feat(tiles): pure layout and state helpers for the tile grid

window.CodemanTileGrid (constants.js), the grid's pure half:

- computeTileLayout: columns x rows by tile count (1x1, 2x1, 3x1 on a grid
  area at least 1800px wide else 2x2, 2x2, 3x2, 3x3), capped at 9, and
  whether every cell clears the minimum tile size (480x240).
- tileGridCapacity: how many tiles a grid area can hold.
- sanitizeTileGridState: a stored grid (ids only) made safe to apply;
  unknown, deleted, detached and duplicate ids are dropped, focus and zoom
  must name a kept tile, track fractions must be sane.
- tileNeighbor / tileInDirection / cycleTile: which tile takes focus when one
  leaves, on a directional chord, and on Ctrl+Tab or Alt+[ ].
- TILE_SCROLLBACK (10,000 lines, not the primary pane's 50,000) and the tile
  font default.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

src/web/public/constants.js

@@ -1633,6 +1633,173 @@ function buildSplitPickerSessions(sessions, sessionOrder, excludeId, detachedIds
   return result;
 }
 
+// ── Tile grid (tile-grid.js) ───────────────────────────────────────────────
+//
+// Pure layout and state helpers for the tile grid (docs/tile-grid-plan.md):
+// 1 to 9 live sessions side by side, each in its own TerminalTile. Desktop
+// only, behind the same 1180px gate as the split pane.
+
+/** Hard cap on tiles in one grid. */
+const TILE_GRID_MAX = 9;
+// The smallest tile worth showing: about 60 columns and a dozen rows at the
+// default tile font. Bounds how many tiles a window can hold.
+const TILE_MIN_W = 480;
+const TILE_MIN_H = 240;
+// Three tiles go side by side (3x1) only when each still gets ~600px;
+// otherwise they take three cells of a 2x2.
+const TILE_GRID_WIDE_3X1 = 1800;
+// A tile's xterm keeps this many lines, not DEFAULT_SCROLLBACK: nine DOM
+// renderers at 50k lines each is a real memory cost, and a tile's load is a
+// bounded 1 MiB window anyway, so more scrollback only fills with live output.
+const TILE_SCROLLBACK = 10000;
+// Tiles have their own per-device font size (a tile is a fraction of the screen).
+const TILE_FONT_SIZE_DEFAULT = 13;
+
+/**
+ * Columns and rows for `count` tiles, by count (the spec's table), and whether
+ * that layout gives every cell at least the minimum tile size in a grid area
+ * of `width` x `height` px.
+ *
+ * @param {{count: number, width?: number, height?: number, minTileW?: number, minTileH?: number}} p
+ * @returns {{cols: number, rows: number, fits: boolean}}
+ */
+function computeTileLayout({ count, width = Infinity, height = Infinity, minTileW = TILE_MIN_W, minTileH = TILE_MIN_H }) {
+  const n = Math.min(Math.max(0, Math.floor(Number(count) || 0)), TILE_GRID_MAX);
+  let cols;
+  let rows;
+  if (n === 0) return { cols: 0, rows: 0, fits: true };
+  if (n === 1) { cols = 1; rows = 1; }
+  else if (n === 2) { cols = 2; rows = 1; }
+  else if (n === 3) {
+    if (width >= TILE_GRID_WIDE_3X1) { cols = 3; rows = 1; }
+    else { cols = 2; rows = 2; }
+  }
+  else if (n === 4) { cols = 2; rows = 2; }
+  else if (n <= 6) { cols = 3; rows = 2; }
+  else { cols = 3; rows = 3; }
+  const fits = width / cols >= minTileW && height / rows >= minTileH;
+  return { cols, rows, fits };
+}
+
+/**
+ * How many tiles a grid area can hold: the largest count up to TILE_GRID_MAX
+ * whose layout, and every smaller count's layout, fits. 0 when not even one
+ * tile fits.
