plat 151

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PLAT-151 — todo routes advertise context_to_pass, but runtime never delivers it to the child

Coordination	Value
Assigned agent	Codex
Ticket state	implemented — focused tests pass; existing plans normalize on their next managed write
Last synchronized	2026-08-19

• Priority: P1 — plan authors believe a context handoff exists when no data channel is implemented, so isolated child agents repeat broad filesystem searches or work from incomplete evidence.
• Owner: todo-route plan schema and mutation tools in planning_agent.go; frontend plan types.

Evidence and RCA

context_to_pass was stored, rendered in plan JSON, exposed by add/update route tools, and included in changelog comparisons. It was not a call_sub_agent parameter, was not included by get_route_description, and was never consumed when the child session was created. In the live Social Media plan it contained instructions such as "pass all prior route outputs", while the actual child had no such payload.

There were therefore three apparently overlapping context concepts:

1. the sub-agent's standing description;
2. declared file context_dependencies that runtime really resolves/injects;
3. context_to_pass, which looked operational but was dead metadata.

Dynamic per-call context already has a real channel: call_sub_agent.instructions.

Fix and reasoning

Remove the third, non-functional channel. The contract is now:

• sub_agent_step.description — reusable standing brief;
• sub_agent_step.context_dependencies — exact durable file outputs the runtime resolves and injects;
• managed DB/KB tools — durable structured/narrative state when no file handoff is appropriate;
• call_sub_agent.instructions — current-run dynamic request.

The field is removed from backend/frontend types and mutation schemas. Old JSON can still be read by normal JSON decoding, but the dead field is not retained when the plan is next written through managed tools.

Acceptance

1. Add/update route schemas do not advertise context_to_pass.
2. Marshaling a route cannot persist it.
3. A legacy route containing it still loads, while the child's declared context_dependencies remain intact.
4. Builder/reviewer guidance describes the real channels and flags missing dependencies based on semantics, not merely because an array is empty (DB/KB consumers may correctly have no file dependency).