diff --git a/go/cmd/compass-app/multiwindow_e2e_reap_linux_test.go b/go/cmd/compass-app/multiwindow_e2e_reap_linux_test.go
new file mode 100644
index 00000000..b21b63c6
--- /dev/null
+++ b/go/cmd/compass-app/multiwindow_e2e_reap_linux_test.go
@@ -0,0 +1,97 @@
+//go:build linux && gtk4
+
+package main
+
+import (
+	"os"
+	"strconv"
+	"strings"
+)
+
+// liveChildren returns every process still descended from this one, discovered
+// by walking /proc for entries whose ppid chains back to os.Getpid(). WebKit's
+// GPU/network helpers are our direct children; scanning the whole subtree also
+// catches any helper-of-a-helper before it reparents to init.
+func liveChildren() []procInfo {
+	self := os.Getpid()
+
+	entries, err := os.ReadDir("/proc")
+	if err != nil {
+		// Without procfs there is nothing to reap and no way to prove otherwise;
+		// treat as clean so the gate never wedges on an unreadable /proc.
+		return nil
+	}
+
+	ppids := make(map[int]int, len(entries))
+	comms := make(map[int]string, len(entries))
+	for _, e := range entries {
+		pid, err := strconv.Atoi(e.Name())
+		if err != nil {
+			continue // not a pid directory
+		}
+		ppid, comm, ok := readStat(pid)
+		if !ok {
+			continue // vanished between readdir and read; not our concern
+		}
+		ppids[pid] = ppid
+		comms[pid] = comm
+	}
+
+	var out []procInfo
+	for pid := range ppids {
+		if pid != self && descendsFrom(pid, self, ppids) {
+			out = append(out, procInfo{pid: pid, comm: comms[pid]})
+		}
+	}
+	return out
+}
+
+// readStat reads ppid and comm for one pid, tolerating a process that exits
+// mid-scan.
+func readStat(pid int) (ppid int, comm string, ok bool) {
+	raw, err := os.ReadFile("/proc/" + strconv.Itoa(pid) + "/stat")
+	if err != nil {
+		return 0, "", false
+	}
+	return parseStat(string(raw))
+}
+
+// parseStat pulls ppid and comm out of a /proc/<pid>/stat line. comm can hold
+// spaces and parens, so key off the final ')': the two fields after it are
+// state then ppid.
+func parseStat(s string) (ppid int, comm string, ok bool) {
+	open := strings.IndexByte(s, '(')
+	shut := strings.LastIndexByte(s, ')')
+	if open < 0 || shut < 0 || shut < open {
+		return 0, "", false
+	}
+	comm = s[open+1 : shut]
+	fields := strings.Fields(s[shut+1:])
+	if len(fields) < 2 {
+		return 0, "", false
+	}
+	ppid, err := strconv.Atoi(fields[1])
+	if err != nil {
+		return 0, "", false
+	}
+	return ppid, comm, true
+}
+
+// descendsFrom reports whether pid chains up to root through the ppid map. The
+// walk is bounded by the map size so pid reuse mid-scan cannot loop forever.
+func descendsFrom(pid, root int, ppids map[int]int) bool {
+	for hops := 0; hops <= len(ppids); hops++ {
+		ppid, seen := ppids[pid]
+		if !seen {
+			return false
+		}
+		if ppid == root {
+			return true
+		}
+		if ppid <= 1 {
+			return false // reached init/kernel without hitting root
+		}
+		pid = ppid
+	}
+	return false
+}
diff --git a/go/cmd/compass-app/multiwindow_e2e_reap_linux_unit_test.go b/go/cmd/compass-app/multiwindow_e2e_reap_linux_unit_test.go
new file mode 100644
index 00000000..291e621c
--- /dev/null
+++ b/go/cmd/compass-app/multiwindow_e2e_reap_linux_unit_test.go
@@ -0,0 +1,66 @@
+//go:build linux && gtk4
+
+package main
+
+import "testing"
+
+// The chain walk decides which pids get signalled, so a regression here would
+// aim SIGKILL at something we do not own. Every non-descendant case must answer
+// false: under-signalling leaks a process, over-signalling kills a stranger.
+func TestDescendsFrom(t *testing.T) {
+	const self = 100
+
+	tests := []struct {
+		name  string
+		pid   int
+		ppids map[int]int
+		want  bool
+	}{
+		{"direct child", 200, map[int]int{200: self, self: 1}, true},
+		{"deep grandchild", 400, map[int]int{400: 300, 300: 200, 200: self, self: 1}, true},
+		{"reparented to init", 200, map[int]int{200: 1, self: 1}, false},
+		{"sibling under a subreaper", 200, map[int]int{200: 50, 50: 1, self: 1}, false},
+		{"broken link", 400, map[int]int{400: 300, self: 1}, false},
+		{"cycle terminates", 200, map[int]int{200: 300, 300: 200, self: 1}, false},
+		{"self is not its own descendant", self, map[int]int{self: 1}, false},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			if got := descendsFrom(tc.pid, self, tc.ppids); got != tc.want {
+				t.Fatalf("descendsFrom(%d, %d) = %v, want %v", tc.pid, self, got, tc.want)
+			}
+		})
+	}
+}
+
+// A comm holding spaces or parens would break a naive field split, and a
+// misparsed ppid is a wrong signal target.
+func TestParseStat(t *testing.T) {
+	tests := []struct {
+		name     string
+		line     string
+		wantPPID int
+		wantComm string
+		wantOK   bool
+	}{
+		{"plain", "42 (bash) S 7 42 42 0 -1 4194304", 7, "bash", true},
+		{"comm with spaces", "42 (Web Content) S 7 42", 7, "Web Content", true},
+		{"comm with parens", "42 (odd (name)) S 7 42", 7, "odd (name)", true},
+		{"comm with a space and a paren", "42 (a b) c) R 9 42", 9, "a b) c", true},
+		{"truncated after comm", "42 (bash)", 0, "", false},
+		{"no parens", "42 bash S 7", 0, "", false},
+		{"non-numeric ppid", "42 (bash) S x 42", 0, "", false},
+		{"empty", "", 0, "", false},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			ppid, comm, ok := parseStat(tc.line)
+			if ok != tc.wantOK || ppid != tc.wantPPID || comm != tc.wantComm {
+				t.Fatalf("parseStat(%q) = (%d, %q, %v), want (%d, %q, %v)",
+					tc.line, ppid, comm, ok, tc.wantPPID, tc.wantComm, tc.wantOK)
+			}
+		})
+	}
+}
diff --git a/go/cmd/compass-app/multiwindow_e2e_reap_other_test.go b/go/cmd/compass-app/multiwindow_e2e_reap_other_test.go
new file mode 100644
index 00000000..c69d0a5f
--- /dev/null
+++ b/go/cmd/compass-app/multiwindow_e2e_reap_other_test.go
@@ -0,0 +1,8 @@
+//go:build unix && gtk4 && !linux
+
+package main
+
+// liveChildren has no portable non-linux implementation; the leaked-child reap
+// targets WebKitGTK under the linux e2e gate, and darwin does not run it. A
+// no-op keeps the non-linux unix build compiling and the reap a clean pass.
+func liveChildren() []procInfo { return nil }
diff --git a/go/cmd/compass-app/multiwindow_e2e_test.go b/go/cmd/compass-app/multiwindow_e2e_test.go
index 40b21ba5..b37f2b71 100644
--- a/go/cmd/compass-app/multiwindow_e2e_test.go
+++ b/go/cmd/compass-app/multiwindow_e2e_test.go
@@ -24,9 +24,14 @@
 package main
 
