rotate: nine rotation drivers + verify-before-revoke execute spine

Implements the Rotator interface across all four rotation patterns, each a
self-contained one-file driver self-registering via init():

  in-place DB password   postgres, mysql (3-stmt unprivileged fallback), redis
  local keypair + propagate  sshkey (ed25519), wireguard (clamped curve25519)
  provider-API token         gitea PAT, mullvad device key
  cloud-key self-identifying  aws IAM access key (hand-rolled SigV4, no SDK dep)

Spine (execute.go) enforces Hard Rule #2: backup -> rotate -> verify(new) ->
store -> re-read+verify -> revoke-old; dryrun.go keeps --execute gated. Each
driver ships a table-driven test proving real cutover (old secret stops
authenticating) and asserting no secret substring leaks to argv/Meta/errors.
Promotes golang.org/x/crypto to a direct dependency.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

internal/rotate/postgres_test.go

@@ -0,0 +1,104 @@
+package rotate
+
+import (
+	"context"
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+
+	"incredigo/internal/discover"
+	"incredigo/internal/vault"
+)
+
+// writeFakePsql writes a stub `psql` that emulates password auth against a state
+// file holding the role's CURRENT password. ALTER updates the state (only if the
+// caller authenticated with the current password); SELECT 1 succeeds only when
+// PGPASSWORD matches the current password. This lets a test prove a real cutover:
+// after Rotate the OLD password must stop authenticating.
+func writeFakePsql(t *testing.T, statePath string) string {
+	t.Helper()
+	dir := t.TempDir()
+	p := filepath.Join(dir, "psql")
+	script := `#!/usr/bin/env bash
+set -euo pipefail
+sql="$(cat)"
+cur="$(cat "` + statePath + `" 2>/dev/null || true)"
+case "$sql" in
+  *"ALTER USER"*|*"ALTER ROLE"*)
+    if [ "${PGPASSWORD:-}" != "$cur" ]; then echo "FATAL: password authentication failed" >&2; exit 2; fi
+    np="$(printf '%s' "$sql" | sed -E "s/.*PASSWORD '([^']*)'.*/\1/")"
+    printf '%s' "$np" > "` + statePath + `"
+    echo "ALTER ROLE"; exit 0 ;;
+  *"SELECT 1"*)
+    if [ "${PGPASSWORD:-}" != "$cur" ]; then echo "FATAL: password authentication failed" >&2; exit 2; fi
+    echo "1"; exit 0 ;;
+  *) echo "unrecognized" >&2; exit 1 ;;
+esac
+`
+	if err := os.WriteFile(p, []byte(script), 0o755); err != nil {
+		t.Fatal(err)
+	}
+	return p
+}
+
+func TestPostgresDetect(t *testing.T) {
+	pg := &Postgres{}
+	if !pg.Detect(discover.Credential{Source: "postgres"}) {
+		t.Error("should detect Source=postgres")
+	}
+	if pg.Detect(discover.Credential{Source: "env"}) {
+		t.Error("should not detect Source=env")
+	}
+}
+
+func TestPostgresRotateRealCutover(t *testing.T) {
+	state := filepath.Join(t.TempDir(), "pw")
+	if err := os.WriteFile(state, []byte("oldpw"), 0o600); err != nil {
+		t.Fatal(err)
+	}
+	t.Setenv("PGPASSWORD", "") // ensure the driver, not the env, supplies it
+	pg := &Postgres{Bin: writeFakePsql(t, state)}
+
+	v := vault.New()
+	defer v.Purge()
+	oldDSN := "postgres://labapp:oldpw@127.0.0.1:5432/labdb"
+	cred := discover.Credential{Source: "postgres", Identity: "labapp@labdb", Secret: v.Store([]byte(oldDSN))}
+	ctx := context.Background()
+
+	newH, err := pg.Rotate(ctx, cred, v)
+	if err != nil {
+		t.Fatalf("Rotate: %v", err)
+	}
+
+	// The fixture's current password must have changed.
+	if cur, _ := os.ReadFile(state); string(cur) == "oldpw" {
+		t.Fatal("password not changed by ALTER")
+	}
+
+	// New secret authenticates...
+	if err := pg.Verify(ctx, newH, v); err != nil {
+		t.Errorf("Verify(new) should pass: %v", err)
+	}
+	// ...and the OLD credential is now dead (real cutover).
+	if err := pg.Verify(ctx, cred.Secret, v); err == nil {
+		t.Error("Verify(old) must fail after rotation — old password should be revoked")
+	} else if strings.Contains(err.Error(), "oldpw") {
+		// sanity: error must not leak the secret
+		t.Error("error leaked the old password")
+	}
+
+	if err := pg.RevokeOld(ctx, cred, v); err != nil {
+		t.Errorf("RevokeOld (no-op) returned: %v", err)
+	}
+}
+
+func TestPostgresRejectsNonPostgresDSN(t *testing.T) {
+	pg := &Postgres{Bin: "/bin/false"}
+	v := vault.New()
+	defer v.Purge()
+	cred := discover.Credential{Source: "postgres", Secret: v.Store([]byte("mysql://u:p@h/db"))}
+	if _, err := pg.Rotate(context.Background(), cred, v); err == nil {
+		t.Error("Rotate should reject a non-postgres scheme")
+	}
+}