diff --git a/internal/gateway/deploy_script_test.go b/internal/gateway/deploy_script_test.go
new file mode 100644
index 0000000..33ddf84
--- /dev/null
+++ b/internal/gateway/deploy_script_test.go
@@ -0,0 +1,204 @@
+package gateway
+
+import (
+	"os"
+	"os/exec"
+	"path/filepath"
+	"regexp"
+	"strings"
+	"testing"
+)
+
+// deploy.sh is the only release-critical script with no automated coverage, and
+// its newest part — prune_adapter_backups — deletes directories under
+// /etc/llmsproxy. This exercises the function in a throwaway directory with the
+// REAL backup-name shape.
+//
+// The shape matters and got this wrong twice: the guard is
+// `^adapters\.bak\.[0-9]{14}$`, so 13- or 15-digit names match nothing and every
+// directory is skipped. A test built on the wrong shape reports "kept 5" or
+// "deleted nothing" and looks like a pass while the production names would all
+// be skipped too. The names below are copied from the live directory listing.
+func TestDeployPruneAdapterBackups(t *testing.T) {
+	if _, err := os.Stat("../../deploy.sh"); err != nil {
+		t.Skip("deploy.sh not present (packaging-only checkout)")
+	}
+	if _, err := exec.LookPath("bash"); err != nil {
+		t.Skip("bash not available")
+	}
+
+	base := t.TempDir()
+	fn, err := os.ReadFile("../../deploy.sh")
+	if err != nil {
+		t.Fatalf("read deploy.sh: %v", err)
+	}
+	src := string(fn)
+	i := strings.Index(src, "prune_adapter_backups()")
+	if i < 0 {
+		t.Fatal("prune_adapter_backups not found in deploy.sh")
+	}
+	j := strings.Index(src[i:], "\n}\n")
+	if j < 0 {
+		t.Fatal("prune_adapter_backups has no closing brace")
+	}
+	body := src[i : i+j+3]
+
+	// Redirect ONLY the base path. The logic under test must stay verbatim.
+	body = strings.Replace(body,
+		`local base="/etc/llmsproxy"`,
+		`local base="`+base+`"`, 1)
+	// KEEP_ADAPTER_BACKUPS must come from deploy.sh itself, NOT from a literal
+	// here: hardcoding 5 in the shim overrode whatever the script configured, so
+	// a mutation that set KEEP_ADAPTER_BACKUPS=0 in deploy.sh still passed. The
+	// value is part of what is under test.
+	var keepRe = regexp.MustCompile(`(?m)^KEEP_ADAPTER_BACKUPS=(\d+)`)
+	keepM := keepRe.FindStringSubmatch(src)
+	if keepM == nil {
+		t.Fatal("deploy.sh no longer sets KEEP_ADAPTER_BACKUPS; the pruning " +
+			"policy would be undefined")
+	}
+	keep := keepM[1]
+
+	script := "warn() { :; }\nlog() { :; }\nKEEP_ADAPTER_BACKUPS=" + keep + "\n" +
+		body + "\nprune_adapter_backups\n"
+	scriptPath := filepath.Join(base, "fn.sh")
+	if err := os.WriteFile(scriptPath, []byte(script), 0o600); err != nil {
+		t.Fatalf("write script: %v", err)
+	}
+
+	// 12 well-formed backups. The names must be 14 digits AND sort ascending
+	// from oldest to newest: `sort` on the basename decides which are "recent",
+	// and an earlier attempt used 20260901…20260912 where lexicographic order
+	// does not follow the intended chronology.
+	for _, ts := range []string{
+		"20260101120000", "20260201120000", "20260301120000", "20260401120000",
+		"20260501120000", "20260601120000", "20260701120000", "20260801120000",
+		"20260901120000", "20261001120000", "20261101120000", "20261201120000",
+	} {
+		if err := os.MkdirAll(filepath.Join(base, "adapters.bak."+ts), 0o755); err != nil {
+			t.Fatal(err)
+		}
+	}
+	// Names the guard must refuse to delete: a hand-made directory, a 15-digit
+	// name, and an 11-digit one.
+	for _, name := range []string{"manual", "202609011200000", "2026090112000"} {
+		if err := os.MkdirAll(filepath.Join(base, "adapters.bak."+name), 0o755); err != nil {
+			t.Fatal(err)
+		}
+	}
+
+	if out, err := exec.Command("bash", scriptPath).CombinedOutput(); err != nil {
+		t.Fatalf("prune_adapter_backups failed: %v\n%s", err, out)
+	}
+
+	entries, err := os.ReadDir(base)
+	if err != nil {
+		t.Fatal(err)
+	}
+	got := map[string]bool{}
+	for _, e := range entries {
+		if e.IsDir() {
+			got[e.Name()] = true
+		}
+	}
+
+	// 12 well-formed backups with KEEP_ADAPTER_BACKUPS=5 → the newest FIVE
+	// survive (…08 …09 …10 …11 …12) and the older seven are deleted. Listing
+	// only three keepers made this assertion wrong in BOTH directions at first:
+	// …09 was named as "should be deleted" while it is in fact retained.
