feat(supplier,gateway,buyer): N-slot chat suppliers + entry-ticket settle mode

Two structural fixes for demo concurrency (3 single-slot suppliers thrashed under Open WebUI's ~3 conversations per message): Multi-slot suppliers (MAX_CHAT_SESSIONS, default 1): - SupplierState is now capacity-aware: a Set of active escrow refs with free-until-full status semantics, ref-scoped release(ref) (also fixes the latent bug where handler catch-alls released another request's slot), and a walletMutex serializing every wallet-spending chain op — Claim, Submit, and wallet-health consolidation queue instead of racing the single working/collateral UTxO. /status gains active_sessions/max_sessions. Entry-ticket settle mode (CHAT_SETTLE_MODE=ticket, default full, both sides): - The buyer's escrow post at session open is the ONLY chain op. The supplier verifies the Open escrow as an entry ticket but never Claims/Submits (/v1/chat/start → {status:"ticket"}; /v1/chat/end → receipt-less {status:"ended"}); no hard-cap timer, so sessions may outlive deliver_by. Used tickets can't reopen sessions (records retained; 409 session_exists). - Buyer SDK: startChat/endChat are settle-mode aware, driven by the supplier's response — mixed-mode rollout windows settle correctly. - Gateway: ticket closes bill cost 0; the sweeper Reclaims Open tickets after deliver_by WITHOUT closing live sessions (the conversation and its affinity mirror survive their reclaimed ticket), gates reclaims on deliver_by, and keeps an in-process settled-refs memory so terminal indexer rows aren't retried every sweep forever. Deployment (kimi-chat trio + gateway): ticket mode, 8 slots per supplier, idle policy gateway 10 min / supplier 15 min (fixes the inversion where the supplier idle-closed before the gateway janitor). Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
2026-07-09 20:48:52 +02:00
parent 9a4f9f0699
commit 2f7b0194a5
34 changed files with 1451 additions and 235 deletions
--- a/buyer/src/sdk/Marketplace.ts
+++ b/buyer/src/sdk/Marketplace.ts
@@ -90,6 +90,7 @@ import type {
  SubmitTtsResult,
  StartChatOptions,
  StartChatResult,
+  ChatSettleMode,
  EndChatOptions,
  EndChatResult,
  AcceptResultOptions,
@@ -899,7 +900,13 @@ export class Marketplace extends EventEmitterBase {
    }

    this.emitProgress({ type: "chat_started", escrow_ref: escrowRefStr });
-    return { escrowRef: escrowOutputRef, sessionNonce, supplierBaseUrl: advertDatum.endpoint_url };
+    // Ticket-mode suppliers answer {status:"ticket"} (no Claim); anything else
+    // — "claimed" or an older supplier without the field — is full settlement.
+    const startStatus = startRes.body && typeof startRes.body === "object"
+      ? (startRes.body as { status?: string }).status
+      : undefined;
+    const settleMode: ChatSettleMode = startStatus === "ticket" ? "ticket" : "full";
+    return { escrowRef: escrowOutputRef, sessionNonce, supplierBaseUrl: advertDatum.endpoint_url, settleMode };
  }

  /**
@@ -937,10 +944,20 @@ export class Marketplace extends EventEmitterBase {
      });
    }
    const endBody = endRes.body as {
+      status?: string;
+      settle_mode?: string;
      receipt?: import("@marketplace/shared/receipt").Receipt;
      receipt_signature?: string;
      submitted_ref?: string;
    };
+    // Ticket sessions produce no receipt and nothing to Accept — the Open
+    // escrow returns via reclaim after deliver_by. Trusting the supplier's
+    // response is incentive-safe: lying in either direction only forfeits the
+    // supplier's own payout (the buyer's sweeper reclaims unsettled escrows).
+    if (endBody.settle_mode === "ticket") {
+      this.emitProgress({ type: "chat_ended", escrow_ref: escrowRefStr });
+      return { settleMode: "ticket", escrowRef };
+    }
    if (!endBody.receipt || !endBody.receipt_signature) {
      throw new SupplierError("malformed_response", { message: "supplier end response missing receipt" });
    }
@@ -1022,7 +1039,7 @@ export class Marketplace extends EventEmitterBase {
    this.emitProgress({ type: "accept_submitted", escrow_ref: refToString(acceptedRef) });
    this.emitProgress({ type: "chat_ended", escrow_ref: escrowRefStr });

-    return { receipt, receiptSignature, escrowRef, acceptedRef };
+    return { settleMode: "full", receipt, receiptSignature, escrowRef, acceptedRef };
  }

  // ─── acceptResult / reclaim ───────────────────────────────────────────
--- a/buyer/src/sdk/index.ts
+++ b/buyer/src/sdk/index.ts
@@ -16,6 +16,9 @@ export type {
  AcceptResultOptions,
  ReclaimOptions,
  GetTaskHistoryOptions,
+  ChatSettleMode,
+  StartChatResult,
+  EndChatResult,
 } from "./types.js";
 export { ReceiptVerificationError, IndexerError, SupplierError } from "./types.js";
 export type { TaskHistoryStore } from "./history.js";
--- a/buyer/src/sdk/types.ts
+++ b/buyer/src/sdk/types.ts
@@ -197,6 +197,11 @@ export interface StartChatOptions {
  advertRef: OutputReference;
  payment_lovelace: bigint;
 }
+/** Chain settlement mode a chat session runs under (reported by the supplier
+ * at /v1/chat/start): "full" = Claim/Submit/Accept lifecycle; "ticket" = the
+ * buyer's escrow post is the only chain op (reclaimed after deliver_by). */
+export type ChatSettleMode = "full" | "ticket";
+
 export interface StartChatResult {
  escrowRef: OutputReference;
  /** Random nonce committed into the escrow's session-init prompt_hash. The
@@ -204,6 +209,8 @@ export interface StartChatResult {
  sessionNonce: string;
  /** Supplier endpoint_url, cached by the buyer-app for message routing. */
  supplierBaseUrl: string;
+  /** How the supplier settles this session ("full" when it Claimed). */
+  settleMode: ChatSettleMode;
 }

 /**
@@ -220,13 +227,21 @@ export interface EndChatOptions {
  /** The browser's local transcript mirror, used to verify response_hash. */
  transcript?: import("@marketplace/shared/tx").ChatMessage[];
 }
-export interface EndChatResult {
-  receipt: Receipt;
-  receiptSignature: string;
-  escrowRef: OutputReference;
-  /** The Submitted escrow UTxO that was Accepted. */
-  acceptedRef: OutputReference;
-}
+export type EndChatResult =
+  | {
+      settleMode: "full";
+      receipt: Receipt;
+      receiptSignature: string;
+      escrowRef: OutputReference;
+      /** The Submitted escrow UTxO that was Accepted. */
+      acceptedRef: OutputReference;
+    }
+  | {
+      /** Ticket session: nothing was Submitted/Accepted — no receipt exists.
+       * The Open escrow returns to the buyer via reclaim after deliver_by. */
+      settleMode: "ticket";
+      escrowRef: OutputReference;
+    };

