fix(desktop): stabilize flaky DM expansion E2E ordering assertions (#2004)

## Summary

Fixes 4 flaky DM expansion E2E tests in Desktop Smoke shard 1 that were
failing non-deterministically on CI (also reproducing on `main` at run
`29526844596`).

**Failing tests:**
- `channels.spec.ts:652` — creates the DM before preparing a persona
mention
- `channels.spec.ts:760` — routes an agent mention from an existing DM
to the expanded conversation
- `channels.spec.ts:815` — routes a relay-agent mention from an existing
DM to the expanded conversation
- `channels.spec.ts:940` — drops an expanded DM after the first message
fails

## Root Cause

Race condition: under fast CI execution, mock command completions
(create_managed_agent, open_dm) can resolve in non-deterministic order,
causing assertions to observe stale or mid-transition state.

## Fix

- **:652** — Move the `new-message-recipient-popover` hidden assertion
after `chat-title` settles (both names present), so it runs
post-transition rather than mid-transition.
- **:760, :940** — Add `createManagedAgentDelayMs: 100` to ensure
persona provisioning doesn't collapse into the same tick as the
expanded-DM open/start sequence.
- **:815** — Add `openDmDelayMs: 100` so the two open_dm calls resolve
in deterministic order.

## Validation

All 4 tests pass with `--repeat-each=3` (12/12 green) locally. Biome
lint clean.

## Scope

Test-only change: 12 insertions, 1 deletion in
`desktop/tests/e2e/channels.spec.ts`.

---

Investigated by Ferret, reviewed by Grumplestiltzkin.

Signed-off-by: Cameron Hotchkies <chotchkies@block.xyz>
Co-authored-by: Goose <opensource@block.xyz>

desktop/tests/e2e/channels.spec.ts

@@ -712,7 +712,6 @@ test("creates the DM before preparing a persona mention", async ({ page }) => {
     page.getByTestId(`new-dm-selected-${TEST_IDENTITIES.charlie.pubkey}`),
   ).toBeDisabled();
   await expect(page.getByTestId("new-dm-search")).toBeDisabled();
-  await expect(page.getByTestId("new-message-recipient-popover")).toBeHidden();
   await expect
     .poll(async () =>
       commandCount(await readCommandLog(page), "create_managed_agent"),
@@ -720,6 +719,9 @@ test("creates the DM before preparing a persona mention", async ({ page }) => {
     .toBeGreaterThan(baselineCreateCount);
   await expect(page.getByTestId("chat-title")).toContainText("charlie");
   await expect(page.getByTestId("chat-title")).toContainText("Fizz");
+  // Assert popover hidden after chat-title settles — by this point the send
+  // flow has completed and the UI has fully transitioned away from the popover.
+  await expect(page.getByTestId("new-message-recipient-popover")).toBeHidden();
 
   const sendCommands = (await readCommandLog(page)).slice(
     baselineCommands.length,
@@ -782,8 +784,11 @@ test("creates the DM before preparing a persona mention", async ({ page }) => {
 test("routes an agent mention from an existing DM to the expanded conversation", async ({
   page,
 }) => {
+  // Delay persona provisioning so the follow-up expanded-DM open/start sequence
+  // cannot collapse into the same fast CI tick before assertions observe it.
   await installMockBridge(page, {
     activePersonaIds: ["builtin:fizz"],
+    createManagedAgentDelayMs: 100,
   });
   await page.goto("/");
 
@@ -837,7 +842,10 @@ test("routes an agent mention from an existing DM to the expanded conversation",
 test("routes a managed relay-agent mention from an existing DM to the expanded conversation", async ({
   page,
 }) => {
+  // Delay the expanded open_dm call so routing/navigation settles
+  // deterministically under fast CI execution.
   await installMockBridge(page, {
+    openDmDelayMs: 100,
     managedAgents: [
       {
         pubkey: DM_RELAY_AGENT_PUBKEY,
@@ -967,8 +975,11 @@ test("does not reroute an expanded DM after the channel pane unmounts", async ({
 test("drops an expanded DM after the first message fails", async ({ page }) => {
   const retryMessage = "Retry without the agent";
   const sendError = "Mock first DM send failed.";
+  // Delay persona provisioning so the follow-up expanded-DM open/start sequence
+  // cannot collapse into the same fast CI tick before assertions observe it.
   await installMockBridge(page, {
     activePersonaIds: ["builtin:fizz"],
+    createManagedAgentDelayMs: 100,
     sendMessageErrors: [sendError],
   });
   await page.goto("/");