08 Chat and Langfuse
Instructor notes for module 08 — timing, talk track, common failures, and reset steps.
macOS terminal: Run workshop commands in Terminal using zsh or bash.
Facilitator companion to the learner lesson 08 Chat and Langfuse.
Timing
About 15 minutes. The runtime LLM key and the Langfuse keys are already in .env.workshop
from module 00, so this is mostly a backend restart plus the trace tour.
Talk track
- The chat panel from module 02 becomes real, and every turn is traced.
- Show a trace on the projector: prompt, completion, tokens, cost.
Common failures
- Missing
OPENAI_API_KEY;POST /api/chatreturns 503 with a setup hint (the rest of the app is unaffected). An unfunded key errors on the model call. - Wrong
LANGFUSE_BASE_URLregion (https://us.cloud.langfuse.comvshttps://cloud.langfuse.com), so traces do not appear. - Back end not restarted after filling
.env.workshop. - The 2026-07 clean-room dry run covered this module; validated failure modes, timings, and human-gated steps were confirmed in the 2026-07 clean-room dry run.
Reset steps
- Hand out a capped loaner LLM key from the pool.
- Re-fill
OPENAI_API_KEY/LLM_MODEL/LLM_BASE_URLand the threeLANGFUSE_*values in.env.workshop, thendocker compose --env-file .env.workshop -f docker-compose.workshop.yml -f docker-compose.otel.yml up -d --build backendso ClickStack telemetry stays enabled.