# Site secrets ride the artifact deploy — design

**Status:** design, 2026-09-28. Plan: `2026-09-28-site-secrets-artifact-deploy.md`.

## 1. Problem

A site resolves secrets at runtime (today: an MxGateway data connection's `ApiKey: "secret:<name>"`,
`DataConnectionLayer/Adapters/MxGatewayDataConnection.cs:101`). The only way a secret reaches a site
is the pull-only gRPC secrets hub (`Secrets:Replication:Mode=Grpc`), which:

- copies **every** central secret to **every** participating site node every 30 s — no per-site scope;
- is invisible to the deployment model: the Sites page *Artifacts current / out of date* badge
  (`Site.ArtifactRevisionHash`, 2026-09-14) knows nothing about secrets, so a site can read *Current*
  while its data connection cannot resolve its key;
- logs nothing on a successful in-sync sweep (library `GrpcSecretSyncService` logs only when rows were
  pulled or on failure) and exposes no status;
- is enabled only on the docker rig's site-a; vd03 and QA run with replication OFF, so each site node's
  `secrets.db` is filled by hand.

## 2. Decisions (user, 2026-09-28)

| # | Decision |
|---|---|
| U1 | A site receives **only the secrets it references** — never other sites' keys. |
| U2 | The artifact deploy **replaces** the gRPC hub as the way secrets reach sites (hub retired for ScadaBridge sites). |
| U3 | Logging = **deploy log lines** (central + site), **audit rows**, and **hub sweep logging** (for the transition until the hub is retired, and for other hub consumers). |
| U4 | Central deploys from **one shared SQL-Server secret store** used by both central nodes. |

## 3. Design

### 3.1 Which secrets a site needs — derived, not configured

`SecretReferenceScanner.Scan(IEnumerable<DataConnectionArtifact>)` walks each connection's
`PrimaryConfigurationJson` and `BackupConfigurationJson` and collects every JSON **string value**
of the form `secret:<name>` (prefix case-insensitive, `<name>` trimmed, must be a valid `SecretName`).
It is protocol-agnostic on purpose: a new adapter that adopts `secret:` references is covered with
no scanner change. Result: a distinct, ordinal-sorted name set per site, each name carrying the
data connections that reference it (for error messages and logs).

**Deliberately NOT included:** bootstrap secrets — the site's gRPC PSK (`SB-GRPC-PSK-{siteId}`), the
LocalDb replication key, the secrets master key. The site needs them *before* it can receive an
artifact deploy, and pushing a rotated PSK through the channel it authenticates would sever that
channel. They stay out-of-band (service environment / hand-seeded store), exactly as today on vd03/QA.
`${secret:X}` references inside a node's own `appsettings` are node-local and invisible to central —
also out of scope.

### 3.2 Central source of truth — the shared SQL store (U4)

New option `Secrets:Store:Provider` (`Sqlite` default | `SqlServer`), read **only on the Central
role**. `SqlServer` registers the library's `AddZbSecretsSqlServerStore` against
`Secrets:SqlServer:ConnectionString` (literal/env value — never `${secret:}`, same bootstrap rule as
today) so both central nodes read and write one store; the `/admin/secrets` page edits it. This is
the store the hub's Grpc-mode central already uses — decoupled from the hub. A clustered Central left
on `Sqlite` boots but `StartupValidator` logs a Warning (same shape as the inbound API key-store
warning, row 108), because the two nodes would deploy different secret sets depending on which is
active.

### 3.3 The wire: ciphertext rows, never plaintext

`DeployArtifactsCommand` gains an additive `Secrets` list of `SecretArtifact` — the library's
`StoredSecret` fields verbatim (name, content type, ciphertext/nonce/tag, wrapped DEK/nonce/tag,
`KekId`, `Revision`, created/updated UTC). Central never decrypts; the site applies the row with
`ISecretStore.ApplyReplicatedAsync` (last-writer-wins on `UpdatedUtc`/`Revision`, the same path the
hub sweep uses). **Every node must therefore share the KEK** (`ZB_SECRETS_MASTER_KEY` / master-key
file) — exactly the hub's existing requirement. A mismatch is detected at deploy time (§3.5), not at
the next reconnect. Proto: `DeployArtifactsCommandDto.secrets = 9` (`SecretArtifactListDto`, absent ⇒
null) and `ArtifactDeploymentResponseDto` gains `secrets_applied` (wrapper `Int32Value`, absent ⇒ null).

