The clipboard keeps its history running and keeps it to itself (hq issues 743, 750)

clipmenud is declared as the operator's user unit, enabled and running, with a launcher that finds the display. Copy reads the clipboard back and fails with the reason. History and paste answer counts, times and lengths, never content.

modules/clipmenu/cmd/clipmenu-tools/clipboard.go

@@ -15,8 +15,7 @@ import (
 )
 
 const (
-	mostCopy  = 1 << 20
-	mostPaste = 64 << 10
+	mostCopy = 1 << 20
 	// majorVersion is clipmenu's store layout: <dir>/clipmenu.<major>.<user>/.
 	majorVersion = 6
 )
@@ -71,15 +70,15 @@ func cksum(data []byte) string {
 
 func entryID(line string) string { return cksum([]byte(line + "\n")) }
 
-// Entry is one clip in the history.
+// Entry is one clip in the history as a caller sees it: when and how long, never what. The text of a
+// clip, its first line and its id (a checksum of that line) stay in clipmenu's store, readable on the
+// operator's own screen through clipmenu (issue 750).
 type Entry struct {
-	ID        string `json:"id"`
-	Line      string `json:"line"`
-	At        string `json:"at"`
-	Bytes     int    `json:"bytes"`
-	Text      string `json:"text,omitempty"`
-	Truncated bool   `json:"truncated,omitempty"`
-	at        int64
+	At    string `json:"at"`
+	Bytes int    `json:"bytes"`
+	id    string
+	line  string
+	at    int64
 }
 
 // HistoryResult is what node-clipboard.history answers.
@@ -119,14 +118,15 @@ func readStore(dir string) ([]Entry, error) {
 	}
 	out := make([]Entry, 0, len(latest))
 	for line, ns := range latest {
-		out = append(out, Entry{ID: entryID(line), Line: line, at: ns, At: time.Unix(0, ns).Format(time.RFC3339)})
+		out = append(out, Entry{id: entryID(line), line: line, at: ns, At: time.Unix(0, ns).Format(time.RFC3339)})
 	}
 	sort.Slice(out, func(i, j int) bool { return out[i].at > out[j].at })
 	return out, scan.Err()
 }
 
-// History is the clipboard's history, newest first.
-func History(limit, maxBytes int) (HistoryResult, error) {
+// History is the clipboard's history, newest first: how many entries, when each was copied and how
+// long each is, and whether the daemon is collecting. It never returns a copied text.
+func History(limit int) (HistoryResult, error) {
 	dir, err := storeDir(findEnvironment())
 	if err != nil {
 		return HistoryResult{}, err
@@ -140,15 +140,8 @@ func History(limit, maxBytes int) (HistoryResult, error) {
 		if i == limit {
 			break
 		}
-		if info, err := os.Stat(filepath.Join(dir, e.ID)); err == nil {
+		if info, err := os.Stat(filepath.Join(dir, e.id)); err == nil {
 			e.Bytes = int(info.Size())
-			if maxBytes > 0 {
-				raw, _ := os.ReadFile(filepath.Join(dir, e.ID))
-				if len(raw) > maxBytes {
-					raw, e.Truncated = raw[:maxBytes], true
-				}
-				e.Text = string(raw)
-			}
 		}
 		out.Entries = append(out.Entries, e)
 	}
@@ -159,6 +152,40 @@ func History(limit, maxBytes int) (HistoryResult, error) {
 type CopyResult struct {
 	Bytes int    `json:"bytes"`
 	Unit  string `json:"unit"`
+	// Verified says the clipboard was read back and held exactly the text.
+	Verified bool `json:"verified"`
+}
+
+// readBackWait is the pause between reads of the clipboard while the owner starts; read-back tries 15 times.
+var readBackWait = 200 * time.Millisecond
+
+// readBack waits for the clipboard to hold text and answers why when it does not.
+func readBack(s Session, unit, text string) error {
+	var last string
+	for i := 0; i < 15; i++ {
+		time.Sleep(readBackWait)
+		r, err := s.run(3*time.Second, "", "xsel", "--output", "--clipboard")
+		switch {
+		case err != nil:
+			last = err.Error()
+		case r.Code != 0:
+			last = "xsel: " + strings.TrimSpace(r.Stderr)
+		case r.Stdout == text:
+			return nil
+		default:
+			last = fmt.Sprintf("it holds %d bytes of something else", len(r.Stdout))
+		}
+	}
+	why := ""
+	if s.Display == "" {
+		why = "; the session has no DISPLAY, so the owner could not reach the screen"
+	}
+	if j, err := s.run(5*time.Second, "", "journalctl", "--user", "-u", unit+".service", "-n", "5", "--no-pager", "-o", "cat"); err == nil {
+		if tail := strings.TrimSpace(j.Stdout); tail != "" {
+			why += "; the owner said: " + tail
+		}
+	}
+	return fmt.Errorf("the clipboard does not hold the text (%d bytes): %s%s", len(text), last, why)
 }
 
