{
  description = "hyperhive — multi-Claude-Code-agent orchestration on nixos-containers";

  inputs = {
    nixpkgs.url = "github:NixOS/nixpkgs/nixos-26.05";
    nixpkgs-unstable.url = "github:NixOS/nixpkgs/nixpkgs-unstable";
    # Crane (replaces naersk #538). Stateless — no nixpkgs input to
    # follow; `crane.mkLib pkgs` returns the lib at whatever pkgs we
    # pass it (we use the project's pinned nixpkgs).
    crane.url = "github:ipetkov/crane";
    treefmt-nix = {
      url = "github:numtide/treefmt-nix";
      inputs.nixpkgs.follows = "nixpkgs";
    };
  };

  outputs =
    inputs@{
      self,
      nixpkgs,
      nixpkgs-unstable,
      crane,
      treefmt-nix,
    }:
    let
      inherit (nixpkgs) lib;
      systems = [
        "aarch64-linux"
        "x86_64-linux"
      ];
      treefmt-config = {
        projectRootFile = "flake.nix";
        programs = {
          keep-sorted.enable = true;
          nixfmt.enable = true;
          rustfmt.enable = true;
          taplo.enable = true;
        };
      };
      forAllSystems =
        f:
        lib.genAttrs systems (
          system:
          f rec {
            inherit system;
            pkgs = nixpkgs.legacyPackages.${system};
            treefmt-eval = treefmt-nix.lib.evalModule pkgs treefmt-config;
            craneLib = crane.mkLib pkgs;
            # Narrowed source tree the rust derivations consume.
            # `cleanCargoSource` is crane's standard "everything cargo
            # cares about" filter (Cargo.toml/Cargo.lock + *.rs). All
            # non-rust runtime assets — branding + the claude system
            # prompt template + claude-settings.json — live in the
            # separate `hyperhive-assets` derivation (#555) and are
            # loaded by the binaries at runtime from `$HIVE_ASSETS_DIR`.
            # The unit tests in `hive-ag3nt::prompt` read the same
            # `prompts/system.md` directly from the workspace tree at
            # *test* runtime (via `env!("CARGO_MANIFEST_DIR")` — a
            # compile-time string, no file open at compile), so the
            # prompt template doesn't have to be in this fileset to
            # keep `cargo test` honest. Net effect: tweaks to any
            # non-`*.rs` / non-`Cargo.*` file (README, branding,
            # nix modules, frontend tree, OR `hive-ag3nt/prompts/*`)
            # do NOT bust this src hash, so the rust derivations
            # stay fully cached.
            cleanSrc = craneLib.cleanCargoSource ./.;
            # Build the workspace's dependency tree once, cached as
            # its own derivation. `buildPackage` and `cargoClippy`
            # both reuse this via `inherit cargoArtifacts;` so a
            # workspace-only edit doesn't rebuild deps. All three
            # derivations consume the same `cleanSrc` so the input
            # hash stays consistent across the chain.
            cargoArtifacts = craneLib.buildDepsOnly {
              src = cleanSrc;
              # Workspace Cargo.toml is virtual (no `[package].name`),
              # so crane can't auto-derive a name. Spell it out
              # explicitly here and below — keeps the derivation name
              # stable across crane bumps + silences the placeholder
              # warning. Same `pname` everywhere so dep + workspace +
              # clippy share a clean naming family.
              pname = "hyperhive-workspace";
              version = "0.1.0";
              inherit nativeBuildInputs;
            };
            # Shared between buildDepsOnly + buildPackage + cargoClippy
            # so the three derivations see the same toolchain shape.
            # git: naersk used to auto-include it; crane is more
            # minimal, so we add it explicitly so hive-c0re's
            # `lifecycle::tests::setup_proposed_*` (which shell out to
            # `git init` + commit) pass under `cargo test` in the
            # sandbox.
            # `librsvg` used to live here for `hive-c0re/build.rs`'s
            # rsvg-convert call — that whole codepath moved into the
            # `hyperhive-assets` derivation in #555, so the rust
            # derivation no longer needs the dependency.
            # `sqlite` required by matrix-sdk's `sqlite` feature
            # (`hive-matrix-mcp` workspace member, #548 phase 3) — the
            # matrix-sdk-sqlite + rusqlite stack links against system
            # libsqlite3 by default.
            nativeBuildInputs = [
              pkgs.git
              pkgs.sqlite
              pkgs.pkg-config
            ];
          }
        );
    in
    {
      packages = forAllSystems (
        {
          pkgs,
          craneLib,
          cleanSrc,
          cargoArtifacts,
          nativeBuildInputs,
          ...
        }:
        let
          docsAttrs = import ./nix/docs {
            inherit pkgs self;
            inherit (nixpkgs) lib;
            inherit (nixpkgs.lib) nixosSystem;
          };
        in
        {
          # Build the workspace binaries without running tests. Tests
          # are run as a separate check (`checks.cargo-test`) that
          # carries the `hyperhive-assets` build input — `hive-ag3nt::
          # prompt::tests` reads the production prompt template at test
          # runtime through `$HIVE_ASSETS_DIR`, so wiring the env var
          # into the build phase here would make the prompt's hash a
          # build input of `default` (defeats #555's cache goal: a
          # prompt edit would still bust the binary derivation, even
          # though no .rs file changed). Keeping tests in a separate
          # check derivation localises the asset-rebuild blast radius
          # to that one check — `nix flake check` still exercises them.
          default = craneLib.buildPackage {
            src = cleanSrc;
            inherit cargoArtifacts nativeBuildInputs;
            pname = "hyperhive-workspace";
            version = "0.1.0";
            meta.description = "hyperhive workspace (hive-c0re, hive-ag3nt, hive-root)";
            doCheck = false;
          };
          # Bundled browser assets — see ./nix/frontend.nix. Output is
          # $out/{dashboard,agent}/ which the Rust binaries serve via
          # tower_http::ServeDir (wired up in Phase 4 of #273).
          frontend = pkgs.callPackage ./nix/frontend.nix {
            branding-svg = ./branding/hyperhive.svg;
          };
          # Static runtime assets the rust binaries read via
          # `hive_sh4re::assets::*` (#555): branding/* + prompts/*,
          # plus the rendered agent-configs.png. Split out of the
          # rust derivation so a tweak to e.g. system.md doesn't bust
          # the cargo cache. Build input of the `cargo-test` check but
          # NOT of `packages.default`, so the binary derivation stays
          # cached when a prompt edit ripples through.
          assets = pkgs.callPackage ./nix/assets.nix { };
          # Pre-built per-container system closures. Exposed as packages
          # so operators can `nix build .#agent-base-toplevel` (or wire
          # them into their host system closure via the
          # `preBuildAgentTemplates` option on the hive-c0re module —
          # see nix/modules/hive-c0re.nix). Speeds up the first agent
          # spawn dramatically because the heavy lifting (nixpkgs +
          # claude-code + hive-ag3nt binary) is already in the store
          # when the meta evaluator goes to build the container.
          # Closes #97.
          #
          # nixosConfigurations are pinned to x86_64-linux (nixos-
          # containers only run native arch), so these toplevels are
          # only useful on an x86_64-linux host — flake check across
          # systems still tolerates evaluating them on aarch64 because
          # they're plain derivations, but `nix build` from a non-x86
          # host would only succeed via a remote x86 builder.
          agent-base-toplevel = self.nixosConfigurations.agent-base.config.system.build.toplevel;
          ruth-toplevel = self.nixosConfigurations.ruth.config.system.build.toplevel;

