Reduce DRY duplication in unit and property tests

Extract shared test helpers for the Memo post and Set Name behavior
slices: fake wallet/profiles, MemoAction tests, page-controller tests,
page build wiring, and shared property-test invariants. Behavior is
preserved; all unit, property, and acceptance tests pass.

By refactorer.

test/property/memo-post.property.test.js

@@ -2,21 +2,18 @@
   Property tests for the Memo post / New Post behavior slices.
 
   These assert useful invariants that unit tests cover only at a few fixed
-  points:
-    - Validation classification is stable across a broad input range: any
-      non-blank string up to the length limit is accepted, any longer string is
-      rejected with a length error, and blank/non-string input is a validation
-      error.
-    - The New Post character counter conserves its relationship to input
-      length: input.length + remainingCount() === MAX_MEMO_CHARS for any string.
-    - setInput round-trips the exact draft text.
+  points. The validation, counter-conservation, setInput round-trip, and
+  broadcast-failure invariants are shared with the Set Name slice and live in
+  behavior-helpers.js; this file supplies the Memo-post specifics and the
+  menu-link idempotence property unique to the New Post page.
 */
 
 'use strict'
 
 const test = require('node:test')
 
-const { seededRandom, forAll, makeStringGen } = require('./harness')
+const { seededRandom, forAll } = require('./harness')
+const { registerBehaviorProperties } = require('./behavior-helpers')
 
 const MemoPost = require('../../src/services/memo-post')
 const NewPostPage = require('../../src/services/new-post')
@@ -24,7 +21,6 @@ const NewPostPage = require('../../src/services/new-post')
 const MAX = MemoPost.MAX_MEMO_CHARS // 217
 
 const rng = seededRandom(20260826)
-const stringOf = makeStringGen(rng)
 
 function buildPage () {
   return new NewPostPage({
@@ -34,86 +30,26 @@ function buildPage () {
   })
 }
 
-// A fake wallet recording broadcast attempts; fails when failWith is set.
-function fakeWallet () {
-  const wallet = {
-    walletInfo: { cashAddress: 'bitcoincash:qqlrzp23w08434twmvr4fxw672whkjy0py26r63g3d' },
-    utxos: [{ txid: 'utxo-fee' }],
-    getUtxos: async function () { return this.utxos },
-    sendOpReturn: async function (walletInfo, bchUtxos, msg, prefix) {
-      if (this.failWith) throw new Error(this.failWith)
-      return 'prop-txid'
-    }
-  }
-  return wallet
-}
-
 function fakeFeed () {
   const posts = []
   return { posts, addPost: (p) => posts.push(p) }
 }
 
-test('memo validation: any non-blank string at or below the limit is valid', async () => {
-  await forAll(
-    (i) => {
-      const len = 1 + Math.floor(rng() * MAX) // 1..MAX
-      return stringOf(len)
-    },
-    (msg) => {
-      // A random ASCII string may occasionally be all whitespace; whitespace-only
-      // input is a validation error, so only assert for non-blank strings.
-      if (msg.trim().length === 0) return true
-      const result = new MemoPost({}).validate(msg)
-      return result.ok === true
-    },
-    { label: 'valid length' }
-  )
-})
+function buildBroadcastPage ({ wallet, navigations }) {
+  return new NewPostPage({
+    memoPost: new MemoPost({ wallet, feed: fakeFeed() }),
+    navigate: (p) => navigations.push(p)
+  })
+}
 
-test('memo validation: any string above the limit is a length error', async () => {
-  await forAll(
-    (i) => stringOf(MAX + 1 + Math.floor(rng() * 100)), // > MAX
-    (msg) => {
-      const result = new MemoPost({}).validate(msg)
-      return result.ok === false && result.type === 'length'
-    },
-    { label: 'over-long rejected as length' }
-  )
-})
-
-test('memo validation: blank and non-string input are validation errors', async () => {
-  await forAll(
-    (i) => (i % 2 === 0 ? '   ' : null),
-    (msg) => {
-      const result = new MemoPost({}).validate(msg)
-      return result.ok === false && result.type === 'validation'
-    },
-    { label: 'blank/non-string rejected as validation' }
-  )
-})
-
-test('character counter conserves length: remaining === MAX - input.length', async () => {
-  await forAll(
-    (i) => stringOf(Math.floor(rng() * (MAX + 8))),
-    (msg) => {
-      const page = buildPage()
-      page.setInput(msg)
-      return page.remainingCount() === MAX - msg.length
-    },
-    { label: 'counter conservation' }
-  )
-})
-
-test('setInput round-trips the draft text exactly', async () => {
-  await forAll(
-    (i) => stringOf(Math.floor(rng() * 50)),
-    (msg) => {
-      const page = buildPage()
-      page.setInput(msg)
-      return page.input === msg
-    },
-    { label: 'setInput round-trip' }
-  )
+registerBehaviorProperties({
+  Module: MemoPost,
+  MAX,
+  label: 'memo',
+  rng,
+  measure: (input) => input.length,
+  buildPage,
+  buildBroadcastPage
 })
 
 test('menu link registration is idempotent', async () => {
@@ -129,27 +65,3 @@ test('menu link registration is idempotent', async () => {
     { label: 'menu link idempotence' }
   )
 })
-
-test('a broadcast failure surfaces the error and never navigates', async () => {
-  await forAll(
-    (i) => ({ message: stringOf(1 + Math.floor(rng() * 40)), failWith: `boom-${i % 97}` }),
-    ({ message, failWith }) => {
-      const wallet = fakeWallet()
-      wallet.failWith = failWith
-      const navigations = []
-      const page = new NewPostPage({
-        memoPost: new MemoPost({ wallet, feed: fakeFeed() }),
-        navigate: (p) => navigations.push(p)
-      })
-      page.setInput(message)
-
-      return page.submit().then((result) => {
-        if (result.ok) return false
-        if (page.submitError !== 'broadcast') return false
-        if (!page.broadcastError || !page.broadcastError.includes('boom')) return false
-        return navigations.length === 0
-      })
-    },
-    { label: 'broadcast failure does not navigate' }
-  )
-})