 // Copy puts text on the clipboard. The clipboard is owned by a process until another copies, so the
@@ -194,17 +221,20 @@ func Copy(text string) (CopyResult, error) {
 		os.Remove(f.Name())
 		return CopyResult{}, err
 	}
-	return CopyResult{Bytes: len(text), Unit: unit + ".service"}, nil
+	if err := readBack(s, unit, text); err != nil {
+		return CopyResult{}, err
+	}
+	return CopyResult{Bytes: len(text), Unit: unit + ".service", Verified: true}, nil
 }
 
-// PasteResult is what clipmenu_paste answers.
+// PasteResult is what clipmenu_paste answers: how much text the clipboard holds, never the text. The
+// clipboard is the newest history entry, and a copied secret must not reach a caller (issue 750).
 type PasteResult struct {
-	Text      string `json:"text"`
-	Bytes     int    `json:"bytes"`
-	Truncated bool   `json:"truncated,omitempty"`
+	Bytes int  `json:"bytes"`
+	Text  bool `json:"holds_text"`
 }
 
-// Paste reads the clipboard now.
+// Paste reads the clipboard now and says how long it is.
 func Paste() (PasteResult, error) {
 	s, err := findSession()
 	if err != nil {
@@ -217,11 +247,7 @@ func Paste() (PasteResult, error) {
 	if r.Code != 0 {
 		return PasteResult{}, fmt.Errorf("xsel: %s", strings.TrimSpace(r.Stderr))
 	}
-	out := PasteResult{Text: r.Stdout, Bytes: len(r.Stdout), Truncated: r.Truncated}
-	if len(out.Text) > mostPaste {
-		out.Text, out.Truncated = out.Text[:mostPaste], true
-	}
-	return out, nil
+	return PasteResult{Bytes: len(r.Stdout), Text: len(r.Stdout) > 0}, nil
 }
 
 // ChangeResult is what clear and delete answer.
@@ -298,10 +324,12 @@ func Clear() (ChangeResult, error) {
 	return out, err
 }
 
-// Delete forgets one entry, by id or by its first line.
-func Delete(id, line string) (ChangeResult, error) {
-	if (id == "") == (line == "") {
-		return ChangeResult{}, errors.New("give the entry's id or its line, one of the two")
+// Delete forgets one entry, by its place in the history as node-clipboard.history lists it (1 is the
+// newest) together with the time it reports, so a copy arriving since the listing cannot shift the
+// place onto another entry. Not by its text or id: either would let a caller confirm a guess of a copied line.
+func Delete(place int, at string) (ChangeResult, error) {
+	if place < 1 {
+		return ChangeResult{}, errors.New("give the entry's place in the history, 1 for the newest")
 	}
 	dir, err := storeOf()
 	if err != nil {
@@ -309,6 +337,17 @@ func Delete(id, line string) (ChangeResult, error) {
 	}
 	var out ChangeResult
 	err = withStoreLock(dir, func() error {
+		entries, err := readStore(dir)
+		if err != nil {
+			return err
+		}
+		if place > len(entries) {
+			return fmt.Errorf("no entry %d: the clipboard history holds %d", place, len(entries))
+		}
+		if entries[place-1].At != at {
+			return fmt.Errorf("entry %d was copied at %s, not at %s: the history changed since it was listed; list it again", place, entries[place-1].At, at)
+		}
+		line := entries[place-1].line
 		raw, err := os.ReadFile(filepath.Join(dir, "line_cache"))
 		if err != nil && !errors.Is(err, os.ErrNotExist) {
 			return err
@@ -319,7 +358,7 @@ func Delete(id, line string) (ChangeResult, error) {
 				continue
 			}
 			_, text, _ := strings.Cut(l, " ")
-			if text == line || (id != "" && entryID(text) == id) {
+			if text == line {
 				out.Removed++
 				_ = os.Remove(filepath.Join(dir, entryID(text)))
 				continue
@@ -327,7 +366,7 @@ func Delete(id, line string) (ChangeResult, error) {
 			kept = append(kept, l)
 		}
 		if out.Removed == 0 {
-			return fmt.Errorf("no entry %s%s in the clipboard history", id, line)
+			return fmt.Errorf("no entry %d in the clipboard history", place)
 		}
 		content := strings.Join(kept, "\n")
 		if content != "" {