          # Auto-generated nix options reference for hyperhive (#616).
          # `docs` bundles host + agent pages into one tree; the split
          # outputs are useful when consumers only want one surface.
          # All three are pure markdown — no rust or frontend deps in
          # the closure, so `nix build .#docs` is cheap.
          docs = docsAttrs.bundle;
          docs-host = docsAttrs.host;
          docs-agent = docsAttrs.agent;
        }
      );

      overlays = {
        default = final: prev: {
          hyperhive = self.packages.${prev.stdenv.hostPlatform.system}.default;
          # Bundled frontend dist (see ./nix/frontend.nix). Output is
          # $out/{dashboard,agent}/; consumers pick the surface they
          # need. Exposed via the overlay so containers' nix evaluations
          # can reach it as `pkgs.hyperhive-frontend` once the overlay
          # is applied (manager + agent containers both apply it via
          # `mkContainer` further down).
          hyperhive-frontend = self.packages.${prev.stdenv.hostPlatform.system}.frontend;
          # Static runtime assets (#555). Exposed alongside the binary
          # so the harness module can wire $HIVE_ASSETS_DIR straight
          # to `${pkgs.hyperhive-assets}/share/hyperhive`.
          hyperhive-assets = self.packages.${prev.stdenv.hostPlatform.system}.assets;
        };
        claude-unstable =
          final: prev:
          let
            # The overlay imports its own nixpkgs-unstable instance to
            # pin claude-code there. That instance has its own config
            # (independent from the user's prev.config), so we have to
            # set allowUnfreePredicate inline to whitelist claude-code
            # specifically — otherwise the unstable import itself
            # refuses to evaluate. This is scoped: only claude-code
            # bypasses unfree, nothing else.
            unstable = import nixpkgs-unstable {
              inherit (prev.stdenv.hostPlatform) system;
              config.allowUnfreePredicate = pkg: builtins.elem (prev.lib.getName pkg) [ "claude-code" ];
            };
          in
          {
            inherit (unstable) claude-code;
          };
      };

