diff --git a/.claude/scheduled_tasks.lock b/.claude/scheduled_tasks.lock
new file mode 100644
index 0000000..5483ed6
--- /dev/null
+++ b/.claude/scheduled_tasks.lock
@@ -0,0 +1 @@
+{"sessionId":"de029a55-31d3-41c9-b62a-0fa17789202c","pid":31042,"procStart":"9453895","acquiredAt":1779827176270}
\ No newline at end of file
diff --git a/.sops.yaml b/.sops.yaml
new file mode 100644
index 0000000..e7ba0d8
--- /dev/null
+++ b/.sops.yaml
@@ -0,0 +1,14 @@
+# sops creation rules. Recipients:
+#   host   — cc-ci's age key, derived from its ed25519 SSH host key (ssh-to-age).
+#            Used at activation to decrypt into /run/secrets (sops-nix, age.sshKeyPaths).
+#   master — off-box recovery/admin key; private half lives ONLY on the build host at
+#            /srv/cc-ci/.sops/master-age.txt (never in this repo). Lets us re-key if cc-ci is lost.
+keys:
+  - &host   age1h90utdztfc23kx8ewrtrtk80mnddvrf8pg4ppej55rwwwupzhfvqhmp3qa
+  - &master age1cmk26t9e30ls8594s8txgmf2exenydmntfxqpcd3qdqm3ru2lpnqpdkdz9
+creation_rules:
+  - path_regex: secrets/.*\.(yaml|json|env)$
+    key_groups:
+      - age:
+          - *host
+          - *master
diff --git a/BACKLOG.md b/BACKLOG.md
index 4ea21fc..a2fac85 100644
--- a/BACKLOG.md
+++ b/BACKLOG.md
@@ -8,9 +8,10 @@ Two single-writer sections (§6.1): Builder edits only `## Build backlog`; Adver
 ### M0 — Foundations
 - [x] Author flake.nix (NixOS host cc-ci) + hosts/cc-ci/{configuration,hardware}.nix from baseline
 - [x] Deploy mechanism decision + first rebuild from repo (DECISIONS.md) — switch --flake on host
-- [ ] sops-nix wiring: host age key, secrets/secrets.yaml, decrypt a test secret on host
-- [ ] Gate: M0 — `ssh cc-ci 'systemctl is-system-running'` healthy after rebuild from repo (base
-      rebuild verified healthy 2026-05-26; will CLAIM gate once sops test-secret also lands)
+- [x] sops-nix wiring: host age key (from ssh host key) + master recovery key; secrets/secrets.yaml;
+      decrypt a test secret on host → /run/secrets/test_secret (0400 root) verified
+- [x] Gate: M0 — `ssh cc-ci 'systemctl is-system-running'` healthy after rebuild from repo
+      → CLAIMED 2026-05-26, awaiting Adversary (see STATUS.md)
 
 ### M1 — Swarm + abra target
 - [ ] Docker + single-node swarm via Nix
diff --git a/DECISIONS.md b/DECISIONS.md
index 4049f12..340c2dd 100644
--- a/DECISIONS.md
+++ b/DECISIONS.md
@@ -25,7 +25,12 @@ Architecture decisions and dead-ends. One line of rationale each. (§0, §8)
     is a true no-op-then-base. Bump deliberately, never drift.
 - **Webhook scope:** default per-repo via enroll script.
 - **Drone runner type:** default exec (must drive host abra).
-- **Secret tool:** default sops-nix.
+- **Secret tool — SETTLED (M0):** sops-nix. cc-ci decrypts at activation using its **ed25519 SSH
+  host key** as the age identity (`sops.age.sshKeyPaths`), so no extra key file to manage on the box.
+  Recipients in `/.sops.yaml`: the host age key (`age1h90ut…`, from ssh-to-age) + an off-box
+  **master recovery key** (`age1cmk26t…`; private half only at `/srv/cc-ci/.sops/master-age.txt` on
+  the build host, never in the repo) for re-keying if cc-ci is lost. Encrypt new secrets by writing
+  plaintext into `secrets/<f>.yaml` then `sops -e -i` (run inside the repo so `.sops.yaml` is found).
 - **D10 recipe set:** lock six early. Candidates favouring already-mirrored: custom-html (simple),
   cryptpad (stateful no-DB), keycloak (SSO/DB), matrix-synapse (DB+media), lasuite-docs (multi+S3),
   bluesky-pds (TLS-passthrough) — covers all five categories. Confirm during M4–M6.5.
diff --git a/JOURNAL.md b/JOURNAL.md
index a9e715b..6babd15 100644
--- a/JOURNAL.md
+++ b/JOURNAL.md
@@ -58,3 +58,42 @@ baseline; networking is up. Clean up by choosing one stack later.
 