**Fail-closed on a missing secret.** If a referenced name is absent or tombstoned in the central
store, that site's deploy fails before anything is sent: `Secret 'X' referenced by data connection(s)
A, B is not in the central secret store`. Shipping the rest would stamp the site *Current* while a
connection cannot resolve its key.

### 3.4 Staleness — secrets are part of the artifact hash

`ArtifactRevisionHashService` adds `Secrets` → `HashableSecret { ContentDigest, KekId, Missing,
Name, Revision }` (alphabetical — the existing ordering test covers it). `ContentDigest` = SHA-256 of
ciphertext‖nonce‖tag‖wrappedDek, so a KEK rewrap (new wrapped DEK, same revision) correctly marks
sites out of date. `ComputeCurrentArtifactHashesAsync` hashes missing names with `Missing = true`, so
a site referencing a not-yet-created secret reads *Out of date*, never *Current*. The list is
null-when-empty and the serializer omits nulls, so **sites with no secret references keep their
current hash** — only sites that reference secrets flip to *Out of date* once after rollout.

### 3.5 Site apply — both nodes, via a replicated table

The artifact apply runs on the active node's `DeploymentManagerActor` singleton, but `secrets.db` is
a per-node file outside LocalDb. So:

1. **`deployed_secrets`** — a new LocalDb table in `SiteStorageSchema` (`name` PK, `row_json` = the
   `SecretArtifact` ciphertext row as JSON, `revision`, `updated_utc`, `is_removed` 0/1,
   `deployment_id`, `applied_at`), added to `SiteLocalDbSetup.ReplicatedTables` (becomes the 11th;
   LocalDb 0.3.x snapshots just that table on an already-replicating pair). No FKs (row 105 guard).
   Ciphertext only — the no-plaintext rule that kept `smtp_configurations` unregistered holds.
   `HandleDeployArtifacts` applies it full-set: upsert every shipped row, mark rows absent from the
   set `is_removed = 1` (kept, so the standby learns about the removal).
2. **`DeployedSecretsMirror`** — a per-node service (every site node, not a singleton) that reconciles
   `deployed_secrets` into the node's own `ISecretStore`: `ApplyReplicatedAsync` for live rows,
   `DeleteAsync` for removed rows **only if the name was previously mirrored** (a local, unreplicated
   `mirrored_secrets` table records names this mirror wrote — an out-of-band secret of the same name
   that was never deployed is never deleted). After applying, it **trial-resolves** each deployed
   secret through `ISecretResolver`; a decrypt failure (KEK mismatch) is an error naming the secret
   and the row's `KekId`. It runs at startup, every `SiteRuntime:DeployedSecretsMirrorInterval`
   (default 15 s — the standby's convergence path), and on demand.
3. The active node's apply calls the mirror **synchronously** after writing the table and fails the
   deploy response if any secret did not apply or verify; on success the response carries
   `SecretsApplied = n`. The standby converges through LocalDb replication + its own mirror within one
   interval.

### 3.6 Mixed versions

A pre-feature site ignores proto field 9 and answers `Success` with `secrets_applied` absent. Central
treats *command carried ≥ 1 secret AND `SecretsApplied` is null* as a **failure** for that site
(`site build predates secret deployment — upgrade the site`) and does not stamp the hash. A command
with no secrets is unaffected, so an old site with no secret references deploys exactly as before.
Upgrade central first, as always.

