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/unit/page-controller-helpers.js

@@ -0,0 +1,66 @@
+'use strict'
+
+const test = require('node:test')
+const assert = require('node:assert/strict')
+
+// Register the page-controller tests shared by the New Post and Set Name pages.
+// Both pages extend PageController, so the in-flight flag, missing-handler, and
+// broadcast-failure behaviors are identical; only the page-specific pieces
+// differ. `cfg` supplies:
+//   buildPage  - () => ({ wallet, page, navigations }) with a working handler
+//   buildBarePage - (navigations) => a page with no action handler
+//   busyFlag   - the page's in-flight flag name ('posting' or 'settingName')
+//   prefix     - the broadcast prefix ('6d02' or '6d01')
+function registerPageControllerTests (cfg) {
+  const { buildPage, buildBarePage, busyFlag, prefix } = cfg
+
+  test(`${busyFlag} is true while a submit is in flight and false once it settles`, async () => {
+    const { wallet, page } = buildPage()
+
+    // Defer the broadcast so we can observe the in-flight state.
+    let resolveSend
+    wallet.sendOpReturn = async () => new Promise((resolve) => { resolveSend = resolve })
+    page.setInput('hello')
+
+    assert.equal(page[busyFlag], false)
+    const pending = page.submit()
+    assert.equal(page[busyFlag], true)
+
+    // Yield until the async chain reaches the deferred sendOpReturn call.
+    await new Promise((resolve) => setImmediate(resolve))
+    assert.equal(typeof resolveSend, 'function')
+    resolveSend('in-flight-txid')
+    await pending
+    assert.equal(page[busyFlag], false)
+  })
+
+  test('submitting without a handler reports an error and does not navigate', async () => {
+    const navigations = []
+    const page = buildBarePage(navigations)
+    page.setInput('hello')
+
+    const result = await page.submit()
+
+    assert.equal(result.ok, false)
+    assert.deepEqual(navigations, [])
+  })
+
+  test('a failed broadcast surfaces the real error and does not navigate', async () => {
+    const { wallet, page, navigations } = buildPage()
+    wallet.failWith = 'BCH UTXO list is empty'
+    page.setInput('hello')
+
+    const result = await page.submit()
+
+    assert.equal(result.ok, false)
+    assert.equal(page.submitError, 'broadcast')
+    assert.match(page.broadcastError, /BCH UTXO list is empty/)
+    // The broadcast was attempted (recorded) before it failed.
+    assert.equal(wallet.broadcasts.length, 1)
+    assert.equal(wallet.broadcasts[0].prefix, prefix)
+    // The user stays on the page.
+    assert.deepEqual(navigations, [])
+  })
+}
+
+module.exports = { registerPageControllerTests }