bundle exported by REA, whose app serves them.",
diff --git a/tests/boundary/mcp/buildWitnessMcp.test.ts b/tests/boundary/mcp/buildWitnessMcp.test.ts
index 2dd4554f1b..6408120ea8 100644
--- a/tests/boundary/mcp/buildWitnessMcp.test.ts
+++ b/tests/boundary/mcp/buildWitnessMcp.test.ts
@@ -157,6 +157,78 @@ const expectUndecided = (
   for (const fact of [stage, ...facts]) expect(error.message).toContain(fact);
 };
 
+it.each([
+  { kind: "file_present", passed: true },
+  { kind: "file_absent", passed: false },
+] as const)(
+  "grades $kind against an own __proto__ state file over MCP",
+  async ({ kind, passed }) => {
+    const witness = await witnessed(
+      0,
+      {},
+      {
+        name: "selected-file",
+        prompt: "Check the selected file.",
+        checks: [{ kind, file: "__proto__" }],
+      },
+    );
+    witness.app.state = JSON.parse(
+      '{"__proto__":{"format":"json","view":{"count":7}}}',
+    );
+    const report = parsed(await witness.check({}));
+    expect(report).toMatchObject({
+      passed: passed ? 1 : 0,
+      failed: passed ? 0 : 1,
+      results: [{ id: "check-1", passed }],
+    });
+  },
+);
+
+it.each([false, true])(
+  "keeps own row conditions through MCP (only special column: %s)",
+  async (onlySpecial) => {
+    const where = onlySpecial
+      ? JSON.parse('{"__proto__":"other"}')
+      : JSON.parse('{"id":1,"__proto__":"wanted"}');
+    const common = { file: "db.sqlite", table: "rows", where };
+    const witness = await witnessed(
+      0,
+      {},
+      {
+        name: "find-row",
+        prompt: "Check every selected column of the row.",
+        checks: [
+          { kind: "row_present", ...common },
+          { kind: "row_absent", ...common },
+          { kind: "row_count", ...common, equals: onlySpecial ? 1 : 0 },
+        ],
+      },
+    );
+    witness.app.state = {
+      "db.sqlite": {
+        format: "sqlite",
+        view: {
+          tables: {
+            rows: {
+              columns: ["id", "__proto__"],
+              primary_key: ["id"],
+              rows: [[1, "other"]],
+              truncated: false,
+            },
+          },
+          tables_truncated: false,
+        },
+        truncated: false,
+      },
+    };
+    const report = parsed(await witness.check({}));
+    expect(report).toMatchObject({ passed: 2, failed: 1 });
+    expect(report.results.map(({ passed }) => passed)).toEqual(
+      onlySpecial ? [true, false, true] : [false, true, true],
+    );
+  },
+);
+
 it("witnesses a task: the seed fails, the edit passes, a near miss fails and so does the reset seed", async () => {
   const { app, computer, directory, check, act } = await witnessed();