Q8: one writing run per workspace directory

Write-granted runs whose directories overlap (same folder, symlink or
junction, or nested) wait for each other, at claim time and for manual
runs.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/main/services/workspace-write-lock.ts

@@ -0,0 +1,39 @@
+import type { DatabaseSync } from "node:sqlite";
+import { existsSync, realpathSync } from "node:fs";
+import { basename, dirname, join, resolve } from "node:path";
+
+/** A running write task whose directory overlaps this task's, or null. */
+export function runningWorkspaceWriter(db: DatabaseSync, taskId: string): { title: string } | null {
+  const task = db.prepare(`
+    select t.requires_filesystem, w.local_path
+    from tasks t left join workspaces w on w.id = t.workspace_id
+    where t.id = ?
+  `).get(taskId) as { requires_filesystem: number; local_path: string | null } | undefined;
+  if (!task) throw new Error(`Task ${taskId} was not found.`);
+  if (task.requires_filesystem !== 1 || !task.local_path) return null;
+  const mine = normalizeDirectory(task.local_path);
+  const writers = db.prepare(`
+    select t.title, w.local_path
+    from task_runs r
+    join tasks t on t.id = r.task_id
+    join workspaces w on w.id = t.workspace_id
+    where r.state = 'running' and t.requires_filesystem = 1
+  `).all() as Array<{ title: string; local_path: string }>;
+  for (const writer of writers) {
+    const other = normalizeDirectory(writer.local_path);
+    if (mine === other || mine.startsWith(`${other}/`) || other.startsWith(`${mine}/`)) return { title: writer.title };
+  }
+  return null;
+}
+
+function normalizeDirectory(localPath: string): string {
+  let existing = resolve(localPath);
+  const missing: string[] = [];
+  while (!existsSync(existing) && dirname(existing) !== existing) {
+    missing.unshift(basename(existing));
+    existing = dirname(existing);
+  }
+  const real = existsSync(existing) ? realpathSync.native(existing) : existing;
+  const path = join(real, ...missing).replace(/\\/g, "/").replace(/\/+$/, "");
+  return process.platform === "win32" ? path.toLowerCase() : path;
+}