diff --git a/app/plugins/builtins/ai_assistant/migrations/0001_initial.sql b/app/plugins/builtins/ai_assistant/migrations/0001_initial.sql
index 9e44b92..67c55d0 100644
--- a/app/plugins/builtins/ai_assistant/migrations/0001_initial.sql
+++ b/app/plugins/builtins/ai_assistant/migrations/0001_initial.sql
@@ -1,4 +1,7 @@
 -- AI Assistant plugin initial migration
+-- FIX 2026-09-16: ai_chat_sessions/ai_chat_messages removed — AI chat moved
+-- to comm_conversations/comm_messages (Alembic 0137 dropped these tables).
+-- Fresh installs must NOT recreate the ghost tables.
 
 CREATE TABLE IF NOT EXISTS ai_providers (
     id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
@@ -68,35 +71,3 @@ CREATE TABLE IF NOT EXISTS ai_agents (
     deleted_at TIMESTAMPTZ
 );
 CREATE INDEX IF NOT EXISTS ix_ai_agents_tenant ON ai_agents(tenant_id);
-
-CREATE TABLE IF NOT EXISTS ai_chat_sessions (
-    id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
-    user_id UUID NOT NULL,
-    agent_id UUID REFERENCES ai_agents(id) ON DELETE SET NULL,
-    title VARCHAR(255) NOT NULL DEFAULT 'Neuer Chat',
-    is_pinned BOOLEAN NOT NULL DEFAULT FALSE,
-    is_sidebar BOOLEAN NOT NULL DEFAULT FALSE,
-    tenant_id UUID NOT NULL,
-    created_at TIMESTAMPTZ NOT NULL DEFAULT now(),
-    updated_at TIMESTAMPTZ NOT NULL DEFAULT now(),
-    deleted_at TIMESTAMPTZ
-);
-CREATE INDEX IF NOT EXISTS ix_ai_sessions_user ON ai_chat_sessions(user_id);
-CREATE INDEX IF NOT EXISTS ix_ai_sessions_tenant ON ai_chat_sessions(tenant_id);
-
-CREATE TABLE IF NOT EXISTS ai_chat_messages (
-    id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
-    session_id UUID NOT NULL REFERENCES ai_chat_sessions(id) ON DELETE CASCADE,
-    role VARCHAR(20) NOT NULL,
-    content TEXT NOT NULL DEFAULT '',
-    tool_calls JSONB,
-    tool_results JSONB,
-    tokens INTEGER NOT NULL DEFAULT 0,
-    model_used VARCHAR(200) NOT NULL DEFAULT '',
-    tenant_id UUID NOT NULL,
-    created_at TIMESTAMPTZ NOT NULL DEFAULT now(),
-    updated_at TIMESTAMPTZ NOT NULL DEFAULT now(),
-    deleted_at TIMESTAMPTZ
-);
-CREATE INDEX IF NOT EXISTS ix_ai_messages_session ON ai_chat_messages(session_id);
-CREATE INDEX IF NOT EXISTS ix_ai_messages_tenant ON ai_chat_messages(tenant_id);
diff --git a/app/plugins/builtins/ai_assistant/migrations/0002_folders_attachments.sql b/app/plugins/builtins/ai_assistant/migrations/0002_folders_attachments.sql
index edfe247..460a95c 100644
--- a/app/plugins/builtins/ai_assistant/migrations/0002_folders_attachments.sql
+++ b/app/plugins/builtins/ai_assistant/migrations/0002_folders_attachments.sql
@@ -1,4 +1,8 @@
--- AI Assistant plugin migration 0002: chat folders + attachments
+-- AI Assistant plugin migration 0002: chat folders
+-- FIX 2026-09-16: ai_chat_attachments and the folder_id ALTER on
+-- ai_chat_sessions removed — AI chat moved to comm_conversations/
+-- comm_messages (Alembic 0137 dropped the legacy tables). Only the
+-- ai_chat_folders table remains (still used for chat folder ordering).
 
 CREATE TABLE IF NOT EXISTS ai_chat_folders (
     id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
@@ -13,22 +17,3 @@ CREATE TABLE IF NOT EXISTS ai_chat_folders (
 CREATE INDEX IF NOT EXISTS ix_ai_folders_user ON ai_chat_folders(user_id);
 CREATE INDEX IF NOT EXISTS ix_ai_folders_tenant ON ai_chat_folders(tenant_id);
 CREATE INDEX IF NOT EXISTS ix_ai_folders_parent ON ai_chat_folders(parent_id);
-
-ALTER TABLE ai_chat_sessions ADD COLUMN IF NOT EXISTS folder_id UUID REFERENCES ai_chat_folders(id) ON DELETE SET NULL;
-
-CREATE TABLE IF NOT EXISTS ai_chat_attachments (
-    id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
-    message_id UUID REFERENCES ai_chat_messages(id) ON DELETE CASCADE,
-    session_id UUID NOT NULL REFERENCES ai_chat_sessions(id) ON DELETE CASCADE,
-    filename VARCHAR(255) NOT NULL,
-    mime_type VARCHAR(255) NOT NULL DEFAULT 'application/octet-stream',
-    size_bytes INTEGER NOT NULL DEFAULT 0,
-    storage_path VARCHAR(1024) NOT NULL,
-    tenant_id UUID NOT NULL,
-    created_at TIMESTAMPTZ NOT NULL DEFAULT now(),
-    updated_at TIMESTAMPTZ NOT NULL DEFAULT now(),
-    deleted_at TIMESTAMPTZ
-);
-CREATE INDEX IF NOT EXISTS ix_ai_attachments_message ON ai_chat_attachments(message_id);
-CREATE INDEX IF NOT EXISTS ix_ai_attachments_session ON ai_chat_attachments(session_id);
-CREATE INDEX IF NOT EXISTS ix_ai_attachments_tenant ON ai_chat_attachments(tenant_id);
diff --git a/app/plugins/builtins/ai_assistant/migrations/0003_sort_order.sql b/app/plugins/builtins/ai_assistant/migrations/0003_sort_order.sql
index f9c5462..41eb18a 100644
--- a/app/plugins/builtins/ai_assistant/migrations/0003_sort_order.sql
+++ b/app/plugins/builtins/ai_assistant/migrations/0003_sort_order.sql
@@ -1,8 +1,11 @@
 -- Migration 0003: Add sort_order columns for drag&drop reordering
+-- FIX 2026-09-16: ai_chat_sessions was dropped by Alembic 0137 (AI chat
+-- moved to comm_conversations/comm_messages). The ALTER/INDEX statements
+-- targeting ai_chat_sessions made this migration fail on every startup
+-- ("relation ai_chat_sessions does not exist"), which deactivated the
+-- whole ai_assistant plugin. Only the ai_chat_folders statements remain
+-- (that table still exists and is used for chat folder ordering).
 
-ALTER TABLE ai_chat_sessions ADD COLUMN IF NOT EXISTS sort_order INTEGER NOT NULL DEFAULT 0;
 ALTER TABLE ai_chat_folders ADD COLUMN IF NOT EXISTS sort_order INTEGER NOT NULL DEFAULT 0;
 
-CREATE INDEX IF NOT EXISTS ix_ai_sessions_folder ON ai_chat_sessions(folder_id);
-CREATE INDEX IF NOT EXISTS ix_ai_sessions_sort ON ai_chat_sessions(sort_order);
 CREATE INDEX IF NOT EXISTS ix_ai_folders_sort ON ai_chat_folders(sort_order);