 /**
 * AcceptResultOptions — arguments to Marketplace.acceptResult().
--- a/buyer/src/server.ts
+++ b/buyer/src/server.ts
@@ -934,6 +934,14 @@ export function createApp(deps: AppDeps): Express {
        supplierBaseUrl: state.supplierBaseUrl,
      });
      chatRouteState.delete(rawRef);
+      if (result.settleMode === "ticket") {
+        // Ticket session: no receipt/Accept — funds return via reclaim.
+        return res.status(200).json({
+          status: "ended",
+          escrow_ref: rawRef,
+          settle_mode: "ticket",
+        });
+      }
      return res.status(200).json({
        status: "accepted",
        escrow_ref: rawRef,
--- a/buyer/src/ui/components/ChatForm.tsx
+++ b/buyer/src/ui/components/ChatForm.tsx
@@ -267,7 +267,18 @@ export default function ChatForm({ advertRef, payment_lovelace }: ChatFormProps
        } catch { /* keep fallback */ }
        throw new Error(msg);
      }
-      setCharged(payment_lovelace !== undefined ? ap3x(payment_lovelace) : "0");
+      let endBody: { settle_mode?: string } = {};
+      try {
+        endBody = (await resp.json()) as { settle_mode?: string };
+      } catch { /* older buyer-app responses stay full-settle */ }
+      // Ticket sessions never charge — the escrow returns via reclaim.
+      setCharged(
+        endBody.settle_mode === "ticket"
+          ? "0 (ticket session — escrow reclaimed)"
+          : payment_lovelace !== undefined
+            ? ap3x(payment_lovelace)
+            : "0",
+      );
    } catch (err) {
      setError(err instanceof Error ? err.message : String(err));
    } finally {
--- a/deploy/mainnet/docker-compose.gateway.yml
+++ b/deploy/mainnet/docker-compose.gateway.yml
@@ -38,6 +38,13 @@ services:
      # frontend's "API Keys" page (served from marketplace.vector…) POSTs to
      # /signup here. Comma-separated; empty disables CORS entirely.
      GATEWAY_CORS_ORIGINS: https://marketplace.vector.apexfusion.org
+      # Ticket mode: the escrow post at session open is the only chain op;
+      # the sweeper reclaims Open escrows after deliver_by. Must match the
+      # kimi-chat suppliers' CHAT_SETTLE_MODE.
+      CHAT_SETTLE_MODE: ticket
+      # Demo janitor closes idle sessions BEFORE the suppliers' 15 min
+      # CHAT_IDLE_TIMEOUT_MS backstop.
+      DEMO_SESSION_IDLE_MS: "600000"
    volumes:
      - gateway-mainnet-data:/repo/data/gateway
    healthcheck:
--- a/deploy/mainnet/docker-compose.supplier-kimi-chat-2.yml
+++ b/deploy/mainnet/docker-compose.supplier-kimi-chat-2.yml
@@ -40,7 +40,9 @@ services:
      OPENAI_TIMEOUT_MS: "300000"
      # 2.5 min idle end: single-slot suppliers must free up quickly for the
      # shared demo endpoint (the gateway transparently reopens on next turn).
-      CHAT_IDLE_TIMEOUT_MS: "150000"
+      CHAT_IDLE_TIMEOUT_MS: "900000"
+      CHAT_SETTLE_MODE: ticket
+      MAX_CHAT_SESSIONS: "8"
      PORT: "8080"
      # Enable LiveOgmiosProvider so Claim/Submit actually broadcast.
      LIVE_CHAIN: "1"
--- a/deploy/mainnet/docker-compose.supplier-kimi-chat-3.yml
+++ b/deploy/mainnet/docker-compose.supplier-kimi-chat-3.yml
@@ -40,7 +40,9 @@ services:
      OPENAI_TIMEOUT_MS: "300000"
      # 2.5 min idle end: single-slot suppliers must free up quickly for the
      # shared demo endpoint (the gateway transparently reopens on next turn).
-      CHAT_IDLE_TIMEOUT_MS: "150000"
+      CHAT_IDLE_TIMEOUT_MS: "900000"
+      CHAT_SETTLE_MODE: ticket
+      MAX_CHAT_SESSIONS: "8"
      PORT: "8080"
      # Enable LiveOgmiosProvider so Claim/Submit actually broadcast.
      LIVE_CHAIN: "1"
--- a/deploy/mainnet/docker-compose.supplier-kimi-chat.yml
+++ b/deploy/mainnet/docker-compose.supplier-kimi-chat.yml
@@ -52,7 +52,9 @@ services:
      # 2.5 min idle end (supplier Submits the transcript): single-slot
      # suppliers must free up quickly for the shared demo endpoint (the
      # gateway transparently reopens a session on the next turn).
-      CHAT_IDLE_TIMEOUT_MS: "150000"
+      CHAT_IDLE_TIMEOUT_MS: "900000"
+      CHAT_SETTLE_MODE: ticket
+      MAX_CHAT_SESSIONS: "8"
      PORT: "8080"
      # Enable LiveOgmiosProvider so Claim/Submit actually broadcast.
      LIVE_CHAIN: "1"
--- a/docs/gateway.md
+++ b/docs/gateway.md
@@ -113,6 +113,12 @@ All on-chain steps run inside the per-key `mutex.run(...)`.
 - **close** → `endChat` (Submit + Accept, awaits) → settle + bond refund; record usage; wallet-health.
 - Sessions are reclaimable by the sweeper if abandoned before close.

+### Settle modes (`CHAT_SETTLE_MODE`, gateway + supplier, default `full`)
+- **full** — the lifecycle above: supplier Claims at start, Submits a transcript receipt at end, gateway Accepts (buyer charged).
+- **ticket** — the buyer's escrow post at open is the ONLY chain op. The supplier verifies the Open escrow as an entry ticket (`/v1/chat/start` → `{status:"ticket"}`) but never Claims/Submits; `/v1/chat/end` → `{status:"ended", settle_mode:"ticket"}` with no receipt; the sweeper Reclaims the Open escrow after `deliver_by`, returning all locked funds (net cost ≈ tx fees). Usage rows record `cost_lovelace: 0`. Sessions may outlive `deliver_by` (no hard-cap) — a live session whose ticket got reclaimed keeps running; only the idle janitor/close ends it. Close behavior is driven per-session by the supplier's `/end` response, so mixed-mode rollout windows settle correctly.
+- Ticket caveats (accepted, demo-grade): a supplier restart forgets used tickets, so an unexpired un-reclaimed escrow ref could reopen a session (bounded by `deliver_by` + the sweep); `/account.locked_in_escrow_lovelace` over-reports because the indexer never updates spent rows.
+- Suppliers additionally take `MAX_CHAT_SESSIONS` (default 1) — concurrent session slots; `/status` reports `active_sessions`/`max_sessions` and stays `free` until all slots are taken.
+
 ## Sweeper & wallet-health
 - **Sweeper** (interval ~60s): per key, classify escrows. Open/Claimed past `deliver_by` → `reclaim`. Submitted **with a verified receipt** still in accept-window → retry `acceptResult`. Submitted past accept-window → leave for supplier Release (log). Never blind-`reclaim` Submitted.
 - **Wallet-health tick**: periodically + after each settle, `planConsolidate` → `consolidateWallet` so every wallet keeps a ≥5 ADA collateral UTxO. Skip if already healthy.
--- a/gateway/.env.example
+++ b/gateway/.env.example
@@ -31,5 +31,6 @@ GATEWAY_DB_DIR=./data/gateway
 # KEY_RATE_WINDOW_MS=60000
 # SWEEPER_INTERVAL_MS=60000
 # DEMO_SESSION_IDLE_MS=180000 # close demo chat sessions idle this long (frees the supplier slot)
+# CHAT_SETTLE_MODE=full       # "full" (Claim/Submit/Accept) or "ticket" (escrow post only; sweeper reclaims) — must match suppliers
 # WALLET_HEALTH_INTERVAL_MS=600000
 # SDK_REGISTRY_MAX=500        # max cached per-key Marketplace instances
--- a/gateway/src/config.ts
+++ b/gateway/src/config.ts
@@ -41,10 +41,15 @@ export interface GatewayConfig {
  keyRate: { max: number; windowMs: number };
  demoIpRate: { max: number; windowMs: number };
  sweeperIntervalMs: number;
-  /** Close demo chat sessions idle this long (frees the single-slot supplier).
-   * Keep below the supplier's CHAT_IDLE_TIMEOUT_MS (default 5 min) so the
-   * gateway closes first and records usage. */
+  /** Close demo chat sessions idle this long (frees the supplier slot).
+   * Keep below the supplier's CHAT_IDLE_TIMEOUT_MS so the gateway closes
+   * first and records usage. */
  demoSessionIdleMs: number;
+  /** Chat-session settlement mode this deployment runs. "full" = suppliers
+   * Claim/Submit and the gateway Accepts; "ticket" = the escrow post at open
+   * is the only chain op and the sweeper Reclaims it after deliver_by.
+   * Must agree with the suppliers' CHAT_SETTLE_MODE. */
+  chatSettleMode: "full" | "ticket";
  walletHealthIntervalMs: number;
  sdkRegistryMax: number;
  corsOrigins: string[];
@@ -58,6 +63,14 @@ function requireField(env: Record<string, string | undefined>, name: string): st
  return v;
 }

+function chatSettleMode(env: Record<string, string | undefined>): "full" | "ticket" {
+  const v = env.CHAT_SETTLE_MODE ?? "full";
+  if (v !== "full" && v !== "ticket") {
+    throw new Error('loadConfig: CHAT_SETTLE_MODE must be "full" or "ticket"');
+  }
+  return v;
+}
+
 function posInt(
  env: Record<string, string | undefined>,
  name: string,
@@ -122,6 +135,7 @@ export function loadConfig(env: Record<string, string | undefined>): GatewayConf
    },
    sweeperIntervalMs: posInt(env, "SWEEPER_INTERVAL_MS", 60 * 1000),
    demoSessionIdleMs: posInt(env, "DEMO_SESSION_IDLE_MS", 3 * 60 * 1000),
+    chatSettleMode: chatSettleMode(env),
    walletHealthIntervalMs: posInt(env, "WALLET_HEALTH_INTERVAL_MS", 10 * 60 * 1000),
    sdkRegistryMax: posInt(env, "SDK_REGISTRY_MAX", 500),
    corsOrigins: (env.GATEWAY_CORS_ORIGINS ?? "")
--- a/gateway/src/onchain/settle.ts
+++ b/gateway/src/onchain/settle.ts
@@ -22,6 +22,8 @@ export interface EscrowRow {
  utxo_ref: string;
  state: string;
  posted_at: number;
+  /** Validator reclaim floor (indexer serves it; absent on very old rows). */
+  deliver_by?: number;
 }

 export async function fetchEscrows(
--- a/gateway/src/openai/demoChat.ts
+++ b/gateway/src/openai/demoChat.ts
@@ -60,8 +60,10 @@ function candidatesFor(keyId: string, model: string): AffinityCandidate[] {
  return out;
 }

