diff --git a/docs/console/utilities.md b/docs/console/utilities.md
index 8123305..8fcc31c 100644
--- a/docs/console/utilities.md
+++ b/docs/console/utilities.md
@@ -42,6 +42,6 @@ summer docs:sync
 summer docs:serve
 ```
 
-`docs:build` fails, and writes nothing, when a page names an identifier that does not exist, links to a missing page or anchor, shows a command that neither `summer` nor an application binary has, or has a `src=` code block that differs from its source. It also fails on a Go code block (including `golang`) without a `src=` reference, a `src=` code block inside a callout, blockquote or list item (`src=` blocks must be top-level), and a `src=` code block in a module README. After you change code that a page shows, run `summer docs:sync` to refresh the copies.
+`docs:build` fails, and writes nothing, when a page names an identifier that does not exist, links to a missing page or anchor, shows a command that neither `summer` nor an application binary has, or has a `src=` code block that differs from its source. It also fails on a Go code block (including `golang`) without a `src=` reference, a `src=` code block inside a callout, blockquote or list item (`src=` blocks must be top-level), and a `src=` code block in a module README. A `src=` target must be code `go test ./...` compiles and runs, that is a file in the default build, inside a `Test` function or an `Example` with an `// Output:` comment, or a function one of them calls. After you change code that a page shows, run `summer docs:sync` to refresh the copies.
 
 `docs:serve` listens only on a loopback address unless you pass `--allow-remote`. Use it to preview search, which browsers block when you open the built files directly from disk.
diff --git a/internal/docsite/check_commands.go b/internal/docsite/check_commands.go
index 4060ab7..3b400ae 100644
--- a/internal/docsite/check_commands.go
+++ b/internal/docsite/check_commands.go
@@ -30,10 +30,6 @@ type Commands struct {
 // are checked as commands and highlighted with prompts.
 var shellLangs = []string{"sh", "shell", "bash", "console"}
 
-// commandToken finds `summer <name>` and `./bin/<app> <name>` at the start
-// of a shell command (after an optional "$ " prompt).
-var commandToken = regexp.MustCompile(`^(?:\$\s+)?(summer|\./bin/[A-Za-z0-9._-]+)\s+(\S+)`)
-
 // commandSeparators split one shell line into its commands.
 var commandSeparators = regexp.MustCompile(`&&|\|\||;|\|`)
 
@@ -64,14 +60,13 @@ func (s *site) checkCommands(docs []parsedDoc) ([]Problem, error) {
 	var problems []Problem
 	check := func(d parsedDoc, line int, text string) {
 		for _, cmd := range commandSeparators.Split(text, -1) {
-			m := commandToken.FindStringSubmatch(strings.TrimSpace(cmd))
-			if m == nil || strings.HasPrefix(m[2], "-") {
+			name, isTool, ok := commandWord(cmd)
+			if !ok {
 				continue
 			}
-			name := m[2]
-			known := tool[name]
-			if m[1] != "summer" {
-				known = app[name]
+			known := app[name]
+			if isTool {
+				known = tool[name]
 			}
 			if !known {
 				problems = append(problems, Problem{File: d.file, Line: line, Rule: "command",
@@ -102,6 +97,91 @@ func (s *site) checkCommands(docs []parsedDoc) ([]Problem, error) {
 	return problems, nil
 }
 
+// commandWord finds the summer or application command word in one shell
+// command. tool is true for summer and `go run ./cmd/summer`, false for
+// ./bin/{app} and bin/{app}. ok is false when the line is not one of
+// those programs or when flags leave no command word. Flag handling
+// matches cobra's stripFlags for a root whose only flag is the bool
+// --help / -h: "--" ends the search, --help and -h take no value, any
+// other --name or two-character -x consumes the next token, and a token
+// that already contains "=" is skipped alone.
