Phase 2/4 done, working on phase 3/5

internal/datasource/epics/noop.go

@@ -0,0 +1,17 @@
+//go:build !epics
+
+// Package epics provides an EPICS Channel Access data source.
+// When built without the "epics" build tag (i.e. without CGo and EPICS Base),
+// this stub is compiled instead, so that the rest of the codebase can call
+// epics.Available() to decide whether to register the data source.
+package epics
+
+import "github.com/uopi/uopi/internal/datasource"
+
+// Available reports whether the EPICS Channel Access data source is compiled in.
+// It always returns false when built without the "epics" build tag.
+func Available() bool { return false }
+
+// New is a placeholder that returns nil when EPICS support is not compiled in.
+// Callers must check Available() before calling New().
+func New(caAddrList, archiveURL string) datasource.DataSource { return nil }