fix(gtea): UPGRADE_SECRET_PREP hook — pre-insert lfs_jwt_secret with correct 43-char format

Blocker 4 fix: abra `secret generate --all` uses .env.sample for length hints; the
lfs-plain-gitea PR has SECRET_LFS_JWT_SECRET_VERSION=v1 COMMENTED OUT, so abra produces
a wrong-length secret. gitea requires exactly 43 chars (32 bytes base64 URL-safe); wrong
length → gitea fatals trying to save the JWT secret to the read-only Docker Config
app.ini → health check fails → swarm rolls back.

Fix: new UPGRADE_SECRET_PREP hook (meta.py) called before `abra secret generate --all`
in the upgrade path. abra's `--all` is idempotent (skips existing secrets), so the
correctly pre-inserted secret survives. gitea's recipe_meta.py implements the hook using
`docker secret create` directly to guarantee correct format regardless of .env.sample.

Also consumes machine-docs/BUILDER-INBOX.md (Adversary Blocker 4 digest).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

tests/gitea/recipe_meta.py

@@ -60,6 +60,45 @@ def UPGRADE_EXTRA_ENV(ctx):
     }
 
 
+def UPGRADE_SECRET_PREP(ctx):
+    """Pre-insert lfs_jwt_secret with the correct 43-char base64 URL-safe format before
+    `abra secret generate --all` runs. The lfs-plain-gitea PR's .env.sample has the
+    SECRET_LFS_JWT_SECRET_VERSION=v1 spec COMMENTED OUT, so abra uses a wrong default length;
+    gitea requires exactly 43 chars (32 bytes) or it fatals on the read-only app.ini."""
+    if not _lfs_enabled():
+        return
+    import base64
+    import subprocess
+
+    env_path = _os.path.expanduser(f"~/.abra/servers/default/{ctx.domain}.env")
+    stack_name = None
+    try:
+        with open(env_path) as fh:
+            for line in fh:
+                if line.startswith("STACK_NAME="):
+                    stack_name = line.split("=", 1)[1].strip().strip('"').strip("'")
+    except OSError:
+        pass
+    if not stack_name:
+        raise RuntimeError(f"UPGRADE_SECRET_PREP: STACK_NAME not found in {env_path}")
+
+    docker_secret = f"{stack_name}_lfs_jwt_secret_v1"
+    value = base64.urlsafe_b64encode(_os.urandom(32)).rstrip(b"=").decode()
+
+    subprocess.run(["docker", "secret", "rm", docker_secret], capture_output=True)
+    result = subprocess.run(
+        ["docker", "secret", "create", docker_secret, "-"],
+        input=value,
+        capture_output=True,
+        text=True,
+    )
+    if result.returncode != 0:
+        raise RuntimeError(
+            f"UPGRADE_SECRET_PREP: docker secret create {docker_secret}: {result.stderr.strip()}"
+        )
+    print(f"  gitea upgrade: pre-created {docker_secret} (43-char lfs_jwt_secret)", flush=True)
+
+
 def EXTRA_ENV(ctx):
     lfs = _lfs_enabled()
     compose_file = "compose.yml:compose.sqlite3.yml"