docs: link the secrets page from setup, fix a dropped word

Per mara: setup should point at it. The link is placed as a precondition
rather than a see-also -- every step below assumes each credential is
generated where it is read, which is only true all-local.

Per argus: 'with a bound' was missing a word; it now names the actual
120s wait instead of gesturing at one.

docs/setup.md

@@ -10,6 +10,12 @@ sequence. All `hivectl` commands below run as **root on the host** (not
 inside an agent container); the `request_*` steps run from ruth's own
 turn via the MCP tools.
 
+**Bringing up a hive that does not host its own swarm services?** Read
+[`swarm/secrets.md`](swarm/secrets.md) first. Everything below assumes
+each credential is generated where it is read, which is true on an
+all-local deploy and not otherwise — that page says which files an
+operator has to place, and where.
+
 ## Step-by-step
 
 ### 1 · Forge

docs/swarm/README.md

@@ -94,6 +94,12 @@ Which secrets the SSO provider generates, which one has a reader in
 another container, and the three ways that one gets delivered:
 [`sso.md`](sso.md).
 
+## Secrets
+
+Every credential the swarm holds, who mints it, where it must live, and
+which of the three topologies makes it the operator's job to place:
+[`secrets.md`](secrets.md).
+
 ## Swarm UI
 
 The operator-only web surface on the swarm apex, why reaching it needs

docs/swarm/secrets.md

@@ -0,0 +1,90 @@
+# Swarm secrets: what exists, and where each one lives
+
+A swarm's credentials are generated in three different places and read in a
+fourth, so "where does this file go" has a different answer per deployment.
+This page is that answer, one row per secret.
+
+Two rules run through all of it.
+
+**A secret is a path, never a value.** Every option that carries a credential
+takes a file path (`*File`), because a literal written into a nix expression is
+rendered into the nix store — which is world-readable and permanent. There is no
+option anywhere in this tree that accepts a secret inline, and adding one would
+be a leak rather than a convenience.
+
+**The generator and the reader are usually in different containers.** They share
+the host's network namespace, which makes them feel co-located, but their
+filesystem roots are separate. That is why delivery is a **host-side copy rather
+than a bind mount**: `nixos-container` refuses to start when a bind source is
+missing, and a secret minted on another container's first boot does not exist
+yet. Binding it would make one container wait on a file that waits on a
+container that starts after it.
+
+## The three topologies
+
+Every row below is read against one of these.
+
+| topology | what it means | who places secrets |
+|---|---|---|
+| **all-local** | one host runs the swarm's shared services and its own hive | nobody — each secret is generated where it is read, or copied by a host unit |
+| **swarm-managed** | the swarm's services run on a host with `swarmctl` | `swarmctl` writes what it owns; the rest is still generated in place |
+| **hive elsewhere** | a hive that federates with a swarm it does not host | the operator provides the file and names it in config |
+
+## Swarm-level — one of each per swarm
+
+| secret | generated by | lives at | hive elsewhere |
+|---|---|---|---|
+| swarm root CA cert | `swarm-ca.nix` first-boot unit, when `autoConfigure` is set | `/var/lib/swarm-ca/root.pem` | operator copies the **cert** in; it is public |
+| swarm root CA key | same unit | `/var/lib/swarm-ca/root-key.pem`, `0600` | stays on whichever host holds it — see the constraint below |
+| swarm-services sub-CA (cert + key) | `swarm-ca.nix`, signed by the root | `/var/lib/swarm-ca/services-ca{,-key}.pem` | issued where the root lives |
+| authelia session, JWT and storage-encryption keys | authelia's first-boot unit, in-container | `/var/lib/authelia-swarm/{session,jwt,storage-encryption}.key` | generated in place; nothing outside that container reads them |
+| authelia OIDC HMAC key | same unit | `/var/lib/authelia-swarm/oidc-hmac.key` | same |
+| authelia OIDC issuer key (RSA) | same unit | `/var/lib/authelia-swarm/oidc-issuer.key` | same — relying parties verify against the **public** half at `/jwks.json` |
+| OIDC client secret, plaintext half | `authelia crypto hash generate --random` | `/var/lib/authelia-swarm/oidc-clients/<id>.secret` | operator provides the file and names it in the service's `sso.clientSecretFile` |
+| OIDC client secret, digest half | the same mint | `oidc-clients/<id>.digest` | authelia's own half; merged at runtime via `settingsFiles` |
+| authelia subject store | `swarmctl` | `users.json` (canonical) → `users.yml` (rendered) | `swarmctl`, on the host that runs authelia |
+| wireguard private key | **the operator** — `wg genkey` | whatever `swarm.wireguard.privateKeyFile` names | always operator-provided; nothing generates this for you |
+
+The three keys authelia mints for itself are generated in-container precisely
+because nothing outside that container ever reads them. **That is the test worth
+applying to any secret added here** — and the client secret's plaintext half is
+the one row that fails it, which is the entire reason a delivery step exists.
+
+## Hive-level — one of each per hive
+
+| secret | generated by | lives at |
+|---|---|---|
+| hive CA cert + key | `hive-tls.nix` first-boot unit | `<tls.stateDir>/ca.pem`, `ca-key.pem` (`0600`) |
+| hive leaf certs | `hive-tls.nix`, signed by the hive CA | `<tls.stateDir>/<name>.pem` |
+| matrix registration token | a host activation script, on first boot | `/var/lib/hyperhive/matrix-register-token` (`0600`) |
+| the forge's copy of its OIDC secret | `hive-forge-oidc-secret.service` copies it from authelia's tree | `/var/lib/forgejo-oidc/<id>.secret` inside the forge container |
+| the homeserver's copy of its OIDC secret | `hive-matrix-oidc-secret.service`, same shape | `/var/lib/tuwunel-oidc/<id>.secret`, handed to tuwunel through `LoadCredential` |
+
+Both delivery units wait for authelia's first boot to mint the secret — a
+bounded wait, 120s — and then **fail loudly** rather than skipping. A silent skip
+produces a service whose login button always fails, which is a symptom several
+layers from its cause.
+
+## The constraint that decides where the root lives
+
+A hive CA carries `nameConstraints=permitted;DNS:<hive domain>`, and **a swarm
+service name is a sibling of the hive domain rather than a child** — `forge.<swarm>`
+next to `<hive>.<swarm>`. So a hive CA cannot issue a certificate for a swarm
+service. Not by policy: by construction, and openssl enforces it.
+
+Whatever holds the swarm root is therefore what makes swarm-service certificates
+possible at all. Two things follow:
+
+- **The root's private key is a runtime file and must never enter the nix
+  store**, so nothing build-time can name it — `security.pki.certificateFiles` is
+  read when the system is built, and is the wrong tool here. Trust reaches
+  containers through a bind-mounted bundle assembled at boot instead.
+- **On any topology other than all-local, placing that key is an operations
+  decision**, not something this module tree makes for you. A hive that hosts no
+  swarm services needs only the root's *cert*, to trust what others issue.
+
+## Adding a secret
+
+State three things, in the row you add above: **who mints it**, **which
+container reads it**, and **what happens when they differ**. If they differ, it
+needs a delivery unit, and the unit copies — it does not bind.