-/** Record the session's flat fee when the demo executor closes its row (the
- * supplier already Submitted; the sweeper Accepts the escrow afterwards). */
+/** Record the session's cost when the demo executor closes its row. Full
+ * mode: the flat session fee (supplier Submitted; the sweeper Accepts the
+ * escrow afterwards). Ticket mode: 0 — nothing settles, the sweeper reclaims
+ * the escrow and the wallet is made whole minus fees. */
 function recordSessionCost(deps: GatewayDeps, session: SessionRow): void {
  deps.store.insertUsage({
    id: randomUUID(),
@@ -72,7 +74,7 @@ function recordSessionCost(deps: GatewayDeps, session: SessionRow): void {
    capability_id: CAPABILITY,
    supplier_pkh: session.supplier_pkh,
    escrow_ref: session.escrow_ref,
-    cost_lovelace: session.price_lovelace,
+    cost_lovelace: deps.config.chatSettleMode === "ticket" ? "0" : session.price_lovelace,
    prompt_tokens: 0,
    completion_tokens: 0,
    status: "completed",
--- a/gateway/src/openai/sessions.ts
+++ b/gateway/src/openai/sessions.ts
@@ -125,6 +125,16 @@ export async function openSessionCore(
  }
  if (!started || !used) throw toGatewayError(lastErr ?? new Error("no chat supplier could be engaged"));

+  // Deployment sanity: supplier and gateway must agree on the settle mode.
+  // Close behavior is driven per-session by the supplier's /end response, so
+  // a mismatch (rollout window) still settles correctly — just warn.
+  if ((started.settleMode === "ticket") !== (deps.config.chatSettleMode === "ticket")) {
+    // eslint-disable-next-line no-console
+    console.warn(
+      `[gateway] settle-mode mismatch: supplier ${used.supplierPkh.slice(0, 8)} ran "${started.settleMode}" but gateway is configured "${deps.config.chatSettleMode}"`,
+    );
+  }
+
  const sessionId = randomUUID();
  deps.store.insertSession({
    id: sessionId,
@@ -399,6 +409,33 @@ async function closeSession(
  deps.store.setSessionState(session.id, "closed", Date.now());
  dropSessionState(session.id);

+  if (result.settleMode === "ticket") {
+    // Nothing was Submitted/Accepted: no receipt, no charge (the escrow
+    // returns via the sweeper's reclaim), and no wallet churn to tidy up.
+    deps.store.insertUsage({
+      id: randomUUID(),
+      key_id: keyRow.id,
+      created_at: Date.now(),
+      kind: "chat_session",
+      model: session.model,
+      capability_id: CAPABILITY,
+      supplier_pkh: session.supplier_pkh,
+      escrow_ref: session.escrow_ref,
+      cost_lovelace: "0",
+      prompt_tokens: 0,
+      completion_tokens: 0,
+      status: "completed",
+      failure_reason: null,
+    });
+    res.status(200).json({
+      status: "ended",
+      escrow_ref: session.escrow_ref,
+      settle_mode: "ticket",
+      model: session.model,
+    });
+    return;
+  }
+
  const prompt = result.receipt.prompt_tokens ?? 0;
  const completion = result.receipt.completion_tokens ?? 0;
  deps.store.insertUsage({
--- a/gateway/src/sweeper.ts
+++ b/gateway/src/sweeper.ts
@@ -25,6 +25,17 @@
 * (terminal spends update nothing), and the validator preserves posted_at
 * across states — so a session's lineage is "rows sharing the posted_at of the
 * session's original Open ref row".
+ *
+ * Because terminal spends never update indexer rows, every settled escrow
+ * would be retried (one doomed chain query each) on every sweep forever. The
+ * in-process `settledRefs` memory skips refs this process has already settled
+ * or found spent; a restart just causes one harmless retry burst.
+ *
+ * Ticket mode (config.chatSettleMode === "ticket"): session escrows are never
+ * Claimed — they sit Open until reclaimed here after deliver_by. Reclaiming
+ * an Open ticket does NOT close a still-open session row: nothing re-checks
+ * the escrow after /v1/chat/start, so the conversation (and its affinity
+ * mirror) lives on, bounded only by the idle janitor.
 */

 import { randomUUID } from "crypto";
@@ -42,6 +53,23 @@ const MIN_AGE_MS = 90_000;
 const RECLAIM_AFTER_MS = 11 * 60 * 1000;
 // Chat-session escrows: deliver_by ≈ posted_at + 30 min, so wait longer.
 const CHAT_RECLAIM_AFTER_MS = 35 * 60 * 1000;
+// Reclaim only fires once the validator allows it (validity lower bound >=
+// deliver_by); attempting earlier is a guaranteed-doomed tx build.
+const DELIVER_BY_BUFFER_MS = 60_000;
+
+/** Refs this process already settled (Accepted/Reclaimed) or found spent.
+ * The indexer never updates terminal rows, so without this every historical
+ * escrow is retried each sweep. Bounded FIFO; restart = one retry burst. */
+const settledRefs = new Set<string>();
+const SETTLED_REFS_MAX = 5_000;
+
+function markSettled(ref: string): void {
+  settledRefs.add(ref);
+  if (settledRefs.size > SETTLED_REFS_MAX) {
+    const first = settledRefs.values().next().value;
+    if (first !== undefined) settledRefs.delete(first);
+  }
+}

 function log(msg: string): void {
  // eslint-disable-next-line no-console
@@ -77,7 +105,16 @@ function closeSessionRow(
  log(`closed abandoned session ${session.id} (${outcome.status})`);
 }

-export async function runSweepOnce(deps: GatewayDeps): Promise<void> {
+/** Chain-settle functions, injectable for tests. */
+export interface SweepSettleFns {
+  accept: typeof acceptAndConfirm;
+  reclaim: typeof reclaimAndConfirm;
+}
+
+export async function runSweepOnce(
+  deps: GatewayDeps,
+  settle: SweepSettleFns = { accept: acceptAndConfirm, reclaim: reclaimAndConfirm },
+): Promise<void> {
  // Idle demo sessions first: closing them makes the supplier Submit, so this
  // sweep (or the next) can Accept the escrow right after.
  await sweepIdleDemoSessions(deps).catch((err) =>
@@ -106,6 +143,7 @@ export async function runSweepOnce(deps: GatewayDeps): Promise<void> {
    for (const row of rows) {
      const ref = parseRef(row.utxo_ref);
      if (!ref) continue;
+      if (settledRefs.has(row.utxo_ref)) continue;
      const ageMs = now - (row.posted_at ?? 0);
      if (ageMs < MIN_AGE_MS) continue;
      const chatSession = sessionByPostedAt.get(row.posted_at);
@@ -113,8 +151,9 @@ export async function runSweepOnce(deps: GatewayDeps): Promise<void> {
      try {
        if (row.state === "Submitted") {
          try {
-            await ctx.mutex.run(() => acceptAndConfirm(deps.chain, ctx.walletKey, ref));
+            await ctx.mutex.run(() => settle.accept(deps.chain, ctx.walletKey, ref));
            log(`accepted stranded Submitted escrow ${row.utxo_ref}`);
+            markSettled(row.utxo_ref);
            if (chatSession) {
              closeSessionRow(deps, chatSession, { status: "completed", costLovelace: chatSession.price_lovelace });
            }
@@ -124,8 +163,11 @@ export async function runSweepOnce(deps: GatewayDeps): Promise<void> {
            // For session lineages, confirm the spend on-chain before closing
            // the row — an Accept that failed for another reason (timeout)
            // must leave the session open for the next sweep.
-            if (chatSession && (await deps.chain.queryUtxo(ref)) === null) {
-              closeSessionRow(deps, chatSession, { status: "completed", costLovelace: chatSession.price_lovelace });
+            if ((await deps.chain.queryUtxo(ref)) === null) {
+              markSettled(row.utxo_ref);
+              if (chatSession) {
+                closeSessionRow(deps, chatSession, { status: "completed", costLovelace: chatSession.price_lovelace });
+              }
            } else if (!chatSession) {
              // Preserve the historical quiet-skip for one-shot escrows.
              void err;
@@ -133,12 +175,25 @@ export async function runSweepOnce(deps: GatewayDeps): Promise<void> {
          }
        } else if (row.state === "Open" || row.state === "Claimed") {
          const reclaimAfterMs = chatSession ? CHAT_RECLAIM_AFTER_MS : RECLAIM_AFTER_MS;
-          if (ageMs > reclaimAfterMs) {
-            await ctx.mutex.run(() => reclaimAndConfirm(deps.chain, ctx.walletKey, ref));
+          // The validator only allows Reclaim at/after deliver_by — skip
+          // attempts that cannot succeed yet (early-closed ticket sessions).
+          const pastDeliverBy =
+            typeof row.deliver_by === "number" ? now > row.deliver_by + DELIVER_BY_BUFFER_MS : true;
+          if (ageMs > reclaimAfterMs && pastDeliverBy) {
+            await ctx.mutex.run(() => settle.reclaim(deps.chain, ctx.walletKey, ref));
            log(`reclaimed stranded ${row.state} escrow ${row.utxo_ref}`);
+            markSettled(row.utxo_ref);
            if (chatSession) {
-              // Funds returned — the session never settled; record no cost.
-              closeSessionRow(deps, chatSession, { status: "reclaimed", costLovelace: null });
+              const ticketOpen = deps.config.chatSettleMode === "ticket" && row.state === "Open";
+              if (ticketOpen) {
+                // Ticket escrow reclaimed out from under a LIVE session —
+                // by design. Keep the session row + mirror; only the idle
+                // janitor / close paths end ticket sessions.
+                log(`ticket mode: escrow reclaimed, session ${chatSession.id} stays open`);
+              } else {
+                // Funds returned — the session never settled; record no cost.
+                closeSessionRow(deps, chatSession, { status: "reclaimed", costLovelace: null });
+              }
            }
          }
        }
--- a/gateway/test/http.test.ts
+++ b/gateway/test/http.test.ts
@@ -22,7 +22,11 @@ const SUPPLIERS = [

