Address Copilot review: require python prefix; robust entry_points parsing

- parsePythonTag now rejects tags without the 'python' prefix (e.g. '3.12'),
  which would otherwise produce a bogus .../lib/3.12/site-packages layout
- parseConsoleScripts iterates with strings.Split instead of bufio.Scanner, so
  a long line/large entry_points.txt can't silently truncate the launcher set
- tests for both

Co-authored-by: Jason Hall <imjasonh@users.noreply.github.com>

pymage/internal/cli/cli.go

@@ -459,9 +459,14 @@ func platformTarget(platform *v1.Platform) wheel.Target {
 	return t
 }
 
-// parsePythonTag parses "python3.12" into (3, 12).
+// parsePythonTag parses "python3.12" into (3, 12). The tag must start with
+// "python" because it is also used verbatim as the site-packages lib directory
+// (".../lib/python3.12/site-packages").
 func parsePythonTag(tag string) (int, int, error) {
-	s := strings.TrimPrefix(tag, "python")
+	s, ok := strings.CutPrefix(tag, "python")
+	if !ok {
+		return 0, 0, fmt.Errorf("--python %q must look like pythonX.Y", tag)
+	}
 	majStr, minStr, ok := strings.Cut(s, ".")
 	if !ok {
 		return 0, 0, fmt.Errorf("--python %q must look like pythonX.Y", tag)

pymage/internal/cli/cli_test.go

@@ -440,6 +440,10 @@ func TestParsePythonTag(t *testing.T) {
 	if _, _, err := parsePythonTag("python3"); err == nil {
 		t.Error("expected error for missing minor version")
 	}
+	// Must require the "python" prefix (it's also the site-packages lib dir).
+	if _, _, err := parsePythonTag("3.12"); err == nil {
+		t.Error("expected error for tag without 'python' prefix")
+	}
 }
 
 func TestPlatformTargetDefaults(t *testing.T) {

pymage/internal/wheel/wheel.go

@@ -14,7 +14,6 @@ package wheel
 
 import (
 	"archive/zip"
-	"bufio"
 	"fmt"
 	"io"
 	"path"
@@ -360,9 +359,10 @@ type entryPoint struct{ module, attr string }
 func parseConsoleScripts(s string) map[string]entryPoint {
 	out := map[string]entryPoint{}
 	section := ""
-	sc := bufio.NewScanner(strings.NewReader(s))
-	for sc.Scan() {
-		line := strings.TrimSpace(sc.Text())
+	// The file is already fully in memory, so split directly rather than using a
+	// bufio.Scanner (whose default token limit would silently drop long lines).
+	for _, raw := range strings.Split(s, "\n") {
+		line := strings.TrimSpace(raw)
 		if line == "" || strings.HasPrefix(line, "#") {
 			continue
 		}

pymage/internal/wheel/wheel_test.go

@@ -196,6 +196,17 @@ func TestConsoleScriptExtrasStripped(t *testing.T) {
 	}
 }
 
+func TestParseConsoleScriptsLongLineNotTruncated(t *testing.T) {
+	// A comment line longer than bufio.Scanner's default 64 KiB token limit
+	// would have made a Scanner stop early and silently drop later entries.
+	longComment := "# " + strings.Repeat("x", 200*1024)
+	content := longComment + "\n[console_scripts]\ntool = pkg.mod:main\n"
+	eps := parseConsoleScripts(content)
+	if ep, ok := eps["tool"]; !ok || ep.module != "pkg.mod" || ep.attr != "main" {
+		t.Fatalf("entry after a very long line was dropped: %+v", eps)
+	}
+}
+
 func TestFilesDeterministic(t *testing.T) {
 	path := writeFixture(t)
 	digest := func() string {