diff --git a/internal/im/service.go b/internal/im/service.go
index cec15c1b..c8a3aa24 100644
--- a/internal/im/service.go
+++ b/internal/im/service.go
@@ -3,6 +3,7 @@ package im
 import (
 	"bytes"
 	"context"
+	"errors"
 	"fmt"
 	"io"
 	"mime/multipart"
@@ -925,7 +926,28 @@ func (s *Service) HandleMessage(ctx context.Context, msg *IncomingMessage, chann
 	// 4. Get the WeKnora session
 	session, err := s.sessionService.GetSession(sessionCtx, channelSession.SessionID)
 	if err != nil {
-		return fmt.Errorf("get session: %w", err)
+		// The underlying session may have been deleted from the UI while the
+		// ChannelSession mapping still exists (GORM soft-delete does not trigger
+		// SQL ON DELETE CASCADE). Recover by soft-deleting the stale mapping and
+		// re-creating a fresh session so the IM bot doesn't become permanently
+		// unresponsive. (fixes #1046)
+		if errors.Is(err, gorm.ErrRecordNotFound) {
+			logger.Warnf(ctx, "[IM] Session %s not found (deleted?), recycling stale channel session %s",
+				channelSession.SessionID, channelSession.ID)
+			if delErr := s.db.Delete(&ChannelSession{}, "id = ?", channelSession.ID).Error; delErr != nil {
+				logger.Warnf(ctx, "[IM] Failed to delete stale channel session %s: %v", channelSession.ID, delErr)
+			}
+			channelSession, err = s.resolveSession(sessionCtx, msg, tenantID, agentID, channelID, channel.SessionMode)
+			if err != nil {
+				return fmt.Errorf("resolve session (retry): %w", err)
+			}
+			session, err = s.sessionService.GetSession(sessionCtx, channelSession.SessionID)
+			if err != nil {
+				return fmt.Errorf("get session (retry): %w", err)
+			}
+		} else {
+			return fmt.Errorf("get session: %w", err)
+		}
 	}
 
 	// 5. Enqueue the QA request into the bounded worker pool.
@@ -1195,12 +1217,12 @@ func (s *Service) resolveSession(ctx context.Context, msg *IncomingMessage, tena
 	}
 }
 
-// resolveUserSession finds or creates a ChannelSession keyed by (platform, user_id, chat_id, tenant_id).
+// resolveUserSession finds or creates a ChannelSession keyed by (platform, user_id, chat_id, tenant_id, agent_id).
 // This is the original session resolution strategy.
 func (s *Service) resolveUserSession(ctx context.Context, msg *IncomingMessage, tenantID uint64, agentID string, imChannelID string) (*ChannelSession, error) {
 	var cs ChannelSession
-	result := s.db.Where("platform = ? AND user_id = ? AND chat_id = ? AND tenant_id = ? AND deleted_at IS NULL",
-		string(msg.Platform), msg.UserID, msg.ChatID, tenantID).
+	result := s.db.Where("platform = ? AND user_id = ? AND chat_id = ? AND tenant_id = ? AND agent_id = ? AND deleted_at IS NULL",
+		string(msg.Platform), msg.UserID, msg.ChatID, tenantID, agentID).
 		First(&cs)
 
 	if result.Error == nil {
@@ -1244,8 +1266,8 @@ func (s *Service) resolveUserSession(ctx context.Context, msg *IncomingMessage,
 			logger.Warnf(ctx, "[IM] Failed to clean up orphaned session %s: %v", createdSession.ID, delErr)
 		}
 		var existing ChannelSession
-		if findErr := s.db.Where("platform = ? AND user_id = ? AND chat_id = ? AND tenant_id = ? AND deleted_at IS NULL",
-			string(msg.Platform), msg.UserID, msg.ChatID, tenantID).
+		if findErr := s.db.Where("platform = ? AND user_id = ? AND chat_id = ? AND tenant_id = ? AND agent_id = ? AND deleted_at IS NULL",
+			string(msg.Platform), msg.UserID, msg.ChatID, tenantID, agentID).
 			First(&existing).Error; findErr != nil {
 			return nil, fmt.Errorf("create channel session: %w (lookup fallback: %v)", err, findErr)
 		}
@@ -1258,7 +1280,7 @@ func (s *Service) resolveUserSession(ctx context.Context, msg *IncomingMessage,
 	return &cs, nil
 }
 