 function makeDeps(
  fetchFn?: typeof globalThis.fetch,
-  overrides?: { demoIpRate?: { max: number; windowMs: number }; chain?: GatewayDeps["chain"] },
+  overrides?: {
+    demoIpRate?: { max: number; windowMs: number };
+    chain?: GatewayDeps["chain"];
+    chatSettleMode?: "full" | "ticket";
+  },
 ): GatewayDeps {
  const dbDir = join(tmpdir(), `gw-test-${randomUUID()}`);
  const store = new GatewayStore(dbDir);
@@ -39,6 +43,7 @@ function makeDeps(
    demoIpRate: overrides?.demoIpRate ?? { max: 1000, windowMs: 60_000 },
    sweeperIntervalMs: 60_000,
    demoSessionIdleMs: 180_000,
+    chatSettleMode: overrides?.chatSettleMode ?? "full",
    walletHealthIntervalMs: 600_000,
    sdkRegistryMax: 100,
    corsOrigins: [],
@@ -417,6 +422,60 @@ describe("gateway demo key", () => {
    expect(endCalls).toHaveLength(0);
  });

+  it("ticket mode: session close settles nothing and bills zero", async () => {
+    const { fetchFn } = demoFetch([
+      () => supplierSse([{ type: "token", value: "Hi" }, doneFrame({ role: "assistant", content: "Hi" }, "stop")]),
+    ]);
+    const deps = makeDeps(fetchFn, { chain: fundedChain, chatSettleMode: "ticket" });
+    const { rawKey, keyRow } = setupDemoKey(deps);
+    const ctx = deps.registry.getContext(keyRow);
+    const endChat = vi.fn(async (opts: { escrowRef: unknown }) => ({
+      settleMode: "ticket" as const,
+      escrowRef: opts.escrowRef,
+    }));
+    (ctx.sdk as { endChat: unknown }).endChat = endChat;
+    const app = createApp(deps);
+
+    const res1 = await request(app)
+      .post("/openai/v1/chat/completions")
+      .set("authorization", `Bearer ${rawKey}`)
+      .send({ model: "kimi", messages: [{ role: "user", content: "hi" }] });
+    expect(res1.status).toBe(200);
+
+    const session = deps.store.listOpenSessionsByKey(keyRow.id)[0];
+    const close = await request(app)
+      .post(`/openai/v1/chat/sessions/${session.id}/close`)
+      .set("authorization", `Bearer ${rawKey}`)
+      .send({});
+    expect(close.status).toBe(200);
+    expect(close.body.settle_mode).toBe("ticket");
+    expect(close.body.accepted_ref).toBeUndefined();
+    expect(endChat).toHaveBeenCalledTimes(1);
+
+    const usage = deps.store.listUsage(keyRow.id, 10);
+    expect(usage.some((u) => u.kind === "chat_session" && u.cost_lovelace === "0")).toBe(true);
+  });
+
+  it("ticket mode: janitor-closed demo sessions bill zero", async () => {
+    const { fetchFn, endCalls } = demoFetch([
+      () => supplierSse([{ type: "token", value: "Hi" }, doneFrame({ role: "assistant", content: "Hi" }, "stop")]),
+    ]);
+    const deps = makeDeps(fetchFn, { chain: fundedChain, chatSettleMode: "ticket" });
+    const { rawKey, keyRow } = setupDemoKey(deps);
+    const app = createApp(deps);
+
+    const res = await request(app)
+      .post("/openai/v1/chat/completions")
+      .set("authorization", `Bearer ${rawKey}`)
+      .send({ model: "kimi", messages: [{ role: "user", content: "hi" }] });
+    expect(res.status).toBe(200);
+
+    await sweepIdleDemoSessions(deps, Date.now() + deps.config.demoSessionIdleMs + 1);
+    expect(endCalls.length).toBeGreaterThan(0);
+    const usage = deps.store.listUsage(keyRow.id, 10);
+    expect(usage.some((u) => u.kind === "chat_session" && u.cost_lovelace === "0")).toBe(true);
+  });
+
  it("janitor closes idle demo sessions so the next request opens fresh", async () => {
    const { fetchFn, messageCalls, endCalls } = demoFetch([
      () => supplierSse([{ type: "token", value: "Hi" }, doneFrame({ role: "assistant", content: "Hi" }, "stop")]),
--- a/gateway/test/sweeper.test.ts
+++ b/gateway/test/sweeper.test.ts
@@ -0,0 +1,186 @@
+/**
+ * sweeper.test.ts — reclaim/close decoupling + settled-refs memory.
+ *
+ * Ticket mode: reclaiming a live session's Open escrow must NOT close the
+ * session row or drop its transcript mirror (the conversation continues on a
+ * spent ticket). Full mode keeps close-on-reclaim. Claimed rows close even
+ * under ticket config (they can only come from full-mode suppliers). The
+ * settled-refs memory prevents re-attempting refs already settled, and the
+ * deliver_by gate skips reclaims the validator would reject.
+ */
+
+import { describe, it, expect, vi } from "vitest";
+import { tmpdir } from "os";
+import { join } from "path";
+import { randomBytes, randomUUID } from "crypto";
+import { GatewayStore } from "../src/db/store.js";
+import { SdkRegistry } from "../src/sdk/registry.js";
+import { genPrivKeyHex, deriveWalletKey } from "../src/wallet.js";
+import { seal } from "../src/crypto/seal.js";
+import { hashApiKey } from "../src/middleware/apiKeyAuth.js";
+import { runSweepOnce } from "../src/sweeper.js";
+import { transcripts } from "../src/openai/transcripts.js";
+import type { GatewayConfig } from "../src/config.js";
+import type { GatewayDeps } from "../src/deps.js";
+import type { EscrowRow } from "../src/onchain/settle.js";
+
+const MASTER = "ab".repeat(32);
+
+function makeSweepDeps(opts: { chatSettleMode: "full" | "ticket"; escrows: EscrowRow[] }) {
+  const dbDir = join(tmpdir(), `gw-sweep-${randomUUID()}`);
+  const store = new GatewayStore(dbDir);
+  const config: GatewayConfig = {
+    masterKeyHex: MASTER,
+    indexerUrl: "http://ix",
+    ogmiosUrl: "http://og",
+    networkId: 0,
+    liveChain: true,
+    port: 0,
+    dbDir,
+    signupRate: { max: 1000, windowMs: 60_000 },
+    keyRate: { max: 1000, windowMs: 60_000 },
+    demoIpRate: { max: 1000, windowMs: 60_000 },
+    sweeperIntervalMs: 60_000,
+    demoSessionIdleMs: 180_000,
+    chatSettleMode: opts.chatSettleMode,
+    walletHealthIntervalMs: 600_000,
+    sdkRegistryMax: 100,
+    corsOrigins: [],
+  };
+  const chain = { queryUtxo: async () => null } as unknown as GatewayDeps["chain"];
+  const registry = new SdkRegistry({
+    chain,
+    indexerUrl: config.indexerUrl,
+    networkId: config.networkId,
+    masterKeyHex: config.masterKeyHex,
+    max: config.sdkRegistryMax,
+  });
+  const fetchFn = (async (url: unknown) => {
+    if (String(url).includes("/escrows")) return new Response(JSON.stringify(opts.escrows), { status: 200 });
+    return new Response("[]", { status: 200 });
+  }) as unknown as typeof globalThis.fetch;
+  const deps: GatewayDeps = { config, store, chain, registry, fetchFn };
+
+  const rawKey = `vk_test_${randomBytes(24).toString("hex")}`;
+  const privHex = genPrivKeyHex();
+  const walletKey = deriveWalletKey(privHex, 0);
+  const sealed = seal(privHex, MASTER);
+  store.insertKey({
+    id: randomUUID(),
+    key_hash: hashApiKey(rawKey),
+    key_prefix: rawKey.slice(0, 12),
+    label: "sweep-test",
+    wallet_pkh: walletKey.pubKeyHash,
+    deposit_address: walletKey.address,
+    enc_priv_nonce: sealed.nonce,
+    enc_priv_ct: sealed.ct,
+    enc_priv_tag: sealed.tag,
+    master_key_version: 1,
+    created_at: Date.now(),
+    demo: 1,
+  });
+  const keyRow = store.getKeyByHash(hashApiKey(rawKey))!;
+  return { deps, keyRow };
+}
+
+function insertOpenSession(deps: GatewayDeps, keyId: string, escrowRef: string): string {
+  const id = randomUUID();
+  deps.store.insertSession({
+    id,
+    key_id: keyId,
+    escrow_ref: escrowRef,
+    session_nonce: "nonce",
+    supplier_base_url: "http://sup",
+    supplier_pkh: "s1",
+    model: "kimi",
+    price_lovelace: "200000",
+    state: "open",
+    opened_at: Date.now() - 40 * 60 * 1000,
+  });
+  return id;
+}
+
+function openRow(refChar: string, opts?: Partial<EscrowRow>): EscrowRow {
+  return {
+    utxo_ref: `${refChar.repeat(64)}#0`,
+    state: "Open",
+    posted_at: Date.now() - 40 * 60 * 1000,
+    deliver_by: Date.now() - 5 * 60 * 1000,
+    ...opts,
+  };
+}
+
+const settleOk = () => ({
+  accept: vi.fn(async () => undefined) as never,
+  reclaim: vi.fn(async () => undefined) as never,
+});
+
+describe("sweeper — ticket-mode reclaim/close decoupling", () => {
+  it("reclaims a live session's Open ticket but keeps the session (and mirror) alive", async () => {
+    const row = openRow("1");
+    const { deps, keyRow } = makeSweepDeps({ chatSettleMode: "ticket", escrows: [row] });
+    const sessionId = insertOpenSession(deps, keyRow.id, row.utxo_ref);
+    transcripts.set(sessionId, [{ role: "user", content: "hi" }]);
+    const settle = settleOk();
+
+    await runSweepOnce(deps, settle);
+
+    expect(settle.reclaim).toHaveBeenCalledTimes(1);
+    expect(deps.store.getSession(sessionId)!.state).toBe("open"); // NOT closed
+    expect(transcripts.get(sessionId)).toBeDefined(); // mirror intact
+    expect(deps.store.listUsage(keyRow.id, 10)).toHaveLength(0); // nothing billed
+
+    transcripts.delete(sessionId);
+  });
+
+  it("full mode: reclaim closes the session row", async () => {
+    const row = openRow("2");
+    const { deps, keyRow } = makeSweepDeps({ chatSettleMode: "full", escrows: [row] });
+    const sessionId = insertOpenSession(deps, keyRow.id, row.utxo_ref);
+    const settle = settleOk();
+
+    await runSweepOnce(deps, settle);
+
+    expect(settle.reclaim).toHaveBeenCalledTimes(1);
+    expect(deps.store.getSession(sessionId)!.state).toBe("closed");
+    const usage = deps.store.listUsage(keyRow.id, 10);
+    expect(usage.some((u) => u.status === "reclaimed")).toBe(true);
+  });
+
+  it("ticket config still closes sessions behind Claimed rows (full-mode suppliers)", async () => {
+    const row = openRow("3", { state: "Claimed" });
+    const { deps, keyRow } = makeSweepDeps({ chatSettleMode: "ticket", escrows: [row] });
+    const sessionId = insertOpenSession(deps, keyRow.id, row.utxo_ref);
+    const settle = settleOk();
+
+    await runSweepOnce(deps, settle);
+
+    expect(settle.reclaim).toHaveBeenCalledTimes(1);
+    expect(deps.store.getSession(sessionId)!.state).toBe("closed");
+  });
+});
+
+describe("sweeper — reclaim gating + settled-refs memory", () => {
+  it("skips reclaim while deliver_by has not passed", async () => {
+    const row = openRow("4", { deliver_by: Date.now() + 10 * 60 * 1000 });
+    const { deps, keyRow } = makeSweepDeps({ chatSettleMode: "ticket", escrows: [row] });
+    insertOpenSession(deps, keyRow.id, row.utxo_ref);
+    const settle = settleOk();
+
+    await runSweepOnce(deps, settle);
+
+    expect(settle.reclaim).not.toHaveBeenCalled();
+  });
+
+  it("does not re-attempt refs it already settled (in-process memory)", async () => {
+    const row = openRow("5");
+    const { deps, keyRow } = makeSweepDeps({ chatSettleMode: "ticket", escrows: [row] });
+    insertOpenSession(deps, keyRow.id, row.utxo_ref);
+    const settle = settleOk();
+
+    await runSweepOnce(deps, settle);
+    await runSweepOnce(deps, settle);
+
+    expect(settle.reclaim).toHaveBeenCalledTimes(1);
+  });
+});
--- a/supplier/.env.example
+++ b/supplier/.env.example
@@ -126,3 +126,9 @@ ADVERT_DETAIL_HASH=
 # `docker compose down && up -d` to apply.
 # ESCROW_REF_UTXO=<txhash>#0
 # ADVERT_REF_UTXO=<txhash>#1
+
+# ─── Optional: chat-session tuning (CAPABILITY_KIND=chat-session only) ─────
+# CHAT_IDLE_TIMEOUT_MS=300000  # auto-end sessions idle this long
+# MAX_CHAT_SESSIONS=1          # concurrent session slots (default 1)
+# CHAT_SETTLE_MODE=full        # "full" (Claim/Submit) or "ticket" (no supplier
+#                              # chain ops; buyer reclaims the Open escrow)
--- a/supplier/src/chatSession.ts
+++ b/supplier/src/chatSession.ts
@@ -8,9 +8,10 @@
 * turns that run fully OFF-CHAIN, and is settled at /v1/chat/end (or by the
 * idle watchdog) when the supplier Submits a receipt over the whole transcript.
 *
- * Single-slot: the supplier serves one paid chat at a time (SupplierState
- * mutex), so at most one record is "active". Ended records are retained so
- * /v1/chat/end is idempotent (returns the same receipt).
+ * Concurrency: up to MAX_CHAT_SESSIONS records are "active" at once
+ * (SupplierState slot admission). Ended records are retained so /v1/chat/end
+ * is idempotent (returns the same receipt) and so a used ticket-mode escrow
+ * ref can never open a second session.
 *
 * Timer handles (idle + hard-cap) live on the record; server.ts arms them and
 * endChatSession clears them.
@@ -31,7 +32,11 @@ export interface ChatSessionEndResult {

