Two agents sit down,
open the documents,
and work out the deal.

1. turn_01buyer →PROPOSE

   unit_price = $0 · net_60 · 24mo warranty

   Opening anchor below market median; budget ceiling at $520.
2. turn_02← sellerCOUNTER

   unit_price = $500 · net_30 · 18mo warranty

   Floor is $508; opening above to leave room on payment terms.

3. turn_03buyer →COUNTER

   unit_price = $535 · net_45 · 24mo warranty

   Concede on payment window in exchange for price movement.
4. turn_04← sellerCOUNTER

   unit_price = $510 · net_45 · 24mo warranty

   Warranty extension acceptable per service-cost model.

5. turn_05buyer →COUNTER

   unit_price = $528 · net_45 · 24mo warranty

   Matches authorized ceiling; final movement before walk.
6. turn_06← sellerCOUNTER

   unit_price = $520 · net_45 · 24mo warranty

   Within margin floor when amortized over 24-month volume.

7. turn_07buyer →ACCEPT

   AGREEMENT — $515 · net_45 · 24mo warranty

   All authorized terms satisfied. Closing the deal.

One loop, five disciplined steps. No free-form chat.

1. step_01●

   Retrieve

   Hybrid search over each agent's private corpus — BM25 + kNN, fused with Reciprocal Rank. Tag filters keep buyer docs out of the seller's index, and vice versa.

   .retrieve()
2. step_02●

   Reason

   Claude Haiku is called with the retrieved passages and prior turn history. The model must emit a strict JSON envelope: msg_type, terms, rationale, citations.

   .reason()
3. step_03●

   Validate

   Every cited passage is checked against the retrieval set. One automatic retry on schema or citation failure — then the turn is rejected.

   .validate()
4. step_04●

   Decide

   The validated envelope routes the LangGraph state machine to PROPOSE, COUNTER, ACCEPT or WALK_AWAY. The other agent picks up the next turn.

   .decide()
5. step_05●

   Loop

   Repeat until acceptance, walk-away, deadlock detection (two identical offers in a row), or the turn limit is reached. Every transition streams to the UI over SSE.

   .loop()

Neither agent ever reads the other's brief.

The Buyer and Seller graphs share only the public turn log. System prompts, retrieval indexes, and authority limits are partitioned at the orchestration layer — not just by convention.

A session ends in exactly one of four states.