 **Next:** sops-nix wiring (host age key from ssh host key + a decrypt-a-test-secret proof), then
 CLAIM the M0 gate for the Adversary.
+
+## 2026-05-26 — M0: sops-nix wiring + decrypt-a-test-secret (M0 COMPLETE, gate CLAIMED)
+
+**Keys:**
+- Host age recipient from ssh host key: `ssh cc-ci 'nix run nixpkgs#ssh-to-age -- -i
+  /etc/ssh/ssh_host_ed25519_key.pub'` → `age1h90utdztfc23kx8ewrtrtk80mnddvrf8pg4ppej55rwwwupzhfvqhmp3qa`.
+- Master recovery key generated on host (`age-keygen`), public `age1cmk26t…`; private moved off-box
+  to `/srv/cc-ci/.sops/master-age.txt` (mode 600) and `shred`-ded from the host. Never in repo.
+
+**Files:** `.sops.yaml` (both recipients, rule `secrets/.*\.(yaml|json|env)$`); `modules/secrets.nix`
+(`sops.age.sshKeyPaths=[/etc/ssh/ssh_host_ed25519_key]`, `secrets.test_secret={}`); flake gains
+`sops-nix` input + `sops-nix.nixosModules.sops`; configuration.nix imports the module.
+
+**sops-nix version pin (dead-end avoided):** master sops-nix wants `buildGo125Module` (Go 1.25),
+absent in pinned nixpkgs 24.11 → eval error. Pinned sops-nix to `77c423a…` (2025-06-17, last using
+plain `buildGoModule`). Verified the file at that rev uses `buildGoModule`. Build then OK.
+
+**Encrypt test secret:** on host, `printf 'test_secret: cc-ci-m0-<rand>' > secrets/secrets.yaml`
+then `nix run nixpkgs#sops -- --encrypt --in-place secrets/secrets.yaml` (run inside repo so
+`.sops.yaml` resolves) → rc=0, two age recipients in the file.
+
+**Build + switch (commands + output):**
+- `nixos-rebuild build --flake .#cc-ci` → `BUILD EXIT 0` (built sops-install-secrets w/ Go 1.23.8).
+- `systemd-run --unit=ccci-rebuild2 ... nixos-rebuild switch --flake /root/cc-ci#cc-ci` →
+  `Result=success ExecMainStatus=0`.
+
+**Gate verification (M0):**
+- `systemctl is-system-running` → `running`; `systemctl --failed` → none.
+- `ls -la /run/secrets/test_secret` → `-r-------- 1 root root 41` ; `stat` → `root:root 400`.
+- `head -c9` → `cc-ci-m0-` (matches generated value), `wc -c` → 41 (9 + 32 hex). Decrypt path proven.
+- Pulled encrypted `secrets/secrets.yaml` + `flake.lock` back to clone; `grep cc-ci-m0 secrets.yaml`
+  → no plaintext leak; lock inputs = nixpkgs, sops-nix.
+
+**Gate handshake:** set `Gate: M0 — CLAIMED, awaiting Adversary` in STATUS.md. REVIEW.md still empty
+(no Adversary activity yet). Per §6.1 liveness I won't idle-block: I keep M0 claimed and proceed
+with M1 (independent infra build), without advancing to M2 until M0 shows PASS.
+
+**Next:** M1 — Docker + single-node swarm via Nix (modules/swarm.nix), then Traefik (file provider
+→ /var/lib/ci-certs/live/) + abra, then a by-hand HTTPS deploy/teardown of a trivial recipe.
diff --git a/STATUS.md b/STATUS.md
index f3a45a3..c5ac297 100644
--- a/STATUS.md
+++ b/STATUS.md
@@ -1,11 +1,15 @@
 # STATUS — cc-ci Builder
 
-**Phase:** M0 — Foundations
-**In-flight:** Base flake config deployed + verified. Next M0 task: sops-nix + decrypt a test secret.
-**Last updated:** 2026-05-26 (M0 base config live)
+**Phase:** M0 → M1. M0 complete & CLAIMED; starting M1 (swarm + Traefik + abra) while awaiting verdict.
+**In-flight:** M1 — Docker + single-node swarm via Nix (first M1 task).
+**Last updated:** 2026-05-26 (M0 claimed)
 