modules/clipmenu/cmd/clipmenu-tools/clipboard_test.go

@@ -1,6 +1,7 @@
 package main
 
 import (
+	"encoding/json"
 	"errors"
 	"os"
 	"os/exec"
@@ -51,46 +52,84 @@ func store(t *testing.T, clips map[string]string, order ...string) string {
 	return dir
 }
 
-func TestTheHistoryIsNewestFirstOnceEachWithItsText(t *testing.T) {
-	store(t, map[string]string{"first": "first", "second (2 lines)": "second\nline two"}, "first", "second (2 lines)", "first")
+func TestTheHistoryAnswersCountTimesAndLengthsNeverContent(t *testing.T) {
+	store(t, map[string]string{"first": "first", "sk-ant-api03-SECRETKEY (2 lines)": "sk-ant-api03-SECRETKEY\nline two"}, "first", "sk-ant-api03-SECRETKEY (2 lines)", "first")
 	fakeProcess(t, nobody, "clipmenud")
-	h, err := History(10, 4096)
+	h, err := History(10)
 	if err != nil {
 		t.Fatal(err)
 	}
-	if !h.Collecting || h.Total != 2 || h.Entries[0].Line != "first" || h.Entries[1].Text != "second\nline two" || h.Entries[1].Bytes != 15 {
+	if !h.Collecting || h.Total != 2 || len(h.Entries) != 2 || h.Entries[0].Bytes != 5 || h.Entries[1].Bytes != 31 || h.Entries[0].At == "" {
 		t.Fatalf("%+v", h)
 	}
-	if h, _ := History(1, 3); len(h.Entries) != 1 || h.Entries[0].Text != "fir" || !h.Entries[0].Truncated {
-		t.Fatalf("limited and cut: %+v", h)
+	raw, _ := json.Marshal(h)
+	for _, leak := range []string{"first", "SECRETKEY", "line two"} {
+		if strings.Contains(string(raw), leak) {
+			t.Fatalf("the history answers %q: %s", leak, raw)
+		}
 	}
-	if h, _ := History(10, 0); h.Entries[0].Text != "" || h.Entries[0].Bytes != 5 {
-		t.Fatalf("without text: %+v", h)
+	if h, _ := History(1); len(h.Entries) != 1 {
+		t.Fatalf("limited: %+v", h)
 	}
 }
 
