feat(fingerprint): password OR fingerprint in parallel at one prompt

Bernardo promoted the PROPOSED item live: with fingerprint PAM on,
sudo/login should accept whichever factor comes first instead of
pam_fprintd's wait-for-the-reader-then-password. Stock PAM cannot
express parallel factors (linux-pam#301), so this packages
pam-fprint-grosshack v0.3.0 (pkgs/, pinned from GitLab — the
field-standard fprintd fork), source-reviewed before packaging: every
failure path (no reader, no prints, fprintd absent/hung, timeout,
password typed) returns PAM_AUTHINFO_UNAVAIL and falls through; a
typed password is only ferried via PAM_AUTHTOK to the stock
`auth sufficient pam_unix.so … try_first_pass` rule — the module never
validates passwords itself, so it cannot lock out password login.

New option nomarchy.hardware.fingerprint.parallel, default TRUE (the
better UX is what opting into fingerprint PAM buys; false = stock
sequential). Wiring swaps the modulePath of stock fprintd's rule slot
(mkForce) so the sufficient-before-pam_unix ordering is inherited, not
recomputed. README + downstream template rows added.

Verified: V2 — checks.hardware-toggles extended to three nodes, green:
parallel node asserts the grosshack auth line precedes pam_unix in
/etc/pam.d/sudo and that with NO reader a correct password still
passes sudo while a wrong one fails (the lockout-safety invariant);
seqpam node gets stock pam_fprintd and no grosshack; nopam gets
neither. flake check + option-docs + template-sot green.
V3 pending (HARDWARE-QUEUE, AMD dev box): the real type-or-touch race,
fprintd-stopped fallback, hyprlock/greeter after a fingerprint win.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

modules/nixos/hardware.nix

@@ -112,6 +112,20 @@ in
           menu) when set; otherwise false.
         '';
       };
+
+      parallel = lib.mkOption {
+        type = lib.types.bool;
+        default = true;
+        description = ''
+          With fingerprint PAM on, accept the password OR a fingerprint at the
+          same prompt (type or touch, whichever comes first) instead of stock
+          pam_fprintd's sequential wait-for-the-reader-then-password. Uses the
+          pam-fprint-grosshack module (an fprintd fork — source-reviewed; every
+          failure path falls through to the normal password rule, so password
+          login can never be locked out by it). Set false for the stock
+          sequential behavior.
+        '';
+      };
     };
 
     npu.enable = lib.mkEnableOption ''
@@ -205,7 +219,20 @@ in
         "passwd" "chsh" "chfn" "chpasswd"
         "polkit-1" "swaylock"
         "groupadd" "groupdel" "groupmod" "groupmems"
-      ] (_: { fprintAuth = cfg.fingerprint.pam; });
+      ] (_: {
+        fprintAuth = cfg.fingerprint.pam;
+      } // lib.optionalAttrs (cfg.fingerprint.pam && cfg.fingerprint.parallel) {
+        # Parallel mode: same rule slot as stock fprintd (so ordering —
+        # sufficient, before pam_unix — is inherited), different module.
+        # grosshack prompts for the password itself while polling the
+        # reader; whichever lands first wins. A typed password makes the
+        # rule FAIL with the token stored, and the stock
+        # `auth sufficient pam_unix.so … try_first_pass` right after it
+        # does the actual validation — password stays sufficient on its
+        # own, so a broken reader/fprintd can never lock login out.
+        rules.auth.fprintd.modulePath = lib.mkForce
+          "${pkgs.pam-fprint-grosshack}/lib/security/pam_fprintd_grosshack.so";
+      });
     })
 
     # ── Newest kernel for very-new hardware (opt-in escape hatch) ──────