+ *
+ * @param {{width: number, height: number, minTileW?: number, minTileH?: number}} p
+ * @returns {number}
+ */
+function tileGridCapacity({ width, height, minTileW = TILE_MIN_W, minTileH = TILE_MIN_H }) {
+  let capacity = 0;
+  for (let n = 1; n <= TILE_GRID_MAX; n++) {
+    if (!computeTileLayout({ count: n, width, height, minTileW, minTileH }).fits) break;
+    capacity = n;
+  }
+  return capacity;
+}
+
+/**
+ * The stored grid (`codeman:tile-grid`, ids only) made safe to apply: unknown,
+ * deleted, detached and duplicate ids are dropped, the list is capped at
+ * TILE_GRID_MAX, `focused` / `zoomed` must name a kept id, and track fractions
+ * must be 1 to 3 finite positive numbers. Anything that is not a v1 object
+ * (or its JSON) gives null.
+ *
+ * @param {unknown} raw - the parsed value, or the stored JSON string
+ * @param {{has(id: string): boolean}|Iterable<string>} liveSessions - ids that exist now
+ * @param {{has(id: string): boolean}} [detachedIds] - sessions popped out to their own window
+ * @returns {{v: 1, open: boolean, ids: string[], focused: string|null, zoomed: string|null,
+ *   colFr: number[]|null, rowFr: number[]|null}|null}
+ */
+function sanitizeTileGridState(raw, liveSessions, detachedIds) {
+  let value = raw;
+  if (typeof value === 'string') {
+    try { value = JSON.parse(value); } catch { return null; }
+  }
+  if (!value || typeof value !== 'object' || Array.isArray(value) || value.v !== 1) return null;
+  const live = liveSessions && typeof liveSessions.has === 'function' ? liveSessions : new Set(liveSessions || []);
+  const ids = [];
+  for (const id of Array.isArray(value.ids) ? value.ids : []) {
+    if (typeof id !== 'string' || !id || ids.includes(id)) continue;
+    if (!live.has(id)) continue;
+    if (detachedIds?.has?.(id)) continue;
+    ids.push(id);
+    if (ids.length === TILE_GRID_MAX) break;
+  }
+  const fractions = (fr) => {
+    if (!Array.isArray(fr) || fr.length < 1 || fr.length > 3) return null;
+    return fr.every((x) => typeof x === 'number' && Number.isFinite(x) && x > 0) ? fr.slice() : null;
+  };
+  return {
+    v: 1,
+    open: value.open === true && ids.length > 0,
+    ids,
+    focused: ids.includes(value.focused) ? value.focused : (ids[0] ?? null),
+    zoomed: ids.includes(value.zoomed) ? value.zoomed : null,
+    colFr: fractions(value.colFr),
+    rowFr: fractions(value.rowFr),
+  };
+}
+
+/**
+ * Which tile takes focus when `id` leaves the grid: the next one in grid
+ * order, else the previous one, else null.
+ *
+ * @param {string[]} ids - the grid's tiles, in reading order
+ * @param {string} id - the tile that is leaving
+ * @returns {string|null}
+ */
+function tileNeighbor(ids, id) {
+  const i = ids.indexOf(id);
+  if (i === -1) return ids[0] ?? null;
+  return ids[i + 1] ?? ids[i - 1] ?? null;
+}
+
+/**
+ * The tile a directional focus chord moves to, in a row-major grid of `cols`
+ * columns. Left and right stay within the row; up and down move a whole row,
+ * and moving down onto a short last row lands on its last tile. Null when
+ * there is nothing in that direction.
+ *
+ * @param {string[]} ids - the grid's tiles, in reading order
+ * @param {string} focusedId - the tile the keyboard is in
+ * @param {'left'|'right'|'up'|'down'} direction
+ * @param {number} cols - the layout's column count
+ * @returns {string|null}
+ */
+function tileInDirection(ids, focusedId, direction, cols) {
+  const n = ids.length;
+  const i = ids.indexOf(focusedId);
+  if (i === -1 || n === 0 || !(cols >= 1)) return null;
+  const col = i % cols;
+  let j = -1;
+  if (direction === 'left') j = col > 0 ? i - 1 : -1;
+  else if (direction === 'right') j = col < cols - 1 && i + 1 < n ? i + 1 : -1;
+  else if (direction === 'up') j = i - cols;
+  else if (direction === 'down') {
+    j = i + cols;
+    const lastRow = Math.floor((n - 1) / cols);
+    if (j >= n && Math.floor(i / cols) < lastRow) j = n - 1;
+  }
+  return j >= 0 && j < n && j !== i ? ids[j] : null;
+}
+
+/**
+ * The tile Ctrl+Tab / Alt+] (delta 1) or Alt+[ (delta -1) moves to while the
+ * grid is open: tiles cycle in reading order and wrap.
