fix(build): complete the threadSummary rename — remove the old casing

The deletions from the git-mv in 992d2b83 were unstaged by a concurrent
worktree operation before commit, so the pushed tree contained BOTH
threadSummary.ts and threadSummaryData.ts (and the Windows case-collision
persisted). This commit removes the stale originals; caseCollision.test.ts
would have failed CI on the incomplete state.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/app/features/room/thread/threadSummaryData.test.ts

@@ -1,7 +1,7 @@
 import { test } from 'node:test';
 import assert from 'node:assert/strict';
 import { EventStatus, MatrixEvent, RelationType } from 'matrix-js-sdk';
-import { getThreadSummary, isPendingThreadReply } from './threadSummary';
+import { getThreadSummary, isPendingThreadReply } from './threadSummaryData';
 
 // getThreadSummary reads either the live Thread (preferred) or the
 // server-aggregated `m.thread` bundle. We stub only the members it touches and

src/app/features/room/thread/useThread.ts

@@ -12,7 +12,7 @@ import {
   ThreadEvent,
 } from 'matrix-js-sdk';
 import { getLinkedTimelines } from '../RoomTimeline';
-import { isPendingThreadReply } from './threadSummary';
+import { isPendingThreadReply } from './threadSummaryData';
 
 /**
  * Resolve (or bootstrap) the live {@link Thread} for a root event.

src/app/hooks/useThreadSummary.ts

@@ -8,7 +8,7 @@ import {
   RoomEventHandlerMap,
   ThreadEvent,
 } from 'matrix-js-sdk';
-import { getThreadSummary, ThreadSummaryData } from '../features/room/thread/threadSummary';
+import { getThreadSummary, ThreadSummaryData } from '../features/room/thread/threadSummaryData';
 import { threadNotificationsAtom } from '../state/threadNotifications';
 import { getThreadNotificationMode, ThreadNotificationMode } from '../utils/threadNotifications';
 

src/app/utils/caseCollision.test.ts

@@ -0,0 +1,43 @@
+import { strict as assert } from 'node:assert';
+import { test } from 'node:test';
+import { readdirSync } from 'node:fs';
+import { join } from 'node:path';
+
+/**
+ * Guard against same-directory filenames that differ only by case (e.g.
+ * `threadSummary.ts` vs `ThreadSummary.tsx`). On case-insensitive filesystems
+ * (the Windows release runner) an extensionless import of one can resolve to
+ * the OTHER file — rolldown tries `.ts` before `.tsx` — producing
+ * MISSING_EXPORT failures that never reproduce on the Linux/macOS machines the
+ * project is developed and web-deployed on. This broke the desktop release
+ * build twice before being diagnosed; this test makes the collision a local,
+ * immediate failure instead.
+ */
+const findCaseCollisions = (dir: string, collisions: string[]): void => {
+  const entries = readdirSync(dir, { withFileTypes: true });
+  const seen = new Map<string, string>();
+  entries.forEach((entry) => {
+    // Compare basenames without extension: `Foo.tsx` collides with `foo.ts`
+    // because module resolution is extensionless.
+    const stem = entry.isDirectory() ? entry.name : entry.name.replace(/\.[^.]+$/, '');
+    const key = stem.toLowerCase();
+    const existing = seen.get(key);
+    if (existing !== undefined && existing !== stem) {
+      collisions.push(`${dir}: "${existing}" vs "${stem}"`);
+    }
+    if (existing === undefined) seen.set(key, stem);
+    if (entry.isDirectory()) {
+      findCaseCollisions(join(dir, entry.name), collisions);
+    }
+  });
+};
+
+test('no same-directory filenames differing only by case under src/', () => {
+  const collisions: string[] = [];
+  findCaseCollisions('src', collisions);
+  assert.deepEqual(
+    collisions,
+    [],
+    `Case-colliding names break Windows builds:\n${collisions.join('\n')}`,
+  );
+});