Speed up cold diffs and wrapped text measurement (#4676)

* perf(app): optimize wrapped measurements and checkpoint native layout experiment

Compute full grapheme geometry only for final wrap fragments. Preserve shaped-text search behavior while bounding additive wrap probes. Keep the Android background layout experiment isolated from the normal diff renderer; native renderer integration and iOS bindings remain unfinished.

* perf(server): reduce cold diff generation work

Keep active diff reads owned across invalidation and wait for the initial watcher inventory before cold generation. Batch patch and blob reads while preserving per-file size isolation, bounded output, and daemon responsiveness. Avoid constructing fallback tokens when full-file highlighting already covers both sides.

* test(server): exercise oversized highlighted diff rejection

The single-line fixture now bypasses highlighting under the long-line guard, so it no longer reaches the structured payload limit. Use short dense lines to keep testing oversized rejection and continued socket usability.

* fix(server): queue fresh diffs for forced reads

A forced request following a repository mutation must not reuse an older active build. Invalidate that result and coalesce waiting callers onto one subsequent build. Give the cache a named object input and completed-value type.

* test(server): share deferred diff loader setup

* test(server): name completed diff cache setup

* refactor(server): use aliases for new diff imports

* fix(server): keep shipped diff imports resolvable by Node

The TypeScript build preserves path aliases without a runtime resolver. Restore relative imports for shipped code and declarations, and correct the server import guideline that prompted the regression.

packages/app/src/git/diff-document/text-measurement.ts

@@ -10,6 +10,7 @@ export interface CachedAsciiTextMetrics {
   measure(text: string): number;
   hasEveryGlyph(text: string): boolean;
   measureAdvances(graphemes: readonly string[]): number[];
+  measureWidth(graphemes: readonly string[]): number;
 }
 
 const CODE_LIGATURE_CANDIDATE = /(?:===?|!==?|=>|<=|>=|->|::|\+\+|--)/;
@@ -68,6 +69,22 @@ export function createChunkedAdvanceMeasurer(
   };
 }
 
+/** Preserve advance chunk boundaries when only the final width is needed. */
+export function createChunkedWidthMeasurer(
+  measure: (graphemes: readonly string[]) => number,
+): (graphemes: readonly string[]) => number {
+  return (graphemes) => {
+    let width = 0;
+    let start = 0;
+    while (start < graphemes.length) {
+      const end = chunkEnd(graphemes, start);
+      width += measure(graphemes.slice(start, end));
+      start = end;
+    }
+    return width;
+  };
+}
+
 /**
  * Advance measurement for a backend that can only measure a whole string, which
  * is every backend except a native paragraph shaper.
@@ -144,6 +161,11 @@ export function createCachedAsciiTextMetrics(primary: PrimaryTextFace): CachedAs
       return true;
     },
     measureAdvances: additiveAdvances(measure),
+    measureWidth(graphemes) {
+      let width = 0;
+      for (const grapheme of graphemes) width += measure(grapheme);
+      return width;
+    },
   };
 }