Workflow stage: flowchart/canvas overlays left sidebar (layout broken) #1450

Symptom

On Workflow stage chat (e.g. 周报汇总流程 / Weekly Report Summary), the workflow flowchart/graph is painted on top of the left sidebar (Inbox / Tasks / Workflows list). Floating pink node chips (e.g. 「数」「W」) also appear mid-page. The main chat content is partially readable but the overall layout looks broken / “ghosted”.

Owner screenshot attached to the implementer agent; URL host *.botawaken.com.

Expected

• Flowchart / mini graph stays inside the Workflow stage / settings canvas area only.
• Left sidebar is never covered by graph nodes, edges, or inspector chips.
• No absolute/fixed-position graph layers escaping their scroll container (overflow / stacking context).

Context

• Recent: Settings → Workflow graphs: canvas-first with inspector #1440 (canvas-first Settings graphs + stage unify), Remove workflow canned demo controls from product UI #1444 (remove demo UI). Prod may still be on earlier tip — reproduce on main (8f5c9ca / post-Settings → Workflow graphs: canvas-first with inspector #1440) and current prod.
• Suspect area (hypothesis only — verify): plugins/workflow MiniFlowchart / GraphCanvas / stage chrome positioning (position:absolute relative to wrong ancestor, missing overflow:hidden / isolation, portal to body).

Acceptance

• Opening a Workflow stage chat does not draw graph nodes/edges over the left sidebar.
• Settings → Workflow graph editor still works (canvas + inspector).
• Regression test or CSS assertion covering containment if practical.
• changelog fragment + Docs-not-needed (or arch-docs update) per repo rules.