# Gotchas

NixOS + nspawn quirks and lessons we hit the hard way. If something
here looks unmotivated in the code, there's usually a story underneath.

## `nixos-container` doesn't expose `--bind` on the CLI

The CLI doesn't accept `--bind`. Path is via `EXTRA_NSPAWN_FLAGS` in
`/etc/nixos-containers/<NAME>.conf` — the start script
(`/nix/store/.../container_-start`) expands it unquoted into the
`systemd-nspawn` invocation. `lifecycle::set_nspawn_flags()` rewrites
this line.

## `/run/systemd/nspawn/*.nspawn` overrides are ignored

`nixos-container`'s start script builds the nspawn command line
directly. Dropping a `.nspawn` file under `/run/systemd/nspawn/`
looks like the obvious extension point and does nothing. Use
`EXTRA_NSPAWN_FLAGS` (above).

## `boot.isNspawnContainer = true`

Not `boot.isContainer = true`. Renamed in nixos-25.11+.

## `nixos-container create` auto-assigns `HOST_ADDRESS` / `LOCAL_ADDRESS`

…in the `.conf`. The start script's `if HOST_ADDRESS set →
--network-veth` branch then forces a private netns — silently fatal
for our web UIs (the bind is invisible from the host). We
force-clear `HOST_ADDRESS` / `LOCAL_ADDRESS` / `HOST_ADDRESS6` /
`LOCAL_ADDRESS6` / `HOST_BRIDGE` and set `PRIVATE_NETWORK=0`.

## systemd service PATH ≠ host PATH

The hive-c0re service sets `path = [ pkgs.git "/run/current-system/sw" ]`.
In-container harness services do the same so anything an agent adds
to its own `agent.nix` (`environment.systemPackages`) is visible to
the `mcp__bash__run` MCP tool (and any other in-container process) without
editing the service definition.
`environment.HYPERHIVE_GIT` bakes git's absolute path in (read by
`lifecycle::git_command()`) for the host.

## `systemd.services.*.path` appends `/bin` to every entry

NixOS's `systemd.services.<unit>.path` list feeds every entry through
`lib.makeBinPath`, which **appends `/bin` unconditionally**. That's
the right thing for Nix packages (their `outPath` is the store root,
not the `bin/` subdir), but it bites when you pass a string that
already ends with `/bin`:

```nix
# ❌ /run/wrappers/bin → /run/wrappers/bin/bin (does not exist)
path = [ "/run/wrappers/bin" "/run/current-system/sw" ];

# ✅ /run/wrappers → /run/wrappers/bin  (the real wrappers dir)
path = [ "/run/wrappers" "/run/current-system/sw" ];
```

The bug is silent: `nix eval` succeeds, the unit starts, but PATH
contains a non-existent directory. The first symptom is usually
`sudo: must be owned by uid 0 and have the setuid bit set` because
the setuid sudo wrapper lives at `/run/wrappers/bin/sudo` and
the path entry resolves to `/run/wrappers/bin/bin` instead.

## `RuntimeDirectoryPreserve = "yes"`

…keeps `/run/hyperhive/` (and the per-agent sub-dirs) across
hive-c0re restarts. Without it, every restart wipes bind sources and
existing containers can't be started.

## `register_agent` is idempotent

Drops any prior socket task before rebinding. Required so a
hive-c0re restart followed by `rebuild alice` recreates the agent's
socket without needing a clean reinstall.

## `claude-code` is unfree

`claude-code` comes from the flake's main `nixpkgs` (nixos-26.05).
It's unfree, so `harness-base.nix` sets `config.allowUnfreePredicate`
at the container level to whitelist `claude-code` specifically —
scoped, only this one package. This is needed because each per-agent
`nixosConfiguration` evaluates its own nixpkgs instance and the
operator's host-level `allowUnfree` does **not** propagate in.
Operators don't need to set anything on their side.

