Worker spawn (start, run_design_worker) + viewport-fit math (fit_design_viewport_to_content,
active_content_bounds, design_canvas_size) move to op_web_daemon::design_session. The
host-coupled UI pumps (pump_commands/pump_progress — take &mut WidgetHostNative) + the
progress-line renderer (render_progress/progress_label, used only by pump_progress, so
kept with their caller per the call graph — deviates from the plan's MOVE list) stay as
the residual. active_content_bounds/design_canvas_size made pub for the KEEP-side fit
tests; residual re-exports DesignSession (pub use) for main.rs zero-churn. web_chat_standard
fit + chat_session_launch start/DesignSession + chat_intent run_design_worker repointed.
Completes Phase 4. design_session 8 + op-web-daemon 215 tests green; no dep/lock change.
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