-- Add `source` to workspaces: record how a workspace was created (web UI /
-- CLI / MCP). Drives the dashboard's has_agent_activity signal — a workspace
-- created through an agent surface (`pad init`, `pad workspace init`, MCP
-- pad_workspace.create) already has an agent wired up before that agent
-- creates its first item, so the "connect an agent" banner should not fire
-- for it (BUG-1557).
--
-- Existing rows predate this tracking, so they default to '' ("unknown /
-- legacy origin") — deliberately NOT 'web', since many pre-existing
-- workspaces were created via `pad init` (CLI). An empty value means
-- "provenance unknown" and is never treated as agent-created. New workspaces
-- set 'web' | 'cli' | 'mcp' explicitly at creation time.
--
-- SQLite has no `ADD COLUMN IF NOT EXISTS`, so this is a bare ADD COLUMN. The
-- migration runner tolerates the "duplicate column name" error for
-- `ALTER TABLE ... ADD COLUMN`, so a partially-applied re-run is idempotent.
-- Adding a NOT NULL column is legal here only because a constant DEFAULT is
-- supplied.
ALTER TABLE workspaces ADD COLUMN source TEXT NOT NULL DEFAULT '';