feat(f8): isAuthorable + widened selectionRejection (file|untitled)

Spec §6.4: replace the scheme!=file / !isUnderRoot rejections with a single
!isAuthorable branch. isUnderRoot retained as a routing input. Per-condition
messaging (#24) kept for no-editor / empty-selection / non-{file,untitled}.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

test/workspacePath.test.ts

@@ -1,5 +1,5 @@
 import { describe, it, expect } from "vitest";
-import { isUnderRoot, selectionRejection } from "../src/workspacePath";
+import { isAuthorable, isUnderRoot, selectionRejection } from "../src/workspacePath";
 
 describe("isUnderRoot", () => {
   const root = "/a/vscode-cowriting-plugin/sandbox";
@@ -24,32 +24,37 @@ describe("isUnderRoot", () => {
   });
 });
 
-describe("selectionRejection", () => {
-  const root = "/ws";
-  const ok = { hasEditor: true, selectionEmpty: false, scheme: "file", fsPath: "/ws/a.md", root };
-
-  it("returns null when everything is valid", () => {
-    expect(selectionRejection(ok)).toBeNull();
+describe("isAuthorable", () => {
+  it("accepts file: and untitled: schemes", () => {
+    expect(isAuthorable("file")).toBe(true);
+    expect(isAuthorable("untitled")).toBe(true);
   });
+  it("rejects read-only / virtual schemes", () => {
+    expect(isAuthorable("git")).toBe(false);
+    expect(isAuthorable("output")).toBe(false);
+    expect(isAuthorable("cowriting-baseline")).toBe(false);
+    expect(isAuthorable("")).toBe(false);
+  });
+});
 
+describe("selectionRejection — F8 widened (accepts out-of-folder + untitled)", () => {
+  const ok = { hasEditor: true, selectionEmpty: false, scheme: "file" };
+
+  it("accepts an in-folder / out-of-folder file (file: scheme)", () => {
+    expect(selectionRejection({ ...ok, scheme: "file" })).toBeNull();
+  });
+  it("accepts an untitled buffer (no longer rejected)", () => {
+    expect(selectionRejection({ ...ok, scheme: "untitled" })).toBeNull();
+  });
   it("names the missing editor", () => {
-    const msg = selectionRejection({ ...ok, hasEditor: false });
-    expect(msg).toMatch(/focus a text editor/i);
+    expect(selectionRejection({ ...ok, hasEditor: false })).toMatch(/focus a text editor/i);
   });
-
   it("names the empty selection (only when there IS an editor)", () => {
-    const msg = selectionRejection({ ...ok, selectionEmpty: true });
-    expect(msg).toMatch(/select some text/i);
+    expect(selectionRejection({ ...ok, selectionEmpty: true })).toMatch(/select some text/i);
   });
-
-  it("names an unsaved/non-file document", () => {
-    const msg = selectionRejection({ ...ok, scheme: "untitled" });
-    expect(msg).toMatch(/save this document/i);
-  });
-
-  it("names an out-of-workspace file (the reported bug — NOT a selection problem)", () => {
-    const msg = selectionRejection({ ...ok, fsPath: "/elsewhere/a.md" });
-    expect(msg).toMatch(/outside your workspace folder/i);
+  it("rejects a non-{file,untitled} scheme with its own message (not 'select some text')", () => {
+    const msg = selectionRejection({ ...ok, scheme: "git" });
+    expect(msg).toMatch(/can.?t be edited|read-only|not a file/i);
     expect(msg).not.toMatch(/select some text/i);
   });
 });