 export interface ChatSessionRecord {
  escrowRef: string;
-  claimedRef: OutputReference;
+  /** Absent in ticket mode (the escrow is never Claimed). */
+  claimedRef?: OutputReference;
+  /** "full" = Claim/Submit lifecycle; "ticket" = no chain ops after the
+   * buyer's escrow post. */
+  settleMode: "full" | "ticket";
  advert: AdvertDatum;
  escrowDatum: EscrowDatum;
  /** Full ordered conversation (user + assistant turns). Hashed at End. */
@@ -49,7 +54,8 @@ export interface ChatSessionRecord {

 export interface CreateChatSessionParams {
  escrowRef: string;
-  claimedRef: OutputReference;
+  claimedRef?: OutputReference;
+  settleMode?: "full" | "ticket";
  advert: AdvertDatum;
  escrowDatum: EscrowDatum;
 }
@@ -62,6 +68,7 @@ export class ChatSessionStore {
    const record: ChatSessionRecord = {
      escrowRef: params.escrowRef,
      claimedRef: params.claimedRef,
+      settleMode: params.settleMode ?? "full",
      advert: params.advert,
      escrowDatum: params.escrowDatum,
      transcript: [],
--- a/supplier/src/chatSessionRunner.ts
+++ b/supplier/src/chatSessionRunner.ts
@@ -1,20 +1,22 @@
 /**
- * supplier/src/chatSessionRunner.ts — settles an open chat session.
+ * supplier/src/chatSessionRunner.ts — ends an open chat session.
 *
- * endChatSession is the chat-session analogue of runChatJob's receipt+Submit
- * tail (jobRunner.ts steps 3-7). It is invoked from BOTH /v1/chat/end (user
- * clicked "End chat") and the idle/hard-cap watchdog (abandoned session). It:
- *   1. atomically flips the session "active" → "ending" (idempotent re-entry)
- *   2. clears the idle + hard-cap timers
- *   3. builds + signs a receipt over the FULL transcript
- *      (response_hash = sha256(canonical(transcript)); the buyer recomputes
- *       this from its local transcript mirror to verify)
- *   4. buildSubmitTx against the Claimed UTxO → awaitTx (60s)
- *   5. stores the terminal result and ALWAYS releases the supplier lock
+ * endChatSession is invoked from BOTH /v1/chat/end (user clicked "End chat")
+ * and the idle/hard-cap watchdog (abandoned session). Behavior branches on
+ * the record's settleMode:
+ *
+ *   full   — chat-session analogue of runChatJob's receipt+Submit tail:
+ *            build + sign a receipt over the FULL transcript
+ *            (response_hash = sha256(canonical(transcript))), then
+ *            buildSubmitTx against the Claimed UTxO → awaitTx (60s), inside
+ *            the wallet mutex (never race another wallet spend).
+ *   ticket — no chain work at all: mark ended and free the slot. The escrow
+ *            was never Claimed; the buyer's sweeper Reclaims it after
+ *            deliver_by.
 *
 * Never throws. On any failure the session is marked "ended" with endFailure
- * and the lock is released (the escrow then lingers Claimed until the buyer
- * Reclaims after deliver_by — same fate as a failed one-off job).
+ * and the slot is released (a full-mode escrow then lingers Claimed until the
+ * buyer Reclaims after deliver_by — same fate as a failed one-off job).
 */

 import { canonicalize } from "@marketplace/shared/cbor";
@@ -41,7 +43,7 @@ export interface EndChatSessionParams {
 }

