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Sage embeds Arize Phoenix. On startup it launches a local Phoenix instance, instruments the LangChain stack through OpenInference, and emits spans from the deterministic execution kernel, with no configuration and nothing leaving the host. Open the Phoenix UI and walk a run span by span: which step ran, what it sent the model, what came back, which tools fired, and where a step failed. Token accounting per run and per step catches a context blow-up or a runaway loop before it burns your budget.
Arize Phoenix trace view showing an MCP_Manager chain span with middleware, model, and tools child spans, trace status OK, cost, latency, and the span's input messages

A Phoenix trace of one MCP Manager turn: the span tree on the left (middleware, the model call with its token count, and the tool call), and the selected span's input on the right.

Phoenix listens on port 6006, and Mythic runs installed agent containers with host networking, so on the Mythic server the UI is at http://localhost:6006 by default. Sage does not configure Phoenix authentication or its bind address, so Phoenix’s own defaults apply. Traces contain prompts and tool output; from another machine, reach the UI through an SSH tunnel rather than by exposing the port.

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Two execution paths, two span trees

Sage’s two execution paths produce different traces. Knowing which one you ran is the difference between reading a trace and misreading it. A run with no LLM spans is not necessarily a broken trace. The kernel’s policy backend can run symbolically or hybridly without consulting a model; when it does, the run legitimately contains zero model spans. Compare against the run’s own model_calls in its runtime telemetry rather than assuming loss. Every seam.policy_select span carries the decision it produced (disposition, rationale, and whether the model responded), so a run that stopped because the model was unreachable says so in the trace instead of only in a failed leaf span.

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Working with traces

Traces persist in .phoenix/phoenix.db. Copy them WAL-inclusively: copying phoenix.db without its -wal sidecar silently drops everything not yet checkpointed. If you work from a Sage source checkout, a helper script checks whether a run is traced at all, rather than you reading span counts by eye. It is not part of a Mythic install:
It reports TRACED, PARTIAL, UNTRACED, or EMPTY, and exits non-zero on anything but TRACED.

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Known limits

  • Kernel spans cover the controller’s own steps; a Mythic task issue and its wait are traced as part of the execute seam rather than as separate spans.
  • Span attribute values are capped (128 KB), so a very large prompt or tool output is truncated in the trace, not dropped.
  • Set SAGE_KERNEL_TRACING=0 to disable kernel spans; LangChain instrumentation is unaffected by it.