Update model switch dialog copy in the agentic UI

[shaunandrews]

How AI was used in this PR

AI located the model-switch confirmation flow, updated the user-facing copy, added regression coverage, and ran the required validation. The resulting diff was reviewed for scope and correctness.

Proposed Changes

• Clarify that switching models starts a fresh chat while previous chats remain available from the Chat history button below the chat box. This replaces the incorrect sidebar reference and reassures users that their previous chats were not lost.

Testing Instructions

1. Open an existing agentic UI conversation.
2. Switch to a model in a different family, such as GPT 5.6 Sol.
3. Confirm the dialog title reads “Start a new chat?”
4. Confirm the dialog explains that previous chats are available from the Chat history button below the chat box and does not mention a sidebar.
5. Confirm that starting the new conversation still switches to the selected model.

Automated validation:

• npx eslint --fix apps/ui/src/ui-classic/components/session-view/composer/family-switch-confirm-dialog.tsx apps/ui/src/ui-classic/components/session-view/composer/index.test.tsx
• npm run typecheck
• npm test -- apps/ui/src/ui-classic/components/session-view/composer/index.test.tsx (11 tests passed)

Pre-merge Checklist

• Have you checked for TypeScript, React or other console errors?

[wpmobilebot]

📊 Performance Test Results

Comparing 1611745 vs trunk

app-size

Metric	trunk	1611745	Diff	Change
App Size (Mac)	1378.88 MB	1378.88 MB	+0.00 MB	⚪ 0.0%

site-editor

Metric	trunk	1611745	Diff	Change
load	1129 ms	1113 ms	16 ms	⚪ 0.0%

site-startup

Metric	trunk	1611745	Diff	Change
siteCreation	6518 ms	6524 ms	+6 ms	⚪ 0.0%
siteStartup	2395 ms	2388 ms	7 ms	⚪ 0.0%

---

Results are median values from multiple test runs.

Legend: 🟢 Improvement (faster) | 🔴 Regression (slower) | ⚪ No change (<50ms diff)

[bcotrim]

Should the button be "start a new chat?" instead of "conversation"?

[shaunandrews]

doh, yes! I'll fix.

[shaunandrews]

Wait @copilot can you fix the button label for me?

[Copilot]

Wait @copilot can you fix the button label for me?

Done — the button now reads "Start a new chat" to match the dialog title. Updated the test to match as well.

[shaunandrews]

Meh @copilot I'm not loving it. I think the button label should answer the question in the heading. So maybe:

Start a new chat?

Switching from Opus 5 to GPT 5.6 Sol starts a fresh chat
because the models don’t share memory. You can find
previous chats using Chat history below the chat box.

                              [ Cancel ] [ Yes, new chat ]

--

I updated the paragraph of text too, to be a little shorter. Anything you can do to avoid the orphaned word? Maybe the shorter text alone does it. Any chance you can spin up the app in the cloud and take a screenshot when you're done, then include it in your reponse.

[Copilot]

Meh @copilot I'm not loving it. I think the button label should answer the question in the heading. So maybe:

Start a new chat?
...

Done — button is now "Yes, new chat" and the body copy is updated to the shorter form. As for a screenshot, I'm not able to spin up the app in this sandbox environment, so that'll need a human visual check.

[shaunandrews]

Copilot did ok, but I ended up having to jump in myself.

I added the pretty CSS, and double-checked the modal. 👍

[bcotrim]

LGTM 👍

Light	Dark

[nightnei]

LGTM 👍