diff --git a/apps/server/src/lib/worktree-metadata.ts b/apps/server/src/lib/worktree-metadata.ts
index ab0ba67c..4742a5b0 100644
--- a/apps/server/src/lib/worktree-metadata.ts
+++ b/apps/server/src/lib/worktree-metadata.ts
@@ -5,22 +5,14 @@
 
 import * as secureFs from './secure-fs.js';
 import * as path from 'path';
+import type { PRState, WorktreePRInfo } from '@automaker/types';
+
+// Re-export types for backwards compatibility
+export type { PRState, WorktreePRInfo };
 
 /** Maximum length for sanitized branch names in filesystem paths */
 const MAX_SANITIZED_BRANCH_PATH_LENGTH = 200;
 
-/** GitHub PR states as returned by the GitHub API */
-export type PRState = 'OPEN' | 'MERGED' | 'CLOSED';
-
-export interface WorktreePRInfo {
-  number: number;
-  url: string;
-  title: string;
-  /** PR state: OPEN, MERGED, or CLOSED */
-  state: PRState;
-  createdAt: string;
-}
-
 export interface WorktreeMetadata {
   branch: string;
   createdAt: string;
diff --git a/apps/server/src/routes/worktree/routes/create-pr.ts b/apps/server/src/routes/worktree/routes/create-pr.ts
index 25211854..87777c69 100644
--- a/apps/server/src/routes/worktree/routes/create-pr.ts
+++ b/apps/server/src/routes/worktree/routes/create-pr.ts
@@ -13,6 +13,7 @@ import {
 } from '../common.js';
 import { updateWorktreePRInfo } from '../../../lib/worktree-metadata.js';
 import { createLogger } from '@automaker/utils';
+import { validatePRState } from '@automaker/types';
 
 const logger = createLogger('CreatePR');
 
@@ -273,7 +274,7 @@ export function createCreatePRHandler() {
               number: existingPr.number,
               url: existingPr.url,
               title: existingPr.title || title,
-              state: existingPr.state || 'OPEN',
+              state: validatePRState(existingPr.state),
               createdAt: new Date().toISOString(),
             });
             logger.debug(
@@ -359,7 +360,7 @@ export function createCreatePRHandler() {
                     number: existingPr.number,
                     url: existingPr.url,
                     title: existingPr.title || title,
-                    state: existingPr.state || 'OPEN',
+                    state: validatePRState(existingPr.state),
                     createdAt: new Date().toISOString(),
                   });
                   logger.debug(`Fetched and stored existing PR: #${existingPr.number}`);
diff --git a/apps/server/src/routes/worktree/routes/list.ts b/apps/server/src/routes/worktree/routes/list.ts
index a911fce7..e82e5c14 100644
--- a/apps/server/src/routes/worktree/routes/list.ts
+++ b/apps/server/src/routes/worktree/routes/list.ts
@@ -18,9 +18,9 @@ import {
   readAllWorktreeMetadata,
   updateWorktreePRInfo,
   type WorktreePRInfo,
-  type PRState,
 } from '../../../lib/worktree-metadata.js';
 import { createLogger } from '@automaker/utils';
+import { validatePRState } from '@automaker/types';
 import {
   checkGitHubRemote,
   type GitHubRemoteStatus,
@@ -221,7 +221,7 @@ async function fetchGitHubPRs(projectPath: string): Promise<Map<string, Worktree
         url: pr.url,
         title: pr.title,
         // GitHub CLI returns state as uppercase: OPEN, MERGED, CLOSED
-        state: pr.state as PRState,
+        state: validatePRState(pr.state),
         createdAt: pr.createdAt,
       });
     }
diff --git a/apps/ui/src/components/views/board-view/worktree-panel/types.ts b/apps/ui/src/components/views/board-view/worktree-panel/types.ts
index 36aa2da7..a9cdedca 100644
--- a/apps/ui/src/components/views/board-view/worktree-panel/types.ts
+++ b/apps/ui/src/components/views/board-view/worktree-panel/types.ts
@@ -1,14 +1,6 @@
-/** GitHub PR states as returned by the GitHub API */
-export type PRState = 'OPEN' | 'MERGED' | 'CLOSED';
-
-export interface WorktreePRInfo {
-  number: number;
-  url: string;
-  title: string;
-  /** PR state: OPEN, MERGED, or CLOSED */
-  state: PRState;
-  createdAt: string;
-}
+// Re-export shared types from @automaker/types
+export type { PRState, WorktreePRInfo } from '@automaker/types';
+import type { PRState, WorktreePRInfo } from '@automaker/types';
 
 export interface WorktreeInfo {
   path: string;
diff --git a/libs/types/src/index.ts b/libs/types/src/index.ts
index a0145782..4a8c6af1 100644
--- a/libs/types/src/index.ts
+++ b/libs/types/src/index.ts
@@ -292,3 +292,7 @@ export type {
   EventReplayHookResult,
 } from './event-history.js';
 export { EVENT_HISTORY_VERSION, DEFAULT_EVENT_HISTORY_INDEX } from './event-history.js';
+
+// Worktree and PR types
+export type { PRState, WorktreePRInfo } from './worktree.js';
+export { PR_STATES, validatePRState } from './worktree.js';
diff --git a/libs/types/src/worktree.ts b/libs/types/src/worktree.ts
new file mode 100644
index 00000000..b81a075d
--- /dev/null
+++ b/libs/types/src/worktree.ts
@@ -0,0 +1,32 @@
+/**
+ * Worktree and PR-related types
+ * Shared across server and UI components
+ */
+
+/** GitHub PR states as returned by the GitHub API (uppercase) */
+export type PRState = 'OPEN' | 'MERGED' | 'CLOSED';
+
+/** Valid PR states for validation */
+export const PR_STATES: readonly PRState[] = ['OPEN', 'MERGED', 'CLOSED'] as const;
+
+/**
+ * Validates a PR state value from external APIs (e.g., GitHub CLI).
+ * Returns the validated state if it matches a known PRState, otherwise returns 'OPEN' as default.
+ * This is safer than type assertions as it handles unexpected values from external APIs.
+ *
+ * @param state - The state string to validate (can be any string)
+ * @returns A valid PRState value
+ */
+export function validatePRState(state: string | undefined | null): PRState {
+  return PR_STATES.find((s) => s === state) ?? 'OPEN';
+}
+
+/** PR information stored in worktree metadata */
+export interface WorktreePRInfo {
+  number: number;
+  url: string;
+  title: string;
+  /** PR state: OPEN, MERGED, or CLOSED */
+  state: PRState;
+  createdAt: string;
+}