Record file mode in the manifest, 0000 unless asked (closes #161)

MFFilePath gains mode (field 304): a file's permission bits, 0777 at
most, or 0000, meaning none recorded. gen and freshen record real modes
only with --include-permissions (ScannerOptions.IncludePermissions); the
builder keeps only mode.Perm(), so setuid, setgid and sticky are never
written. list -l and export show the mode in octal. check reports
MODE_MISMATCH for a recorded mode other than 0000 the file lacks. fetch
refuses a manifest with a mode above 0777 before requesting any file,
sets each recorded mode on the files it writes, and downloads again a
present file whose mode differs. The decoding-cost bound counts a file
entry at 176 bytes, up from 160.

Model: opus-5-5

internal/cli/entry_test.go

@@ -3,6 +3,7 @@ package cli
 
 import (
 	"bytes"
+	"encoding/json"
 	"errors"
 	"fmt"
 	"io"
@@ -374,6 +375,98 @@ func TestGenerateAndCheckCommand(t *testing.T) {
 	assert.Equal(t, 0, exitCode, "check failed: %s", testStderr(t, opts))
 }
 
+// TestGenerateRecordsModeOnlyWhenAsked runs gen with and without
+// --include-permissions: without it every mode is recorded as 0000, with
+// it each file's permission bits. list -l and export show the recorded
+// modes.
+func TestGenerateRecordsModeOnlyWhenAsked(t *testing.T) {
+	t.Parallel()
+
+	fs := afero.NewMemMapFs()
+	require.NoError(t, fs.MkdirAll(testDir, 0o755))
+	writeTestFile(t, fs, "/testdir/notes.txt", "hello world")
+	writeTestFile(t, fs, "/testdir/run.sh", "#!/bin/sh\n")
+	require.NoError(t, fs.Chmod("/testdir/run.sh", 0o755))
+
+	for _, tc := range []struct {
+		flags []string
+		want  map[string]string // recorded mode by path
+	}{
+		{nil, map[string]string{"notes.txt": "0000", "run.sh": "0000"}},
+		{
+			[]string{"--" + flagIncludePermissions},
+			map[string]string{"notes.txt": "0644", "run.sh": "0755"},
+		},
+	} {
+		opts := testOpts(slices.Concat(
+			[]string{testApp, cmdGenerate, "-q", "-f", "-o", testOutput}, tc.flags,
+			[]string{testDir},
+		), fs)
+		require.Equal(t, 0, runCLI(opts), "stderr: %s", testStderr(t, opts))
+
+		opts = testOpts([]string{testApp, cmdList, "-l", testOutput}, fs)
+		require.Equal(t, 0, runCLI(opts), "stderr: %s", testStderr(t, opts))
+
+		listed := map[string]string{}
+		out := strings.TrimSuffix(testStdout(t, opts), "\n")
+
+		for _, line := range strings.Split(out, "\n") {
+			fields := strings.Split(line, "\t") // mode, size, mtime, path
+			require.Len(t, fields, 4, line)
+			listed[fields[3]] = fields[0]
+		}
+
+		assert.Equal(t, tc.want, listed, "list -l %v", tc.flags)
+
+		opts = testOpts([]string{testApp, cmdExport, testOutput}, fs)
+		require.Equal(t, 0, runCLI(opts), "stderr: %s", testStderr(t, opts))
+
+		var entries []ExportEntry
+		require.NoError(t, json.Unmarshal([]byte(testStdout(t, opts)), &entries))
+
+		exported := map[string]string{}
+		for _, e := range entries {
+			exported[e.Path] = e.Mode
+		}
+
+		assert.Equal(t, tc.want, exported, "export %v", tc.flags)
+	}
+}
+
+// TestCheckComparesRecordedMode changes a file's mode after gen: check
+// must fail on it when gen recorded the file's mode, and pass when gen
+// recorded 0000.
+func TestCheckComparesRecordedMode(t *testing.T) {
+	t.Parallel()
+
+	for _, tc := range []struct {
+		flags    []string
+		exitCode int
+	}{
+		{nil, 0},
+		{[]string{"--" + flagIncludePermissions}, 1},
+	} {
+		fs := afero.NewMemMapFs()
+		require.NoError(t, fs.MkdirAll(testDir, 0o755))
+		writeTestFile(t, fs, testFile1, "hello world")
+
+		opts := testOpts(slices.Concat(
+			[]string{testApp, cmdGenerate, "-q", "-o", testMF}, tc.flags,
+			[]string{testDir},
+		), fs)
+		require.Equal(t, 0, runCLI(opts), "stderr: %s", testStderr(t, opts))
+
+		require.NoError(t, fs.Chmod(testFile1, 0o600))
+
+		opts = testOpts([]string{testApp, cmdCheck, testFlagBase, testDir, testMF}, fs)
+		assert.Equal(t, tc.exitCode, runCLI(opts), "%v: %s", tc.flags, testStderr(t, opts))
+
+		if tc.exitCode != 0 {
+			assert.Contains(t, testStderr(t, opts), "MODE_MISMATCH: file1.txt")
+		}
+	}
+}
+
 // sharedWriter appends to a buffer shared with other sharedWriters, so
 // output written to stdout and stderr is kept in the order it was written.
 // Each write first waits for delay.