Orchestrator dock: active-session "seamless tab" border lost in the tree redesign

Interactive tmux reproduction of the UX regression where the current session's dock card no longer visually connects to the editor area. Before the dock's folder-tree redesign, the active card's border merged into the editor (the dock's right-edge divider was scooped away across the card); now the card is only marked by a background highlight.

Root cause

The "connected border" is the dock's seamless active tab, painted by paint_dock_seamless_active_tab (crates/fresh-editor/src/app/render.rs). It erases the dock's right-edge divider (the "wall") across the active card's rows and draws ╭──…──╯ / ╰──…──╮ scoop corners so the card flows into the editor, like a file-folder tab.

That painter locates the active card by the heavy box glyphs (┏ ┓ ┗ ┛ ┃) that the old list-widget selection styling (mark_list_card_selected in crates/fresh-editor/src/widgets/render.rs) stamped onto exactly one card's rows.

The dock redesign (71d7428 "redesign dock as a hierarchical folder tree") replaced the list with a tree widget. The tree's selection styling is a plain background fill (ui.popup_selection_bg, applied in collect_tree / select_style) — it never promotes border glyphs to their heavy forms. So paint_dock_seamless_active_tab finds no ┏┓┗┛┃ rows and silently no-ops. 251dccd ("bordered dock cards…", issue #2703) restored the rounded card borders via render_tree_card, but not the heavy-glyph selection marking the seamless-tab painter keys on — which is why cards look right again but the active one is "just highlighted".

The painter and its doc comments (and the doc comment on creating_session_moves_dock_highlight_to_new_session in crates/fresh-editor/tests/e2e/orchestrator_dock.rs, which still describes reading state off the seamless tab) are now dead letters: no e2e test asserts the scooped wall, which is why the regression went unnoticed.

Interactive reproduction (tmux)

Debug build at HEAD (6f5f4a1), tmux 160×45, fresh XDG_* dirs, three git projects (alpha-proj, beta-proj, gamma-proj):

1. tmux new-session -d -x 160 -y 45 -c .../alpha-proj then run target/debug/fresh.
2. Ctrl+P, type Toggle Dock, Enter — the dock opens with the launch session's card. (Gotcha for scripted driving: don't type the full Orchestrator: Toggle Dock — the : switches the palette to :line mode and swallows the rest.)
3. Ctrl+P, New Workspace, Enter, type the beta-proj path, raw Ctrl+Enter (\033[13;5u) to submit; repeat for gamma-proj.
4. Alt+O to focus the dock, ↑ to live-switch to beta-proj.

HEAD (regressed) — wall unbroken, selection is bg-fill only

beta-proj-2 is the selected/active session here; its highlight is a pure background fill (48;2;0;100;200 in the ANSI capture), invisible in plain text, and the wall │ runs past every card:

╭────────────────────────────────────╮ │
│· alpha-proj  ▣ alpha-proj          │ │
│▸ master   clean                    │ │
│                                    │ │
╰────────────────────────────────────╯ │
╭────────────────────────────────────╮ │
│· beta-proj-2  ▣ beta-proj          │ │   <- ACTIVE (bg highlight only)
│▸ beta-proj-2   clean               │ │
│                                    │ │
╰────────────────────────────────────╯ │
╭────────────────────────────────────╮ │
│· gamma-proj-3  ▣ gamma-proj        │ │
│▸ gamma-proj-3   clean              │ │
│                                    │ │
╰────────────────────────────────────╯ │

No row of the dock contains a heavy glyph (grep -c '┏\|┃\|┗\|━' over the captures = 0), confirming the painter's trigger can never fire.

Pre-tree (923056c, parent of 71d7428) — same scenario, same keys

The active card's top edge runs to the wall and scoops up (╯), its right side is open (no card border, no wall), and the bottom edge scoops down (╮); the tab follows ↑/↓ live-switching:

╭────────────────────────────────────╮ │
│ · alpha-proj          ▣ alpha-proj │ │
│ ▸ master                     clean │ │
│                                    │ │
╰────────────────────────────────────╯ │
╭──────────────────────────────────────╯
│ · beta-proj-3          ▣ beta-proj        <- ACTIVE: merges into editor
│ ▸ beta-proj-3                clean
│
╰──────────────────────────────────────╮
╭────────────────────────────────────╮ │
│ · gamma-proj-4        ▣ gamma-proj │ │
│ ▸ gamma-proj-4               clean │ │
│                                    │ │
╰────────────────────────────────────╯ │

Fix (implemented)

The tree's bordered-card path now marks the selected card the way the pre-tree card list did: render_widget_tree applies mark_list_card_selected (heavy box frame, bold, no background band) to a selected card node's rows instead of the bg fill, which non-card rows (folder headers, plain single-line trees) keep. The heavy glyphs restore the marker paint_dock_seamless_active_tab keys on, so the active card merges into the editor again; mark_list_card_selected also learned to recognise border rows behind the tree's depth indent.

The e2e test active_session_card_is_a_seamless_tab_and_follows_focus now asserts the rendered scooped wall (╯/╮ at the wall column, no │ across the active card's content rows, inactive cards keeping the divider, the tab following ↑/↓ live-switches). It times out without the fix and passes with it. Verified interactively in tmux with the same scenario as above — the active card scoops into the wall and the tab follows live-switching in both directions.