docs/swarm/sso.md

@@ -90,17 +90,16 @@ an attribute edit can invalidate a login by accident.
 
 ## What secrets exist, and where each one lives
 
-| secret | generated by | rests in | read by |
+Every secret in the swarm, with its generator and its path, is tabulated
-|---|---|---|---|
+in one place: [`secrets.md`](secrets.md). The rows relevant here are
-| `jwt.key`, `session.key`, `storage-encryption.key` | authelia's first-boot unit | `/var/lib/authelia-swarm/` | authelia |
+authelia's own keys (session, JWT, storage-encryption, OIDC HMAC, OIDC
-| `oidc-hmac.key` | same unit | same directory | authelia |
+issuer) plus the two halves of each client secret.
-| `oidc-issuer.key` (RSA) | same unit | same directory | authelia signs with it; clients verify the **public** half at `/jwks.json` |
-| `oidc-clients/<id>.digest` | same unit, via `authelia crypto hash generate` | same directory, merged in through `settingsFiles` | authelia |
-| `oidc-clients/<id>.secret` | the same mint — this is its plaintext half | same directory | **the relying party, in another container** |
 
-Everything above the last row is generated in-container because nothing
+What matters for this page is the shape rather than the paths. Authelia's
-outside that container ever reads it. That is the test worth applying to
+own keys are generated **in-container**, because nothing outside that
-any secret added here. The last row fails it, and that is the entire
+container ever reads them — that is the test worth applying to any secret
+added here. The plaintext half of a client secret is the one that fails
+it: its reader lives in a different container, and that is the entire
 reason a delivery step exists.
 
 **None of it is ever written into a nix expression.** authelia's