fix(web): move the new thread button under the project selector

[jmclaren7]

What Changed

The sidebar header's new thread button moves out of the search row and down below the project row, where it renders as a full-width button — the pencil icon plus a New thread label, content centered. The search row keeps only the search box; the new project button stays where it was, beside the project selector.

The button is now scope-aware, following the selector directly above it:

• a project is selected → the thread is created in that project immediately, no picker;
• All projects is selected → unchanged behavior: create in the current project when there is nothing to pick (or shift is held), otherwise open the command palette's "New thread in…" picker.

The branch lives in a pure helper, resolveNewThreadClickTarget, which delegates the unscoped case to the existing shouldCreateNewThreadInCurrentProject, so the old rule is untouched. The scoped target resolves through buildSidebarProjectPickerEntries — the same entry builder the palette picker uses — so a grouped project (several checkouts of one repo) lands on the same member either way.

Two smaller consequences: the scoped tooltip names the project ("New thread in Foo") and drops the shortcut, because chat.new is not scope-aware and would promise the wrong target; and the button no longer renders disabled when there are no projects, since it now renders with the project row, which is already hidden in that state (the list's "No projects yet → Add project" empty state remains the way in).

FORK.md gains entry 18 recording the intent (17 is main's configurable worktree branch prefix), and docs/user/thread-sidebar.md gains a short "Starting a thread" section.

Why

The header stacked its controls against the reading order. Row one was the thread search box with an icon-only new thread button pinned to its right; row two was the project scope menu with the new project button pinned to its right. The two "create" affordances sat on different rows, the new thread one above the project selector that gives it its context, and it was a bare glyph next to a text field it has nothing to do with. Reading order is now search → scope → act.

Behaviorally, the button also ignored the scope menu directly beneath it: with several projects a plain click always opened the picker, even when the sidebar was already scoped to one project and the answer was on screen.

UI Changes

No before/after screenshots — this was implemented in a headless remote session with no browser. The change is a header re-stack plus one label; it wants a look in a real client before merge.

Checklist

• This PR is small and focused
• I explained what changed and why
• I included before/after screenshots for any UI changes — not captured, see above
• I included a video for animation/interaction changes — no motion changes

Verification

• vp test run apps/web/src/components/Sidebar.logic.test.ts — 110 passed, 5 of them new (scoped target wins at any project count and on shift+click; picker from "All projects" with several projects; both unscoped direct-create cases)
• tsgo --noEmit clean in apps/web
• vp fmt --check clean repo-wide; vp lint clean on the touched files

Not touched: LegacySidebar.tsx (opt-in legacy layout, different header), the mobile home header, and the chat.new / chat.newLocal keybindings.

History note

This branch briefly carried a merge of main, whose FORK.md conflict resolution left two entries numbered 17. The branch has since been rebased onto main and is linear again: the merge commit and the follow-up that repaired it are both gone, and the entry-18 renumbering is folded into the first commit. The rebased tree is byte-identical to the pre-rebase one (same tree hash), so nothing was lost — only the shape of the history changed.

[github-actions]

Thread transfer impact

✅ Thread transfer remains within every enforced ceiling.

Provider	Metric	Main baseline	This PR	Impact	PR ceiling
Codex	Total thread wire	13.4 KiB	13.4 KiB	−10 B (−0.1%)	15.1 KiB	✅
Codex	Thread snapshot wire	6.9 KiB	6.9 KiB	+3 B (+0.0%)	7.3 KiB	✅
Codex	Live turn WebSocket wire	6.5 KiB	6.5 KiB	−13 B (−0.2%)	7.8 KiB	✅
Codex	Live turn WebSocket decoded	55.0 KiB	55.0 KiB	0 B (0.0%)	66.4 KiB	✅
Codex	Live turn messages	16	16	0 (0.0%)	21	✅
Claude	Total thread wire	13.5 KiB	13.4 KiB	−18 B (−0.1%)	15.1 KiB	✅
Claude	Thread snapshot wire	6.9 KiB	6.9 KiB	−5 B (−0.1%)	7.3 KiB	✅
Claude	Live turn WebSocket wire	6.6 KiB	6.5 KiB	−13 B (−0.2%)	7.8 KiB	✅
Claude	Live turn WebSocket decoded	55.8 KiB	55.8 KiB	0 B (0.0%)	66.4 KiB	✅
Claude	Live turn messages	16	16	0 (0.0%)	21	✅

Baseline: b790ff0 · PR result: 0a73055 · Source CI: success

Scenario and decoded snapshot size

10 historical turns, 5 command tools per turn, 878.9 KiB retained MCP result per historical turn, and a 1.05 MiB retained result in the measured turn.

• Codex decoded thread snapshot: 109.4 KiB
• Claude decoded thread snapshot: 110.1 KiB

Updated in place by a trusted workflow. PR artifacts are strictly validated and never executed.

[Copilot]

Pull request overview

Moves the web sidebar’s new-thread action below the project selector and makes it respect the selected project scope.

Changes:

• Adds a full-width, scope-aware New thread button.
• Introduces and tests pure click-target resolution logic.
• Documents the behavior and fork-specific change.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
FORK.md	Records the fork-specific sidebar change.
docs/user/thread-sidebar.md	Documents scoped thread creation.
apps/web/src/components/Sidebar.tsx	Moves the button and wires scoped behavior.
apps/web/src/components/Sidebar.logic.ts	Adds click-target resolution.
apps/web/src/components/Sidebar.logic.test.ts	Tests scoped and unscoped outcomes.

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