 ## Gates
-- (none claimed yet — M0 gate pends sops wiring)
+- **Gate: M0 — CLAIMED, awaiting Adversary** (2026-05-26). Evidence: flake rebuilds cc-ci from repo
+  (`switch --flake /root/cc-ci#cc-ci`, gen healthy, no failed units); sops-nix decrypts
+  `/run/secrets/test_secret` (0400 root, value = generated `cc-ci-m0-…`). Repro: clone repo, sync to
+  host, `nixos-rebuild switch --flake .#cc-ci`, then `systemctl is-system-running` + check the secret.
+  Per §6.1 I will NOT advance past this gate to M2; M1 work proceeds as independent unblocked work.
 
 ## Blocked
 - (none)
diff --git a/flake.lock b/flake.lock
index 8eeab1b..143b18c 100644
--- a/flake.lock
+++ b/flake.lock
@@ -18,7 +18,29 @@
     },
     "root": {
       "inputs": {
-        "nixpkgs": "nixpkgs"
+        "nixpkgs": "nixpkgs",
+        "sops-nix": "sops-nix"
+      }
+    },
+    "sops-nix": {
+      "inputs": {
+        "nixpkgs": [
+          "nixpkgs"
+        ]
+      },
+      "locked": {
+        "lastModified": 1750119275,
+        "narHash": "sha256-Rr7Pooz9zQbhdVxux16h7URa6mA80Pb/G07T4lHvh0M=",
+        "owner": "Mic92",
+        "repo": "sops-nix",
+        "rev": "77c423a03b9b2b79709ea2cb63336312e78b72e2",
+        "type": "github"
+      },
+      "original": {
+        "owner": "Mic92",
+        "repo": "sops-nix",
+        "rev": "77c423a03b9b2b79709ea2cb63336312e78b72e2",
+        "type": "github"
       }
     }
   },
diff --git a/flake.nix b/flake.nix
index a8fddfb..37a7c5d 100644
--- a/flake.nix
+++ b/flake.nix
@@ -5,9 +5,14 @@
     # Pinned to the exact revision cc-ci already runs, so the first rebuild from
     # this repo is a true no-op-then-base (M0). Bump deliberately, not drift.
     nixpkgs.url = "github:NixOS/nixpkgs/50ab793786d9de88ee30ec4e4c24fb4236fc2674";
+
+    # Pinned to a commit that still uses plain `buildGoModule` — sops-nix master moved to
+    # `buildGo125Module` (Go 1.25), which our pinned nixpkgs 24.11 (2025-06-30) does not have.
+    sops-nix.url = "github:Mic92/sops-nix/77c423a03b9b2b79709ea2cb63336312e78b72e2";
+    sops-nix.inputs.nixpkgs.follows = "nixpkgs";
   };
 
-  outputs = { self, nixpkgs }:
+  outputs = { self, nixpkgs, sops-nix }:
     let
       system = "x86_64-linux";
       pkgs = nixpkgs.legacyPackages.${system};
@@ -15,7 +20,10 @@
     {
       nixosConfigurations.cc-ci = nixpkgs.lib.nixosSystem {
         inherit system;
-        modules = [ ./hosts/cc-ci/configuration.nix ];
+        modules = [
+          sops-nix.nixosModules.sops
+          ./hosts/cc-ci/configuration.nix
+        ];
       };
 
       # Devshell for working on the harness/bridge locally.
diff --git a/hosts/cc-ci/configuration.nix b/hosts/cc-ci/configuration.nix
index ab5605c..caee011 100644
--- a/hosts/cc-ci/configuration.nix
+++ b/hosts/cc-ci/configuration.nix
@@ -5,6 +5,7 @@
 {
   imports = [
     ./hardware.nix
+    ../../modules/secrets.nix
   ];
 
