§6A layout, riding the Stages 1-3 registry with no protocol change:
- vdisplay/layout.rs: pure arrangement engine — auto-row (left-to-right in
acquire order, top-aligned) + manual (per-identity-slot offsets, auto-row
fallback for unpinned members). Unit-tested.
- Registry group model (Linux): group = backend (one desktop per compositor
session). /display/state groups entries, orders by acquire (gen), and computes
each member's position via the engine (pure `assemble_displays`, unit-tested).
DisplayInfo carries group/display_index/position/identity_slot/topology. The
backend reports its resolved slot via the new VirtualDisplay::last_identity_slot
(KWin only), so the arrangement + state key on per-client identity.
- Registry-driven position apply: new VirtualDisplay::apply_position(x,y) (default
no-op; KWin drives kscreen-doctor). Right after create the registry computes the
new display's position over its whole group (pure `position_for_new`, unit-tested)
and applies it — one seam for BOTH deterministic auto-row AND manual placement.
Guarded: the origin (0,0) is skipped, so a single-display / first-of-group session
(and every non-KWin backend) issues no positioning — the historical single-display
path is unchanged. On-glass-validation-pending.
- PUT /api/v1/display/layout: persists the console's manual arrangement via the pure
EffectivePolicy::with_manual_layout transform (locks current effective behavior
into explicit Custom fields + sets a manual layout, so arranging is orthogonal to
the other axes). OpenAPI regenerated.
- /display/settings `enforced` now lists all five axes (keep_alive, topology,
mode_conflict [Stage 4], identity [Stage 3], layout [Stage 5]) — was stale at
keep_alive+topology; the console reads it to know which controls are live.
Still Stage-5 TODO (design/display-management.md §11): Mutter/wlroots group-aware
analogues, per-group topology restore, the web arrangement table, gamescope decline.
cargo build/test/clippy/fmt green; OpenAPI in sync.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
enricobuehler
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