fix: retain completed results during live editing

src/components/Workbench.test.tsx

@@ -37,6 +37,7 @@ const syntaxHarness = vi.hoisted(() => ({
 
 const engineHarness = vi.hoisted(() => ({
   requests: [] as RegexExecutionRequest[],
+  emitWholeFirstCharacterMatch: false,
 }));
 
 vi.mock("../editors/CodeEditor", () => ({
@@ -45,18 +46,35 @@ vi.mock("../editors/CodeEditor", () => ({
     onChange,
     label,
     readOnly,
+    marks,
+    selectedRange,
+    onSelectionChange,
   }: {
     readonly value: string;
     readonly onChange?: (value: string) => void;
     readonly label: string;
     readonly readOnly?: boolean;
+    readonly marks?: readonly unknown[];
+    readonly selectedRange?: { readonly startUtf16: number };
+    readonly onSelectionChange?: (range: {
+      readonly startUtf16: number;
+      readonly endUtf16: number;
+    }) => void;
   }) {
     return (
       <textarea
         aria-label={label}
         value={value}
         readOnly={readOnly}
+        data-mark-count={marks?.length ?? 0}
+        data-selected-start={selectedRange?.startUtf16}
         onChange={(event) => onChange?.(event.target.value)}
+        onSelect={(event) =>
+          onSelectionChange?.({
+            startUtf16: event.currentTarget.selectionStart,
+            endUtf16: event.currentTarget.selectionEnd,
+          })
+        }
       />
     );
   },
@@ -115,7 +133,18 @@ vi.mock("../regex/execution/EngineSupervisor", () => ({
           internallyAddedIndicesFlag: false,
           internallyAddedGlobalFlag: false,
         },
-        matches: [],
+        matches: engineHarness.emitWholeFirstCharacterMatch
+          ? [
+              {
+                matchNumber: 1,
+                value: request.subject.slice(0, 1),
+                valueStatus: "complete" as const,
+                range: { startUtf16: 0, endUtf16: 1 },
+                nativeRange: { start: 0, end: 1, unit: "utf16" as const },
+                captures: [],
+              },
+            ]
+          : [],
         diagnostics: [],
         elapsedMs: 1,
         truncated: false,
@@ -231,6 +260,7 @@ afterEach(() => {
   syntaxHarness.patterns.length = 0;
   syntaxHarness.replacements.length = 0;
   engineHarness.requests.length = 0;
+  engineHarness.emitWholeFirstCharacterMatch = false;
 });
 
 describe("Workbench syntax coordination", () => {
@@ -346,6 +376,79 @@ describe("Workbench syntax coordination", () => {
     });
   });
 
+  it("does not revive an old syntax snapshot when rapid edits return to the same text", async () => {
+    vi.useFakeTimers();
+    render(<Workbench />);
+    fireEvent.click(screen.getByRole("checkbox", { name: "Live" }));
+
+    await advanceParseDebounce();
+    await resolvePattern(0, []);
+    const patternInput = screen.getByRole("textbox", {
+      name: "Regular expression pattern",
+    });
+    const initialPattern = (patternInput as HTMLTextAreaElement).value;
+    const runButton = screen.getByRole("button", { name: "Run" });
+    expect(runButton).toBeEnabled();
+
+    fireEvent.change(patternInput, { target: { value: "temporary" } });
+    fireEvent.change(patternInput, { target: { value: initialPattern } });
+
+    expect(runButton).toBeDisabled();
+    fireEvent.click(screen.getByRole("treeitem"));
+    expect(patternInput).toHaveAttribute("data-mark-count", "0");
+    await advanceParseDebounce();
+    await resolvePattern(1, []);
+    expect(patternInput).toHaveAttribute("data-mark-count", "0");
+    expect(runButton).toBeEnabled();
+  });
+
+  it("retains one exact result frame until the edited subject has a replacement frame", async () => {
+    vi.useFakeTimers();
+    engineHarness.emitWholeFirstCharacterMatch = true;
+    render(<Workbench />);
+    fireEvent.click(screen.getByRole("checkbox", { name: "Live" }));
+
+    await advanceParseDebounce();
+    await resolvePattern(0, []);
+    fireEvent.click(screen.getByRole("button", { name: "Run" }));
+    await act(async () => {
+      await Promise.resolve();
+    });
+
+    const subjectInput = screen.getByRole("textbox", { name: "Test text" });
+    const originalSubject = (subjectInput as HTMLTextAreaElement).value;
+    expect(subjectInput).toHaveAttribute("data-mark-count", "1");
+    expect(document.querySelector(".extraction-row")).toHaveTextContent("2");
+
+    fireEvent.change(subjectInput, { target: { value: "Z new subject" } });
+
+    expect(screen.getByTestId("stale-result-frame")).toHaveTextContent(
+      "bound to the last completed inputs",
+    );
+    expect(subjectInput).toHaveAttribute("data-mark-count", "0");
+    expect(document.querySelector(".extraction-row")).toHaveTextContent("2");
+
+    fireEvent.change(subjectInput, { target: { value: originalSubject } });
+    expect(screen.getByTestId("stale-result-frame")).toBeInTheDocument();
+    expect(subjectInput).toHaveAttribute("data-mark-count", "0");
+
+    fireEvent.change(subjectInput, { target: { value: "Z new subject" } });
+    (subjectInput as HTMLTextAreaElement).setSelectionRange(0, 1);
+    fireEvent.select(subjectInput);
+    expect(
+      document.querySelector(".extraction-row.is-selected"),
+    ).not.toBeInTheDocument();
+
+    fireEvent.click(screen.getByRole("button", { name: "Run" }));
+    await act(async () => {
+      await Promise.resolve();
+    });
+
+    expect(screen.queryByTestId("stale-result-frame")).not.toBeInTheDocument();
+    expect(subjectInput).toHaveAttribute("data-mark-count", "1");
+    expect(document.querySelector(".extraction-row")).toHaveTextContent("Z");
+  });
+
   it("captures a complete result and reruns only the selected saved test", async () => {
     vi.useFakeTimers();
     render(<Workbench />);