chore: the editor reads the selected preset's database, and the config states no history

clangd's database is the one CMake Tools copies from the selected preset,
as in libavr, rather than one chip's tree. .gitattributes drops two Studio
patterns nothing here matches, .clangd is ASCII, and the comments in it,
check.sh and .gitattributes state the reason without the account of how it
was found.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

.vscode/settings.json

@@ -7,25 +7,28 @@
 	// --query-driver lets clangd ask the cross compiler for its own system
 	// includes and target. The database is named here rather than in .clangd
 	// because that file travels with the driver into a consumer's submodule,
-	// where a build tree of this repo's own need not exist.
+	// where a build tree of this repo's own need not exist. It sits one level
+	// above the trees, and CMake Tools copies the selected preset's into it on
+	// every configure: the database carries `-mmcu`, so a fixed tree would
+	// check the driver against one chip.
 	"clangd.arguments": [
-		"--compile-commands-dir=${workspaceFolder}/build/atmega328p-generated",
+		"--compile-commands-dir=${workspaceFolder}/build",
 		"--query-driver=**avr-g++*",
 		"--header-insertion=never"
 	],
+	"cmake.copyCompileCommands": "${workspaceFolder}/build/compile_commands.json",
 
 	// The presets are the build interface, and the toolchain file inside the
-	// libavr submodule is the one place the compiler is chosen. **No prefix is
-	// named here**: a committed file may not name a path that is true of one
-	// machine (libavr guidance rule 50), so the gitignored local/machine.cmake
-	// at this repository's root is where a checkout says where its toolchain
-	// is - one file, and it answers for both hosts.
+	// libavr submodule is the one place the compiler is chosen. No prefix is
+	// named here: the gitignored local/machine.cmake at this repository's root
+	// is where a checkout says where its toolchain is (libavr guidance rule 50).
 	"cmake.useCMakePresets": "always",
 	"cmake.configureOnOpen": true,
 	"cmake.options.statusBarVisibility": "compact",
 
 	"files.watcherExclude": {
 		"**/build/**": true,
+		"**/local/**": true,
 		"**/libavr/**": true
 	},