Discord perms: partial guild payload is unknown, not a deny (#225 S1 review)

A guild without its @everyone role (or that role's permissions) was read
as base 0, a definite deny that would block a start. It now raises
ValueError, which S3 treats as unknown and lets the start go ahead.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

drb-c2-core/app/internal/discord_perms.py

@@ -178,9 +178,14 @@ def effective_permissions(
     if member_id and member_id == _sid(guild.get("owner_id")):
         return ALL_PERMISSIONS, {}
 
-    # 2. Base from @everyone + the member's roles.
+    # 2. Base from @everyone + the member's roles. Every guild has an
+    # @everyone role (id == guild id) with a permissions value; without one
+    # the payload is partial, and reading it as "no permissions" would turn
+    # it into a definite deny instead of "unknown" (the plan is fail-open).
     everyone_role = roles.get(guild_id)
-    base = parse_permissions(everyone_role.get("permissions")) if everyone_role else 0
+    if not guild_id or everyone_role is None or everyone_role.get("permissions") in (None, ""):
+        raise ValueError(f"guild payload has no @everyone role permissions (guild {guild_id or '?'})")
+    base = parse_permissions(everyone_role.get("permissions"))
     for rid in member_role_ids:
         role = roles.get(rid)
         if role is not None and rid != guild_id:

drb-c2-core/tests/test_discord_perms.py

@@ -245,9 +245,21 @@ def test_unknown_member_role_ids_are_ignored():
     assert bits == VOICE
 
 
-def test_missing_everyone_role_means_empty_base():
-    g = {"id": GUILD, "owner_id": OWNER, "roles": []}
-    bits, trace = eff(g, member(), channel())
+@pytest.mark.parametrize("g", [
+    {"id": GUILD, "owner_id": OWNER, "roles": []},
+    {"id": GUILD, "owner_id": OWNER},
+    {"id": GUILD, "owner_id": OWNER, "roles": [{"id": GUILD, "name": "@everyone"}]},
+    {"owner_id": OWNER, "roles": [{"id": GUILD, "name": "@everyone", "permissions": "0"}]},
+])
+def test_partial_guild_payload_raises_not_silently_denies(g):
+    # A guild without its @everyone role (or its permissions) is a partial
+    # payload: "unknown" (ValueError, start goes ahead), never a definite deny.
+    with pytest.raises(ValueError):
+        eff(g, member(), channel())
+
+
+def test_everyone_role_granting_nothing_is_a_real_deny():
+    bits, trace = eff(guild(everyone=0), member(), channel())
     assert bits == 0 and "not granted" in trace["View Channel"]