 import (
+	"errors"
+	"fmt"
 	"net/http"
 	"os"
+	"strings"
+	"syscall"
 	"testing"
+	"time"
 
 	"github.com/RigelBuild/compass/go/internal/bridge"
 	"github.com/wailsapp/wails/v3/pkg/application"
@@ -69,7 +74,72 @@ func TestMain(m *testing.M) {
 		os.Stderr.WriteString("compass-app multi-window e2e: app.Run: " + err.Error() + "\n")
 		os.Exit(1)
 	}
-	os.Exit(e2eExitCode)
+	// WebKitGTK fork+execs its GPU/network helpers in C as our direct children;
+	// upstream teardown never joins them. Left alive they hold go test's captured
+	// pipe until its WaitDelay fires (a PASS turns into "Test I/O incomplete"), or
+	// orphan to init on a reused runner. Reap them here, bounded and loud.
+	os.Exit(reapChildren(e2eExitCode))
+}
+
+// reapWait hard-bounds the join; past it a child is wedged, so the gate reds
+// loudly instead of tripping go test's opaque WaitDelay. reapEscalate is the
+// SIGTERM grace before SIGKILL — the helpers honor SIGTERM slowly.
+const (
+	reapWait     = 10 * time.Second
+	reapEscalate = 2 * time.Second
+)
+
+// procInfo names one surviving child for the timeout diagnostic.
+type procInfo struct {
+	pid  int
+	comm string
+}
+
+// reapChildren joins the WebKit helpers WebKitGTK fork+exec'd as our children.
+// They block until signaled (the app has quit), so a passive wait never ends:
+// SIGTERM, then SIGKILL if they dawdle, until none remain or reapWait elapses.
+// A survivor past the bound reds loudly and non-zero, never masking a failure.
+func reapChildren(exitCode int) int {
+	start := time.Now()
+	signalChildren(liveChildren(), syscall.SIGTERM)
+
+	ticker := time.NewTicker(100 * time.Millisecond)
+	defer ticker.Stop()
+	for {
+		remaining := liveChildren()
+		if len(remaining) == 0 {
+			return exitCode
+		}
+		if time.Since(start) >= reapWait {
+			var b strings.Builder
+			fmt.Fprintf(&b, "compass-app multi-window e2e: %d child process(es) survived the %s reap deadline:\n", len(remaining), reapWait)
+			for _, p := range remaining {
+				fmt.Fprintf(&b, "  pid=%d comm=%q\n", p.pid, p.comm)
+			}
+			os.Stderr.WriteString(b.String())
+			if exitCode == 0 {
+				return 1
+			}
+			return exitCode
+		}
+		// Re-signal each pass rather than latching: a helper first seen after
+		// the grace would otherwise get neither SIGTERM nor SIGKILL.
+		if time.Since(start) >= reapEscalate {
+			signalChildren(remaining, syscall.SIGKILL)
+		}
+		<-ticker.C
+	}
+}
+
+// signalChildren sends sig to each named process. ESRCH is expected and ignored
+// — the child exited between discovery and the signal; any other error is a real
+// fault worth surfacing, never swallowed.
+func signalChildren(procs []procInfo, sig syscall.Signal) {
+	for _, p := range procs {
+		if err := syscall.Kill(p.pid, sig); err != nil && !errors.Is(err, syscall.ESRCH) {
+			fmt.Fprintf(os.Stderr, "compass-app multi-window e2e: signal %d pid=%d: %v\n", sig, p.pid, err)
+		}
+	}
 }
 
 // TestMultiWindowCloseCancelsOnlyClosingWindowE2E is the leak-gate proof through