docs: fill the untested items and record why the B layer has no graphs

The forward upgrade to 26.7.3 was zero downtime across 87 samples, and since databasechangelog stayed at 210 the rollback to 26.7.0 also succeeded, which narrows D-2's conclusion: rolling back fails when the schema moved, not because of the version number. The row count is the check.

Role changes never reach the upstream through request repetition; the session is a snapshot taken at login and only a new session picks up the new claim. Auditing the docs also surfaced that Prometheus scrapes only keycloak, kubelet, node-exporter and itself, so the B-layer experiments have no metrics to screenshot rather than missing screenshots.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

docs/diagrams/b1-store-split.svg

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+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 700 330" width="700" height="330" font-family="system-ui,-apple-system,Segoe UI,Roboto,sans-serif">
+  <style>
+    .t{font-size:13px;fill:#1f2328}.s{font-size:11px;fill:#59636e}.h{font-size:14px;font-weight:600;fill:#1f2328}
+    .r{font-size:12px;fill:#cf222e;font-weight:600}
+    .box{fill:#fff;stroke:#8c959f;stroke-width:1.4;rx:6}
+    .dead{fill:#fff5f5;stroke:#cf222e;stroke-width:1.6;stroke-dasharray:5 3;rx:6}
+    .ok{fill:#f6fdf6;stroke:#1a7f37;stroke-width:1.6;rx:6}
+    .ln{stroke:#59636e;stroke-width:1.4;fill:none;marker-end:url(#a)}
+    .bad{stroke:#cf222e;stroke-width:1.6;stroke-dasharray:5 3;fill:none;marker-end:url(#b)}
+  </style>
+  <defs>
+    <marker id="a" markerWidth="9" markerHeight="9" refX="8" refY="4.5" orient="auto"><path d="M0,0 L9,4.5 L0,9 z" fill="#59636e"/></marker>
+    <marker id="b" markerWidth="9" markerHeight="9" refX="8" refY="4.5" orient="auto"><path d="M0,0 L9,4.5 L0,9 z" fill="#cf222e"/></marker>
+  </defs>
+  <text class="h" x="16" y="24">B-1 · Redis 는 세션만 옮기고 토큰은 두고 간다</text>
+  <rect class="box" x="30" y="46" width="140" height="46"/><text class="t" x="100" y="66" text-anchor="middle">bff-0</text><text class="s" x="100" y="82" text-anchor="middle">kc-lab-1</text>
+  <rect class="box" x="30" y="104" width="140" height="46"/><text class="t" x="100" y="124" text-anchor="middle">bff-1</text><text class="s" x="100" y="140" text-anchor="middle">kc-lab-2</text>
+  <rect class="ok" x="330" y="46" width="330" height="60"/>
+  <text class="t" x="495" y="68" text-anchor="middle">Redis — Application Session</text>
+  <text class="s" x="495" y="86" text-anchor="middle">sessionRepository → RedisSessionRepository ✔ 옮겨졌다</text>
+  <text class="s" x="495" y="100" text-anchor="middle">필드: SPRING_SECURITY_CONTEXT · TTL 1772초</text>
+  <rect class="dead" x="330" y="122" width="330" height="60"/>
+  <text class="r" x="495" y="144" text-anchor="middle">프로세스 메모리 — OAuth2AuthorizedClient</text>
+  <text class="s" x="495" y="162" text-anchor="middle">InMemoryOAuth2AuthorizedClientService ✗ 그대로</text>
+  <text class="s" x="495" y="176" text-anchor="middle">access token · refresh token 이 여기 있다</text>
+  <path class="ln" d="M170,69 L330,69"/><path class="ln" d="M170,127 L330,80"/>
+  <path class="bad" d="M170,140 L330,150"/>
+  <rect class="box" x="30" y="210" width="630" height="90"/>
+  <text class="t" x="345" y="234" text-anchor="middle">그 결과 사용자에게 보이는 것</text>
+  <text class="s" x="345" y="256" text-anchor="middle">principal: labuser        ← 로그인은 되어 있다</text>
+  <text class="s" x="345" y="272" text-anchor="middle">accessTokenStoredOnServer: false   ← 토큰이 없다</text>
+  <text class="r" x="345" y="292" text-anchor="middle">완전히 로그아웃되는 편이 차라리 낫다</text>
+</svg>