+func commandWord(cmd string) (name string, tool bool, ok bool) {
+	fields := strings.Fields(strings.TrimSpace(cmd))
+	if len(fields) > 0 && fields[0] == "$" {
+		fields = fields[1:]
+	}
+	for len(fields) > 0 && isAssignment(fields[0]) {
+		fields = fields[1:]
+	}
+	switch {
+	case len(fields) == 0:
+		return "", false, false
+	case fields[0] == "summer":
+		tool = true
+		fields = fields[1:]
+	case len(fields) >= 3 && fields[0] == "go" && fields[1] == "run" && fields[2] == "./cmd/summer":
+		tool = true
+		fields = fields[3:]
+	case isAppBin(fields[0]):
+		fields = fields[1:]
+	default:
+		return "", false, false
+	}
+	for len(fields) > 0 {
+		s := fields[0]
+		switch {
+		case s == "--":
+			return "", tool, false
+		case strings.HasPrefix(s, "-") && strings.Contains(s, "="):
+			fields = fields[1:]
+		case s == "--help" || s == "-h":
+			fields = fields[1:]
+		case strings.HasPrefix(s, "--") || (strings.HasPrefix(s, "-") && len(s) == 2):
+			if len(fields) < 3 {
+				return "", tool, false
+			}
+			fields = fields[2:]
+		case strings.HasPrefix(s, "-"):
+			fields = fields[1:]
+		default:
+			return s, tool, true
+		}
+	}
+	return "", tool, false
+}
+
+// isAssignment reports a leading VAR=value token: a name of letters,
+// digits and underscores that does not start with a digit.
+func isAssignment(tok string) bool {
+	name, _, ok := strings.Cut(tok, "=")
+	if !ok || name == "" || (name[0] >= '0' && name[0] <= '9') {
+		return false
+	}
+	for _, r := range name {
+		if r != '_' && (r < '0' || r > '9') && (r < 'A' || r > 'Z') && (r < 'a' || r > 'z') {
+			return false
+		}
+	}
+	return true
+}
+
+// isAppBin reports ./bin/{app} and bin/{app}, with app in [A-Za-z0-9._-].
+func isAppBin(tok string) bool {
+	rest, ok := strings.CutPrefix(tok, "./bin/")
+	if !ok {
+		rest, ok = strings.CutPrefix(tok, "bin/")
+	}
+	if !ok || rest == "" || strings.Contains(rest, "/") {
+		return false
+	}
+	for _, r := range rest {
+		if r != '.' && r != '_' && r != '-' && (r < '0' || r > '9') && (r < 'A' || r > 'Z') && (r < 'a' || r > 'z') {
+			return false
+		}
+	}
+	return true
+}
+
 // exampleCommandNames returns the string-literal Name of every
 // bonfire.Command composite literal (including the elided elements of a
 // []bonfire.Command literal) in the non-test Go files under dir. It parses
diff --git a/internal/docsite/check_identifiers.go b/internal/docsite/check_identifiers.go
index 65f7ddb..45afa45 100644
--- a/internal/docsite/check_identifiers.go
+++ b/internal/docsite/check_identifiers.go
@@ -284,10 +284,10 @@ func isUpper(s string) bool {
 // optionally followed by one ".Member".
 var goDocIdent = regexp.MustCompile(`^[A-Za-z_][A-Za-z0-9_]*(\.[A-Za-z_][A-Za-z0-9_]*)?$`)
 
-// goDoc is the fallback for an index miss: `go doc ./<dir> <query>` run in
-// the repository root, so a declaration the index does not model still
-// counts. It runs without a shell, on an argument list whose query matches
-// goDocIdent.
+// goDoc is the fallback for an index miss: `go doc -c ./<dir> <query>`
+// run in the repository root, so a declaration the index does not model
+// still counts. -c makes the match case-sensitive. It runs without a
+// shell, on an argument list whose query matches goDocIdent.