-func TestAnEntryIsDeletedByIdOrLineWithItsText(t *testing.T) {
+// at is the time History reports for the entry at place.
+func at(t *testing.T, place int) string {
+	t.Helper()
+	h, err := History(100)
+	if err != nil || place > len(h.Entries) {
+		t.Fatalf("%+v, %v", h, err)
+	}
+	return h.Entries[place-1].At
+}
+
+func TestADeleteWhoseListingIsStaleIsRefused(t *testing.T) {
+	dir := store(t, map[string]string{"a": "a", "b": "b"}, "a", "b")
+	listed := at(t, 1) // b
+	f, _ := os.OpenFile(filepath.Join(dir, "line_cache"), os.O_APPEND|os.O_WRONLY, 0o600)
+	f.WriteString("1800000000000000000 a\n") // a copy arrives: place 1 is now a
+	f.Close()
+	if _, err := Delete(1, listed); err == nil || !strings.Contains(err.Error(), "list it again") {
+		t.Fatalf("the wrong entry was deleted: %v", err)
+	}
+	if h, _ := History(10); h.Total != 2 {
+		t.Fatalf("%+v", h)
+	}
+}
+
+func TestAnEntryIsDeletedByItsPlaceWithItsTextAndNeverByItsText(t *testing.T) {
 	dir := store(t, map[string]string{"a": "a", "b": "b", "c": "c"}, "a", "b", "c", "a")
-	r, err := Delete(entryID("a"), "")
+	// newest first: a, c, b
+	r, err := Delete(1, at(t, 1))
 	if err != nil || r.Removed != 2 || r.Remaining != 2 {
-		t.Fatalf("by id, both copies: %+v, %v", r, err)
+		t.Fatalf("by place, both copies: %+v, %v", r, err)
 	}
 	if _, err := os.Stat(filepath.Join(dir, entryID("a"))); !errors.Is(err, os.ErrNotExist) {
 		t.Fatal("the text stayed")
 	}
-	if r, err := Delete("", "b"); err != nil || r.Removed != 1 || r.Remaining != 1 {
-		t.Fatalf("by line: %+v, %v", r, err)
+	if r, err := Delete(2, at(t, 2)); err != nil || r.Removed != 1 || r.Remaining != 1 {
+		t.Fatalf("second place (b): %+v, %v", r, err)
 	}
-	if _, err := Delete("", "zzz"); err == nil {
-		t.Fatal("a missing entry was reported deleted")
+	if _, err := Delete(5, "x"); err == nil {
+		t.Fatal("a missing place was reported deleted")
 	}
-	if _, err := Delete("x", "y"); err == nil {
-		t.Fatal("both an id and a line were accepted")
+	if _, err := Delete(0, "x"); err == nil {
+		t.Fatal("place 0 was accepted")
 	}
 	cache, _ := os.ReadFile(filepath.Join(dir, "line_cache"))
 	if !strings.HasSuffix(string(cache), " c\n") || strings.Count(string(cache), "\n") != 1 {
 		t.Fatalf("line cache: %q", cache)
 	}
+	for _, tool := range tools() {
+		if tool.Name == "clipmenu_delete" {
+			if _, ok := tool.Input["line"]; ok {
+				t.Fatal("delete still takes a line")
+			}
+			if _, ok := tool.Input["id"]; ok {
+				t.Fatal("delete still takes an id")
+			}
+		}
+	}
 }
 
 func TestClearForgetsEverythingButKeepsTheDaemonsLocks(t *testing.T) {
@@ -112,13 +151,21 @@ func TestClearForgetsEverythingButKeepsTheDaemonsLocks(t *testing.T) {
 	}
 }
 
-func TestCopyHandsTheTextToAnOwnerUnderTheAccountsServiceManager(t *testing.T) {
+func copyBed(t *testing.T, xsel string) string {
+	t.Helper()
 	store(t, nil)
 	fakeProcess(t, nobody, "i3", "DISPLAY=:1")
-	bin := fakeBinaries(t, map[string]string{"systemctl": "true", "systemd-run": `echo "$*" > "$LOG"; for last; do :; done; cat "$last" > "$LOG.text"`})
+	bin := fakeBinaries(t, map[string]string{"systemctl": "true", "xsel": xsel,
+		"systemd-run": `echo "$*" > "$LOG"; for last; do :; done; cat "$last" > "$LOG.text"`})
 	t.Setenv("LOG", filepath.Join(bin, "log"))
+	readBackWait = 0
+	return bin
+}
+
+func TestCopyHandsTheTextToAnOwnerUnderTheAccountsServiceManagerAndReadsItBack(t *testing.T) {
+	bin := copyBed(t, `cat "$LOG.text"`)
 	r, err := Copy("secret-free text")
-	if err != nil || r.Bytes != 16 || !strings.HasPrefix(r.Unit, "clipmenu-copy-") {
+	if err != nil || r.Bytes != 16 || !r.Verified || !strings.HasPrefix(r.Unit, "clipmenu-copy-") {
 		t.Fatalf("%+v, %v", r, err)
 	}
 	asked, _ := os.ReadFile(filepath.Join(bin, "log"))
@@ -134,7 +181,23 @@ func TestCopyHandsTheTextToAnOwnerUnderTheAccountsServiceManager(t *testing.T) {
 	}
 }
 