 /**
- * Settle a chat session. Returns the (now terminal) record, or null if no
+ * End a chat session. Returns the (now terminal) record, or null if no
 * session exists for the ref. Idempotent: a second call returns the same
 * record without re-submitting.
 */
@@ -59,6 +61,21 @@ export async function endChatSession(
  deps.sessions.clearTimers(record);

  try {
+    if (record.settleMode === "ticket") {
+      // No chain work: the un-Claimed escrow is the buyer's to reclaim.
+      record.status = "ended";
+      return record;
+    }
+    const claimedRef = record.claimedRef;
+    if (!claimedRef) {
+      // Full-mode record without a Claim ref should be impossible; end
+      // defensively rather than throw (this path must never leak the slot).
+      console.warn(`[chat_end_failed] escrow=${escrowRef} trigger=${trigger ?? "end"} reason=missing_claimed_ref`);
+      record.endFailure = { reason: "missing_claimed_ref", message: "full-mode session has no claimedRef" };
+      record.status = "ended";
+      return record;
+    }
+
    // ── Receipt over the full transcript ──────────────────────────────────
    const transcriptHash = sha256Hex(canonicalize(record.transcript));
    const receipt = buildReceipt({
@@ -74,27 +91,35 @@ export async function endChatSession(
    const signed = signReceipt(receipt, deps.supplierKey.privateKeyHex);
    const resultHash = receiptResultHash(signed);

-    // ── Submit (Claimed → Submitted) ──────────────────────────────────────
-    let buildResult: { txCborHex: string; expectedTxHash: string };
-    try {
-      buildResult = await buildSubmitTx({
-        chain: deps.chain,
-        supplierKey: deps.supplierKey,
-        escrowRef: record.claimedRef,
-        receiptHash: resultHash,
-      });
-    } catch (err) {
-      const message = err instanceof Error ? err.message : String(err);
+    // ── Submit (Claimed → Submitted): one wallet critical section ─────────
+    const submitOutcome = await deps.state.walletMutex.run(async () => {
+      let built: { txCborHex: string; expectedTxHash: string };
+      try {
+        built = await buildSubmitTx({
+          chain: deps.chain,
+          supplierKey: deps.supplierKey,
+          escrowRef: claimedRef,
+          receiptHash: resultHash,
+        });
+      } catch (err) {
+        return { kind: "build_failed" as const, err };
+      }
+      try {
+        await deps.chain.awaitTx(built.expectedTxHash, 60_000);
+      } catch (err) {
+        return { kind: "await_failed" as const, err };
+      }
+      return { kind: "ok" as const, built };
+    });
+    if (submitOutcome.kind === "build_failed") {
+      const message = submitOutcome.err instanceof Error ? submitOutcome.err.message : String(submitOutcome.err);
      console.warn(`[chat_end_failed] escrow=${escrowRef} trigger=${trigger ?? "end"} reason=submit_failed msg=${message}`);
      record.endFailure = { reason: "submit_failed", message: `Submit tx failed: ${message}` };
      record.status = "ended";
      return record;
    }
-
-    try {
-      await deps.chain.awaitTx(buildResult.expectedTxHash, 60_000);
-    } catch (err) {
-      const message = err instanceof Error ? err.message : String(err);
+    if (submitOutcome.kind === "await_failed") {
+      const message = submitOutcome.err instanceof Error ? submitOutcome.err.message : String(submitOutcome.err);
      console.warn(`[chat_end_failed] escrow=${escrowRef} trigger=${trigger ?? "end"} reason=submit_timeout msg=${message}`);
      record.endFailure = { reason: "submit_timeout", message: `Submit awaitTx failed: ${message}` };
      record.status = "ended";
@@ -105,14 +130,14 @@ export async function endChatSession(
      receipt: signed.receipt as unknown as Record<string, unknown>,
      receipt_signature: signed.signature,
      // The Submit tx output (index 0) is the new Submitted UTxO the buyer Accepts.
-      submitted_ref: `${buildResult.expectedTxHash}#0`,
+      submitted_ref: `${submitOutcome.built.expectedTxHash}#0`,
    };
    record.status = "ended";
    return record;
  } finally {
-    // Always release the single-slot lock so the next chat can start.
+    // Always release this session's slot so the next chat can start.
    try {
-      deps.state.release();
+      deps.state.release(record.escrowRef);
    } catch {
      /* never let lock-release escape */
    }
--- a/supplier/src/config.ts
+++ b/supplier/src/config.ts
@@ -66,6 +66,13 @@ export type CapabilityKind = "chat" | "tts" | "chat-session";
 /** LLM backend selected for the chat capability. */
 export type LlmBackend = "ollama" | "openai";

+/** Chain settlement mode for chat sessions.
+ *   "full"   — Claim at start, Submit receipt at end (buyer Accepts). Default.
+ *   "ticket" — the buyer's escrow post is the only chain op; the supplier
+ *              verifies it as an entry ticket but never Claims/Submits, and
+ *              the buyer's sweeper Reclaims the Open escrow after deliver_by. */
+export type ChatSettleMode = "full" | "ticket";
+
 export interface SupplierConfig {
  supplierPrivKeyHex: string;
  ogmiosUrl: string;
@@ -109,6 +116,13 @@ export interface SupplierConfig {
   * 300_000 (5 min).
   */
  chatIdleTimeoutMs: number;
+  /**
+   * Concurrent chat-session slots (capabilityKind="chat-session" only).
+   * Default 1 = legacy single-slot behavior.
+   */
+  maxChatSessions: number;
+  /** Chain settlement mode for chat sessions. Default "full". */
+  chatSettleMode: ChatSettleMode;
  /**
   * When true, the supplier boots a LiveOgmiosProvider (real submitTx/awaitTx).
   * Default false → ReadOnlyOgmiosProvider (safe; no chain writes).
@@ -278,6 +292,32 @@ export function loadConfig(env: Record<string, string | undefined>): SupplierCon
    chatIdleTimeoutMs = Number(chatIdleStr);
  }

+  // MAX_CHAT_SESSIONS — concurrent chat-session slots (default 1 = legacy
+  // single-slot). Only meaningful for capabilityKind="chat-session".
+  const maxSessionsStr = env.MAX_CHAT_SESSIONS;
+  let maxChatSessions = 1;
+  if (maxSessionsStr !== undefined && maxSessionsStr !== "") {
+    if (!POS_INT_RE.test(maxSessionsStr)) {
+      throw new Error("loadConfig: MAX_CHAT_SESSIONS must be a positive integer");
+    }
+    maxChatSessions = Number(maxSessionsStr);
+  }
+  if (maxChatSessions > 1 && capabilityKind !== "chat-session") {
+    throw new Error('loadConfig: MAX_CHAT_SESSIONS > 1 requires CAPABILITY_KIND="chat-session"');
+  }
+
+  // CHAT_SETTLE_MODE — "full" (default; Claim at start, Submit receipt at end)
+  // or "ticket" (the buyer's escrow post is the only chain op; the supplier
+  // never Claims/Submits and the buyer reclaims the escrow after deliver_by).
+  const settleModeStr = env.CHAT_SETTLE_MODE ?? "full";
+  if (settleModeStr !== "full" && settleModeStr !== "ticket") {
+    throw new Error('loadConfig: CHAT_SETTLE_MODE must be "full" or "ticket"');
+  }
+  if (settleModeStr === "ticket" && capabilityKind !== "chat-session") {
+    throw new Error('loadConfig: CHAT_SETTLE_MODE="ticket" requires CAPABILITY_KIND="chat-session"');
+  }
+  const chatSettleMode: ChatSettleMode = settleModeStr;
+
  const piperTimeoutStr = env.PIPER_TIMEOUT_MS;
  let piperTimeoutMs = 120_000;
  if (piperTimeoutStr !== undefined && piperTimeoutStr !== "") {
@@ -320,6 +360,8 @@ export function loadConfig(env: Record<string, string | undefined>): SupplierCon
    capabilityKind,
    llmBackend,
    chatIdleTimeoutMs,
+    maxChatSessions,
+    chatSettleMode,
    liveChain,
    walletHealthIntervalMs,
  };
--- a/supplier/src/index.ts
+++ b/supplier/src/index.ts
@@ -42,7 +42,8 @@ async function main(): Promise<void> {
  // M1-F-2: provider selection is driven by cfg.liveChain (LIVE_CHAIN=1).
  // ReadOnly is the safe default; live mode is explicit opt-in.
  const chain = buildChainProvider(cfg);
-  const state = new SupplierState();
+  // chat-session kind serves N concurrent sessions; one-shot kinds stay 1.
+  const state = new SupplierState(cfg.capabilityKind === "chat-session" ? cfg.maxChatSessions : 1);
  const jobs = new JobStore();

  const deps: SupplierDeps = { chain, state, config: cfg, supplierKey, jobs };
--- a/supplier/src/jobRunner.ts
+++ b/supplier/src/jobRunner.ts
@@ -143,17 +143,28 @@ export async function runChatJob(params: RunChatJobParams): Promise<void> {
    const signed = signReceipt(receipt, deps.supplierKey.privateKeyHex);
    const resultHash = receiptResultHash(signed);

