Why: Q3 WP2 retires the SpawnSubagent-compression execution path: all
WorkflowDef execution now goes through the wfcompile compiled graph, and
squad steps run on the agent-native kernel backend instead of the
agent-system step backend.
Evidence: runtime-level P4 parity tests (workflow_compiled_test.go):
registered branch lookup/errors, planned branch confirmation gate +
dynamic 8-step cap fail-closed before any HITL, model script switch
default-off, missing-slot HITL collection with compile-time rendering,
judge stream routed to the configured lightweight model (nil = fail-closed
verifier-unavailable). squadadapter TestOrchestrateRunsOnKernelStub:
four-phase skeleton runs end-to-end on the kernel stub (write_file
materialization, seeded skills, exec allowlist). server TestSquadOrchestration
reworked: kernel steps run in-process (no subagent child runs). Full
backend suite green; wfcompile/squadadapter/runmgr green with -race
(pre-existing llm_test fake race on main recorded as debt, CI does not
gate -race).
Impact: DELETED runtime/workflow.go + workflow_script.go (legacy step loop,
critic, script host) and their tests; squadadapter stepBackend
'agent-system' + profileForRole deleted; BuildBackends exported and
registers only agent-native; Orchestrate DefaultBackend -> agent-native;
builtin roles declare agent-native with write_file added to allowlists and
writer run_shell -> run_command (kernel tool name); runmgr default workflow
runner -> CompiledWorkflowRunner; mock #workflow demo runs compiled
(host-only steps). Model script branch keeps the single script-level
confirmation (no extra plan confirmation), matching legacy.
Refs: Q3 plan WP2 (2026-10-07-agent-stack-q2q3-plans.md); task card
.task/feature-agent-stack-q3.md
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