+ *
+ * @param {string[]} ids
+ * @param {string} focusedId
+ * @param {number} delta - +1 or -1
+ * @returns {string|null}
+ */
+function cycleTile(ids, focusedId, delta) {
+  if (ids.length === 0) return null;
+  const i = ids.indexOf(focusedId);
+  if (i === -1) return ids[0];
+  return ids[(i + delta + ids.length) % ids.length];
+}
+
 // ── Renderer liveness ──────────────────────────────────────────────────────
 //
 // iOS DISCARDS scheduled requestAnimationFrame callbacks when a PWA goes to
@@ -1879,6 +2046,19 @@ if (typeof window !== 'undefined') {
     buildSplitPickerSessions,
     SPLIT_PANE_MIN_WIDTH,
   };
+  window.CodemanTileGrid = {
+    computeTileLayout,
+    tileGridCapacity,
+    sanitizeTileGridState,
+    tileNeighbor,
+    tileInDirection,
+    cycleTile,
+    TILE_GRID_MAX,
+    TILE_MIN_W,
+    TILE_MIN_H,
+    TILE_SCROLLBACK,
+    TILE_FONT_SIZE_DEFAULT,
+  };
   window.CodemanRenderLiveness = { shouldKickRenderer, RENDER_STALL_MS, RENDER_LIVENESS_POLL_MS };
   window.CodemanFetchDeadline = {
     terminalFetchDeadlineMs,

test/tile-grid-layout.test.ts

@@ -0,0 +1,195 @@
+/**
+ * @fileoverview The tile grid's pure helpers (constants.js, `window.CodemanTileGrid`).
+ *
+ * - `computeTileLayout`: columns x rows by tile count (the spec's table), with
+ *   the 3-tile special case (3x1 only on a wide grid area) and whether every
+ *   cell clears the minimum tile size.
+ * - `tileGridCapacity`: how many tiles a grid area can hold.
+ * - `sanitizeTileGridState`: the stored `codeman:tile-grid` value made safe to
+ *   apply (unknown, deleted, detached and duplicate ids dropped).
+ * - `tileNeighbor`, `tileInDirection`, `cycleTile`: which tile takes focus when
+ *   one leaves, on a directional chord, and on Ctrl+Tab / Alt+[ ].
+ *
+ * Loaded via `vm` like split-pane-helpers.test.ts. Port: N/A.
+ */
+import { readFileSync } from 'node:fs';
+import { resolve } from 'node:path';
+import vm from 'node:vm';
+import { describe, expect, it } from 'vitest';
+
+type Layout = { cols: number; rows: number; fits: boolean };
+type TileGrid = {
+  computeTileLayout(p: Record<string, number>): Layout;
+  tileGridCapacity(p: Record<string, number>): number;
+  sanitizeTileGridState(raw: unknown, live: unknown, detached?: Set<string>): Record<string, unknown> | null;
+  tileNeighbor(ids: string[], id: string): string | null;
+  tileInDirection(ids: string[], focused: string, dir: string, cols: number): string | null;
+  cycleTile(ids: string[], focused: string, delta: number): string | null;
+  TILE_GRID_MAX: number;
+  TILE_MIN_W: number;
+  TILE_MIN_H: number;
+  TILE_SCROLLBACK: number;
+};
+
+function loadTileGrid(): TileGrid {
+  const context = vm.createContext({ window: {}, globalThis: {} });
+  const source = readFileSync(resolve(import.meta.dirname, '../src/web/public/constants.js'), 'utf8');
+  vm.runInContext(source, context, { filename: 'constants.js' });
+  return (context.window as { CodemanTileGrid: TileGrid }).CodemanTileGrid;
+}
+
+const T = loadTileGrid();
+// Plenty of room: every layout fits.