### 3.7 Logging and audit (U3)

- **Central, per site:** Information `Deploying {Count} secret(s) to site {SiteId}: {Name}@r{Revision},…`;
  Error on a missing secret (names + referencing connections). Never values or ciphertext.
- **Site, active apply and every mirror pass that changes something:** Information per secret
  `Applied deployed secret {Name} r{Revision} (kek {KekId})` / `Removed deployed secret {Name}`;
  Error on apply/verify failure; one Information summary per pass. An in-sync mirror pass logs at
  Debug only.
- **Audit:** one `IAuditService` row per site deploy that carried secrets — action `DeploySiteSecrets`,
  entity type `SiteSecrets`, entity id = site identifier, after-state `{ deploymentId, secrets:
  [{name, revision}], removed: [name], success }`. Same config-change audit as the existing
  `DeployArtifacts` row.
- **Hub sweep (library `ZB.MOM.WW.Secrets` 0.6.3, scadaproj):** every sweep outcome is observable —
  in-sync sweeps at Debug plus an Information heartbeat at most once per `InSyncLogInterval`
  (default 1 h), a `Recovered after {Failures} failed sweep(s)` Information line, and a public
  `ISecretsHubSyncStatus` (`LastSweepUtc`, `LastSuccessUtc`, `ConsecutiveFailures`, `LastError`).
  Useful for the rig until the hub is retired and for any other hub consumer.

### 3.8 Hub retirement (U2)

Once the artifact path is live on the rig, ScadaBridge stops composing the hub: the Site role no
longer registers `AddZbSecretsGrpcHubClient`, the Central role no longer maps the hub endpoint, and
`StartupValidator` refuses `Secrets:Replication:Enabled=true` with `Mode=Grpc` with a message pointing
at the artifact deploy. The library keeps the hub (other consumers); only ScadaBridge stops using it.
The rig's site-a moves from the hub to the artifact path; central keeps the shared SQL store through
`Secrets:Store:Provider=SqlServer`.

## 4. Rollout (deployment records, not code)

vd03 and QA need, per environment: the `zbsecrets` store in the configuration SQL Server + both
centrals on `Secrets:Store:Provider=SqlServer`; **one KEK across every central and site node**
(verify before enabling — the mirror's verify step reports a mismatch by name); existing hand-seeded
site secrets recreated at central; then *Deploy Artifacts*. Tracked as a deferred-work register row.

## 5. Out of scope

Per-site explicit secret lists; secrets for external systems / database connections (they ship
literal values today); plaintext transport; moving bootstrap secrets through the deploy.

## 6. Implementation notes (as built)

Execution (tasks 1–11, ledger `.superpowers/sdd/2026-09-28-site-secrets-artifact-deploy/progress.md`)
matched this design in shape but landed several deviations, called out here so the doc stays
accurate as the spec:

