fix(c-generative-ui): emit_state → get_stream_writer (LangGraph 1.x)

[blove]

Summary

• Dashboard cards/charts/tables in the c-generative-ui demo never populated past the "Building UI…" skeleton — verified via chrome MCP that 7 placeholders remained and ~67 NG0303 input-spam errors fired per turn.
• Root cause: adispatch_custom_event no longer flows into the custom stream channel in LangGraph 1.x. Live SSE inspection: 0 custom events with the old API, 1 custom event with get_stream_writer().
• Payload also needed to match the chat-lib bridge contract — {name: "state_update", data: <flat-patches>} — so the bridge's eventData.name routing and eventData.data extraction hit the right slots, then signal-state-store.update() receives the flat {"/on_time/value": "84.2%", …} map it expects.

Test plan

• Direct uv test of adispatch_custom_event in a minimal graph → 0 custom events emitted (confirms the regression)
• Direct uv test of get_stream_writer() in a minimal graph → custom events emit correctly
• Curl-driven SSE test against the umbrella backend with my fix → 1 event: custom with all 7 state paths in payload
• Manual chrome MCP smoke (real LLM via repo-root .env): "Show me the dashboard" → 4 stat_cards populated, 1 line_chart with 12 monthly data points, 1 bar_chart with 4 airlines, 1 data_grid with 5 disruptions, zero render-default-fallback components, zero NG0303 errors

Files

• cockpit/langgraph/streaming/python/src/dashboard_graph.py — switch emit_state to get_stream_writer(), wrap payload as {name, data}
• cockpit/chat/generative-ui/python/src/graph.py — same fix in the standalone copy

🤖 Generated with Claude Code

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