-func TestPasteReadsTheClipboardOrSaysThereIsNoSession(t *testing.T) {
+func TestCopyFailsWhenTheClipboardHoldsSomethingElse(t *testing.T) {
+	copyBed(t, `printf 'old contents'`)
+	_, err := Copy("new text")
+	if err == nil || !strings.Contains(err.Error(), "does not hold") || strings.Contains(err.Error(), "old contents") {
+		t.Fatalf("a copy that did not land was reported: %v", err)
+	}
+}
+
+func TestCopyFailsSayingWhyWhenTheOwnerCannotReachTheDisplay(t *testing.T) {
+	copyBed(t, `echo "xsel: Can't open display: (null)" >&2; exit 1`)
+	_, err := Copy("new text")
+	if err == nil || !strings.Contains(err.Error(), "Can't open display") {
+		t.Fatalf("the reason was not given: %v", err)
+	}
+}
+
+func TestPasteSaysHowMuchTheClipboardHoldsNeverWhat(t *testing.T) {
 	fakeMachine(t)
 	if _, err := Paste(); !errors.Is(err, ErrNoSession) {
 		t.Fatal(err)
@@ -142,8 +205,9 @@ func TestPasteReadsTheClipboardOrSaysThereIsNoSession(t *testing.T) {
 	fakeProcess(t, nobody, "i3", "DISPLAY=:1")
 	fakeBinaries(t, map[string]string{"xsel": `[ "$*" = "--output --clipboard" ] && printf 'on the clipboard'`})
 	p, err := Paste()
-	if err != nil || p.Text != "on the clipboard" || p.Bytes != 16 {
-		t.Fatalf("%+v, %v", p, err)
+	raw, _ := json.Marshal(p)
+	if err != nil || p.Bytes != 16 || strings.Contains(string(raw), "on the clipboard") {
+		t.Fatalf("%s, %v", raw, err)
 	}
 }
 
@@ -157,7 +221,7 @@ func TestWithoutAStoreTheChangesSayWhy(t *testing.T) {
 	if _, err := Clear(); err == nil || !strings.Contains(err.Error(), "clipmenud has not run") {
 		t.Fatal(err)
 	}
-	if h, err := History(5, 0); err != nil || h.Total != 0 || h.Collecting {
+	if h, err := History(5); err != nil || h.Total != 0 || h.Collecting {
 		t.Fatalf("an empty history: %+v, %v", h, err)
 	}
 }

modules/clipmenu/cmd/clipmenu-tools/main.go

@@ -22,28 +22,23 @@ func tools() []stdio.Tool {
 	return []stdio.Tool{
 		{
 			Name: "node-clipboard.history",
-			Description: "What the operator copied, newest first: each entry's id, its first line, when, its size " +
-				"and its text (each cut at max_bytes). Whether the clipboard daemon is collecting.",
+			Description: "What the operator copied, newest first: how many entries, when each was copied and how long " +
+				"it is, never what it says. Whether the clipboard daemon is collecting. The text is read on the operator's own screen, through clipmenu.",
 			Input: map[string]any{
-				"limit":     map[string]any{"type": "integer", "description": "at most this many entries (default 20, at most 500)"},
-				"max_bytes": map[string]any{"type": "integer", "description": "cut each entry's text at this many bytes; 0 leaves the text out (default 4096, at most 65536)"},
+				"limit": map[string]any{"type": "integer", "description": "at most this many entries (default 20, at most 500)"},
 			},
 			Run: func(args map[string]any) (any, error) {
 				limit, err := whole(args, "limit", 20, 1, 500)
 				if err != nil {
 					return nil, err
 				}
-				most, err := whole(args, "max_bytes", 4096, 0, 65536)
-				if err != nil {
-					return nil, err
-				}
-				return History(limit, most)
+				return History(limit)
 			},
 		},
 		{
 			Name: "node-clipboard.copy",
 			Description: "Put text on the operator's clipboard, as if they had copied it; it enters the history " +
-				"like any copy. Answers how many bytes.",
+				"like any copy. Reads the clipboard back and answers an error with the reason when it does not hold the text.",
 			Input: map[string]any{
 				"type": "object",
 				"properties": map[string]any{
@@ -61,7 +56,7 @@ func tools() []stdio.Tool {
 		},
 		{
 			Name:        "clipmenu_paste",
-			Description: "What the operator's clipboard holds right now, as text (cut at 64 KiB, said in truncated).",
+			Description: "How many bytes of text the operator's clipboard holds right now, never the text itself.",
 			Run:         func(map[string]any) (any, error) { return Paste() },
 		},
 		{
@@ -71,19 +66,22 @@ func tools() []stdio.Tool {
 		},
 		{
 			Name: "clipmenu_delete",
-			Description: "Forget one entry of the clipboard history, by its id as the history answers it, or by " +
-				"its first line exactly.",
+			Description: "Forget one entry of the clipboard history, by its place in node-clipboard.history's list " +
+				"(1 is the newest) and its time as the history gives it; refused when the two no longer match.",
 			Input: map[string]any{
-				"id":   map[string]any{"type": "string", "description": "the entry's id"},
-				"line": map[string]any{"type": "string", "description": "the entry's first line, exactly"},
+				"place": map[string]any{"type": "integer", "description": "the entry's place in the history, 1 for the newest"},
+				"at":    map[string]any{"type": "string", "description": "the entry's time, as the history reports it"},
 			},
 			Run: func(args map[string]any) (any, error) {
-				id, err := text(args, "id", false)
+				place, err := whole(args, "place", 0, 0, 100000)
 				if err != nil {
 					return nil, err
 				}
-				line, _ := args["line"].(string)
-				return Delete(id, line)
+				at, err := text(args, "at", true)
+				if err != nil {
+					return nil, err
+				}
+				return Delete(place, at)
 			},
 		},
 	}

