fix: the disabled sweep's shape assertion pinned the pre-E3 payload

My own E2 test asserted `sweep`'s disabled return by exact equality, and E3
added `images_joined` to it — a rule 90 miss on a consumer I wrote an hour
earlier. Every E3 test passed; this was the only failure (1 failed, 1202
passed).

Fixed by extending the assertion, NOT by loosening it to a subset check. The
exactness is the point: a disabled sweep reports a complete zeroed shape
rather than a shorter one, so a caller can read any counter unconditionally,
and this assertion is what notices when a new counter skips that path.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01LNXXULQDjVZmbuNa2G9mD9

tests/test_discord_grouping.py

@@ -367,7 +367,14 @@ async def test_the_sweep_is_a_no_op_when_the_switch_is_off(db):
     await db.commit()
 
     result = await sweep(db)
-    assert result == {"enabled": False, "sources": 0, "posts_created": 0}
+    # Exact equality on purpose, not a subset check: a disabled sweep reports a
+    # COMPLETE zeroed shape rather than a shorter one, so a caller can read any
+    # counter unconditionally. (Today's caller short-circuits on `enabled`, so
+    # nothing would KeyError — the point is that it does not HAVE to.) E3 adding
+    # `images_joined` broke this assertion, which is exactly what it is for.
+    assert result == {
+        "enabled": False, "sources": 0, "posts_created": 0, "images_joined": 0,
+    }
 
 
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