ADR 0178 — Instructions carry a role

Decision

System sections are policy outside history. User sections are ordinary durable user messages, prepended atomically once under prompt.user-instructions. The receipt survives compaction and history replacement; removed instructions are not silently resurrected on the next turn. Archive replay includes seed transitions. SQLite schema version 3 adds receipts; custom drivers implement seeds.load/create and the seed history mutation in their transaction. A complete imported seed can reconstruct its receipt. A partial identity match is refused explicitly, leaving the history unchanged for repair by the host.

The runtime calls the prompt resolver once before a provider loop, with event: 'session.started' for the first recorded run and turn.started for later runs. Forward this event into composeAgentPrompt; section render receives it. Standalone composition defaults to turn.started. step.started is refused. Recovery may resolve the same run again: resolvers must be idempotent. System sections refresh on each run; changing a user section after its first seed does not rewrite the conversation.

Budget

historyTokens counts existing history, including any surviving seed. The composer reserves system instructions and provider/tool/output overhead. After the atomic seed the runtime calls finalizeSeed(inserted) to reserve user text only when this invocation actually introduced it. Already-seeded or compacted text adds no second reservation. Unknown counts stay unavailable.

Validation

Runtime first/second-turn budget tests, once-seeding conformance for custom stores, partial-import refusal, SQLite reopen and explicit v2→v3 migration.