 func (idx *identIndex) goDoc(dir, query string) bool {
 	if !goDocIdent.MatchString(query) {
 		return false
@@ -298,7 +298,7 @@ func (idx *identIndex) goDoc(dir, query string) bool {
 	}
 	ctx, cancel := context.WithTimeout(context.Background(), 30*time.Second)
 	defer cancel()
-	cmd := exec.CommandContext(ctx, "go", "doc", "./"+dir, query)
+	cmd := exec.CommandContext(ctx, "go", "doc", "-c", "./"+dir, query)
 	cmd.Dir = idx.root
 	cmd.Stdout, cmd.Stderr = nil, nil
 	ok := cmd.Run() == nil
diff --git a/internal/docsite/snippet.go b/internal/docsite/snippet.go
index 92d5b97..a318369 100644
--- a/internal/docsite/snippet.go
+++ b/internal/docsite/snippet.go
@@ -5,6 +5,7 @@ import (
 	"errors"
 	"fmt"
 	"go/ast"
+	"go/build"
 	"go/doc"
 	"go/parser"
 	"go/token"
@@ -14,6 +15,8 @@ import (
 	"path/filepath"
 	"slices"
 	"strings"
+	"unicode"
+	"unicode/utf8"
 )
 
 // Ref is a src= reference in a code fence info string: a
@@ -106,11 +109,8 @@ func Extract(root string, ref Ref) (string, error) {
 		if err := checkRootModule(rootReal, filepath.Dir(real)); err != nil {
 			return "", err
 		}
-		if !isTest {
-			tests, _ := filepath.Glob(filepath.Join(filepath.Dir(real), "*_test.go"))
-			if len(tests) == 0 {
-				return "", snippetError("package has no _test.go files, so go test does not cover it")
-			}
+		if err := checkBuiltGo(ref.Path, real, isTest); err != nil {
+			return "", err
 		}
 	}
 	if ref.Fragment == "" {
@@ -161,6 +161,53 @@ func checkRefPath(p string) error {
 	return nil
 }
 
+// buildPackage loads dir the way go test ./... does: build.Default, so
+// the host GOOS, GOARCH, CGO_ENABLED and release tags apply.
+func buildPackage(dir string) (*build.Package, error) {
+	return build.ImportDir(dir, 0)
+}
+
+// checkBuiltGo refuses a .go src= target go test ./... does not compile:
+// a testdata or underscore directory, a file left out of the default
+// build, or a non-test file in a package with no tests.
+func checkBuiltGo(refPath, real string, isTest bool) error {
+	for _, seg := range strings.Split(refPath, "/") {
+		if seg == "testdata" || strings.HasPrefix(seg, "_") {
+			return snippetError("file is in a directory go test ./... skips (testdata or a _-prefixed directory)")
+		}
+	}
+	pkg, err := buildPackage(filepath.Dir(real))
+	if err != nil {
+		var noGo *build.NoGoError
+		if errors.As(err, &noGo) {
+			return snippetError("file is excluded from the default build (build constraint or GOOS/GOARCH file-name suffix)")
+		}
+		return snippetError("cannot load package: " + firstLine(err.Error()))
+	}
+	base := filepath.Base(real)
+	listed := func(groups ...[]string) bool {
+		for _, g := range groups {
+			if slices.Contains(g, base) {
+				return true
+			}
+		}
+		return false
+	}
+	if isTest {
+		if !listed(pkg.TestGoFiles, pkg.XTestGoFiles) {
+			return snippetError("file is excluded from the default build (build constraint or GOOS/GOARCH file-name suffix)")
+		}
+		return nil
+	}
+	if !listed(pkg.GoFiles, pkg.CgoFiles) {
+		return snippetError("file is excluded from the default build (build constraint or GOOS/GOARCH file-name suffix)")
+	}
+	if len(pkg.TestGoFiles) == 0 && len(pkg.XTestGoFiles) == 0 {
+		return snippetError("package has no _test.go files, so go test does not cover it")
+	}
+	return nil
+}
+
 // checkRootModule refuses a Go source that sits in a nested module (a
 // directory between it and the root holds a go.mod): root go test does not
 // run it.
@@ -246,11 +293,9 @@ func extractIdent(file string, raw []byte, name string, isTest bool) (string, er
 			if funcKey(d) != name {
 				continue
 			}
-			if isTest {
-				if err := checkTestIdent(file, name, true); err != nil {
-					return "", err
-				}
-			}
+			// An Example with output is a root, so it is not also asked
+			// to be reachable from some other test. Without output, go
+			// test compiles it and never runs it.