+const BIG = { width: 3000, height: 2000 };
+
+describe('computeTileLayout', () => {
+  it.each([
+    [1, 1, 1],
+    [2, 2, 1],
+    [4, 2, 2],
+    [5, 3, 2],
+    [6, 3, 2],
+    [7, 3, 3],
+    [8, 3, 3],
+    [9, 3, 3],
+  ])('%i tiles lay out as %ix%i', (count, cols, rows) => {
+    expect(T.computeTileLayout({ count, ...BIG })).toMatchObject({ cols, rows, fits: true });
+  });
+
+  it('puts 3 tiles side by side only on a grid area at least 1800px wide', () => {
+    expect(T.computeTileLayout({ count: 3, width: 1800, height: 900 })).toMatchObject({ cols: 3, rows: 1 });
+    expect(T.computeTileLayout({ count: 3, width: 1799, height: 900 })).toMatchObject({ cols: 2, rows: 2 });
+  });
+
+  it('caps the count at 9 and treats nothing as an empty grid', () => {
+    expect(T.computeTileLayout({ count: 12, ...BIG })).toMatchObject({ cols: 3, rows: 3 });
+    expect(T.computeTileLayout({ count: 0, ...BIG })).toMatchObject({ cols: 0, rows: 0 });
+  });
+
+  it('reports whether every cell clears the minimum tile size', () => {
+    // 3x2 needs 3 * 480 = 1440 wide and 2 * 240 = 480 high.
+    expect(T.computeTileLayout({ count: 6, width: 1440, height: 480 }).fits).toBe(true);
+    expect(T.computeTileLayout({ count: 6, width: 1439, height: 480 }).fits).toBe(false);
+    expect(T.computeTileLayout({ count: 6, width: 1440, height: 479 }).fits).toBe(false);
+  });
+});
+
+describe('tileGridCapacity', () => {
+  it('holds all nine on a large monitor', () => {
+    expect(T.tileGridCapacity(BIG)).toBe(T.TILE_GRID_MAX);
+  });
+
+  it('stops at the first count whose layout does not fit', () => {
+    // 1440 x 600: 3x2 fits (480 x 300) but 3x3 (480 x 200) does not.
+    expect(T.tileGridCapacity({ width: 1440, height: 600 })).toBe(6);
+    // 1200 x 900: 2x2 fits (600 x 450), 3x2 does not (400 wide).
+    expect(T.tileGridCapacity({ width: 1200, height: 900 })).toBe(4);
+    // 1000 x 400: 2x1 fits (500 x 400); three tiles take a 2x2 (200 high), which does not.
+    expect(T.tileGridCapacity({ width: 1000, height: 400 })).toBe(2);
+  });
+
+  it('is 0 when not even one tile fits', () => {
+    expect(T.tileGridCapacity({ width: 400, height: 900 })).toBe(0);
+  });
+});
+
+describe('sanitizeTileGridState', () => {
+  const live = new Map([
+    ['a', {}],
+    ['b', {}],
+    ['c', {}],
+    ['d', {}],
+  ]);
+
+  it('keeps a valid stored grid as it is', () => {
+    const raw = { v: 1, open: true, ids: ['a', 'b'], focused: 'b', zoomed: 'a', colFr: [1, 2], rowFr: [1] };
+    expect(T.sanitizeTileGridState(raw, live, new Set())).toEqual({
+      v: 1,
+      open: true,
+      ids: ['a', 'b'],
+      focused: 'b',
+      zoomed: 'a',
+      colFr: [1, 2],
+      rowFr: [1],
+    });
+  });
+
+  it('accepts the stored JSON string', () => {
+    const raw = JSON.stringify({ v: 1, open: true, ids: ['c'], focused: 'c' });
+    expect(T.sanitizeTileGridState(raw, live)?.ids).toEqual(['c']);
+  });
+
+  it('drops unknown (deleted), detached and duplicate ids', () => {
