G4: R2 buckets live, Gitea storage wired, checksum trap pinned

Three buckets created. S3 round-trip against R2 proven end to end
(PUT/GET/DELETE) before any of it was wired in.

Includes the R2 checksum trap: R2 rejects the algorithm S3 clients send by
default, and the resulting error reads like a credential problem and is not one.

Records a NAMED DEBT in SUBSTRATE.md: the R2 credential is currently the
account-wide god token, because no available token can mint a scoped one. Gated
— it must be replaced before G7 puts CI runners on this host, since I-5 exists
precisely to keep untrusted job code away from broadly-scoped credentials.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

SUBSTRATE.md

@@ -72,10 +72,28 @@ consulted, so a perfect service presents as "the app is broken."
 All in the fleet lockbox, injected by env, **never committed**. `make check`
 fails on any `cfat_` / `cfut_` / `gh[pousr]_` / `et_plt_` literal in the tree.
 
-⚠️ The R2 credential should be **scoped to this cell**. The sites cell ended up
-holding the account-wide god token because v4 R2 object endpoints reject
-restricted tokens. Whichever we end up with, record it here — an account-wide
-token is an acceptable named debt and an unacceptable invisible one.
+### ⚠️ NAMED DEBT — the R2 credential is account-wide
+
+**As of 2026-08-11 this cell holds the Cloudflare god token as its R2
+credential.** R2's S3 credentials are derived from an API token (access key id =
+the token's id, secret = SHA-256 of its value), and **no token available to this
+session has permission to mint a new one** — creating tokens is dashboard-only
+or needs a token-creating token. So the wiring was proven with the god token
+rather than blocked on it.
+
+This is recorded, not hidden, because an account-wide token is an acceptable
+named debt and an unacceptable invisible one.
+
+**GATE: this must be replaced with a scoped R2 token BEFORE strand G7 lands
+CI runners on this host.** I-5 says runners execute untrusted code and must not
+share a kernel with credentials scoped beyond their own job; a god token with
+R2 + Workers + Pages + WAF + SSL rights sitting on the same box as a runner is
+exactly the thing I-5 exists to prevent.
+
+Minting one is a two-minute job in the Cloudflare dashboard: **R2 → Manage R2
+API Tokens → Create → Object Read & Write, scoped to the three `windy-git-*`
+buckets.** Then set `R2_ACCESS_KEY_ID` / `R2_SECRET_ACCESS_KEY` in
+`/srv/windygit/src/.env` and redeploy.
 
 ⚠️ The Cloudflare **god token has Zone:Read but no DNS:Edit.** Use the DNS:Edit
 token for record creation.

docker-compose.yml

@@ -53,7 +53,22 @@ services:
       # G2.2 — OIDC only. No local password login, no self-registration.
       GITEA__service__DISABLE_REGISTRATION: "true"
       GITEA__service__ALLOW_ONLY_EXTERNAL_REGISTRATION: "true"
-      GITEA__lfs__PATH: /data/lfs
+      # G4.3 — heavy bytes to R2 at ZERO egress. Git object databases stay on
+      # local NVMe (I-3); this covers LFS, attachments, packages, avatars and
+      # Actions artifacts, which is where GitHub's painful bills actually come
+      # from and where R2's free egress is a structural, permanent advantage.
+      GITEA__storage__STORAGE_TYPE: minio
+      GITEA__storage__MINIO_ENDPOINT: ${R2_ACCOUNT_ID}.r2.cloudflarestorage.com
+      GITEA__storage__MINIO_ACCESS_KEY_ID: ${R2_ACCESS_KEY_ID}
+      GITEA__storage__MINIO_SECRET_ACCESS_KEY: ${R2_SECRET_ACCESS_KEY}
+      GITEA__storage__MINIO_BUCKET: ${R2_BUCKET_LFS:-windy-git-lfs}
+      GITEA__storage__MINIO_LOCATION: auto
+      GITEA__storage__MINIO_USE_SSL: "true"
+      # ⚠️ THE R2 TRAP. R2 rejects the checksum algorithm S3 clients send by
+      # default; without this, uploads fail with an opaque checksum error that
+      # reads like a credential problem and is not one.
+      GITEA__storage__MINIO_CHECKSUM_ALGORITHM: md5
+      GITEA__lfs__STORAGE_TYPE: minio
     volumes:
       # I-3: git object databases on a POSIX filesystem. Never object storage.
       - ${GIT_DATA_ROOT:-./data/gitea}:/data