diff --git a/bootstrap/components/credentials.ts b/bootstrap/components/credentials.ts
index e74b3f6..8cd1d9d 100644
--- a/bootstrap/components/credentials.ts
+++ b/bootstrap/components/credentials.ts
@@ -15,6 +15,7 @@
 import * as pulumi from "@pulumi/pulumi";
 import * as command from "@pulumi/command";
 import { RandomPassword } from "@pulumi/random";
+import { BackupSecrets } from "../config";
 import { DeployCtx } from "../lib/context";
 import { vmConnection } from "../lib/remote";
 import { VaultOutputs } from "./vault";
@@ -167,3 +168,65 @@ ${creds.forgejo.adminPassword}
     { dependsOn: [vault.init] },
   );
 }
+
+// Mirrors the config-seeded backup credentials (offsite S3 creds + the age key)
+// into Vault at foundation/backup/backup-credentials (CONTRACT_002 §2.3). Unlike
+// the generated data-plane creds these are seeded once into passphrase-encrypted
+// config (the age IDENTITY MUST also live there so {repo + passphrase} can decrypt
+// a bundle after total Vault loss — CONTRACT_004 §4.3); this writer makes them
+// available to in-Vault consumers (Layer-1 ESO, the backup-verify job). Secret
+// values on stdin (ADR-007 D2); non-secrets (endpoint, recipient) as shell vars.
+const WRITE_BACKUP_CREDS = `set -eu
+IFS= read -r ROOT_TOKEN
+IFS= read -r OFF_AK
+IFS= read -r OFF_SK
+IFS= read -r AGE_IDENTITY
+C=foundation-vault
+VE="-e VAULT_ADDR=http://127.0.0.1:8200 -e VAULT_TOKEN=$ROOT_TOKEN"
+
+if ! docker exec $VE "$C" vault secrets list -format=json 2>/dev/null | jq -e 'has("foundation/")' >/dev/null; then
+  docker exec $VE "$C" vault secrets enable -path=foundation kv-v2 >/dev/null
+fi
+
+jq -n --arg ep "$OFF_EP" --arg ak "$OFF_AK" --arg sk "$OFF_SK" --arg ar "$AGE_RECIPIENT" --arg ai "$AGE_IDENTITY" \
+  '{offsiteEndpoint:$ep,offsiteAccessKey:$ak,offsiteSecretKey:$sk,backupAgeRecipient:$ar,backupAgeIdentity:$ai}' \
+  | docker exec -i $VE "$C" vault kv put foundation/backup/backup-credentials - >/dev/null
+
+echo "vault: wrote backup/backup-credentials (offsite + age key)"`;
+
+/**
+ * Mirror the backup credentials (incl. the age key) into Vault (CONTRACT_002 §2.3).
+ * Depends on Vault being unsealed (GATE A) via vault.init — same pattern as the
+ * data-plane creds writer above.
+ */
+export function writeBackupCredentialsToVault(
+  ctx: DeployCtx,
+  vault: VaultOutputs,
+  backup: BackupSecrets,
+): command.remote.Command {
+  const create = pulumi.interpolate`OFF_EP='${backup.offsiteEndpoint}'
+AGE_RECIPIENT='${backup.ageRecipient}'
+${WRITE_BACKUP_CREDS}`;
+
+  return new command.remote.Command(
+    "foundation-backup-credentials",
+    {
+      connection: vmConnection(ctx),
+      create,
+      update: create,
+      stdin: pulumi.interpolate`${vault.rootToken}
+${backup.offsiteAccessKey}
+${backup.offsiteSecretKey}
+${backup.ageIdentity}
+`,
+      addPreviousOutputInEnv: false,
+      triggers: [
+        vault.init.id,
+        backup.offsiteAccessKey,
+        backup.offsiteSecretKey,
+        backup.ageIdentity,
+      ],
+    },
+    { dependsOn: [vault.init] },
+  );
+}
diff --git a/bootstrap/config.ts b/bootstrap/config.ts
index 762c19d..d737a00 100644
--- a/bootstrap/config.ts
+++ b/bootstrap/config.ts
@@ -88,6 +88,33 @@ export interface FoundationConfig {
   };
 }
 
+/**
+ * The backup secret slice (CONTRACT_001 §1.3 + CONTRACT_002 `foundation/backup/
+ * backup-credentials`). Kept OUT of the non-secret FoundationConfig surface: these
+ * are `secure:`-encrypted (offsite creds, age identity) or a public key that only
+ * the Vault mirror + backup scripts consume. `loadBackupSecrets()` is the single
+ * reader (composition point), so components still never touch raw pulumi.Config.
