A + on each tab to start a session beside it, in any installed CLI (opt-in)

[JDProfresh]

When I want a second session in the case I'm already working in, I have to go to the toolbar, pick the case in the case dropdown, switch the Run button to the CLI I want, and run. Then the Run button is left on that case and CLI for every later launch. With a few cases open at once, that's most of the times I start a session.

I built a small shortcut for it and have it on a branch (feat/tab-new-session on my fork), held until you weigh in, because it's close to something you removed from the tiles (more on that below).

What it does

• A + sits in each session tab's action icons, between the gear and the ×, and shows and hides exactly like the gear does.
• Tapping it opens a small row of logos for the CLIs installed on this machine, in the Run menu's order: the agents in catalog order, the shell last. Each logo has a tooltip and an aria-label.
• A pick starts one session next to that tab: in its case (or the managed worktree it runs in), and in its named group if it has one. It goes through run() with the same temporary _runMode swap the worktree and custom-model launches use, so the Run button's mode and selected case are left alone. That's the same pattern as aakhter's Cmd+K agent picker in feat(palette): choose the agent when starting a session from Cmd+K #685.
• In the compact rail, where the row icons are hidden, the row's ⋯ menu gets a "New session here…" entry that opens the same picker. The tile ⋯ menu doesn't get it.
• A tab whose folder isn't a case shows a short toast instead of the picker.

Opt-in, and phones

It's a per-device setting next to the pop-out button's: App Settings, "New Session Button on Tabs", off by default everywhere, the same way the tab layouts from #426 ship opt-in with Classic as the default.

On a phone, switching it on puts the + on the active tab next to gear and close, so the active tab gets wider: the label reserve in the phone block grows from 44px to 68px, so the tab's centre still lands on the name and not on an icon. test/mobile-tab-tap-zones.test.ts pins that with the same arithmetic it uses for gear and close. Off, the phone strip is unchanged.

The tile + you removed

I know you took a + with "New session in this case" out of the tile headers (owner decision 9, caf5248e), so I want to raise that before anything else. The reason I think tabs are different: the tile + added tiles to the grid, while this one only starts a session beside the tab you're looking at, with a choice of CLI. It's also off unless you switch it on. But if "no +" was meant for tabs too, I'd rather know now, and I'm happy to reshape it as one of the alternatives below.

How I tested it

• Tested on my iPhone 17 Pro Max in Safari, plus Chromium on desktop against a throwaway instance (header strip, a named group in the vertical rail, the compact rail, and the setting off and on, on phone and desktop).
• On the iPhone the first version did nothing when I picked a CLI: Safari doesn't focus a clicked button, so the menu's focusout handler closed it before the click ran. The branch fixes that in _openTabLayoutMenu with the rule your tile count menu already follows (a focus with nowhere to go doesn't count as leaving). I couldn't reproduce it on the named-group menu with Safari on my Mac or iPad, and phones can't reach that menu, so I'm not filing it separately.
• npm test is green, and the new tests fail without their change (the caseName override on all three run paths, the Safari focus rule, and the phone tap reserve).

The branch is +245/-18 across 11 files, mostly app.js and CSS, with zh-CN strings for the new texts.

Questions

1. Does decision 9 cover session tabs, or is a tab + OK?
2. If it's OK, is the tab's action row the right place? The alternatives I'd be just as happy to build:
   • only a "New session here…" item in the tab's ⋯ and right-click menu, no new icon;
   • a + on the case cluster and named group headers instead of on each tab.
3. Off by default everywhere, and opt-in on phones with the wider active tab: does that match what you'd want?
4. Logos only in the picker, or a labelled list like the Run menu?
5. One gap I left: for a Docker case the picker lists the CLIs installed on this machine, not the ones inside the container. Fine as a follow-up, or should it read the container's list from the start?

If it's a yes in some shape, I'll send it as one PR referencing this thread.

[Ark0N]

Thanks @JDProfresh for asking before opening the PR.

Decision 9 and tabs. Decision 9 was about the tile header. caf5248e took the + and its "New session in this case" menu out of the tile header and changed nothing else, and the tile-grid notes in src/web/CLAUDE.md record the decision there ("no +, owner decision"). It doesn't cover session tabs, and an opt-in + on the tab is fine with me.

Where it goes. Keep it in the tab's action row. Neither alternative reaches the default layout:

• On the header strip a tab has no ⋯ button (.session-tab .tab-more is display: none outside the expanded sidebar and the vertical rail, src/web/public/styles.css:2982-3003).
• Right-click on a tab starts an inline rename (oncontextmenu in the tab markup, src/web/public/app.js:7112).
• A named group's menu already has "New session" (createSessionInTabGroup, app.js:8299), but it uses the toolbar's case and Run mode. The case arrangement's boxes carry only a label, with no menu.

The action row is the one place every layout has.

Default and phones. Off by default on every device, as a per-device key next to showTabDetachButton, is what I'd want. I checked the phone arithmetic. Gear 32 + + 28 + close 20, less close's 2px margin, needs a 64px label (66 with the test's rounding allowance). So 68px holds and stays under the 80px max-width. The rule in src/web/CLAUDE.md only says the reserve must never shrink, so growing it while the setting is on is fine.

Logos or labels. Labels, please. The other two CLI pickers both show the logo with the name: the toolbar Run menu (built by renderRegistryRunOptions) and the phone overview's Run picker. A title tooltip never shows on a phone, and phones get this too.

Docker. Read the container's list from the start. The toolbar Run menu already does this in _refreshRunModeAvailability (src/web/public/session-ui.js:784): it uses the live probe in _dockerCaseModes, then the case's docker.availableModes, and doesn't gate at all for an owned container, whose image ships every CLI. Host-only gating would hide a CLI the container has and offer one it lacks. The + always knows its case, so sharing that rule through one helper is a small change. The phone overview's picker has the same host-only gap today; that's a separate fix.

For the PR:

• POST /api/quick-start saves lastUsedCase on every launch (src/web/routes/session-routes.ts:4613), and the toolbar selects it on the next page load. So a + launch through quick-start (any CLI other than Claude or Shell, and Claude or Shell in a remote or Docker case) leaves the toolbar on the tab's case after a reload. A worktree launch in those CLIs does the same today, so it isn't a blocker, but say so in the PR description.
• An ungrouped tab sends no tabGroupId, so TabLayoutService.sessionCreated() falls back to the case's default session group from 1.44.0 (feat(tabs): per-case default session group #676). The create schema has no way to say "Ungrouped", so from an ungrouped tab whose case has a default group, the new session lands in that group. That's probably right, but choose it on purpose and pin it in a test.
• Enter does nothing on a tab's focusable icon spans today, the gear included: the strip's key handler only acts when the tab itself has focus. So outside the compact rail's row menu, the + has no keyboard route. Offering "New session here…" in the row menu wherever that menu shows (session tabs only, not tiles) would give the full rail and the sidebar one.
• The Safari fix changes the shared _openTabLayoutMenu, so it changes the named-group menu too. Matching the tile count menu's rule is right. Please update the "Every way in has a keyboard path" bullet in docs/architecture-invariants.md, which still says the menu closes on "focus leaving it".
• The three screenshots in the post didn't come through (they're HTML comments). Please attach them to the PR, including the phone one.

Send it as one PR referencing this thread.