modules/clipmenu/cmd/clipmenu-tools/manifest_test.go

@@ -1,9 +1,14 @@
 package main
 
 import (
+	"context"
+	"net"
+	"os"
+	"os/exec"
 	"reflect"
 	"strings"
 	"testing"
+	"time"
 )
 
 // clipmenu's shape (novox/hq ADR 0208, research 026/04): it claims node-clipboard serving history
@@ -27,20 +32,43 @@ func TestItClaimsTheClipboardSeatServingHistoryAndCopy(t *testing.T) {
 	}
 }
 
-func TestTheDaemonStartsOnceFromTheSessionsStart(t *testing.T) {
+func TestTheDaemonIsTheOperatorsUserUnitEnabledAndRunning(t *testing.T) {
 	m := readManifest(t)
-	if len(m.Shell) != 1 || m.Shell[0].For != "xinitrc" || m.Shell[0].Slot != "normal" {
-		t.Fatalf("%+v", m.Shell)
+	if len(m.Shell) != 0 {
+		t.Fatalf("a second start from the session: %+v", m.Shell)
 	}
-	code := m.Shell[0].Code
-	// Started once, through the module's text-only xsel (a selection holding an image is never read).
-	if strings.Count(code, "clipmenud &\n") != 1 || !strings.Contains(code, `PATH="/usr/local/lib/mesh-clipmenu:$PATH" clipmenud &`) ||
-		strings.Contains(code, "greenclip") {
-		t.Fatalf("%q", code)
+	svc := m.resource(t, "daemon")
+	want := map[string]any{"id": "daemon", "type": "service", "unit": "clipmenud.service", "scope": "user",
+		"user": "${machine:account}", "state": "running", "boot": "enabled", "reload-on": nil}
+	for k, v := range want {
+		if k != "reload-on" && svc[k] != v {
+			t.Fatalf("daemon %s = %v, want %v: %v", k, svc[k], v, svc)
+		}
 	}
-	for _, r := range m.Resources {
-		if r["type"] == "service" || r["type"] == "process" {
-			t.Fatalf("a second start: %v", r)
+	dropin := m.resource(t, "daemon-dropin")
+	content, _ := dropin["content"].(string)
+	if dropin["path"] != "${machine:account-home}/.config/systemd/user/clipmenud.service.d/mesh.conf" ||
+		dropin["owner"] != "${machine:account}" ||
+		!strings.Contains(content, "ExecStart=/usr/local/lib/mesh-clipmenu/clipmenud-session") ||
+		strings.Contains(content, "greenclip") {
+		t.Fatalf("drop-in: %v", dropin)
+	}
+	launcher, _ := m.resource(t, "launcher")["content"].(string)
+	if !strings.Contains(launcher, "DISPLAY") || !strings.Contains(launcher, "/tmp/.X11-unix") ||
+		!strings.Contains(launcher, `PATH="/usr/local/lib/mesh-clipmenu:$PATH"`) || !strings.Contains(launcher, "exec clipmenud") {
+		t.Fatalf("launcher: %q", launcher)
+	}
+	// Waits for the display instead of exiting into the start limit; DISPLAY from the manager wins.
+	if !strings.Contains(launcher, "until [ -n \"$DISPLAY\" ]") || !strings.Contains(launcher, "sleep 1") ||
