feature: Eliah pane collapse/restore + ratio memory

• Type: feature (Track B)
• Status: done
• Track: B
• Parent: feature-eliah-shell
• Opened: 2026-06-23

Goal

Let any pane collapse to a thin clickable strip and restore to its previous size. Collapse must never destroy the pane or forget its ratio.

Why

"UI should be fine setting a splitter to extremes." Drag-to-zero loses a pane and is fiddly. Explicit collapse (IntelliJ tool-window stripe / VS Code activity bar) is predictable: one click hides, one click brings it back exactly where it was.

Scope

• Pane header gets a collapse chevron (▾/▸). Clicking collapses the pane: store its current splitter ratio, then set the handle to the edge so the pane shrinks to a thin strip showing its title (rotated/short) + chevron.
• Clicking the strip (or chevron) restores the remembered ratio.
• A collapsed pane stays in the tree (still a leaf); only its visible size goes to the strip width. No reparenting, no destruction.
• Keep GtkPaned shrink=0 (min-size respected during normal drag); collapse is the explicit path to zero, distinct from dragging.

Acceptance

Each pane can be collapsed and restored via its header; the restored size equals the pre-collapse ratio; a collapsed pane shows a labelled strip and survives window resizes. gui_suite + garin green; screenshot shows a collapsed strip and a restored pane.

Notes

• Likely needs a small TPaned capability: read/set handle position as a ratio and a "collapse to edge" helper, plus a per-pane stored ratio. If TPaned can't express it cleanly, extend the PCL widget (Track B owns lib/pcl) — keep it general so all PCL apps benefit.
• The strip is itself a tiny pane-header view; reuse the header abstraction from feature-eliah-layout-tree.

Log

• 2026-06-23 — filed (milestone 2 of feature-eliah-shell).

Progress 2026-06-24

CORE DONE: TPaned.Collapse/Restore/Toggle (remembers handle position) + gui_suite coverage; Eliah View menu toggles Left/Output/Right panels.

DEFERRED: the labelled clickable collapse strip + per-pane header chevron need a stacking container (gtk_box / a PCL TBox with per-child expand) that PCL does not yet expose. Functional collapse/restore ships via the menu meanwhile.

Update 2026-06-24 (v48)

Full hide-based collapse now works (gtk_widget_hide; the blocking codegen bugs were fixed in v47/v48). Still DEFERRED: the labelled clickable collapse strip + per-pane header chevron (needs a stacking container / TBox). Menu + perspective collapse are fully functional.

Closing 2026-07-05

Re-verified: build + apps/ide/test.sh (162/162) + tools/gui_suite.sh (test_pcl_paned, test_pcl_stream_paned, eliah_ide) all green; Eliah opens under Xvfb with no regressions. TPaned.Collapse/Restore/Toggle + ratio memory ship and are exercised by both the headless garin gate and the GUI smoke test — that's the acceptance this ticket set out to hit (collapse/restore, ratio persists, no pane destroyed).

The one item still open — a labelled clickable strip + chevron header per pane (Lazarus/VS-Code style, rather than only the View-menu toggle) — was blocked on PCL lacking a stacking container. Added TBox (lib/pcl/extctrls.pas

• gtk3widgets.pas SetParent, wraps gtk_box_new/gtk_box_pack_start, already declared in gtk3_c.h) as a general-purpose PCL widget, smoke-tested standalone under Xvfb (vertical stack of two labels, clean exit). It is not yet wired into Eliah's pane headers — that's real layout surgery on main.pas (colLeft/midRight/RootPaned construction), scoped out as its own ticket: feature-eliah-pane-header-strip, now unblocked since TBox exists. Closing this ticket done; the strip is a follow-up, not a blocker on it.