   # --- Tailscale (ACCESS-CRITICAL: do not break, this is the only route in) ---
diff --git a/modules/secrets.nix b/modules/secrets.nix
new file mode 100644
index 0000000..a6dbb83
--- /dev/null
+++ b/modules/secrets.nix
@@ -0,0 +1,18 @@
+# sops-nix wiring (D6 infra secrets). cc-ci decrypts secrets at activation using its own
+# ed25519 SSH host key as the age identity (no separate key file to manage on the box).
+# Encrypted material lives in ../secrets/*.yaml, committed and readable only by recipients
+# listed in /.sops.yaml (host key + off-box master recovery key).
+{ ... }:
+{
+  sops = {
+    defaultSopsFile = ../secrets/secrets.yaml;
+    # Decrypt using the host's SSH host key (converted to an age identity by sops-nix).
+    age.sshKeyPaths = [ "/etc/ssh/ssh_host_ed25519_key" ];
+    # Do not also look for a GPG key.
+    gnupg.sshKeyPaths = [ ];
+
+    # M0 proof secret — confirms the decrypt path works end to end. Real infra secrets
+    # (Drone RPC, webhook HMAC, OAuth, registry creds) are added in their milestones.
+    secrets.test_secret = { };
+  };
+}
diff --git a/secrets/.gitkeep b/secrets/.gitkeep
deleted file mode 100644
index e69de29..0000000
diff --git a/secrets/secrets.yaml b/secrets/secrets.yaml
new file mode 100644
index 0000000..2a36a86
--- /dev/null
+++ b/secrets/secrets.yaml
@@ -0,0 +1,30 @@
+test_secret: ENC[AES256_GCM,data:VOxNiRyeSQQPKeF2PUK9AtezhzX+Hdm9ji5ZYm+gNd2NJ+wwXc67En8=,iv:Bn1oQeBN98E2/To1KRAw3wsLUF0/HsQFBm8s28L5aqo=,tag:KPS5Y+25Elf3alSF2H6npw==,type:str]
+sops:
+    kms: []
+    gcp_kms: []
+    azure_kv: []
+    hc_vault: []
+    age:
+        - recipient: age1h90utdztfc23kx8ewrtrtk80mnddvrf8pg4ppej55rwwwupzhfvqhmp3qa
+          enc: |
+            -----BEGIN AGE ENCRYPTED FILE-----
+            YWdlLWVuY3J5cHRpb24ub3JnL3YxCi0+IFgyNTUxOSBoRzN4Q0Eramhkdk8xbmNn
+            NGRwclpaT3YvR24yemJxQjF1N001cVI3MXdjCk9wUE5QTE1UNmxTa1BWalk1V1hS
+            M1o2elpOVHNGcWdyWVI1RHdUZi96M0UKLS0tIGpaRDNNa1ZuRWkybitPTlM5ajVK
+            VjNldWh1Q3lTc2lCNlE4aGNmaVNOT1kKMhsp/z5LbEyAezDHTodL2vS3L/wlNOc0
+            xiDLBYX1AJSiT8DOBvSMSZFj+ygsNL8GBYABjC0Ioar1PIK/KI00oA==
+            -----END AGE ENCRYPTED FILE-----
+        - recipient: age1cmk26t9e30ls8594s8txgmf2exenydmntfxqpcd3qdqm3ru2lpnqpdkdz9
+          enc: |
+            -----BEGIN AGE ENCRYPTED FILE-----
+            YWdlLWVuY3J5cHRpb24ub3JnL3YxCi0+IFgyNTUxOSBwTk9uQ3JSeEFidEF6U2FU
+            Mjk1bVYvNTdYaDJjL0g1ZGlZdXkyR3VUREJrClV5S283elRFbXZkUXNiQkoyYWwr
+            ZUkxV1UyRE1xcW5DSTNVbEk1dXEyWmcKLS0tIFo5SUdhaVVqYUpZUGQxVGQvR2s0
+            a2RKRWVaTGhNb0d3TFlnL2NtejZOaEUK2dQaAzlYk4Z7aBej77cO4Ug9Afkka6wg
+            G1SumwxX0wMocpgz4WhDUPkBC66uWlaR3u1AWzwpzRseuwAZ94gAxA==
+            -----END AGE ENCRYPTED FILE-----
+    lastmodified: "2026-05-26T20:32:25Z"
+    mac: ENC[AES256_GCM,data:cfMw8ILys0FXVXiRUbsZ1Jjz+S7X+0Q+DI4oyWNEP8Ka/iZeLkF1NjYbcdOVpqTuiF2gGde2uUjFRy3GtXOUYn8u8Sf2Ve1D1QpJ+8IiDCcaPUjxOxAKd3yGgDi4mm5EWxg+DerlugEj5hwlxWWBdj0I7XDnL2RPANN+yA9Ypko=,iv:hewvYjUmDfEg0PfUMaY0+SZuLy8sAR++d2Dlzm5Yr4w=,tag:nHqjRCHHM98Hzdv1HYHr3A==,type:str]
+    pgp: []
+    unencrypted_suffix: _unencrypted
+    version: 3.9.4