-    // ── 4. Build + submit Submit tx ─────────────────────────────────────
-    let buildResult: { txCborHex: string; expectedTxHash: string };
-    try {
-      buildResult = await buildSubmitTx({
-        chain: deps.chain,
-        supplierKey: deps.supplierKey,
-        escrowRef: claimedRef,
-        receiptHash: resultHash,
-      });
-    } catch (err) {
-      const message = err instanceof Error ? err.message : String(err);
+    // ── 4+5. Submit tx: build + confirm as ONE wallet critical section ──
+    const submitOutcome = await deps.state.walletMutex.run(async () => {
+      let built: { txCborHex: string; expectedTxHash: string };
+      try {
+        built = await buildSubmitTx({
+          chain: deps.chain,
+          supplierKey: deps.supplierKey,
+          escrowRef: claimedRef,
+          receiptHash: resultHash,
+        });
+      } catch (err) {
+        return { kind: "build_failed" as const, err };
+      }
+      try {
+        await deps.chain.awaitTx(built.expectedTxHash, 60_000);
+      } catch (err) {
+        return { kind: "await_failed" as const, err };
+      }
+      return { kind: "ok" as const };
+    });
+    if (submitOutcome.kind === "build_failed") {
+      const message = submitOutcome.err instanceof Error ? submitOutcome.err.message : String(submitOutcome.err);
      console.warn(
        `[job_failed] jobId=${jobId} reason=submit_failed httpStatus=502 msg=${message}`,
      );
@@ -164,12 +175,8 @@ export async function runChatJob(params: RunChatJobParams): Promise<void> {
      });
      return;
    }
-
-    // ── 5. Submit confirmation (awaitTx, 60s budget) ───────────────────
-    try {
-      await deps.chain.awaitTx(buildResult.expectedTxHash, 60_000);
-    } catch (err) {
-      const msg = err instanceof Error ? err.message : String(err);
+    if (submitOutcome.kind === "await_failed") {
+      const msg = submitOutcome.err instanceof Error ? submitOutcome.err.message : String(submitOutcome.err);
      console.warn(
        `[job_failed] jobId=${jobId} reason=submit_timeout httpStatus=502 msg=${msg}`,
      );
@@ -201,9 +208,9 @@ export async function runChatJob(params: RunChatJobParams): Promise<void> {
    };
    deps.jobs.complete(jobId, payload);
  } finally {
-    // ── 7. Always release the lock ──────────────────────────────────────
+    // ── 7. Always release this job's slot ───────────────────────────────
    try {
-      deps.state.release();
+      deps.state.release(escrowRef);
    } catch {
      // never let a lock-release error escape the runner
    }
@@ -292,17 +299,28 @@ export async function runTtsJob(params: RunTtsJobParams): Promise<void> {
    const signed = signReceipt(receipt, deps.supplierKey.privateKeyHex);
    const resultHash = receiptResultHash(signed);

-    // ── 4. Build + submit Submit tx ───────────────────────────────────
-    let buildResult: { txCborHex: string; expectedTxHash: string };
-    try {
-      buildResult = await buildSubmitTx({
-        chain: deps.chain,
-        supplierKey: deps.supplierKey,
-        escrowRef: claimedRef,
-        receiptHash: resultHash,
-      });
-    } catch (err) {
-      const message = err instanceof Error ? err.message : String(err);
+    // ── 4+5. Submit tx: build + confirm as ONE wallet critical section ──
+    const submitOutcome = await deps.state.walletMutex.run(async () => {
+      let built: { txCborHex: string; expectedTxHash: string };
+      try {
+        built = await buildSubmitTx({
+          chain: deps.chain,
+          supplierKey: deps.supplierKey,
+          escrowRef: claimedRef,
+          receiptHash: resultHash,
+        });
+      } catch (err) {
+        return { kind: "build_failed" as const, err };
+      }
+      try {
+        await deps.chain.awaitTx(built.expectedTxHash, 60_000);
+      } catch (err) {
+        return { kind: "await_failed" as const, err };
+      }
+      return { kind: "ok" as const };
+    });
+    if (submitOutcome.kind === "build_failed") {
+      const message = submitOutcome.err instanceof Error ? submitOutcome.err.message : String(submitOutcome.err);
      console.warn(
        `[job_failed] jobId=${jobId} reason=submit_failed httpStatus=502 msg=${message}`,
      );
@@ -313,12 +331,8 @@ export async function runTtsJob(params: RunTtsJobParams): Promise<void> {
      });
      return;
    }
-
-    // ── 5. Submit confirmation ────────────────────────────────────────
-    try {
-      await deps.chain.awaitTx(buildResult.expectedTxHash, 60_000);
-    } catch (err) {
-      const msg = err instanceof Error ? err.message : String(err);
+    if (submitOutcome.kind === "await_failed") {
+      const msg = submitOutcome.err instanceof Error ? submitOutcome.err.message : String(submitOutcome.err);
      console.warn(
        `[job_failed] jobId=${jobId} reason=submit_timeout httpStatus=502 msg=${msg}`,
      );
@@ -344,7 +358,7 @@ export async function runTtsJob(params: RunTtsJobParams): Promise<void> {
    deps.jobs.complete(jobId, payload);
  } finally {
    try {
-      deps.state.release();
+      deps.state.release(escrowRef);
    } catch {
      /* never let lock-release escape */
    }
--- a/supplier/src/server.ts
+++ b/supplier/src/server.ts
@@ -147,6 +147,8 @@ function makeStatusHandler(deps: ResolvedDeps) {
    const payload: Record<string, unknown> = {
      status: snap.status,
      last_seen: snap.lastSeenIso,
+      active_sessions: snap.activeSessions,
+      max_sessions: snap.maxSessions,
    };
    if (snap.status === "working" && snap.currentEscrowRef) {
      payload.current_escrow_ref = snap.currentEscrowRef;
@@ -190,6 +192,9 @@ async function fetchActiveAdvert(deps: ResolvedDeps): Promise<AdvertResult> {

 function makeChatHandler(deps: ResolvedDeps) {
  return async (req: Request, res: Response, next: NextFunction) => {
+    // Slot held by THIS request (null until acquired / after hand-off to the
+    // job runner) — the catch-all must only release its own acquisition.
+    let acquiredRef: string | null = null;
    try {
      // ── 1. Header validation ──────────────────────────────────────────
      const headerVal = req.header("X-Escrow-Ref");
@@ -303,23 +308,37 @@ function makeChatHandler(deps: ResolvedDeps) {
          `now ${nowMs} >= deliver_by ${escrowDatum.deliver_by}`);
      }

-      // ── 8. Acquire single-slot lock ──────────────────────────────────
+      // ── 8. Acquire session slot ──────────────────────────────────────
      if (!deps.state.tryAcquire(escrowRefStr)) {
        return jsonError(res, 409, "supplier_busy", "supplier is already working another job");
      }
-      // From here on, every error path MUST release the lock until the
-      // runner takes ownership of the lock.
+      acquiredRef = escrowRefStr;
+      // From here on, every error path MUST release the slot until the
+      // runner takes ownership of it.

