docs: design the circuit-open wait policy for issue 14

The breaker conflates "this source is unhealthy" with "kill this call
now". Limiter rejections already choose between wait and fail_fast;
breaker rejections had no such choice, so a single-source scope loses
its whole retry budget the moment the gate opens.

Design adds {SCOPE}__CIRCUIT_OPEN (default fail_fast, so existing
deployments keep their control flow) and pins retry_after_s to "time
until a *certain* retry moment" across all six gate exits. The latter
also fixes a separate bug the issue missed: a half-open rejection fed
the probe lease (up to 2x timeout) into the source cooldown memo, whose
set_until only moves forward -- so a recovered source stayed blacklisted
in-process long after the gate closed. That one bites multi-source
deployments too, it is just hidden when other sources absorb the load.

Human-approved 2026-08-19; both documents revised after Codex review.

research-wiki/graph/edges.json

@@ -334,6 +334,13 @@
       "relation": "implements",
       "evidence": "research-wiki/plans/2026-08-19-issue12-telemetry-retention.md",
       "added": "2026-08-19T13:10:57.986963+00:00"
+    },
+    {
+      "source": "plan:plan-issue14-admission-wait-policy",
+      "target": "design:2026-08-19-issue14-admission-wait-policy-design",
+      "relation": "implements",
+      "evidence": "research-wiki/plans/plan-issue14-admission-wait-policy.md;T0-T8 逐节映射设计 §3.1-§3.6",
+      "added": "2026-08-20T03:30:06.280582+00:00"
     }
   ]
-}
+}