feat: let web search widen past the focused session's workspace

[saucam]

Third and last surface. #309 gave the TUI a Tab toggle, #311 gave Telegram a button, and the web UI still had no way to ask for a cross-workspace search while a session was focused.

The gap

The web UI's anchoring was already correct — it passed the focused session's workdir, which is what Telegram had to be fixed to do. But the scope was derived and never overridable:

...(focusedSession()?.workdir
  ? { workdir: focusedSession()!.workdir, scope: "workspace" }
  : { scope: "all" })

Global search was reachable only by accident, when nothing happened to be focused. With a session open you searched one directory, and the 73% precision@1 path the feature exists for was unreachable.

The change

A segmented control in the modal header switches This workspace / All workspaces.

• It's an override on top of the derived default, not a replacement — so focusing a session later doesn't silently undo a choice the user made
• Hidden entirely when nothing is focused; a toggle with one meaningful position is noise
• The debounce effect now depends on scope as well as query, so flipping re-runs the current query instead of leaving stale hits from the other regime on screen
• Zero hits under workspace scope offers a widen button inline — same reasoning as the Telegram keyboard, since an empty scoped result is exactly when widening helps

Ctrl+K is taken for open/close, so this is a click target rather than a key. Results already render hit.workdir, so global hits were legible without further work.

A workspace is a directory, not a session family

Worth recording because it's easy to misread. workspaceIdFromPath hashes workdir + account_id + project_id, so:

• Every session that ever ran in that directory under the same tenant shares the workspace, related or not
• A fork isolated into a git worktree gets a different path, so it lands outside its parent's scope

That second point is precisely the history cross-workspace search recovers, and it's invisible unless you can ask for it.

Verification

• bun run typecheck clean (root + web)
• bun run lint clean (360 files)
• daemon suite: 2401 pass, 19 skip, 0 fail
• web suite: 430 pass (41 files), 5 new
• The two behavioural tests were confirmed to fail without the scope dependency in the effect, so they're real rather than passing either way

Co-authored-by: Claude Opus 5 (1M context) noreply@anthropic.com

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