      nixosModules = {
        agent-base = ./nix/templates/agent-base.nix;
        ruth = ./nix/templates/manager.nix;
        # The hive-c0re module wants `pkgs.hyperhive` for its default
        # `services.hyperhive.c0re.package`. To avoid making operators apply an
        # overlay (which would also pollute their host pkgs with our
        # build), we thread the package straight from this flake's
        # `packages.<system>.default` via a `hyperhivePackage` argument.
        # The `claude-unstable` overlay only matters inside our container
        # builds (already applied internally in `nixosConfigurations`).
        hive-c0re = import ./nix/modules/hive-c0re.nix {
          hyperhivePackage = system: self.packages.${system}.default;
          hyperhiveFrontend = system: self.packages.${system}.frontend;
          hyperhiveAssets = system: self.packages.${system}.assets;
          hyperhiveFlake = "${self}";
          # Store path of the nixpkgs-unstable input this flake was evaluated
          # with — the channel that carries claude-code. Passed as the default
          # for `services.hyperhive.c0re.nixpkgsUnstableFlake` so operators can
          # override it without touching this file.
          hyperhiveNixpkgsUnstable = "path:${nixpkgs-unstable}";
          # Per-container toplevels — wired into `system.extraDependencies`
          # when `services.hyperhive.c0re.preBuildAgentTemplates` is on so the
          # host system closure pre-fetches the heavy build inputs (#97).
          # Defined only for x86_64-linux because nixosConfigurations are
          # hardcoded to that system; the option's default keeps the
          # extra deps gated so aarch64 hosts don't accidentally pull
          # them in via cross-build.
          agentBaseToplevel = self.packages.x86_64-linux.agent-base-toplevel;
          managerToplevel = self.packages.x86_64-linux.ruth-toplevel;
        };
        hive-ci = ./nix/modules/hive-ci.nix;
        hive-forge = ./nix/modules/hive-forge.nix;
        # Convenience alias: one import covers the full hyperhive host
        # stack (hive-c0re + hive-forge, since hive-c0re already pulls
        # in hive-forge). Intended usage:
        #
        #   imports = [ hyperhive.nixosModules.default ];
        #   services.hyperhive.enable = true;
        #
        default = self.nixosModules.hive-c0re;
      };

      nixosConfigurations =
        let
          mkContainer =
            module:
            nixpkgs.lib.nixosSystem {
              system = "x86_64-linux";
              modules = [
                module
                {
                  nixpkgs.overlays = [
                    self.overlays.default
                    self.overlays.claude-unstable
                  ];
                }
              ];
            };
        in
        {
          agent-base = mkContainer self.nixosModules.agent-base;
          ruth = mkContainer self.nixosModules.ruth;
        };

      devShells = forAllSystems (
        { pkgs, ... }:
        {
          default = pkgs.mkShell {
            packages = with pkgs; [
              cargo
              clippy
              librsvg # rsvg-convert — hive-c0re/build.rs invokes it (#424)
              pkg-config
              rust-analyzer
              rustc
              rustfmt
              sqlite
            ];
          };
        }
      );

      formatter = forAllSystems ({ treefmt-eval, ... }: treefmt-eval.config.build.wrapper);

      checks = forAllSystems (
        {
          pkgs,
          system,
          treefmt-eval,
          craneLib,
          cleanSrc,
          cargoArtifacts,
          nativeBuildInputs,
          ...
        }:
        {
          formatting = treefmt-eval.config.build.check self;
          # Clippy as a check via crane's first-class `cargoClippy`
          # builder. Reuses the shared `cargoArtifacts` (deps already
          # built) and runs `cargo clippy --workspace --all-targets
          # -- -D warnings` directly — no `overrideAttrs` hack needed,
          # because crane parses `cargoClippyExtraArgs` correctly
          # (naersk's `mode = "clippy"` used to mangle the `--`
          # separator, which is why the old wiring went through
          # overrideAttrs).
          clippy = craneLib.cargoClippy {
            src = cleanSrc;
            inherit cargoArtifacts nativeBuildInputs;
            pname = "hyperhive-workspace";
            version = "0.1.0";
            cargoClippyExtraArgs = "--workspace --all-targets -- -D warnings";
          };
          # `cargo test --workspace` lifted out of `buildPackage` so the
          # `hyperhive-assets` dep (which `hive-ag3nt::prompt::tests`
          # needs via `HIVE_ASSETS_DIR` to assert against the actual
          # production prompt template) is scoped to this one check
          # instead of bleeding into the binary derivation's input
          # hash. Net: editing `hive-ag3nt/prompts/system.md` still
          # rebuilds this test check (correct — the tests assert
          # against its wording), but `packages.default` and the
          # per-container toplevels stay fully cached.
          cargo-test = craneLib.cargoTest {
            src = cleanSrc;
            inherit cargoArtifacts nativeBuildInputs;
            pname = "hyperhive-workspace";
            version = "0.1.0";
            cargoTestExtraArgs = "--workspace";
            HIVE_ASSETS_DIR = "${self.packages.${system}.assets}/share/hyperhive";
          };
          # Nix options docs evaluation (#616). Cheap: pulls in
          # `nixosOptionsDoc` + the host module's stub eval, no rust or
          # frontend deps. CI fails fast if a module change breaks
          # option declarations or the doc rendering. Reuses the
          # `packages.<system>.docs` derivation so the per-system eval
          # of `nix/docs/default.nix` happens once.
          inherit (self.packages.${system}) docs;
        }
      );
    };
}