perf(tui): carry measured widths through rendering

Carry exact visible widths from Text and Box render results into their owners, and through Editor wrap/layout/render state. Stamp derived widths and render caches with a monotonic Hangul width-config epoch. Retain sidecar entries only by WeakMap owner identity, with immutable publication-time line/width proof, and conservatively remeasure escape-leading padded rows.

Before:
  static_redraw 1633.11 us/op
  editor_edits  1249.71 us/op
After hardened repair:
  static_redraw 1321.51 us/op (1.236x)
  editor_edits  1150.32 us/op (1.086x)
Win:
  Exact byte/grid/scrollback hashes match across all five phases; every phase CV is below 20%, with no B/C regression.
Memory:
  retained heap 251,393,541 -> 251,500,114 bytes (+0.042%).

Op: carry exact widths through render ownership and editor layout
Restores: repeated visible-width measurement in core TUI hot paths

packages/tui/src/utils.ts

@@ -30,14 +30,62 @@ export function getHangulCompatibilityJamoWidth(): HangulCompatibilityJamoWidth
 	return hangulCompatibilityJamoWidth;
 }
 
+// Monotonic epoch for width-affecting runtime configuration. Any cache or
+// carried-width sidecar derived from `visibleWidth` results must be stamped
+// with the epoch at computation time and discarded on mismatch, so a Hangul
+// Compatibility Jamo width change invalidates every derived width.
+let widthConfigEpoch = 0;
+
+export function getWidthConfigEpoch(): number {
+	return widthConfigEpoch;
+}
+
+interface LineWidthsEntry {
+	epoch: number;
+	lines: readonly string[];
+	widths: readonly number[];
+}
+
+// Per-render-result visible widths, keyed by the exact lines array a component
+// returned. The copied strings and widths are the single publication snapshot:
+// they cannot be changed through either publisher array and do not retain the
+// WeakMap key. Entries therefore die with their lines-array owners.
+const lineWidthSidecar = new WeakMap<readonly string[], LineWidthsEntry>();
+
+/** Publish exact per-line visible widths for a rendered lines array. */
+export function publishLineWidths(lines: readonly string[], widths: readonly number[]): void {
+	if (lines.length !== widths.length) {
+		throw new RangeError(`Cannot publish ${widths.length} widths for ${lines.length} lines`);
+	}
+	lineWidthSidecar.set(lines, {
+		epoch: widthConfigEpoch,
+		lines: [...lines],
+		widths: Object.freeze([...widths]),
+	});
+}
+
+/** Exact per-line visible widths for an unchanged `lines` array under the current width config. */
+export function getPublishedLineWidths(lines: readonly string[]): readonly number[] | undefined {
+	const entry = lineWidthSidecar.get(lines);
+	if (entry === undefined || entry.epoch !== widthConfigEpoch || entry.lines.length !== lines.length) {
+		return undefined;
+	}
+	for (let i = 0; i < lines.length; i++) {
+		if (entry.lines[i] !== lines[i]) return undefined;
+	}
+	return entry.widths;
+}
+
 export function setHangulCompatibilityJamoWidth(width: HangulCompatibilityJamoWidth): boolean {
 	const changed = hangulCompatibilityJamoWidth !== width;
 	hangulCompatibilityJamoWidth = width;
+	if (changed) widthConfigEpoch++;
 	nativeSetHangulCompatJamoWidthOverride(nativeHangulCompatibilityJamoOverride(width));
 	return changed;
 }
 
 export function resetHangulCompatibilityJamoWidthForTests(): void {
+	if (hangulCompatibilityJamoWidth !== "platform") widthConfigEpoch++;
 	hangulCompatibilityJamoWidth = "platform";
 	nativeSetHangulCompatJamoWidthOverride(0);
 }