+		strings.Contains(launcher, "exit 1") || strings.Contains(launcher, "exit 0") {
+		t.Fatalf("the launcher must wait, not exit: %q", launcher)
+	}
+	if !strings.Contains(content, "StartLimitIntervalSec=0") || !strings.Contains(content, "RestartSec=2s") {
+		t.Fatalf("drop-in lacks the safety net: %q", content)
+	}
+	for k, v := range m.Environment.Variables {
+		if !strings.Contains(content, "Environment="+k+"="+v) {
+			t.Fatalf("the unit lacks %s=%s", k, v)
 		}
 	}
 }
@@ -64,3 +92,51 @@ func TestTheToolsAgreeWithTheManifest(t *testing.T) {
 	checkTheToolsAgree(t, m)
 	checkNoSecretsOrInstallationNames(t)
 }
+
+// Run for real: DISPLAY from the manager is used at once; several sockets and no DISPLAY wait.
+func TestTheLauncherUsesTheManagersDisplayAndWaitsOtherwise(t *testing.T) {
+	m := readManifest(t)
+	script, _ := m.resource(t, "launcher")["content"].(string)
+	dir := t.TempDir()
+	file := dir + "/launcher"
+	// clipmenud and the socket directory are faked: the script's own paths are rewritten.
+	body := strings.ReplaceAll(script, "/tmp/.X11-unix", dir+"/x11")
+	body = strings.Replace(body, "exec clipmenud", `echo "DISPLAY=$DISPLAY"`, 1)
+	if err := os.WriteFile(file, []byte(body), 0o755); err != nil {
+		t.Fatal(err)
+	}
+	os.MkdirAll(dir+"/x11", 0o755)
+	fakeBin := dir + "/bin"
+	os.MkdirAll(fakeBin, 0o755)
+	// the manager's environment: empty until the file appears
+	os.WriteFile(fakeBin+"/systemctl", []byte("#!/bin/sh\n[ -f \""+dir+"/env\" ] && cat \""+dir+"/env\"\nexit 0\n"), 0o755)
+	run := func(env ...string) (string, bool) {
+		ctx, cancel := context.WithTimeout(context.Background(), 2500*time.Millisecond)
+		defer cancel()
+		cmd := exec.CommandContext(ctx, "sh", file)
+		cmd.Env = append([]string{"PATH=" + fakeBin + ":" + os.Getenv("PATH"), "HOME=" + dir}, env...)
+		out, _ := cmd.Output()
+		return strings.TrimSpace(string(out)), ctx.Err() == nil
+	}
+	if out, ok := run("DISPLAY=:7"); !ok || out != "DISPLAY=:7" {
+		t.Fatalf("with DISPLAY: %q %v", out, ok)
+	}
+	if _, ok := run(); ok {
+		t.Fatal("it exited with no X server")
+	}
+	for _, n := range []string{"X0", "X1"} {
+		l, _ := net.Listen("unix", dir+"/x11/"+n)
+		defer l.Close()
+	}
+	if _, ok := run(); ok {
+		t.Fatal("it chose one of two servers")
+	}
+	// the session hands the manager its display while the launcher waits
+	go func() {
+		time.Sleep(1200 * time.Millisecond)
+		os.WriteFile(dir+"/env", []byte("DISPLAY=:1\nOTHER=x\n"), 0o644)
+	}()
+	if out, ok := run(); !ok || out != "DISPLAY=:1" {
+		t.Fatalf("the display that arrived while waiting: %q %v", out, ok)
+	}
+}