lsp/sema: recognise the implicit 'context' global

context (the context system — context.allocator, context.data) was reported as an 'undefined variable'. It's now registered as a Context-typed global when Context is in scope, so the field chain (context.allocator) resolves too, with a builtins-list fallback when Context isn't present.

src/sema.zig

@@ -118,6 +118,13 @@ pub const Analyzer = struct {
             try self.registerTopLevelDecl(decl);
         }
 
+        // Implicit `context` global (the context system — `context.allocator`,
+        // `context.data`). Registered with its `Context` type when that's in
+        // scope so the field chain resolves.
+        if (self.struct_types.contains("Context")) {
+            try self.addSymbol("context", .variable, .{ .struct_type = "Context" }, .{ .start = 0, .end = 0 });
+        }
+
         // Pass 2: Analyze bodies (all top-level names are now in scope).
         for (root.data.root.decls) |decl| {
             try self.analyzeTopLevelDecl(decl);
@@ -854,7 +861,7 @@ pub const Analyzer = struct {
         }
 
         // Built-in names that aren't declared in source
-        const builtins = [_][]const u8{ "io", "true", "false", "cast", "closure", "out", "size_of", "align_of", "malloc", "free", "memcpy", "memset" };
+        const builtins = [_][]const u8{ "io", "true", "false", "cast", "closure", "out", "size_of", "align_of", "malloc", "free", "memcpy", "memset", "context" };
         for (builtins) |b| {
             if (std.mem.eql(u8, name, b)) return;
         }