Use type: terminate for polyphony error-terminal nodes (conductor type:terminate)

[PolyphonyRequiem]

Summary

conductor v0.1.18 ships type: terminate (#219) — a step that ends a workflow explicitly with status: success or status: failed, producing:

• A typed workflow_completed / workflow_failed event with is_explicit: true
• CLI exit code 0 (success) or non-zero (failed)
• A termination_reason field in the event

Polyphony currently routes error-terminal paths to $end with no typed signal. Wagner's PR #535 (error-gate migration) auto-routes 16 error gates to abort_run which calls polyphony run abort — but the workflow still exits through $end, not a typed terminal.

What to do

After error-routing PR #229 merges (it adds CLI exit code 3 for UnhandledWorkflowError), replace abort-path $end routes with type: terminate nodes:

abort_terminal:
  type: terminate
  status: failed
  reason: "{{ abort_run.output.reason | default('run aborted') }}"

This aligns with P7 (Fail Honestly, Don't Auto-Approve) — makes the failure mode explicit and machine-readable.

Dependencies

• Requires conductor PR fix(workflows): for_each.outputs singleton-array bug (Bug B from AB#3064 dogfood) #229 (on_error: / error-routing) to merge first
• Wagner owns workflow YAML changes; Mahler owns the schema contract

Effort/Risk

~1-2h. Low semantic risk — additive change to terminal paths only.

References

• Conductor feat: type: terminate step (Closed-loop step 8: invoke seed-children on merged_unseeded resume gap #219)
• Conductor-design P7: Fail Honestly
• Mahler adoption survey 2026-05-28 (decision inbox)
• Wagner PR feat(#528): remove 19 trivial error gates across 6 workflows #535 (error-gate migration)

/cc Epic #521