## Claude credentials are per-agent

`/var/lib/hyperhive/agents/<name>/claude/` bind-mounts to
`/home/<name>/.claude` (RW). Sharing one dir across agents is NOT viable —
OAuth refresh tokens rotate, so any sibling refresh invalidates all
the others. Login flow runs from the per-agent web UI; creds persist
across `destroy`/recreate (`--purge` wipes them).

## Persistent notes dir per agent

`/var/lib/hyperhive/agents/<name>/state/` bind-mounts to
`/agents/<name>/state` (RW; uniform for all agents).
The harness exposes the same path
via `$HYPERHIVE_STATE_DIR`. System prompts tell agents to keep
durable knowledge here (`notes.md`, anything else). The harness also
writes its events log here (`hyperhive-events.sqlite`).
Survives `destroy`/recreate alongside the claude dir.

## Web UI ports collide on hash

Sub-agent web UI ports are deterministic FNV-1a of the agent name
modulo 900 (range 8100..8999). With ~30 agents the birthday-paradox
collision rate gets meaningful; at 2–3 agents you can still get
unlucky. Operator resolves a collision by renaming the offending
agent (different hash → different port) and rebuilding. No state
file, no probing, no port-allocation drift — the value is
reproducible from just the name. Every agent hashes into
8100..8999 via the same FNV-1a; dashboard
at `cfg.dashboardPort` (default 7000).

## Restart races on TCP bind

Both the dashboard and per-agent web UI use `tokio::net::TcpSocket`
with `SO_REUSEADDR` plus a retry-on-`AddrInUse` loop (12 tries,
exponential backoff capped at 2s, ~22s total). REUSEADDR handles
the `TIME_WAIT` case from a clean previous exit; retry covers the
genuine "previous process is still alive during a systemd restart
overlap" case. REUSEADDR does **not** allow two simultaneous
`LISTEN` sockets on the same port (that would be `SO_REUSEPORT`,
which we don't use) — exclusivity is preserved.

## Orphan approvals

If state dirs are wiped out from under a pending approval (test
scripts, manual `rm -rf`), the dashboard's next render marks them
`failed` with note `"agent state dir missing"` so they fall out of
`pending`. They stay in sqlite for audit.

## Nix store `cp -r` preserves read-only bits

Copying a nix store path with `cp -r src/. $out/` inside a
`pkgs.runCommand` derivation preserves the read-only permissions of
store files. Any subsequent write into the copied tree (adding new
files in subdirectories) fails with `EPERM`. Fix: pass
`--no-preserve=mode,ownership` so the output tree is writable.

## SPA fallback: use `Accept` header map, not `try_files ... /index.html`

The naive nginx pattern for a path-prefix SPA (`try_files $uri $uri/
/matrix/index.html`) silently swallows asset 404s — a missing JS file
returns `index.html` with a 200, so the JS runtime never loads and the
page renders blank with no visible error. Extension allowlists (tried
as an alternative) have the same maintenance problem: any new file
extension the SPA ships breaks silently.

The pattern that works (`hive-gateway.nix`) keys the fallback on the
HTTP `Accept` header:

```nginx
# Outside the server block (appendHttpConfig):
map $http_accept $matrix_spa_target {
  default          "/__matrix_spa_no_html_fallback";
  "~*text/html"    "/matrix/index.html";
}

# Inside the location:
try_files $uri $uri/ $matrix_spa_target =404;
```

Top-frame navigations always send `Accept: text/html,...` (chrome /
firefox / safari are consistent). Asset fetches (`image/*`,
`application/javascript`, `*/*`) don't carry `text/html`, so they
fall through to the trailing `=404`. No extension list to maintain;
no named-location indirection needed.