- **Central collection.** The scanner and per-site resolve described in §3.1/§3.3 are implemented
  as `SiteSecretsCollector` (`ZB.MOM.WW.ScadaBridge.DeploymentManager`), not inline in
  `ArtifactDeploymentService`. Fail-closed (§3.3) is per site, not per batch: a site with an
  unresolved reference is skipped (`_communicationService` is never called for it) while every
  other site in the same sweep proceeds normally.
- **Audit (§3.7).** The `DeploySiteSecrets` / `SiteSecrets` audit row is written on **both**
  `DeployCoreAsync` (the sweep) and `RetryForSiteAsync` (the per-site retry), including the
  fail-closed path on each — the design's §3.7 wording ("one row per site deploy that carried
  secrets") did not call out the retry path explicitly; it is in scope and covered.
- **Stamp gating (§3.6).** Implemented as designed, plus one addition: a **partial apply**
  (`SecretsApplied` less than the shipped count, not just the mixed-version `null` case) is also
  treated as a failure and is not stamped, with its own message (`Site applied {n} of {m}
  secrets`) distinct from the "predates secret deployment" wording.
- **Hash (§3.4).** Implemented as designed. Confirmed explicitly (not just implied by
  "null-when-empty"): an **empty** `Secrets`/`MissingSecrets` list and a **null** one hash
  identically, and the pre-existing golden hash for a site with no secret references is
  unchanged by this feature (pinned by a dedicated regression test).
- **Site apply (§3.5).** `HandleDeployArtifacts` writes the full `deployed_secrets` set and then
  runs `DeployedSecretsMirror.ReconcileAsync` **synchronously** before replying, exactly as
  designed. `SecretsApplied` counts only the names *this deploy shipped* that applied and
  verified without error — a mirror failure for a name this deploy did not ship (e.g. another,
  already-broken deployed secret, or an unrelated removal) is logged at Warning, excluded from
  the count, and does not fail the deploy. Removal failures are likewise Warnings, never deploy
  failures.
- **`DeployedSecretsMirror` — apply is confirm-then-ledger, not the blind `ApplyReplicatedAsync`
  §3.5 originally described.** The real library store is strict last-writer-wins on
  `(UpdatedUtc, Revision)` (a tie is a no-op) and tombstones rather than hard-deletes, which the
  naive "apply then ledger" sequence gets wrong in two ways: a routine remove-then-re-add can
  no-op against a still-live tombstone while the ledger is written anyway (silently broken), and
  an out-of-band local secret with a genuinely newer stamp can be ledgered and later deleted by a
  central tombstone (destroying the operator's own secret). The mirror now always reads the row
  back after applying and only ledgers when the local ciphertext matches what was shipped; a
  tombstoned or ledger-owned row is safely re-stamped (`UpdatedUtc`/`Revision` bumped past the
  local value, including across clock skew) and re-applied, while a live row with different
  ciphertext that the ledger does **not** already own is left completely untouched and reported
  as a distinct out-of-band-conflict failure. Ownership is decided from `mirrored_secrets`
  membership at any revision, not from tombstone state alone — so a mirror-owned name that drifts
  locally (an operator's edit over an already-deployed name) is re-stamped back to the deployed
  value on the next pass: **central is authoritative for every name it deploys.** Every apply/
  delete also invalidates the shared `ISecretResolver` cache before the verify step, and one
  poisoned row never blocks the rest of the pass.
- **Hub retirement (§3.8) — scope widened to ALL secrets replication, not just the gRPC hub.**
  ScadaBridge also retires the historical SQL-Server *replication* mode
  (`Secrets:Replication:Mode=SqlServer`, distinct from the still-supported
  `Secrets:Store:Provider=SqlServer` shared-store feature) for the same reason the gRPC hub goes:
  a site's `ISecretStore` must be the plain, undecorated local SQLite store, because
  `DeployedSecretsMirror` calls `DeleteAsync` directly and a replication decorator would publish
  that delete fleet-wide. `Secrets:Replication:Enabled` set to anything other than
  absent/empty/`false` (a deliberately strict, non-boolean-coerced check — `"0"`/`"1"`/`"yes"`
  all count as "set") now fails `StartupValidator.Validate` on **either** role. A leftover
  `Secrets:Replication:Mode` or any `Secrets:GrpcHub:*` key logs a startup Warning naming both
  sections. The pre-host `${secret:}` expander was fixed in the same task set to read the shared
  SQL store on a `Store:Provider=SqlServer` central (it previously only did this for the retired
  Grpc mode) — without that fix a central's boot-time `${secret:}` tokens and its running
  `ISecretResolver` could resolve a token differently.
- **`ZB.MOM.WW.Secrets` 0.6.3 (hub sweep logging, §3.7's third bullet — `EventId`s 4/5/6,
  `ISecretsHubSyncStatus`) is published to the Gitea feed (2026-09-28, after merge), but
  ScadaBridge does not consume it** — hub retirement (above) removes ScadaBridge's only dependency
  on the hub client, so it stays on 0.6.2. It is there for the library's other hub consumers
  (OtOpcUa).
