doc: Remove ideas for marks and registers from plans.

docs/DEVPLAN.md

@@ -170,19 +170,26 @@ through hooks and structured I/O. A handler hook can
 receive hover events and emit commands to modify menu
 state.
 
-## Phase 4: Multi-Select & Registers
+## Phase 4: Multi-Select
 
-Power selection features.
+Selection with undo/redo. No marks or registers: filtering
+already handles navigation, and selections surviving filter
+changes covers the register use case.
 
 **Deliverables:**
-- Space to toggle select, V for visual line mode
-- Multi-select output (multiple JSON lines)
-- Named registers (`"a` through `"z`)
-- Marks (`m{a-z}`, `'{a-z}`)
-- `--multi` flag to enable multi-select mode
+- `--multi` flag to gate all multi-select behaviour
+- `Space`/`Tab` toggle-select, `Shift+Tab` toggle-up
+- `V` visual line mode (force-select ranges)
+- `u`/`Ctrl+R` undo/redo selection changes, `U` clear all
+- Selections survive filter changes (tracked by original index)
+- `--selection-order` flag for insertion-order output
+- Multi-item output: one JSON line per selected item
+- Action-fd commands: toggle-select, select-all, deselect-all,
+  undo-selection, redo-selection
+- Test DSL: `multi` fixture, `selected_items` assertion
 
-**Done when:** You can select multiple items, store them
-in registers, and get them all in the output.
+**Done when:** `seq 1 20 | pikl --multi`, toggle a few items
+with Space, confirm, and all selected items appear on stdout.
 
 ## Phase 5: Table Mode & CSV
 
@@ -204,8 +211,7 @@ Persistence and external control.
 
 **Deliverables:**
 - `--session name` for state persistence
-- Session state: filter, scroll position, selections,
-  marks, registers
+- Session state: filter, scroll position, selections
 - Session history log file
 - Unix socket IPC while running
 - IPC commands: push/remove/update items, set filter,