fix(webui): let Tab focus the Playbook selection menu

[edwin-zvs]

Root cause

Selecting text in the web Playbook editor pops up the selection action menu, but playbookOnKeyDown gave Tab exactly one job:

if (e.key === "Tab" && !mod) {
  e.preventDefault();
  document.execCommand("insertText", false, "  ");
  return;
}

With a selection live, insertText replaces it. So Tab both failed to reach the menu and destroyed the very text the menu was offering to act on. The menu was pointer-only: nothing moved focus into it, and its rows were not reachable from the keyboard at all.

The TUI contract I matched

The TUI settled this over #1240 → #1285 → #1286 → #1289, and spec 0196 records it. I derived the end state from crates/cli/src/app/editor.rs as it stands on main (handle_playbook_selection_menu_key), not from any single commit message:

	behavior
Tab, menu visible	focus the menu, document untouched
Tab/S-Tab, menu focused	walk rows forward/back (arrows too)
Enter, menu focused	run the focused row (Shift: in a fork)
Escape, menu open	dismiss the menu only, selection stays live
Tab, menu dismissed	nest every list line the selection spans; S-Tab un-nests
Escape again	cancel the region
C-o	focus the menu, reopening one Escape dismissed
C-g	cancel selection and menu together

The web now mirrors all of it. Note the ordering subtlety #1286/#1289 encode and that this reproduces: Escape's menu-dismissal stage runs before the region cancel, and an empty region retires the dismissal so the menu returns after a C-Space keyboard selection (whose range is momentarily empty between the mark and the first motion).

Composing with #1298

playbookOnKeyDown had just gained the emacs mark. Two details that path forced:

• The editor's blur handler calls playbookDeactivateMark(), so focusing a menu button disarmed the region — costing Escape its second stage on a keyboard selection.
• A blurred contenteditable does not reliably keep a readable Range, and playbookRun/playbookRunVerb read the live selection.

Both are snapshotted when focus enters the menu and restored when it comes back, so a mouse-drag selection and a C-Space region behave identically.

Accessibility

Focus is real focus, not a highlight: the menu is role="menu", rows are role="menuitem" <button>s that the browser reports as document.activeElement and renders with :focus-visible. Dismissal returns focus deliberately to the editor.

Evidence

Driven against real Chrome over CDP with trusted key events (a synthetic dispatchEvent never runs the default action a preventDefault assertion needs to be meaningful), for both a real mouse drag and a C-Space + motion region.

selection made	Tab → menu focused	Escape → editor, selection intact

Verified end-to-end: Tab focuses playbookSelectionRunBtn with playbookSerialize() unchanged; a second Tab moves to ▸ Challenge assumptions; Enter genuinely ran the selection (run sent (selection, v7)); dismissed-menu Tab turned - alpha item into - alpha item across a 3-line selection while leaving the prose line alone; plain Tab with no selection still inserts a tab stop.

Tests

New web_smoke coverage asserts activeElement moves into the menu and playbookSerialize() is unchanged, then that Escape→Tab indents instead of clobbering. Tab is dispatched with its text so the browser's insertion default action is genuinely in play — otherwise "document unchanged" would pass with the handler removed.

Proved non-vacuous by reverting the Tab branch and re-running:

assertion `left == right` failed: Tab must move focus into the selection menu:
  {"activeInMenu": Bool(false), "menuVisible": Bool(false),
   "selection": String(""), "text": String("-    item\nbeta item\n")}

That failure output is the reported bug — "alpha" replaced by two spaces.

cargo build then cargo test --workspace unfiltered: 2836 passed, 0 failed.

Spec

Spec 0196 scoped itself to the TUI and listed "Web UI menu focus" as an explicit non-goal, which this change contradicts. Rather than add an 0208 that conflicts, I updated 0196 to state the contract for any client that shows the menu, and recorded the two consequences this PR discovered (focus must be real focus; borrowing focus must not cost the user their region).

Scope

crates/daemon/assets/index.html only — the change lives in the construct binary (assets are include_str!'d into the daemon). Expect a trivial merge with the concurrent playbook font-size branch.