- **Empty, not null, when a site references no secrets (Task 13 live-gate fix).** The command
  builder first shipped `Secrets = null` for a site with no references ("null-when-empty", borrowed
  from the hash convention). But the site treats `null` as "central shipped no secrets" and touches
  nothing, so dropping a site's LAST `secret:` reference never soft-removed the row and the secret
  stayed live on both nodes. Central now always ships a list (empty when there are no references);
  the hash is unchanged because an empty and a null list hash identically.
- **Final-review fixes.**
  - *Same-revision drift is healed.* A name already ledgered at the shipped revision is still read
    back every pass; a missing, tombstoned or edited local row is re-stamped back to the shipped
    ciphertext before verify (previously a local delete was misreported as a KEK mismatch and
    blocked the site's deploys).
  - *Unreadable `row_json`* is a per-name failure, not a pass-wide exception.
  - *Site ordering:* secrets are written and mirrored before the deploy's data connections are
    pushed to the DCL; a rotation with unchanged connection config takes effect on the connection's
    next (re)connect (no forced reconnect).
  - *One `secret:` parser* (`SecretReferenceScanner.TryParseSecretReference`) shared by the scanner
    and `MxGatewayDataConnection`, so a padded/case-variant reference resolves the shipped name.
  - *Audit shape (§3.7).* The `DeploySiteSecrets` row carries `secrets`, `missing` and `removed`.
    (Shipped first without `removed`, so a removal-only deploy wrote no central row; closed by the
    follow-ups below.)
  - *Deployment prerequisite:* a site pair using deployed secrets must run LocalDb replication
    (topology guide), since on an unreplicated pair only the node active at deploy time gets them.
- **Follow-ups closed after merge (2026-09-28).**
  - *Secret-store outage is per site (review M5).* `SiteSecretsCollector` returns a store read
    failure as `SiteSecretsCollection.StoreError` instead of throwing. A deploy fails only the
    sites that reference a secret (nothing is sent to them; they get a `DeploySiteSecrets` row
    with the error), and `ComputeCurrentArtifactHashesAsync` leaves those sites out of its map,
    which the pending-updates evaluator reads as *Out of date*. Sites with no secret references
    never touch the store and are unaffected. Before this, one `GetAsync` exception aborted the
    whole sweep and the fleet-wide pending-updates check.
  - *Removal-only deploys are audited.* The site's reply gained `SecretsRemoved` (proto
    `ArtifactDeploymentResponseDto.secrets_removed = 7`, names only; absent/empty reads as null):
    the `deployed_secrets` rows that deploy soft-removed. Central carries it on
    `SiteArtifactResult.SecretsRemoved` and writes the `DeploySiteSecrets` row whenever it is
    non-empty, with a `removed` list. An old site never sends it, so its removals stay unaudited
    centrally, as before.
  - *CLI exit code.* `site deploy-artifacts` and `deploy artifacts` exit `1` when the summary's
    `failureCount` is non-zero (same rule `deploy site` already had).
  - *Hub-era site-a secrets (review M8).* The retired hub had copied six `hub-gate-*`/`shared-gate-*`
    test secrets (2026-08-07) into both rig site-a nodes' local stores. The mirror deliberately
    never deletes a name it did not ledger, so they were removed once by hand on the rig (both
    nodes stopped together; see the live-gate doc). QA and vd03 never ran the hub
    (`Secrets:Replication:Enabled=false`), so nothing like this exists there.
- **Standby mirror failures reach central (follow-up, review finding M1).** A `DeployedSecretsMirror`
  failure on the standby (e.g. a KEK mismatch) was only logged on that node — site health reports
  are sent by the active node only. Each node now records its current failure set (names +
  messages, never values) in a new, **12th LocalDb-replicated table `secret_mirror_status`** (one
  row per node keyed by `node_name`), written only when the set changes plus once per start-up; a
  per-node `SecretMirrorStatusReporter` puts every node's row on the active node's report as
  `SiteHealthReport.SecretMirrorStatuses` (proto `SiteHealthReportDto` field 33, presence-wrapped),
  and the Central UI health card shows a *Secret mirror failing* badge + per-node list. Requires
  LocalDb replication for the standby's row to be visible, the same prerequisite as the secrets.
  **Stale rows (2026-09-29):** each node also re-writes its row every
  `SiteRuntime:SecretMirrorStatusRefreshInterval` (10 min) as a heartbeat, and the reporter drops
  and deletes rows not refreshed for `SiteRuntime:SecretMirrorStatusStaleAfter` (1 h), so a
  decommissioned or renamed node no longer leaves its row on the Health page.
- **Rig posture.** `docker/docker-compose.yml`'s central nodes now carry
  `Secrets__Store__Provider=SqlServer` plus a shared KEK; site-a shares that KEK (it is the
  secrets-via-artifact-deploy site); site-b/site-c deliberately carry a **mismatched** KEK so the
  `DeployedSecretsMirror` verify-failure path has a real, provable negative on the rig rather than
  an assumed one.