## `nix build flake#name` does not walk into `nixosConfigurations`

`nix build` resolves the fragment (`#name`) against the flake's
**top-level output attrs** — not against `nixosConfigurations`
specifically. `nixos-container` and `nixos-rebuild` use their own
internal convention that routes an agent name to
`nixosConfigurations.<name>.config.system.build.toplevel`, but
`nix build` has no such convention.

```
# ❌ silently builds the wrong thing (or errors if attr doesn't exist)
nix build /var/lib/hyperhive/meta#argus.config.system.build.toplevel

# ✅ explicit path nix build actually resolves
nix build /var/lib/hyperhive/meta#nixosConfigurations.argus.config.system.build.toplevel
```

`lifecycle::prebuild_toplevel` hit this once by constructing the attr
path as `{flake_ref}.config…` — which produced `meta#argus.config…`
instead of `meta#nixosConfigurations.argus.config…`. The fix:
`split_once('#')` to separate flake path from name, then template
`{path}#nixosConfigurations.{name}.config.system.build.toplevel`.

## `hive-forge`: prefer over raw curl pipelines

Full CLI reference: [`docs/tools/forge.md`](tools/forge.md).
Never use raw `curl` for forge access.

## Containerized nix-daemon needs `sandbox-fallback = true`

Agent containers bind-mount the host's nix-daemon socket. nspawn
containers don't get user-namespaces by default, so `nix build`
invocations _inside_ the container can't set up the build sandbox
and fail outright if the host daemon's
`nix.settings.sandbox-fallback` is `false` (nixpkgs default).
`nix/templates/harness-base.nix` does `lib.mkForce true` so builds
fall back to unsandboxed local builds rather than failing. Security
implications: `docs/security.md`.

## Linking workspace binaries locally needs `nix develop`

The Rust workspace links `libsqlite3-sys` (rusqlite) against the
system `libsqlite3`. Agent containers carry no system libsqlite3 on
the linker path, so a plain `cargo build` of any binary dies with
`cannot find -lsqlite3` (deps and `ring` compile fine — only the
final link fails). `cargo check` / `cargo clippy` still work in the
ambient shell since they never link.

Build + run binaries through the dev shell, which carries `sqlite`
on `NIX_LDFLAGS`:

```bash
nix develop -c cargo build -p hive-c0re --bin hivectl
nix develop -c cargo run -p hive-c0re --bin hivectl -- <args>
```

This is also how you regenerate committed generated docs locally —
e.g. `docs/tools/hivectl-cli.md` via the `hivectl markdown-docs`
subcommand (its `hivectl-docs` flake check otherwise only fails in
CI on drift).

## Split asset derivations away from the rust workspace

`nix/assets.nix` builds the branding SVG/PNG family + claude
system-prompt template + claude-settings JSON as its own derivation,
separate from the hive-ag3nt / hive-c0re crates. Reason: when the
rust build's `src` was the whole repo tree, any tweak to
`branding/agent-configs.svg` or `hive-ag3nt/prompts/system.md`
invalidated the cargo cache and forced a full rebuild. crane (and
naersk before it) couldn't see "these inputs are unused by rust" on
its own — the split breaks the coupling at the derivation boundary.
The agent-configs PNG is rendered from the SVG via `rsvg-convert` at
build time; librsvg dependency lives here, not in the rust
derivation's `nativeBuildInputs`.

## Weston VNC compositor (per-agent `hyperhive.gui.enable`)

`nix/templates/weston-vnc.nix` adds an optional Weston Wayland
compositor with the VNC backend, surfaced as
`hyperhive.gui.enable = true` per-agent. The harness's
`/screen/ws` WebSocket relay (`docs/web-ui/agent.md::Per-agent endpoints`)
connects to the compositor at `127.0.0.1:<vnc_port>`.

