docs: register the est_tokens design in the research wiki

Records the approved option, the four rejected alternatives with their
reasons, the intentionally dropped CHS migration item, and the two
defects the independent review caught. Links the entry to m1-core-design
as a refinement, since that milestone is where est_tokens froze with
both jobs attached.

research-wiki/graph/edges.json

@@ -100,6 +100,11 @@
       "id": "design:settings-invariants-round-2",
       "label": "GatewaySettings 装配校验补齐(第二轮)",
       "type": "design"
+    },
+    {
+      "id": "design:est-tokens-decoupling",
+      "label": "est_tokens 解耦: 拆分限流预扣与遥测用量兜底(issue #2)",
+      "type": "design"
     }
   ],
   "links": [
@@ -165,6 +170,13 @@
       "relation": "implements",
       "evidence": "T0-T14 逐节实现设计 §4-§10/§15",
       "added": "2026-07-22T09:33:05.357964+00:00"
+    },
+    {
+      "source": "design:est-tokens-decoupling",
+      "target": "design:m1-core-design",
+      "relation": "refines",
+      "evidence": "精化 M1 冻结的 est_tokens 双职责语义: 保留 TPM 预扣、推翻 usage 缺失按 est 兜底(m1-core-design.md:59,222),改记 0/0 + unavailable + cost NULL",
+      "added": "2026-07-30T09:33:55.383401+00:00"
     }
   ]
 }