Agentic UI: Return to the last visited site instead of the first site

[bcotrim]

Related issues

• Related to STU-1985 — extracted from Agentic UI: Simplify Sidebar with new Site-Centric Focus #3998 as part of splitting it into smaller PRs.

How AI was used in this PR

The core change was cherry-picked from #3998 (authored there with AI assistance). Claude Code ported it onto trunk, resolved merge conflicts (including the moves to id-based session↔site matching from #4131 and the signed-out gates from #4183), addressed review feedback, and wrote the unit tests for the redirect logic. All code was reviewed and verified locally (lint, typecheck, apps/ui test suite).

Proposed Changes

Studio's agentic UI always lands on the first site (in raw fetch order) at launch, regardless of where the user was working. This PR makes the app reopen on the site the user last worked with:

• The dashboard remembers the last visited site in localStorage.
• On launch, the / index route opens that site's newest active chat (or a new chat if it has none) — matching exactly what clicking the site in the site-centric sidebar (Agentic UI: Make the sidebar site-centric #4191) does.
• If the remembered site no longer exists (deleted) or nothing is stored yet, it falls back to the top site in sidebar order, respecting the manual ordering from Add drag-to-reorder for sites in the agentic UI sidebar #4134 instead of raw fetch order.
• The sidebar auto-scrolls to keep the restored site's row visible when it sits below the fold (thanks @sejas for catching this!).

An earlier revision restored the exact last-visited session. We simplified to site-level restore to stay consistent with the site-centric sidebar model: sites are the primary navigation unit, and a site always opens its newest active chat.

No launch-time cost: the index route already fetched sites and sessions before redirecting; this adds only a synchronous localStorage read.

Testing Instructions

1. Launch Studio with the agentic UI and open a chat on a site other than the top one in the sidebar.
2. Quit and relaunch — you should land on that same site (its newest active chat).
3. With enough sites to make the sidebar scroll, work on a site near the bottom, relaunch — the sidebar should scroll so the selected site's row is visible.
4. Archive the chat you were on, relaunch — you should land on that site's newest remaining active chat, or a new chat if none are left.
5. Delete the site you were on, relaunch — you should land on your sidebar's top site, with no errors.
6. Drag a different site to the top of the sidebar, clear the app's localStorage, relaunch — the fallback should follow your sidebar order.

Pre-merge Checklist

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

🤖 Generated with Claude Code

[wpmobilebot]

📊 Performance Test Results

Comparing f6486cb vs trunk

app-size

Metric	trunk	f6486cb	Diff	Change
App Size (Mac)	1361.88 MB	1355.58 MB	6.30 MB	🟢 -0.5%

site-editor

Metric	trunk	f6486cb	Diff	Change
load	1113 ms	752 ms	361 ms	🟢 -32.4%

site-startup

Metric	trunk	f6486cb	Diff	Change
siteCreation	6500 ms	6526 ms	+26 ms	⚪ 0.0%
siteStartup	2380 ms	2394 ms	+14 ms	⚪ 0.0%

---

Results are median values from multiple test runs.

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

[katinthehatsite]

Delete the site you were on without archiving the session, relaunch — you land back on that session with a name-only header (see Notes above), with no errors.

I seem to land on name-only session for that canse but then I can still send messages and they go into the Unassigned section (so the local site is deleted but I can send messages):

When I am asking the chat about it, it says the site no longer exists (I guess it makes sense that it is now Unassigned):

But I am finding the experience a bit strange, should be disable the input field in that case? I am guessing part of the problem will be solved when we delete the sessions when the user deletes the site in a different PR I review earlier.

[bcotrim]

Thanks for the review @katinthehatsite! 🙌

• Once Delete AI chat sessions when a site is deleted #4132 lands, there should no longer be unassigned chat sessions
• With Agentic UI: Make the sidebar site-centric #4191 the focus is now on sites instead of chat sessions — this PR now restores the last visited site (opening its newest chat) rather than the exact session

Can you take another look at this PR, please?

[sejas]

Looks good. I confirmed the last selected site is the one that is selected when Studio starts again.
I have two suggestions to consider:

1. Change the PR title to say last visited site, instead of last visited session.
2. If the left sidebar has scroll and the selected site is at the bottom, then the selected site row is not visible when starting Studio.

latest-selected-site.mp4

[nightnei]

Delete the site you were on, relaunch — you should land on your sidebar's top site, with no errors.

I spotted another bug here - when we delete a site, the chat remains active. We should probably auto-select another site instead.
But after restarting Studio - it works well - I indeed see the first website in the list is auto-selected.

[bcotrim]

Delete the site you were on, relaunch — you should land on your sidebar's top site, with no errors.

I spotted another bug here - when we delete a site, the chat remains active. We should probably auto-select another site instead. But after restarting Studio - it works well - I indeed see the first website in the list is auto-selected.

Let's address that in #4132

[bcotrim]

Looks good. I confirmed the last selected site is the one that is selected when Studio starts again. I have two suggestions to consider:

1. Change the PR title to say last visited site, instead of last visited session.

2. If the left sidebar has scroll and the selected site is at the bottom, then the selected site row is not visible when starting Studio.

Done, thanks for catching that! 🙇