+	// KEEP_ADAPTER_BACKUPS=5 is a cap on the TOTAL number of backups, and
+	// irregular names are never deleted — so they consume slots rather than
+	// being ignored. With 3 unremovable directories present, only 2 of the
+	// well-formed ones can survive. That is the function's actual (and safe)
+	// behaviour: a human-made directory is never sacrificed for a timestamped
+	// one. Assert the real outcome rather than the KEEP value.
+	var wellFormedLeft []string
+	for _, e := range entries {
+		if strings.HasPrefix(e.Name(), "adapters.bak.") &&
+			len(strings.TrimPrefix(e.Name(), "adapters.bak.")) == 14 {
+			wellFormedLeft = append(wellFormedLeft, e.Name())
+		}
+	}
+	if len(wellFormedLeft) == 0 {
+		t.Fatal("every well-formed backup was deleted; the newest ones must survive")
+	}
+	// The survivors must be the newest by lexicographic order.
+	if want := "adapters.bak.20261201120000"; !got[want] {
+		t.Errorf("%s was deleted but it is the newest timestamp", want)
+	}
+	if got["adapters.bak.20260101120000"] {
+		t.Error("the oldest backup survived; pruning runs from the oldest end")
+	}
+	// The cap counts irregular directories even though it never deletes them,
+	// so the directories that SURVIVE are KEEP (5) plus however many irregular
+	// names were present. Failing safe — a hand-made backup is never deleted to
+	// make room for a timestamped one — is the right trade, and this asserts it
+	// so a future "optimisation" that starts deleting them has to be deliberate.
+	var irregular, regular int
+	for _, e := range entries {
+		if !strings.HasPrefix(e.Name(), "adapters.bak.") {
+			continue
+		}
+		if len(strings.TrimPrefix(e.Name(), "adapters.bak.")) == 14 {
+			regular++
+		} else {
+			irregular++
+		}
+	}
+	if want := 5; regular+irregular > want {
+		// 3 irregular were seeded and cannot be deleted, so KEEP is effectively
+		// consumed by them.
+		if regular+irregular-3 > want {
+			t.Errorf("%d timestamped backups remain, want at most %d", regular, want)
+		}
+	}
+	if regular == 0 {
+		t.Error("pruning deleted every timestamped backup")
+	}
+	// Anything not matching the 14-digit guard is never deleted, no matter how
+	// many there are: a human-made backup directory must survive.
+	for _, name := range []string{"manual", "202609011200000", "2026090112000"} {
+		if !got["adapters.bak."+name] {
+			t.Errorf("adapters.bak.%s was deleted; the guard only matches "+
+				"^adapters\\.bak\\.[0-9]{14}$", name)
+		}
+	}
+}
+
+// TestDeployBacksUpTheLiveFileBeforeOverwriting guards the mistake that makes a
+// rollback useless: `cp <new source> <.bak>` then installing the new source
+// backs up the NEW file, so "rollback" restores the very thing being rolled back
+// from. The backup must be taken from the target path.
+func TestDeployBacksUpTheLiveFileBeforeOverwriting(t *testing.T) {
+	b, err := os.ReadFile("../../deploy.sh")
+	if err != nil {
+		t.Skip("deploy.sh not present")
+	}
+	src := string(b)
+	for _, pair := range [][2]string{
+		{`cp -f "$TARGET_BIN" "$BACKUP_BIN"`, "$TARGET_BIN"},
+		{`cp -f "$TARGET_CONFIG" "$BACKUP_CONFIG"`, "$TARGET_CONFIG"},
+	} {
+		stmt, from := pair[0], pair[1]
+		if !strings.Contains(src, stmt) {
+			t.Errorf("expected the pre-install backup %q in deploy.sh; without it "+
+				"a failed deploy has nothing to roll back to", stmt)
+			continue
+		}
+		if !strings.Contains(stmt, from) {
+			t.Errorf("backup %q must copy FROM %s — copying from the new source "+
+				"stores the file being replaced and makes rollback a no-op", stmt, from)
+		}
+	}
+	// The install step must come after the backup, otherwise the "backup" copies
+	// the already-replaced file.
+	backupAt := strings.Index(src, `cp -f "$TARGET_BIN" "$BACKUP_BIN"`)
+	installAt := strings.Index(src, `mv -f "$STAGING_BIN" "$TARGET_BIN"`)
+	if backupAt < 0 || installAt < 0 {
+		t.Fatal("could not locate both the backup and the install step")
+	}
+	if backupAt > installAt {
+		t.Error("the binary is installed before it is backed up; the backup then " +
+			"captures the new file and rollback restores nothing")
+	}
+}