fix: update nix flakes to work with nixpkgs 26.11

- Update nixpkgs lock (Feb → Jul 2026) for erlang_29 availability
- Fix erlang_29 reference: use beam.interpreters.erlang_29 instead of
  nonexistent top-level erlang_29
- Filter x86_64-darwin from systems (dropped in nixpkgs 26.11)
- Fix shell.nix flake-compat tarball hash

flake.lock

@@ -59,11 +59,11 @@
     },
     "nixpkgs": {
       "locked": {
-        "lastModified": 1770197578,
-        "narHash": "sha256-AYqlWrX09+HvGs8zM6ebZ1pwUqjkfpnv8mewYwAo+iM=",
+        "lastModified": 1784120854,
+        "narHash": "sha256-KesHgItiZPgGX740axSiQLcIQ8D24MDqNpkKYWIek8k=",
         "owner": "NixOS",
         "repo": "nixpkgs",
-        "rev": "00c21e4c93d963c50d4c0c89bfa84ed6e0694df2",
+        "rev": "753cc8a3a87467296ddd1fa93f0cc3e81120ee46",
         "type": "github"
       },
       "original": {

flake.nix

@@ -26,7 +26,8 @@
       pre-commit-hooks,
     }:
     flake-parts.lib.mkFlake { inherit inputs; } {
-      systems = import systems;
+      # nixpkgs 26.11 dropped x86_64-darwin support
+      systems = builtins.filter (s: s != "x86_64-darwin") (import systems);
 
       perSystem =
         {
@@ -45,17 +46,16 @@
             };
             overlays = [
               # Pin specific Elixir and Erlang versions to match .tool-versions
-              # Elixir 1.20.2-otp-29, Erlang 29.0
+              # Elixir 1.20.2-otp-29, Erlang 29.0.3
               (final: prev: {
-                # Use Erlang 29 (OTP 29.0)
-                erlang = prev.erlang_29;
+                # Use Erlang 29 (OTP 29.0.3) — no top-level erlang_29 yet, use beam.interpreters
+                erlang = prev.beam.interpreters.erlang_29;
 
                 # Use Elixir 1.20 with Erlang 29 (1.20.2-otp-29)
                 elixir = prev.beam.packages.erlang_29.elixir_1_20;
 
                 # Ensure beam packages use our pinned versions
                 # This affects mixRelease and all BEAM-related builds
-                # Override the default elixir within beamPackages to use 1.20
                 beamPackages = prev.beam.packages.erlang_29.extend (
                   self: super: {
                     elixir = super.elixir_1_20;

shell.nix

@@ -5,7 +5,7 @@
   import (
     fetchTarball {
       url = "https://github.com/edolstra/flake-compat/archive/35bb57c0c8d8b62bbfd284272c928ceb64ddbde9.tar.gz";
-      sha256 = "sha256-1prd9qvMxmK/v5qPbX8z1bwDOzocQFGKFQqz3EQ9MSY=";
+      sha256 = "sha256-4gtG9iQuiKITOjNQQeQIpoIB6b16fm+504Ch3sNKLd8=";
     }
   ) { src = ./.; }
 ).shellNix.default