feat(conformance): implement ReadOnly brand and reader generator

- Add ReadOnly<F> phantom brand to core-shared/conformance (compile-time
  enforcement that readers only wrap non-mutating use cases)
- Add isReadOnly runtime predicate for boot-time assertReaderPurity
- Scaffold pnpm turbo gen reader: creates integrations/readers/ with
  interface, implementation, test, barrel, and adds ./reader export
  subpath to package.json

turbo/generators/config.ts

@@ -476,6 +476,50 @@ export default function generator(plop: PlopTypes.NodePlopAPI): void {
     },
   });
 
+  /**
+   * Turbo generator: `reader`
+   *
+   * Scaffolds a cross-feature reader under
+   * `packages/<feature>/src/integrations/readers/` and adds the `./reader`
+   * export subpath to the feature's `package.json`. The reader interface is
+   * the public contract; the implementation and test are internal.
+   *
+   * See ADR-026 for the full design (rules Q0–Q3).
+   */
+  plop.setGenerator("reader", {
+    description:
+      "Scaffold a cross-feature reader interface + implementation (ADR-026)",
+    prompts: [
+      {
+        type: "input",
+        name: "feature",
+        message: "Feature that will EXPOSE the reader (kebab-case):",
+        validate(input: string) {
+          if (!/^[a-z][a-z0-9-]*$/.test(input)) return "Must be kebab-case";
+          if (!existsSync(join(process.cwd(), "packages", input, "src"))) {
+            return `packages/${input}/src does not exist`;
+          }
+          const readersDir = join(
+            process.cwd(),
+            "packages",
+            input,
+            "src",
+            "integrations",
+            "readers",
+          );
+          if (existsSync(readersDir)) {
+            return `packages/${input}/src/integrations/readers/ already exists — this feature already has a reader`;
+          }
+          return true;
+        },
+      },
+    ],
+    actions(answers) {
+      const a = answers as { feature: string };
+      return readerActions(a);
+    },
+  });
+
   /**
    * Turbo generator: `realtime`
    *
@@ -1034,6 +1078,82 @@ function jobBindBlock(a: { feature: string; job: string }): string {
   ${containerVar}.bind(${symbol}).toConstantValue(wrapped${pascalCase(a.job)});`;
 }
 
+function readerActions(a: { feature: string }): PlopTypes.ActionType[] {
+  const base = `packages/${a.feature}/src/integrations/readers`;
+  const pkgJsonPath = `packages/${a.feature}/package.json`;
+  return [
+    {
+      type: "add",
+      path: `${base}/${a.feature}.reader.interface.ts`,
+      templateFile: "templates/reader/reader.interface.ts.hbs",
+      data: a,
+    },
+    {
+      type: "add",
+      path: `${base}/${a.feature}.reader.ts`,
+      templateFile: "templates/reader/reader.ts.hbs",
+      data: a,
+    },
+    {
+      type: "add",
+      path: `${base}/${a.feature}.reader.test.ts`,
+      templateFile: "templates/reader/reader.test.ts.hbs",
+      data: a,
+    },
+    {
+      type: "add",
+      path: `${base}/index.ts`,
+      templateFile: "templates/reader/index.ts.hbs",
+      data: a,
+    },
+    // Add ./reader subpath to package.json exports map
+    () => {
+      const fs = require("node:fs");
+      const pkgPath = join(process.cwd(), pkgJsonPath);
+      const pkg = JSON.parse(fs.readFileSync(pkgPath, "utf8"));
+      if (!pkg.exports) pkg.exports = {};
+      pkg.exports["./reader"] = "./src/integrations/readers/index.ts";
+      fs.writeFileSync(pkgPath, JSON.stringify(pkg, null, 2) + "\n");
+      return `Added "./reader" export to ${pkgJsonPath}`;
+    },
+    () => printReaderNextSteps(a),
+  ];
+}
+
+function printReaderNextSteps(a: { feature: string }): string {
+  const pascal = pascalCase(a.feature);
+  return [
+    "",
+    "─────────────────────────────────────────────────────────────",
+    `  Reader scaffolded for @repo/${a.feature}`,
+    "─────────────────────────────────────────────────────────────",
+    "",
+    "  Next steps:",
+    "",
+    `  1. Add methods to I${pascal}Reader interface:`,
+    `     packages/${a.feature}/src/integrations/readers/${a.feature}.reader.interface.ts`,
+    "",
+    `  2. Implement methods in ${pascal}Reader (delegate to use cases):`,
+    `     packages/${a.feature}/src/integrations/readers/${a.feature}.reader.ts`,
+    "",
+    `  3. Construct the reader in bind-production.ts and return it:`,
+    `     const reader = new ${pascal}Reader(/* injected use cases */);`,
+    `     return { reader };`,
+    "",
+    `  4. In bindAll(), pass the reader to consuming features:`,
+    `     const ${a.feature}Result = bindProduction${pascal}(ctx);`,
+    `     bindProductionConsumer(ctx, { ${a.feature}Reader: ${a.feature}Result.reader });`,
+    "",
+    `  5. In consuming features' manifest, declare: reads: ["${a.feature}"]`,
+    "",
+    "  Rules: Q0 (cross-feature only), Q1 (interface public, impl private),",
+    "         Q2 (read-only — wraps only mutates:false use cases),",
+    "         Q3 (reader cycles are a design error)",
+    "",
+    "─────────────────────────────────────────────────────────────",
+  ].join("\n");
+}
+
 function printJobNextSteps(a: { feature: string; job: string }): string {
   return [
     "",