+ */
+export interface BackupSecrets {
+  offsiteEndpoint: string; // non-secret (also in FoundationConfig.backup)
+  offsiteAccessKey: pulumi.Output<string>;
+  offsiteSecretKey: pulumi.Output<string>;
+  ageRecipient: string; // age1… public key (non-secret)
+  ageIdentity: pulumi.Output<string>; // AGE-SECRET-KEY-… (secret; survives Vault loss via config)
+}
+
+/** Reads the backup secret slice for the Vault mirror (CONTRACT_002 §2.3). */
+export function loadBackupSecrets(): BackupSecrets {
+  const c = new pulumi.Config("foundation");
+  return {
+    offsiteEndpoint: c.require("backup.offsiteEndpoint"),
+    offsiteAccessKey: c.requireSecret("backup.offsiteAccessKey"),
+    offsiteSecretKey: c.requireSecret("backup.offsiteSecretKey"),
+    ageRecipient: c.require("backup.ageRecipient"),
+    ageIdentity: c.requireSecret("backup.ageIdentity"),
+  };
+}
+
 /**
  * The SSH private key path is supplied by ENV (CONTRACT_001 §1: `SSH_PRIVATE_KEY_PATH`,
  * default ~/.ssh/id_rsa) — NEVER by Pulumi config. Exposed separately from
diff --git a/bootstrap/index.ts b/bootstrap/index.ts
index 1c1ed20..6d925fb 100644
--- a/bootstrap/index.ts
+++ b/bootstrap/index.ts
@@ -6,13 +6,14 @@
 // fill the marked slots — this file is the single composition point; components stay
 // pure factories in components/*.
 import * as pulumi from "@pulumi/pulumi";
-import { loadConfig } from "./config";
+import { loadConfig, loadBackupSecrets } from "./config";
 import { buildBaseContext, DeployCtx } from "./lib/context";
 import { deployNetwork } from "./components/network";
 import { deployDns } from "./components/dns";
 import {
   generateCredentials,
   writeCredentialsToVault,
+  writeBackupCredentialsToVault,
 } from "./components/credentials";
 import { deployPostgres } from "./components/postgres";
 import { deployRustfs } from "./components/rustfs";
@@ -47,6 +48,8 @@ const vault = deployVault(ctx);
 // --- GATE A: Vault init + unseal (T05). T06 writes the generated data-plane creds
 //     into Vault (CONTRACT_002), dependsOn vault.init so it runs only once unsealed.
 const vaultCreds = writeCredentialsToVault(ctx, credentials, vault);
+// Mirror the config-seeded backup creds + age key into Vault (CONTRACT_002 §2.3).
+const backupCreds = writeBackupCredentialsToVault(ctx, vault, loadBackupSecrets());
 // =============================================================================
 // PHASE 6 — FORGE  (depends on: credentials, GATE A)
 //   T07 caddy ✓ · T08 forgejo · T10 runner
@@ -77,6 +80,7 @@ const runner = cfg.features.runner ? deployRunner(ctx, forgejo) : undefined;
 // Stack outputs (extended as phases land).
 // vaultCreds (T06) is a gate for Forgejo (T08) — it has no output to export yet.
 void vaultCreds;
+void backupCreds; // CONTRACT_002 backup/backup-credentials mirror; no secret output
 
 export const phase = "T10-runner"; // forge + CI runner live
 export const caddyImageId = proxy.imageId;