- **Port allocation**: a **fixed** port (`hyperhive.gui.vncPort`,
  default 5900). No per-agent hashing: network isolation is
  unconditional (each agent has its own netns — see
  `docs/network.md#container-isolation`), so the VNC port is
  container-local and can't collide across agents. The harness learns
  the port from the `HIVE_GUI_VNC_PORT` env var (set on the harness
  service when `gui.enable`) — no marker file, no runtime hash. (Unlike
  the agent **web-UI** port, which is still an FNV-1a hash because those
  listen on the shared host stack — see `Web UI ports collide on hash`.)
- **Non-root, shared user session**: weston runs as the agent's own
  user (`hyperhive.user.name`, the same user hive-ag3nt runs as), not
  root, so the GUI and the agent share one session. The runtime dir is a
  fixed `/run/gui` (systemd `RuntimeDirectory=gui`, `0700`,
  `RuntimeDirectoryPreserve=yes` so it survives weston restarts for the
  wayland client sharing the `/run/gui/wayland-0` socket). Wayland
  clients in the agent's config (e.g. bitburner electron) must run as the
  same user with `XDG_RUNTIME_DIR=/run/gui`.
- **One shared D-Bus session bus (`gui-dbus.service`)**: a single
  persistent `dbus-daemon --session` bound at `/run/gui/bus`, run as the
  agent user, ordered `before weston.service` (it shares the same
  `RuntimeDirectory=gui`, creating the dir first). Chromium/electron via
  ozone refuse to map an `xdg_toplevel` without a reachable session bus
  ("Failed to connect to the bus" → binds `xdg_wm_base` then destroys it
  = invisible window even though CDP works). The fix is **not** to wrap
  each client in its own `dbus-run-session` (a private throwaway bus per
  process — that's a _separate_ session, defeating the one-session
  model); it's this one shared bus, whose address is exported as
  `DBUS_SESSION_BUS_ADDRESS=unix:path=/run/gui/bus` via
  `systemd.globalEnvironment` so weston, the harness and every GUI client
  inherit it.
- **Fixed Wayland socket name (`--socket=wayland-0`)**: weston is
  launched with `--socket=wayland-0` so the socket path is
  deterministic. `harness-base.nix` exports `WAYLAND_DISPLAY=wayland-0`
  and `XDG_RUNTIME_DIR=/run/gui` as global system environment
  variables (gated on `hyperhive.gui.enable`) so every systemd service
  in the container inherits them. Without this, services starting
  Wayland clients could not find the compositor — libwayland falls
  back to a headless display or errors out, the app "works" on a
  second invisible display, and the VNC session shows a blank weston
  desktop (#540 double-screen).
- **VNC bind address**: weston's VNC backend has no CLI
  bind-address flag (unlike the RDP backend's `--address`), so the
  listener binds `0.0.0.0`. The harness relay only connects via
  `127.0.0.1`; the host firewall blocks the per-agent VNC port range
  from external access. A future weston.ini `[vnc] address=` will
  let us restrict the bind directly once upstream supports it.
- **PAM service name**: literal `weston-remote-access` — that's the
  string libweston passes to `pam_start()` in `libweston/auth.c`.
  Using `weston` falls back to the system default PAM stack and
  rejects auth. The service is configured to `pam_permit.so` for
  all three module types (auth / account / session) so the
  browser's empty Apple-DH credentials (type 30) always pass —
  neatvnc ≥ 0.9 calls the PAM auth callback regardless of
  `weston.ini` `auth-method=none`, so the permit fallback is what
  actually lets the empty-cred client through.
- **`Type = "simple"` (not `notify`)**: `switch-to-configuration`
  must never block on weston signalling readiness. A misconfigured
  weston degrades to a `Restart=on-failure` loop visible in
  `journalctl`, it does not abort the `nixos-container update`.
  Same reasoning as the `tea-login` unit in `harness-base.nix`.
- **`[core] idle-time=0`**: disables weston's 300-second idle
  timeout. Without it the VNC desktop fades to black and
  desktop-shell shows its click-to-unlock screen — useless for an
  agent desktop viewed over `/screen`. `idle-time=0` updates the
  idle timer with a 0ms delay, which
  `wl_event_source_timer_update` treats as "disarm", so the
  compositor never goes idle and never locks.

## Nix options reference (`nix/docs/default.nix`)

`pkgs.nixosOptionsDoc` over two evaluated module trees:
`hostEval` (a stub NixOS system loading `hive-c0re.nix` with every
hyperhive subsystem `mkForce false` so heavy build inputs stay out of
the eval) and `agentEval` (evaluates `agent-base.nix` fresh for the
per-agent options tree).

