diff --git a/src/clients/pull-request-client.ts b/src/clients/pull-request-client.ts
index ddbd5c2..e803930 100644
--- a/src/clients/pull-request-client.ts
+++ b/src/clients/pull-request-client.ts
@@ -30,7 +30,7 @@ export class PullRequestClient extends BaseClient {
   async listPullRequests(
     workspace: string,
     repoSlug: string,
-    options?: { state?: string; author?: string; reviewer?: string; since?: string },
+    options?: { state?: 'OPEN' | 'MERGED' | 'DECLINED' | 'SUPERSEDED'; author?: string; reviewer?: string; since?: string },
   ): Promise<any[]> {
     await this.ensureInitialized();
     try {
@@ -69,7 +69,7 @@ export class PullRequestClient extends BaseClient {
     try {
       const params: Record<string, any> = {};
       if (options?.limit) params.limit = options.limit;
-      if (options?.start) params.start = options.start;
+      if (options?.start !== undefined) params.start = options.start;
       const response = await this.axiosInstance.get(
         `/repositories/${workspace}/${repoSlug}/pullrequests/${prId}/activity`,
         { params },
@@ -88,7 +88,7 @@ export class PullRequestClient extends BaseClient {
     try {
       const params: Record<string, any> = {};
       if (options?.limit) params.limit = options.limit;
-      if (options?.start) params.start = options.start;
+      if (options?.start !== undefined) params.start = options.start;
       const prResponse = await this.axiosInstance.get(
         `/repositories/${workspace}/${repoSlug}/pullrequests/${prId}`,
       );
@@ -115,7 +115,7 @@ export class PullRequestClient extends BaseClient {
     try {
       const params: Record<string, any> = {};
       if (options?.limit) params.limit = options.limit;
-      if (options?.start) params.start = options.start;
+      if (options?.start !== undefined) params.start = options.start;
       const response = await this.axiosInstance.get(
         `/repositories/${workspace}/${repoSlug}/pullrequests/${prId}/commits`,
         { params },
@@ -243,7 +243,7 @@ export class PullRequestClient extends BaseClient {
       const response = await this.axiosInstance.get(
         `/repositories/${workspace}/${repoSlug}/pullrequests/${prId}/tasks`,
       );
-      return { count: response.data.values?.length || 0 };
+      return { count: response.data.size ?? response.data.values?.length ?? 0 };
     } catch (error) {
       throw new Error(`Failed to get task count: ${this.formatError(error)}`);
     }