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diff --git a/surfaces/vega.h b/surfaces/vega.h
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+#ifndef VEGA_H
+#define VEGA_H
+#include "module.h"
+#include <stdio.h>
+
+/* Vega reads a verified Pure module by convention (docs/design/001-first-component.md):
+ *  - a text view named `title` is the screen's title;
+ *  - a table view with a text column `label` is a list; any other table is a
+ *    table. A number column `tone` gives a row its tone; text columns `detail`
+ *    and `badge` add to a list row;
+ *  - a number view named `<table>_focus` is the focused row of that table;
+ *  - every other number or text view is a field.
+ * A tone says what a value means (lib/vega.aup); each surface decides how it
+ * looks or sounds. Surfaces evaluate only the cells they present. */
+enum { VEGA_PARTS = 64, VEGA_TEXT = 1024 };
+typedef enum { VEGA_NORMAL, VEGA_MUTED, VEGA_ACCENT, VEGA_GOOD, VEGA_WARNING, VEGA_DANGER, VEGA_TONES } VegaTone;
+typedef enum { VEGA_FIELD, VEGA_LIST, VEGA_TABLE } VegaKind;
+
+typedef struct {
+    VegaKind kind;
+    uint32_t view;
+    int focus;                      /* number view with the focused row, or -1 */
+    int pointer;                    /* the index state that view shows, or -1: a surface may move it */
+    int label, tone, detail, badge; /* columns, or -1 */
+    uint32_t columns[PURE_MODULE_VIEWS]; /* a table's shown columns, in order */
+    unsigned column_count;
+} VegaPart;
+
+typedef struct {
+    const PureModule *module;
+    int title;  /* text view, or -1 */
+    int prompt; /* the first text input, or -1 */
+    bool ticks; /* it handles frames: a surface runs them, about 60 a second */
+    VegaPart parts[VEGA_PARTS];
+    unsigned count;
+} VegaScreen;
+
+void vega_screen(VegaScreen *, const PureModule *);
+
+/* The wall-clock time events see on a live surface: milliseconds since 1970
+ * (UTC). Scripts set their own (time MS). */
+double vega_now(void);
+/* When each timer input ticks next. run ticks every one due at now (a tick
+ * sees now) and gives the milliseconds until the next, or -1 without timers;
+ * ticked says whether any did. Missed ticks are not made up. */
+typedef struct { double next[PURE_MODULE_INPUTS]; } VegaTimers;
+void vega_timers_start(VegaTimers *, const PureModule *, double now);
+long vega_timers_run(VegaTimers *, PureApp *, double now, bool *ticked);
+/* What a module seems to mean but does not meet: a list label that is not
+ * text, a _focus view without its table, a column a list never shows, a
+ * second text input. Each finding names the view or input it is about;
+ * returns how many there were. */
+unsigned vega_check(const PureModule *, void (*report)(void *, const char *name, const char *message), void *context);
+
+/* A view (row ignored) or a column at a row as text; numbers in Pure's
+ * shortest form. false when it has no value (for example a missing item). */
+bool vega_text(PureApp *, uint32_t view, size_t row, char out[VEGA_TEXT], size_t *length);
+bool vega_number(PureApp *, uint32_t view, size_t row, double *out);
+size_t vega_rows(PureApp *, const VegaPart *);
+/* The row of the focused item: the focus view names an item (an index's
+ * position), shown on the row that holds it; VEGA_NO_ROW when a filtered
+ * list leaves that item out. Clamped to the rows without a filter; 0
+ * without a focus view. */
+#define VEGA_NO_ROW SIZE_MAX
+size_t vega_focus(PureApp *, const VegaPart *);
+/* Focus a row, as a user pointing at it (a click); false when the part's
+ * focus is not a plain index position or the row is not there. */
+bool vega_point(PureApp *, const VegaPart *, size_t row);
+/* The first row to show of `rows` when `visible` fit: the least scrolling
+ * from first that keeps the focused row in view (any, without one). */
+size_t vega_scroll(size_t first, size_t focus, size_t visible, size_t rows);
+/* The key input answering a key name (Pure's names, as KeyboardEvent.code
+ * spells them), or -1; press sends its press and release. */
+int vega_key_input(const PureModule *, const char *key);
+bool vega_press(PureApp *, const char *key);
+/* Commit text to the screen's text input. */
+bool vega_commit(PureApp *, const VegaScreen *, const char *text, size_t length);
+VegaTone vega_tone(PureApp *, const VegaPart *, size_t row);
+/* Values evaluated so far, for checking that surfaces stay lazy. */
+unsigned long vega_evaluations(void);
+
+/* Display cells of a code point in a terminal: 0 for combining and
+ * zero-width characters, 2 for East Asian wide and emoji, else 1. */
+unsigned vega_width(uint32_t codepoint);
+/* The code point at text[at] (valid UTF-8) and the bytes it takes. */
+size_t vega_decode(const char *text, size_t length, size_t at, uint32_t *codepoint);
+/* A control character shown as its control picture (U+2400 block), else itself. */
+uint32_t vega_visible(uint32_t codepoint);
+unsigned vega_text_width(const char *text, size_t length);
+
+/* CLI: everything, as plain lines for pipes; color only when asked. */
+void vega_print(FILE *, PureApp *, const VegaScreen *, bool color);
+/* NUI: the screen as sentences (all), or only the focused item of the first list. */
+void vega_say(FILE *, PureApp *, const VegaScreen *, bool all);
+/* GUI: the screen as a web page on listen:port (0: any free port, printed as
+ * {"port":N}); runs until SIGINT or SIGTERM. reload, when given, is asked
+ * a few times a second whether the module was replaced (the screen with it). */
+int vega_web(PureApp *, const VegaScreen *, const char *listen, unsigned port, bool (*reload)(void));
+
+/* TUI: a grid of cells, redrawn from the app on every change. first keeps each
+ * list's scroll between frames; the focused row stays visible. shown is what
+ * the terminal shows, so a paint sends only the cells that changed (all of
+ * them until the first paint after a resize). */
+typedef struct {
+    uint32_t ch, mark; /* a character and at most one combining mark; ch 0 continues a wide one */
+    uint8_t tone;
+    bool focus, strong;
+} VegaCell;
+typedef struct {
+    unsigned width, height;
+    VegaCell *cells, *shown;
+    struct VegaRow { int part; size_t item; } *rows; /* the item each line shows, or part -1 */
+    bool painted; /* shown holds what the terminal shows */
+    size_t first[VEGA_PARTS];
+    int cursor_row, cursor_column; /* where the terminal cursor goes, or -1 */
+} VegaGrid;
+bool vega_grid(VegaGrid *, unsigned width, unsigned height);
+void vega_grid_free(VegaGrid *);
+/* prompt is the text being typed for the screen's text input; typing says
+ * whether keys go to it. */
+void vega_draw(VegaGrid *, PureApp *, const VegaScreen *, const char *prompt, size_t prompt_length, bool typing);
+/* The part and item a line of the last drawn grid shows. */
+bool vega_hit(const VegaGrid *, unsigned line, unsigned *part, size_t *item);
+#endif