diff --git a/clients/web/src/components/groups/AppDetailPanel/AppDetailPanel.test.tsx b/clients/web/src/components/groups/AppDetailPanel/AppDetailPanel.test.tsx
index 0c40d0ae..effbd5a2 100644
--- a/clients/web/src/components/groups/AppDetailPanel/AppDetailPanel.test.tsx
+++ b/clients/web/src/components/groups/AppDetailPanel/AppDetailPanel.test.tsx
@@ -149,4 +149,28 @@ describe("AppDetailPanel", () => {
     await user.click(screen.getByRole("button", { name: /open app/i }));
     expect(onOpenApp).toHaveBeenCalledTimes(1);
   });
+
+  it("drops a previous app's in-progress number text when the app changes", async () => {
+    const user = userEvent.setup();
+    // AppsScreen swaps selectedAppName + formValues in place rather than
+    // remounting this panel, so two apps exposing a same-named number field
+    // share the field component. Both values here are undefined, which the
+    // draft/value re-sync cannot distinguish — only the resetKey identity can.
+    const numberFieldTool = (name: string): Tool => ({
+      name,
+      title: name,
+      inputSchema: {
+        type: "object",
+        properties: { scale: { type: "number", title: "Scale" } },
+      },
+    });
+    const { rerender } = renderWithMantine(
+      <AppDetailPanel {...baseProps} tool={numberFieldTool("app_a")} />,
+    );
+    const input = () => screen.getByLabelText(/Scale/) as HTMLInputElement;
+    await user.type(input(), "-");
+    expect(input().value).toBe("-");
+    rerender(<AppDetailPanel {...baseProps} tool={numberFieldTool("app_b")} />);
+    expect(input().value).toBe("");
+  });
 });
diff --git a/clients/web/src/components/groups/AppDetailPanel/AppDetailPanel.tsx b/clients/web/src/components/groups/AppDetailPanel/AppDetailPanel.tsx
index 51bf14c6..8d5a2135 100644
--- a/clients/web/src/components/groups/AppDetailPanel/AppDetailPanel.tsx
+++ b/clients/web/src/components/groups/AppDetailPanel/AppDetailPanel.tsx
@@ -76,6 +76,12 @@ export function AppDetailPanel({
           values={formValues}
           onChange={onFormChange}
           disabled={isOpening}
+          // Like ToolDetailPanel, this panel is reused across app selections
+          // rather than remounted (AppsScreen.handleSelect swaps
+          // selectedAppName + formValues in place), so the form needs the app
+          // tool's name to drop another app's in-progress field text. See
+          // SchemaFormProps.resetKey.
+          resetKey={tool.name}
         />
 
         <OpenAppButton
diff --git a/clients/web/src/components/groups/SchemaForm/SchemaForm.test.tsx b/clients/web/src/components/groups/SchemaForm/SchemaForm.test.tsx
index 32263e9a..5b9f064a 100644
--- a/clients/web/src/components/groups/SchemaForm/SchemaForm.test.tsx
+++ b/clients/web/src/components/groups/SchemaForm/SchemaForm.test.tsx
@@ -336,6 +336,34 @@ describe("SchemaForm", () => {
       expect(onChange).toHaveBeenLastCalledWith({ count: 15 });
     });
 
+    it("reports no value for a magnitude JS cannot hold exactly", async () => {
+      const user = userEvent.setup();
+      const onChange = vi.fn();
+      renderWithMantine(
+        <ControlledSchemaForm schema={numberSchema} onChange={onChange} />,
+      );
+      const input = screen.getByLabelText(/Divisor/) as HTMLInputElement;
+      // Past Number.MAX_SAFE_INTEGER, Mantine stops emitting a number and hands
+      // back the raw string to avoid destroying precision. Number() would round
+      // this to ...904, so parsing it would send a value the user never typed.
+      await user.type(input, "90071992547409910");
+      expect(input.value).toBe("90071992547409910");
+      expect(onChange).toHaveBeenLastCalledWith({ divisor: undefined });
+    });
+
+    it("still parses a long decimal, which stays exactly representable", async () => {
+      const user = userEvent.setup();
+      const onChange = vi.fn();
+      renderWithMantine(
+        <ControlledSchemaForm schema={numberSchema} onChange={onChange} />,
+      );
+      const input = screen.getByLabelText(/Divisor/) as HTMLInputElement;
+      // Guards the safe-integer check against over-rejecting: the fractional
+      // digits are not what overflows, so this must not be dropped.
+      await user.type(input, "3.14159265358979");
+      expect(onChange).toHaveBeenLastCalledWith({ divisor: 3.14159265358979 });
+    });
+
     it("drops in-progress text when resetKey moves the form to another entity", async () => {
       const user = userEvent.setup();
       // Both "tools" expose the same-named number field with no default, so the
diff --git a/clients/web/src/components/groups/SchemaForm/SchemaForm.tsx b/clients/web/src/components/groups/SchemaForm/SchemaForm.tsx
index efcb32e3..232b5327 100644
--- a/clients/web/src/components/groups/SchemaForm/SchemaForm.tsx
+++ b/clients/web/src/components/groups/SchemaForm/SchemaForm.tsx
@@ -53,10 +53,26 @@ function toEnumData(
 
 /**
  * Interpret whatever Mantine's `NumberInput` reported as the JSON value for the
- * field. It emits a `number` once the text parses cleanly, and the **raw string**
- * while it does not — `""` when cleared, but also the in-progress `"1."`, `"-"`,
- * and `"1e"`. Anything that is not a finite number becomes `undefined`, which is
- * how an absent optional argument is represented everywhere else in this form.
+ * field. Anything that is not a finite number becomes `undefined`, which is how
+ * an absent optional argument is represented everywhere else in this form.
+ *
+ * `NumberInput` emits a `number` only when the text both parses *and* is exactly
+ * representable; otherwise it hands back the **raw string** (see its
+ * `isValidNumber` guard). Two quite different situations produce a string, and
+ * they are treated differently here:
+ *
+ * 1. **Mid-entry text** — `""` when cleared, plus `"1."`, `"1.50"`, and a lone
+ *    `"-"`. These are parsed: `"1."` really does mean `1`. (Note that an
+ *    exponent is *not* in this set — `NumberInput` masks input through
+ *    `NumericFormat`, which rejects `e` outright, so `"1e"` can never be typed.)
+ * 2. **Values JS cannot hold exactly** — anything at or beyond
+ *    `Number.MAX_SAFE_INTEGER`. `Number("90071992547409910")` silently yields
+ *    `90071992547409904`, so parsing here would send the server a number the
+ *    user never entered. An inspector must not misreport what it transmits, so
+ *    these report no value instead — which is also what this field did with such
+ *    input before #1888, making it no regression. Preserving them properly needs
+ *    an exact-serialization path down the whole `tools/call` chain, which is a
+ *    separate concern from being able to type a decimal.
  */
 function toNumericValue(raw: string | number): number | undefined {
   if (typeof raw === "number") {
@@ -66,7 +82,12 @@ function toNumericValue(raw: string | number): number | undefined {
     return undefined;
   }
   const parsed = Number(raw);
-  return Number.isFinite(parsed) ? parsed : undefined;
+  if (!Number.isFinite(parsed)) {
+    return undefined;
+  }
+  // Case 2 above. The integer part is what overflows exact representation; the
+  // fractional digits are bounded by the same guard and stay lossless.
+  return Number.isSafeInteger(Math.trunc(parsed)) ? parsed : undefined;
 }
 
 interface SchemaNumberInputProps {