ClosingPanes rules into cmux-layout-reducer (closing_panes) over the app FFI, step A: Rust port, C ABI, Swift split and parity corpus (no behavior change)

cmux-tui/crates/cmux-layout-reducer-ffi/include/cmux_layout_reducer_ffi.h

@@ -631,6 +631,121 @@ CmuxScrollEffects cmux_scroll_page(CmuxScroll *scroll, CmuxScrollSpring *spring,
 CmuxScrollStatus cmux_scroll_status(const CmuxScroll *scroll);
 uint8_t cmux_scroll_gesture_active(const CmuxScroll *scroll); /* per frame: no focus lookup */
 
+/*
+ * The springing-close rules (cmux-layout-reducer closing_panes; FRAME OWNER
+ * S3c/S3d): which panes border a closing pane and the gaps it keeps, the panes
+ * nothing moves over, where every closing pane shows this frame (per display
+ * frame during a close), the strip's carries and a row column's stop, and a
+ * taken-back close. One handle per screen; panes, scroll areas and row columns
+ * are numbers the caller hands out (0: none). No JSON; a call allocates
+ * nothing once the handle's buffers have grown.
+ *
+ * Return codes: begin and remove return 1 when they answer and 0 when they do
+ * not, with nothing written. 1 and 0 are answers, not
+ * CMUX_LAYOUT_REDUCER_OK (also 0): check for 1. settle and rects return
+ * CMUX_LAYOUT_REDUCER_OK and write a list that borrows the handle's buffer,
+ * valid until the next call on the same handle. Any call returns ERR_NULL,
+ * ERR_INVALID (an unknown handle kind) or ERR_PANIC with nothing written.
+ * Each input array holds `count` elements; an `out` pointer must not overlap
+ * an input array or the handle. One thread at a time per handle.
+ */
+typedef struct CmuxClosingPanes CmuxClosingPanes;
+
+#define CMUX_CLOSING_HANDLE_SPLIT 0
+#define CMUX_CLOSING_HANDLE_COLUMN_EDGE 1
+#define CMUX_CLOSING_HANDLE_ROW_EDGE 2
+
+typedef struct CmuxClosingEdges {
+    double min_x;
+    double max_x;
+    double min_y;
+    double max_y;
+} CmuxClosingEdges;
+
+typedef struct CmuxClosingRect {
+    double x;
+    double y;
+    double width;
+    double height;
+} CmuxClosingRect;
+
+typedef struct CmuxClosingPane {
+    uint64_t id;
+    uint64_t area;
+    uint64_t row_column;
+    CmuxClosingEdges edges;
+    uint8_t scrolls;
+    uint8_t reserved[7];
+} CmuxClosingPane;
+
+typedef struct CmuxClosingHandle {
+    CmuxClosingEdges hit;
+    double mid_x;
+    double mid_y;
+    uint64_t area;   /* a split's scroll area (0: none) */
+    uint64_t column; /* a row edge's column */
+    uint8_t kind;    /* CMUX_CLOSING_HANDLE_* */
+    uint8_t horizontal;
+    uint8_t kept;
+    uint8_t fixed_split;
+    uint8_t docked;
+    uint8_t reserved[3];
+} CmuxClosingHandle;
+
+typedef struct CmuxClosingFrame {
+    uint64_t id;
+    CmuxClosingEdges now;
+    CmuxClosingEdges target;
+    double vx;
+    double vy;
+    double vw;
+    double vh;
+    uint8_t moving;
+    uint8_t reserved[7];
+} CmuxClosingFrame;
+
+typedef struct CmuxClosingRow {
+    uint64_t column;
+    double now;
+    double target;
+} CmuxClosingRow;
+
+typedef struct CmuxClosingPlaced {
+    uint64_t pane;
+    CmuxClosingRect rect;
+} CmuxClosingPlaced;
+
+typedef struct CmuxClosingTaken {
+    CmuxClosingRect rect;
+    double vx;
+    double vw;
+    double vy;
+    double vh;
+} CmuxClosingTaken;
+
+typedef struct CmuxClosingIds {
+    const uint64_t *ids;
+    size_t count;
+} CmuxClosingIds;
+
+typedef struct CmuxClosingPlacedList {
+    const CmuxClosingPlaced *placed;
+    size_t count;
+} CmuxClosingPlacedList;
+
+CmuxClosingPanes *cmux_closing_panes_new(void);
+void cmux_closing_panes_free(CmuxClosingPanes *closing);
+int32_t cmux_closing_panes_begin(CmuxClosingPanes *closing, uint64_t pane, const CmuxClosingEdges *shown, const CmuxClosingPane *panes, size_t pane_count, const CmuxClosingHandle *handles, size_t handle_count, double max_gap, uint8_t has_view_shift, double view_shift);
+int32_t cmux_closing_panes_settle(CmuxClosingPanes *closing, const CmuxClosingFrame *frames, size_t frame_count, const CmuxClosingRow *rows, size_t row_count, CmuxClosingIds *out);
+int32_t cmux_closing_panes_rects(CmuxClosingPanes *closing, const CmuxClosingFrame *frames, size_t frame_count, const CmuxClosingRow *rows, size_t row_count, CmuxClosingPlacedList *out);
+int32_t cmux_closing_panes_carry(CmuxClosingPanes *closing, double drift, uint8_t has_view_shift, double view_shift);
+int32_t cmux_closing_panes_settle_carried(CmuxClosingPanes *closing, double strip_shift);
+int32_t cmux_closing_panes_shift_y(CmuxClosingPanes *closing, uint64_t column, double delta);
+int32_t cmux_closing_panes_remove(CmuxClosingPanes *closing, uint64_t pane, const CmuxClosingFrame *frames, size_t frame_count, CmuxClosingTaken *out);
+int32_t cmux_closing_panes_drop(CmuxClosingPanes *closing, uint64_t pane);
+uint8_t cmux_closing_panes_has_awaiting(const CmuxClosingPanes *closing);
+uint64_t cmux_closing_panes_state_hash(const CmuxClosingPanes *closing); /* tests: the whole state, hashed */
+
 /*
  * The sidebar row face (cmux-layout-reducer sidebar_face): which tab a
  * workspace's row stands for and is named for, its folder line and Group by