fix(examples-chat): use get_stream_writer (not adispatch_custom_event)#268
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PR #266 fixed the on_llm_new_token signature, after which live diagnostics confirmed the handler ran per token and adispatch_custom_event completed successfully — yet the SSE stream still carried zero a2ui-partial events. Root cause: adispatch_custom_event (langchain_core) and stream_mode= 'custom' (LangGraph) are different layers. langchain_core dispatches visible via stream_mode='events'; LangGraph's 'custom' channel is fed by get_stream_writer() returned from langgraph.config. The transport already requests stream_mode='custom', but the handler was writing to the wrong sink. Fix: replace adispatch_custom_event with get_stream_writer(). The writer is contextvar-scoped to the currently-executing LangGraph node and is inherited by nested callbacks, so the handler can call it from inside the LLM's callback chain. The payload shape is {name, data} so the existing transport-side parser (stream-manager.bridge.ts:509) extracts name + data correctly. Tests updated to mock get_stream_writer (instead of adispatch_custom_event) and assert on writer.call_args. Adds a new test asserting graceful behavior when invoked outside a stream context (writer raises RuntimeError; handler swallows). Live smoke now confirms 758 a2ui-partial events on the wire across a 2.5MB SSE stream for a dashboard prompt. The bridge consumes all events into agent.customEvents() and forwards them to the partial-args bridge. Note: a follow-up frontend issue remains in the partial-args bridge's incremental dispatch logic — early surfaceUpdate envelopes dispatch with incomplete components arrays (no ids yet), preventing beginRendering synthesis, and the dispatchedCount counter then skips re-attempt. Tracking separately.
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…rk (#271) Brings the canonical smoke checklist current with 29 PRs that landed between Phase 7 (#239) and today without checklist updates. Specifically: Updated sections: - chat-debug devtools — replaced bottom-drawer model with floating launcher + status pill + switch (PRs #249, #251) - Control palette — palette v2 (status pill, shadcn-styled panel, PR #244) - Generative UI / A2UI surfaces — single-bubble invariant (PR #255), parent-emits-envelopes architecture (PR #259), wrapped-content + tool_calls coexistence (PR #255), envelope reorder - Server-side wire format — tool_calls preserved on the final AI - Replaced 'Multi-thread' section with 'Sidenav (thread management)' reflecting the permanent semantic <nav> + Active/Archived sections (PR #253) and removing the old palette-toggled drawer model Added sections: - Cmd+K history search — palette open/search/select/close, archived result subtitle, keyboard navigation (PR #253) - Per-row thread actions — kebab menu order per state (active, pinned, archived), rename + pin/unpin + archive/unarchive + delete flows (PRs #258, #260, #267) - Thread titles — first-user-message derivation, idempotent writes, manual rename precedence (PR #242) - Progressive A2UI streaming — per-component fallback transition observable during streaming window (PRs #252, #261, #262, #268, #269) - Inline checkpoint markers — render between messages during multi-step runs (PR #243) - Responsive sidenav — viewport breakpoints, auto-collapse behavior (PR #240) Total: ~58 new check items across 6 new sections, plus rewrites to 5 existing sections. Original 333-line checklist → 391 lines / 237 check items.
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Summary
PR #266 fixed the `on_llm_new_token` signature, after which live diagnostics confirmed the handler runs per token and `adispatch_custom_event` completes successfully — yet the SSE stream still carried zero `a2ui-partial` events.
Root cause
`adispatch_custom_event` (langchain_core) and `stream_mode='custom'` (LangGraph) are different layers:
The transport already requests `stream_mode='custom'`, but the handler was writing to the wrong sink.
Fix
Replace `adispatch_custom_event` with `get_stream_writer()`. The writer is contextvar-scoped to the currently-executing LangGraph node and inherited by nested callbacks, so the handler can call it from inside the LLM's callback chain. Payload shape `{name, data}` matches what `stream-manager.bridge.ts:509` already expects.
Tests
Live smoke
`a2uiPartialEvents: 758` across a 2.5 MB SSE stream for a dashboard prompt. `agent.customEvents()` now populates with all 758 events.
Known follow-up
A frontend partial-args-bridge bug remains: early surfaceUpdate envelopes dispatch with incomplete `components` arrays (ids not yet streamed), so `pickRoot` returns null and synthesis is skipped. Subsequent pushes then skip the surfaceUpdate envelope because `dispatchedCount` already advanced. Live `liveSurfaceStore` stays empty even though events flow correctly. Tracking separately — out of scope for this PR.
Test plan