-// resolveThreadSession finds or creates a ChannelSession keyed by (platform, chat_id, thread_id, tenant_id).
+// resolveThreadSession finds or creates a ChannelSession keyed by (platform, chat_id, thread_id, tenant_id, agent_id).
 // In thread mode, each message thread gets its own session. Multiple users in the
 // same thread share the same session. Top-level messages use their own ID as
 // ThreadID, creating a new session per top-level message.
@@ -1274,8 +1296,8 @@ func (s *Service) resolveThreadSession(ctx context.Context, msg *IncomingMessage
 
 	var cs ChannelSession
 	result := s.db.Where(
-		"platform = ? AND chat_id = ? AND thread_id = ? AND tenant_id = ? AND deleted_at IS NULL",
-		string(msg.Platform), threadID, msg.ChatID, tenantID,
+		"platform = ? AND chat_id = ? AND thread_id = ? AND tenant_id = ? AND agent_id = ? AND deleted_at IS NULL",
+		string(msg.Platform), msg.ChatID, threadID, tenantID, agentID,
 	).First(&cs)
 
 	if result.Error == nil {
@@ -1322,8 +1344,8 @@ func (s *Service) resolveThreadSession(ctx context.Context, msg *IncomingMessage
 		}
 		var existing ChannelSession
 		if findErr := s.db.Where(
-			"platform = ? AND chat_id = ? AND thread_id = ? AND tenant_id = ? AND deleted_at IS NULL",
-			string(msg.Platform), msg.ChatID, threadID, tenantID,
+			"platform = ? AND chat_id = ? AND thread_id = ? AND tenant_id = ? AND agent_id = ? AND deleted_at IS NULL",
+			string(msg.Platform), msg.ChatID, threadID, tenantID, agentID,
 		).First(&existing).Error; findErr != nil {
 			return nil, fmt.Errorf("create thread session: %w (lookup fallback: %v)", err, findErr)
 		}
diff --git a/migrations/versioned/000038_im_session_agent_id.down.sql b/migrations/versioned/000038_im_session_agent_id.down.sql
new file mode 100644
index 00000000..e919e5ed
--- /dev/null
+++ b/migrations/versioned/000038_im_session_agent_id.down.sql
@@ -0,0 +1,12 @@
+-- Rollback: 000038_im_session_agent_id
+-- Restores the original indexes without agent_id.
+
+DROP INDEX IF EXISTS idx_channel_lookup;
+CREATE UNIQUE INDEX idx_channel_lookup
+    ON im_channel_sessions (platform, user_id, chat_id, tenant_id)
+    WHERE deleted_at IS NULL;
+
+DROP INDEX IF EXISTS idx_channel_thread_lookup;
+CREATE UNIQUE INDEX idx_channel_thread_lookup
+    ON im_channel_sessions (platform, chat_id, thread_id, tenant_id)
+    WHERE deleted_at IS NULL AND thread_id != '';
diff --git a/migrations/versioned/000038_im_session_agent_id.up.sql b/migrations/versioned/000038_im_session_agent_id.up.sql
new file mode 100644
index 00000000..c651c5cb
--- /dev/null
+++ b/migrations/versioned/000038_im_session_agent_id.up.sql
@@ -0,0 +1,19 @@
+-- Migration: 000038_im_session_agent_id
+-- Description: Add agent_id to IM channel session unique indexes to isolate sessions per agent.
+-- Fixes: GitHub #1066 (cross-agent session contamination)
+DO $$ BEGIN RAISE NOTICE '[Migration 000038] Adding agent_id to IM channel session indexes'; END $$;
+
+-- 1. User-mode lookup: include agent_id so the same user talking to
+--    different agents gets separate sessions.
+DROP INDEX IF EXISTS idx_channel_lookup;
+CREATE UNIQUE INDEX idx_channel_lookup
+    ON im_channel_sessions (platform, user_id, chat_id, tenant_id, agent_id)
+    WHERE deleted_at IS NULL;
+
+-- 2. Thread-mode lookup: same fix for thread-based sessions.
+DROP INDEX IF EXISTS idx_channel_thread_lookup;
+CREATE UNIQUE INDEX idx_channel_thread_lookup
+    ON im_channel_sessions (platform, chat_id, thread_id, tenant_id, agent_id)
+    WHERE deleted_at IS NULL AND thread_id != '';
+
+DO $$ BEGIN RAISE NOTICE '[Migration 000038] IM session agent_id indexes updated'; END $$;