diff --git a/src/services/sqlite/PendingMessageStore.ts b/src/services/sqlite/PendingMessageStore.ts
index 583b0847..155ae5da 100644
--- a/src/services/sqlite/PendingMessageStore.ts
+++ b/src/services/sqlite/PendingMessageStore.ts
@@ -204,6 +204,23 @@ export class PendingMessageStore {
     return result.changes;
   }
 
+  /**
+   * Mark all pending and processing messages for a session as failed (abandoned).
+   * Used when SDK session is terminated and no fallback agent is available:
+   * prevents the session from appearing in getSessionsWithPendingMessages forever.
+   * @returns Number of messages marked failed
+   */
+  markAllSessionMessagesAbandoned(sessionDbId: number): number {
+    const now = Date.now();
+    const stmt = this.db.prepare(`
+      UPDATE pending_messages
+      SET status = 'failed', failed_at_epoch = ?
+      WHERE session_db_id = ? AND status IN ('pending', 'processing')
+    `);
+    const result = stmt.run(now, sessionDbId);
+    return result.changes;
+  }
+
   /**
    * Abort a specific message (delete from queue)
    */
diff --git a/src/services/worker-service.ts b/src/services/worker-service.ts
index 065fb8ee..9bcbd11d 100644
--- a/src/services/worker-service.ts
+++ b/src/services/worker-service.ts
@@ -92,8 +92,8 @@ import { DatabaseManager } from './worker/DatabaseManager.js';
 import { SessionManager } from './worker/SessionManager.js';
 import { SSEBroadcaster } from './worker/SSEBroadcaster.js';
 import { SDKAgent } from './worker/SDKAgent.js';
-import { GeminiAgent } from './worker/GeminiAgent.js';
-import { OpenRouterAgent } from './worker/OpenRouterAgent.js';
+import { GeminiAgent, isGeminiAvailable } from './worker/GeminiAgent.js';
+import { OpenRouterAgent, isOpenRouterAvailable } from './worker/OpenRouterAgent.js';
 import { PaginationHelper } from './worker/PaginationHelper.js';
 import { SettingsManager } from './worker/SettingsManager.js';
 import { SearchManager } from './worker/SearchManager.js';
@@ -394,6 +394,8 @@ export class WorkerService {
 
   /**
    * Start a session processor
+   * On SDK resume failure (terminated session), falls back to Gemini/OpenRouter if available,
+   * otherwise marks messages abandoned and removes session so queue does not grow unbounded.
    */
   private startSessionProcessor(
     session: ReturnType<typeof this.sessionManager.getSession>,
@@ -405,11 +407,20 @@ export class WorkerService {
     logger.info('SYSTEM', `Starting generator (${source})`, { sessionId: sid });
 
     session.generatorPromise = this.sdkAgent.startSession(session, this)
-      .catch(error => {
+      .catch(async (error: unknown) => {
+        if (this.isSessionTerminatedError(error)) {
+          logger.warn('SDK', 'SDK resume failed, falling back to standalone processing', {
+            sessionId: session.sessionDbId,
+            project: session.project,
+            reason: error instanceof Error ? error.message : String(error)
+          });
+          return this.runFallbackForTerminatedSession(session, error);
+        }
         logger.error('SDK', 'Session generator failed', {
           sessionId: session.sessionDbId,
           project: session.project
         }, error as Error);
+        throw error;
       })
       .finally(() => {
         session.generatorPromise = null;
@@ -417,6 +428,78 @@ export class WorkerService {
       });
   }
 
+  /**
+   * Match errors that indicate the Claude Code process/session is gone (resume impossible).
+   * Used to trigger graceful fallback instead of leaving pending messages stuck forever.
+   */
+  private isSessionTerminatedError(error: unknown): boolean {
+    const msg = error instanceof Error ? error.message : String(error);
+    const normalized = msg.toLowerCase();
+    return (
+      normalized.includes('process aborted by user') ||
+      normalized.includes('processtransport') ||
+      normalized.includes('not ready for writing') ||
+      normalized.includes('session generator failed') ||
+      normalized.includes('claude code process')
+    );
+  }
+
+  /**
+   * When SDK resume fails due to terminated session: try Gemini then OpenRouter to drain
+   * pending messages; if no fallback available, mark messages abandoned and remove session.
+   */
+  private async runFallbackForTerminatedSession(
+    session: ReturnType<typeof this.sessionManager.getSession>,
+    _originalError: unknown
+  ): Promise<void> {
+    if (!session) return;
+
+    const sessionDbId = session.sessionDbId;
+
+    // Fallback agents need memorySessionId for storeObservations
+    if (!session.memorySessionId) {
+      const syntheticId = `fallback-${sessionDbId}-${Date.now()}`;
+      session.memorySessionId = syntheticId;
+      this.dbManager.getSessionStore().updateMemorySessionId(sessionDbId, syntheticId);
+    }
+
+    if (isGeminiAvailable()) {
+      try {
+        await this.geminiAgent.startSession(session, this);
+        return;
+      } catch (e) {
+        logger.warn('SDK', 'Fallback Gemini failed, trying OpenRouter', {
+          sessionId: sessionDbId,
+          error: e instanceof Error ? e.message : String(e)
+        });
+      }
+    }
+
+    if (isOpenRouterAvailable()) {
+      try {
+        await this.openRouterAgent.startSession(session, this);
+        return;
+      } catch (e) {
+        logger.warn('SDK', 'Fallback OpenRouter failed', {
+          sessionId: sessionDbId,
+          error: e instanceof Error ? e.message : String(e)
+        });
+      }
+    }
+
+    // No fallback or both failed: mark messages abandoned and remove session so queue doesn't grow
+    const pendingStore = this.sessionManager.getPendingMessageStore();
+    const abandoned = pendingStore.markAllSessionMessagesAbandoned(sessionDbId);
+    if (abandoned > 0) {
+      logger.warn('SDK', 'No fallback available; marked pending messages abandoned', {
+        sessionId: sessionDbId,
+        abandoned
+      });
+    }
+    this.sessionManager.removeSessionImmediate(sessionDbId);
+    this.sessionEventBroadcaster.broadcastSessionCompleted(sessionDbId);
+  }
+
   /**
    * Process pending session queues
    */
diff --git a/src/services/worker/SessionManager.ts b/src/services/worker/SessionManager.ts
index 4ebe3920..639add09 100644
--- a/src/services/worker/SessionManager.ts
+++ b/src/services/worker/SessionManager.ts
@@ -318,6 +318,28 @@ export class SessionManager {
     }
   }
 
+  /**
+   * Remove session from in-memory maps and notify without awaiting generator.
+   * Used when SDK resume fails and we give up (no fallback): avoids deadlock
+   * from deleteSession() awaiting the same generator promise we're inside.
+   */
+  removeSessionImmediate(sessionDbId: number): void {
+    const session = this.sessions.get(sessionDbId);
+    if (!session) return;
+
+    this.sessions.delete(sessionDbId);
+    this.sessionQueues.delete(sessionDbId);
+
+    logger.info('SESSION', 'Session removed (orphaned after SDK termination)', {
+      sessionId: sessionDbId,
+      project: session.project
+    });
+
+    if (this.onSessionDeletedCallback) {
+      this.onSessionDeletedCallback();
+    }
+  }
+
   /**
    * Shutdown all active sessions
    */