handoff compaction leaks <behavioral_directive> from spawn prompts into parent context

[worldofgeese]

Bug

After handoff compaction, <behavioral_directive> blocks injected by spawn into child agent prompts leak into the parent orchestrator session. This causes the parent to believe it is a child agent and refuse orchestration duties.

Root cause

spawn/index.ts:229 injects:

You are a focused child agent spawned by a parent agent...

into child prompts via a <behavioral_directive> wrapper.

When the parent session later calls handoff, handoff/compact.ts compacts the full conversation history — including the spawn prompt text that contained this directive. The compacted output preserves the <behavioral_directive> tag verbatim, promoting it to system-level context in the new clean window.

Reproduction

1. Parent orchestrator spawns a child agent
2. Child completes, result returns to parent
3. Parent calls handoff (or auto-compaction triggers)
4. Post-compaction, parent session now has <behavioral_directive>You are a focused child agent...</behavioral_directive> in its context
5. Parent refuses to orchestrate, claiming it cannot spawn further children

Expected behavior

handoff/compact.ts should strip <behavioral_directive> blocks from the session history before/during compaction. These are transient injection markers for child sessions, not durable parent state.

Workaround

None clean — user must start a new session after the leak occurs.

Environment

• pi 0.78.0
• pi-agenticoding (latest as of 2026-05-31)