feat(gateway): add Slack external chat platform

surfsense_backend/alembic/versions/145_add_slack_gateway_platform.py

@@ -0,0 +1,102 @@
+"""add slack gateway platform
+
+Revision ID: 145
+Revises: 144
+Create Date: 2026-05-31
+"""
+
+from __future__ import annotations
+
+from collections.abc import Sequence
+
+import sqlalchemy as sa
+
+from alembic import op
+
+revision: str = "145"
+down_revision: str | None = "144"
+branch_labels: str | Sequence[str] | None = None
+depends_on: str | Sequence[str] | None = None
+
+
+def _enum_value_exists(enum_name: str, value: str) -> bool:
+    conn = op.get_bind()
+    return (
+        conn.execute(
+            sa.text(
+                "SELECT 1 FROM pg_enum e "
+                "JOIN pg_type t ON t.oid = e.enumtypid "
+                "WHERE t.typname = :enum_name AND e.enumlabel = :value"
+            ),
+            {"enum_name": enum_name, "value": value},
+        ).fetchone()
+        is not None
+    )
+
+
+def _index_exists(index_name: str) -> bool:
+    conn = op.get_bind()
+    return (
+        conn.execute(
+            sa.text(
+                "SELECT 1 FROM pg_indexes "
+                "WHERE schemaname = current_schema() AND indexname = :index_name"
+            ),
+            {"index_name": index_name},
+        ).fetchone()
+        is not None
+    )
+
+
+def upgrade() -> None:
+    if not _enum_value_exists("external_chat_platform", "slack"):
+        op.execute("ALTER TYPE external_chat_platform ADD VALUE 'slack'")
+
+    if _index_exists("uq_external_chat_accounts_system_platform"):
+        op.drop_index(
+            "uq_external_chat_accounts_system_platform",
+            table_name="external_chat_accounts",
+        )
+
+    op.create_index(
+        "uq_external_chat_accounts_system_platform",
+        "external_chat_accounts",
+        ["platform"],
+        unique=True,
+        postgresql_where=sa.text(
+            "is_system_account = true AND NOT (cursor_state ? 'team_id')"
+        ),
+        if_not_exists=True,
+    )
+    op.create_index(
+        "uq_external_chat_accounts_slack_team",
+        "external_chat_accounts",
+        ["platform", sa.text("(cursor_state ->> 'team_id')")],
+        unique=True,
+        postgresql_where=sa.text(
+            "is_system_account = true AND cursor_state ? 'team_id'"
+        ),
+        if_not_exists=True,
+    )
+
+
+def downgrade() -> None:
+    if _index_exists("uq_external_chat_accounts_slack_team"):
+        op.drop_index(
+            "uq_external_chat_accounts_slack_team",
+            table_name="external_chat_accounts",
+        )
+    if _index_exists("uq_external_chat_accounts_system_platform"):
+        op.drop_index(
+            "uq_external_chat_accounts_system_platform",
+            table_name="external_chat_accounts",
+        )
+    op.create_index(
+        "uq_external_chat_accounts_system_platform",
+        "external_chat_accounts",
+        ["platform"],
+        unique=True,
+        postgresql_where=sa.text("is_system_account = true"),
+        if_not_exists=True,
+    )
+    # PostgreSQL enum values are intentionally not removed on downgrade.

surfsense_backend/app/db.py

@@ -577,6 +577,7 @@ class ChatVisibility(StrEnum):
 class ExternalChatPlatform(StrEnum):
     TELEGRAM = "telegram"
     WHATSAPP = "whatsapp"
+    SLACK = "slack"
     SIGNAL = "signal"
 
 
@@ -888,7 +889,18 @@ class ExternalChatAccount(Base, TimestampMixin):
             "uq_external_chat_accounts_system_platform",
             "platform",
             unique=True,
-            postgresql_where=text("is_system_account = true"),
+            postgresql_where=text(
+                "is_system_account = true AND NOT (cursor_state ? 'team_id')"
+            ),
+        ),
+        Index(
+            "uq_external_chat_accounts_slack_team",
+            "platform",
+            text("(cursor_state ->> 'team_id')"),
+            unique=True,
+            postgresql_where=text(
+                "is_system_account = true AND cursor_state ? 'team_id'"
+            ),
         ),
         Index(
             "uq_external_chat_accounts_webhook_secret",