+    const raw = { v: 1, open: true, ids: ['a', 'gone', 'b', 'a', 'c', 7, ''], focused: 'a' };
+    const out = T.sanitizeTileGridState(raw, live, new Set(['b']));
+    expect(out?.ids).toEqual(['a', 'c']);
+  });
+
+  it('moves focus to the first kept tile when the focused one was dropped, and drops a dropped zoom', () => {
+    const raw = { v: 1, open: true, ids: ['gone', 'b', 'c'], focused: 'gone', zoomed: 'gone' };
+    const out = T.sanitizeTileGridState(raw, live);
+    expect(out?.focused).toBe('b');
+    expect(out?.zoomed).toBeNull();
+  });
+
+  it('is closed when no tile survives', () => {
+    const out = T.sanitizeTileGridState({ v: 1, open: true, ids: ['gone'] }, live);
+    expect(out).toMatchObject({ open: false, ids: [], focused: null });
+  });
+
+  it('caps the list at nine tiles', () => {
+    const many = Array.from({ length: 12 }, (_, i) => `s${i}`);
+    const out = T.sanitizeTileGridState({ v: 1, open: true, ids: many }, many);
+    expect(out?.ids).toEqual(many.slice(0, 9));
+  });
+
+  it('drops malformed track fractions', () => {
+    const out = T.sanitizeTileGridState(
+      { v: 1, open: true, ids: ['a'], colFr: [1, -1], rowFr: [1, 1, 1, 1] },
+      live
+    );
+    expect(out?.colFr).toBeNull();
+    expect(out?.rowFr).toBeNull();
+  });
+
+  it.each([null, 'not json', '[]', 42, { v: 2, ids: ['a'] }, { ids: ['a'] }])('rejects %j', (raw) => {
+    expect(T.sanitizeTileGridState(raw, live)).toBeNull();
+  });
+});
+
+describe('focus helpers', () => {
+  it('tileNeighbor prefers the next tile, then the previous one', () => {
+    expect(T.tileNeighbor(['a', 'b', 'c'], 'b')).toBe('c');
+    expect(T.tileNeighbor(['a', 'b', 'c'], 'c')).toBe('b');
+    expect(T.tileNeighbor(['a'], 'a')).toBeNull();
+  });
+
+  it('tileInDirection moves within a row-major grid', () => {
+    // 3x2:  a b c
+    //       d e
+    const ids = ['a', 'b', 'c', 'd', 'e'];
+    expect(T.tileInDirection(ids, 'b', 'left', 3)).toBe('a');
+    expect(T.tileInDirection(ids, 'a', 'left', 3)).toBeNull();
+    expect(T.tileInDirection(ids, 'b', 'right', 3)).toBe('c');
+    expect(T.tileInDirection(ids, 'c', 'right', 3)).toBeNull();
+    expect(T.tileInDirection(ids, 'e', 'right', 3)).toBeNull();
+    expect(T.tileInDirection(ids, 'd', 'up', 3)).toBe('a');
+    expect(T.tileInDirection(ids, 'a', 'up', 3)).toBeNull();
+    expect(T.tileInDirection(ids, 'b', 'down', 3)).toBe('e');
+    // Nothing below c in that column: the short last row's last tile.
+    expect(T.tileInDirection(ids, 'c', 'down', 3)).toBe('e');
+    expect(T.tileInDirection(ids, 'e', 'down', 3)).toBeNull();
+  });
+
+  it('cycleTile wraps in reading order', () => {
+    expect(T.cycleTile(['a', 'b', 'c'], 'c', 1)).toBe('a');
+    expect(T.cycleTile(['a', 'b', 'c'], 'a', -1)).toBe('c');
+    expect(T.cycleTile([], 'a', 1)).toBeNull();
+  });
+});
+
+describe('tile constants', () => {
+  it('a tile keeps 10,000 lines of scrollback, not the primary pane 50,000', () => {
+    expect(T.TILE_SCROLLBACK).toBe(10000);
+  });
+});