 			if d.Recv == nil && strings.HasPrefix(name, "Example") && isTest {
 				if !exampleHasOutput(f, name) {
 					return "", snippetError(name + " has no // Output: comment, so go test compiles it but never runs it")
@@ -258,6 +303,11 @@ func extractIdent(file string, raw []byte, name string, isTest bool) (string, er
 				body := string(raw[offset(d.Body.Lbrace)+1 : offset(d.Body.Rbrace)])
 				return strings.Join(dedent(strings.Split(body, "\n")), "\n"), nil
 			}
+			if isTest {
+				if err := checkTestIdent(file, name, true); err != nil {
+					return "", err
+				}
+			}
 			start := d.Pos()
 			if d.Doc != nil {
 				start = d.Doc.Pos()
@@ -342,25 +392,43 @@ type testGraph struct {
 	files      map[string]*ast.File       // by path
 }
 
-func isRoot(d *ast.FuncDecl) bool {
-	return d.Recv == nil && (strings.HasPrefix(d.Name.Name, "Test") || strings.HasPrefix(d.Name.Name, "Example"))
+// isTestName is the cmd/go rule for a test function: "Test" alone, or
+// "Test" followed by a rune that is not a lowercase letter. Testable
+// is not a test. Benchmark and Fuzz are not roots.
+func isTestName(name string) bool {
+	rest, ok := strings.CutPrefix(name, "Test")
+	if !ok {
+		return false
+	}
+	if rest == "" {
+		return true
+	}
+	r, _ := utf8.DecodeRuneInString(rest)
+	return !unicode.IsLower(r)
 }
 
 func loadTestGraph(dir string) (*testGraph, error) {
-	paths, err := filepath.Glob(filepath.Join(dir, "*_test.go"))
+	pkg, err := buildPackage(dir)
 	if err != nil {
-		return nil, fmt.Errorf("docsite: %w", err)
+		var noGo *build.NoGoError
+		if !errors.As(err, &noGo) {
+			return nil, snippetError("cannot load package: " + firstLine(err.Error()))
+		}
+		pkg = &build.Package{}
 	}
 	g := &testGraph{fset: token.NewFileSet(), funcs: map[string][]*ast.FuncDecl{},
 		reachable: map[string]bool{}, referenced: map[string]bool{}, files: map[string]*ast.File{}}
 	byName := map[string][]string{} // plain or method name -> keys
 	var queue []string
-	for _, p := range paths {
-		f, err := parser.ParseFile(g.fset, p, nil, 0)
+	var files []*ast.File
+	for _, name := range append(append([]string{}, pkg.TestGoFiles...), pkg.XTestGoFiles...) {
+		p := filepath.Join(dir, name)
+		f, err := parser.ParseFile(g.fset, p, nil, parser.ParseComments)
 		if err != nil {
 			return nil, snippetError("cannot parse " + filepath.Base(p) + ": " + firstLine(err.Error()))
 		}
 		g.files[p] = f
+		files = append(files, f)
 		for _, decl := range f.Decls {
 			d, ok := decl.(*ast.FuncDecl)
 			if !ok {
@@ -369,12 +437,22 @@ func loadTestGraph(dir string) (*testGraph, error) {
 			key := funcKey(d)
 			g.funcs[key] = append(g.funcs[key], d)
 			byName[d.Name.Name] = append(byName[d.Name.Name], key)
-			if isRoot(d) && !g.reachable[key] {
+			if d.Recv == nil && isTestName(d.Name.Name) && !g.reachable[key] {
 				g.reachable[key] = true
 				queue = append(queue, key)
 			}
 		}
 	}
+	for _, ex := range doc.Examples(files...) {
+		if ex.Output == "" && !ex.EmptyOutput {
+			continue
+		}
+		key := "Example" + ex.Name
+		if !g.reachable[key] {
+			g.reachable[key] = true
+			queue = append(queue, key)
+		}
+	}
 	for len(queue) > 0 {
 		key := queue[0]
 		queue = queue[1:]
@@ -401,7 +479,7 @@ func loadTestGraph(dir string) (*testGraph, error) {
 	return g, nil
 }
 
-const notRunMessage = "fragment is not inside a Test or Example function, or a function one of them calls, so go test does not run it"
+const notRunMessage = "fragment is not inside a Test or Example function (an Example counts only with an // Output: comment), or a function one of them calls, so go test does not run it"
 
 // checkTestIdent requires a _test.go declaration to be run by go test: a
 // function reachable from a Test or Example, or a type, var or const that