Three output trees consumed by `flake.nix`, all **markdown**:

- `docs-host` — operator-facing host module options
  (`services.hyperhive.*`)
- `docs-agent` — per-agent harness options (`hyperhive.*`
  declared in `nix/templates/harness-base.nix`)
- `docs` — bundle of `index.md` + `host.md` + `agent.md`

Pipeline:

- CommonMark from `nixosOptionsDoc.optionsCommonMark` is the only
  output — the source of truth, emitted as `.md`.
- **HTML + CSS is rendered downstream by the website repo**
  (`nix/options.nix` there), which consumes this bundle's `host.md` /
  `agent.md`, renders them with `cmark-gfm`, and shares one
  stylesheet (`docs.css`) across `/options/` and the prose `/docs/`
  tree. Keeping rendering in the website means the theme has a single
  home and the colours are shared.
- `transformOptions` strips the nix-store prefix from option
  declaration paths and rewrites them as forge URLs, so the
  rendered docs link back to the source.

Host options live entirely under `services.hyperhive.*`. The
`pickSubtrees` filter is rooted at `["services" "hyperhive"]` so the
options tree picks up everything under that root — picking against
stray roots produces an empty tree and renders the host page as
template chrome with no `<h2>` headers.

### Docs drv stability: `nixSrc` + stub overlay

Naively, the docs evaluation depends on `self` (the flake's store path),
so every commit — even Rust-only or frontend-only changes — produces new
docs drv hashes. The remote builder must rebuild docs from scratch for
every PR branch, and if its store is full the build fails with a cached
failure that blocks CI for the whole branch.

The fix (`nix/docs/default.nix`):

1. **`nixSrc`** — `builtins.path` on the `nix/` directory, wrapped in
   `builtins.unsafeDiscardStringContext` to strip `self`'s store-path
   context. The resulting store path is content-addressed from the nix/
   file contents only. Docs drvs only change when a `.nix` file changes.

2. **`docsStubOverlay`** — replaces `self.overlays.default` with stub
   packages (`pkgs.emptyFile` / `pkgs.emptyDirectory`) for the docs eval.
   `nixosOptionsDoc` renders `defaultText` for all package options anyway;
   the stubs prevent attribute-missing eval errors without pulling in the
   Rust or frontend build closure.

3. Both `hostEval` and `agentEval` are evaluated from `nixSrc` paths
   (not `self`), so the docs drv dependency chain ends at `nixSrc`.

Why `builtins.unsafeDiscardStringContext`? The path string
`toString self + "/nix"` carries `self`'s string context, which would
make `builtins.path` include `self` as a build dependency even after
content-addressing the directory. Discarding the context makes the
resulting `nixSrc` truly independent of `self`'s store path.

### `nix fmt` fails in a git worktree with "object not found"

`nix fmt` (and any `nix` command that fetches a `git+file://` flake
URL) uses libgit2 internally to compute `revCount` — the number of
commits reachable from HEAD. This walk fails with:

```
error: getting Git object '<hash>': object not found (libgit2 error code = 9)
```

when a commit that was reachable at some earlier evaluation is now gone
(GC'd, rebased away, or pruned). The failure is persistent: clearing
`~/.cache/nix/{eval-cache-v6,gitv3,fetcher-cache-v4.sqlite}` does not
help because the missing object is a structural gap in the git object
graph itself, not in nix's caches.

**Workaround: use a plain clone, not a git worktree.**

```bash
git clone http://<forge>/hyperhive/hyperhive.git ~/hh-work
cd ~/hh-work && nix fmt
```

The root cause is specific to worktrees: a worktree shares the object
store with its parent repo. If the parent repo's history was rewritten
(rebase, force-push, `git gc --prune`) while the worktree was checked
out at a branch tip that references the pruned commits via its reflog or
history, libgit2's rev-walk encounters the gap. A plain clone has its
own self-consistent object store and is immune to the issue.