-      // ── 9. Submit Claim tx ───────────────────────────────────────────
-      let claimResult;
-      try {
-        claimResult = await buildClaimTx({
-          chain: deps.chain,
-          supplierKey: deps.supplierKey,
-          escrowRef,
-        });
-      } catch (err) {
-        deps.state.release();
+      // ── 9+10. Claim tx: build + confirm as ONE wallet critical section ─
+      // (splitting them would let another wallet spend coin-select mid-flight)
+      const claimOutcome = await deps.state.walletMutex.run(async () => {
+        let built;
+        try {
+          built = await buildClaimTx({
+            chain: deps.chain,
+            supplierKey: deps.supplierKey,
+            escrowRef,
+          });
+        } catch (err) {
+          return { kind: "build_failed" as const, err };
+        }
+        try {
+          await deps.chain.awaitTx(built.expectedTxHash, 60_000);
+        } catch (err) {
+          return { kind: "await_failed" as const, err };
+        }
+        return { kind: "ok" as const, built };
+      });
+      if (claimOutcome.kind === "build_failed") {
+        deps.state.release(escrowRefStr);
+        acquiredRef = null;
        // Backstop the periodic wallet-health ticker: most Claim build failures
        // we see in practice are wallet-shape problems (fragmentation, dust).
        // Fire-and-forget a debounced consolidate so the NEXT buyer retry
@@ -330,17 +349,15 @@ function makeChatHandler(deps: ResolvedDeps) {
          supplierKey: deps.supplierKey,
        });
        return jsonError(res, 503, "chain_submit_failed",
-          `Claim tx submit failed: ${(err as Error).message}`);
+          `Claim tx submit failed: ${(claimOutcome.err as Error).message}`);
      }
-
-      // ── 10. Await Claim confirmation ─────────────────────────────────
-      try {
-        await deps.chain.awaitTx(claimResult.expectedTxHash, 60_000);
-      } catch (err) {
-        deps.state.release();
+      if (claimOutcome.kind === "await_failed") {
+        deps.state.release(escrowRefStr);
+        acquiredRef = null;
        return jsonError(res, 504, "claim_timeout",
-          `Claim awaitTx failed: ${(err as Error).message}`);
+          `Claim awaitTx failed: ${(claimOutcome.err as Error).message}`);
      }
+      const claimResult = claimOutcome.built;

      // ── 11. Continuing-output ref + create job + fire-and-forget ─────
      const claimedRef: OutputReference = {
@@ -349,7 +366,8 @@ function makeChatHandler(deps: ResolvedDeps) {
      };
      const jobId = deps.jobs.create(escrowRefStr);

-      // Lock release now happens inside runChatJob's finally.
+      // Slot release now happens inside runChatJob's finally.
+      acquiredRef = null;
      void runChatJob({
        deps: {
          chain: deps.chain,
@@ -373,7 +391,9 @@ function makeChatHandler(deps: ResolvedDeps) {
        escrow_ref: escrowRefStr,
      });
    } catch (err) {
-      try { deps.state.release(); } catch { /* ignore */ }
+      if (acquiredRef) {
+        try { deps.state.release(acquiredRef); } catch { /* ignore */ }
+      }
      next(err);
      return;
    }
@@ -447,6 +467,8 @@ const ALLOWED_TTS_FORMATS = new Set(["mp3", "wav", "opus", "aac", "flac"]);

 function makeTtsHandler(deps: ResolvedDeps) {
  return async (req: Request, res: Response, next: NextFunction) => {
+    // Slot held by THIS request (null until acquired / after hand-off).
+    let acquiredRef: string | null = null;
    try {
      // ── 1. Header ───────────────────────────────────────────────────
      const headerVal = req.header("X-Escrow-Ref");
@@ -550,39 +572,53 @@ function makeTtsHandler(deps: ResolvedDeps) {
          `now ${nowMs} >= deliver_by ${escrowDatum.deliver_by}`);
      }

-      // ── 8. Lock ─────────────────────────────────────────────────────
+      // ── 8. Acquire session slot ─────────────────────────────────────
      if (!deps.state.tryAcquire(escrowRefStr)) {
        return jsonError(res, 409, "supplier_busy", "supplier is already working another job");
      }
+      acquiredRef = escrowRefStr;

-      // ── 9. Claim tx ─────────────────────────────────────────────────
-      let claimResult;
-      try {
-        claimResult = await buildClaimTx({
-          chain: deps.chain,
-          supplierKey: deps.supplierKey,
-          escrowRef,
-        });
-      } catch (err) {
-        deps.state.release();
+      // ── 9. Claim tx: build + confirm as ONE wallet critical section ──
+      const claimOutcome = await deps.state.walletMutex.run(async () => {
+        let built;
+        try {
+          built = await buildClaimTx({
+            chain: deps.chain,
+            supplierKey: deps.supplierKey,
+            escrowRef,
+          });
+        } catch (err) {
+          return { kind: "build_failed" as const, err };
+        }
+        try {
+          await deps.chain.awaitTx(built.expectedTxHash, 60_000);
+        } catch (err) {
+          return { kind: "await_failed" as const, err };
+        }
+        return { kind: "ok" as const, built };
+      });
+      if (claimOutcome.kind === "build_failed") {
+        deps.state.release(escrowRefStr);
+        acquiredRef = null;
        return jsonError(res, 503, "chain_submit_failed",
-          `Claim tx submit failed: ${(err as Error).message}`);
+          `Claim tx submit failed: ${(claimOutcome.err as Error).message}`);
      }
-      try {
-        await deps.chain.awaitTx(claimResult.expectedTxHash, 60_000);
-      } catch (err) {
-        deps.state.release();
+      if (claimOutcome.kind === "await_failed") {
+        deps.state.release(escrowRefStr);
+        acquiredRef = null;
        return jsonError(res, 504, "claim_timeout",
-          `Claim awaitTx failed: ${(err as Error).message}`);
+          `Claim awaitTx failed: ${(claimOutcome.err as Error).message}`);
      }

      // ── 10. Spawn runner + 202 ──────────────────────────────────────
      const claimedRef: OutputReference = {
-        txHash: claimResult.expectedTxHash,
+        txHash: claimOutcome.built.expectedTxHash,
        index: 0,
      };
      const jobId = deps.jobs.create(escrowRefStr);

+      // Slot release now happens inside runTtsJob's finally.
+      acquiredRef = null;
      void runTtsJob({
        deps: {
          chain: deps.chain,
@@ -605,7 +641,9 @@ function makeTtsHandler(deps: ResolvedDeps) {
        escrow_ref: escrowRefStr,
      });
    } catch (err) {
-      try { deps.state.release(); } catch { /* ignore */ }
+      if (acquiredRef) {
+        try { deps.state.release(acquiredRef); } catch { /* ignore */ }
+      }
      next(err);
      return;
    }
@@ -705,6 +743,9 @@ function makeChatSessionHandlers(deps: ResolvedDeps) {
  }

  const start = async (req: Request, res: Response, next: NextFunction) => {
+    // Slot held by THIS request (null until acquired / after the session
+    // record takes ownership) — the catch-all only releases its own.
+    let acquiredRef: string | null = null;
    try {
      // ── 1. Header ───────────────────────────────────────────────────
      const headerVal = req.header("X-Escrow-Ref");
@@ -717,6 +758,15 @@ function makeChatSessionHandlers(deps: ResolvedDeps) {
      }
      const escrowRefStr = `${escrowRef.txHash}#${escrowRef.index}`;

+      // ── 1.5 Duplicate-session guard ───────────────────────────────────
+      // Ended records are retained, so this also blocks replaying a used
+      // ticket-mode escrow (which stays Open on-chain — the state check below
+      // wouldn't catch it). In full mode the on-chain Claim already prevents
+      // reuse; this check just fails faster.
+      if (deps.chatSessions.get(escrowRefStr)) {
+        return jsonError(res, 409, "session_exists", "a chat session already exists for this escrow ref");
+      }
+
      // ── 2. Body (session_nonce; no messages) ─────────────────────────
      const body = (req.body ?? {}) as ChatStartBody;
      const sessionNonce = typeof body.session_nonce === "string" ? body.session_nonce : "";
@@ -780,36 +830,68 @@ function makeChatSessionHandlers(deps: ResolvedDeps) {
        return jsonError(res, 408, "past_deliver_by", `now ${nowMs} >= deliver_by ${escrowDatum.deliver_by}`);
      }

-      // ── 8. Single-slot lock ──────────────────────────────────────────
+      // ── 8. Acquire session slot ──────────────────────────────────────
      if (!deps.state.tryAcquire(escrowRefStr)) {
        return jsonError(res, 409, "supplier_busy", "supplier is already working another chat");
      }
+      acquiredRef = escrowRefStr;

-      // ── 9. Claim (Open → Claimed) — hold the lock on success ─────────
-      let claimResult;
-      try {
-        claimResult = await buildClaimTx({ chain: deps.chain, supplierKey: deps.supplierKey, escrowRef });
-      } catch (err) {
-        deps.state.release();
-        triggerOnFailureConsolidate({ chain: deps.chain, state: deps.state, supplierKey: deps.supplierKey });
-        return jsonError(res, 503, "chain_submit_failed", `Claim tx submit failed: ${(err as Error).message}`);
+      if (deps.config.chatSettleMode === "ticket") {
+        // ── 9-ticket. No Claim: the verified Open escrow IS the entry
+        // ticket. No hard-cap timer either — there is no Submit deadline, so
+        // the session may outlive deliver_by (the buyer reclaims the escrow
+        // independently). The idle timer is the only lifetime bound.
+        const record = deps.chatSessions.create({
+          escrowRef: escrowRefStr,
+          settleMode: "ticket",
+          advert,
+          escrowDatum,
+        });
+        acquiredRef = null; // record owns the slot; endChatSession releases it
+        armIdleTimer(record);
+        return res.status(200).json({ status: "ticket", escrow_ref: escrowRefStr, settle_mode: "ticket" });
      }
-      try {
-        await deps.chain.awaitTx(claimResult.expectedTxHash, 60_000);
-      } catch (err) {
-        deps.state.release();
-        return jsonError(res, 504, "claim_timeout", `Claim awaitTx failed: ${(err as Error).message}`);
+
+      // ── 9-full. Claim (Open → Claimed): build + confirm as ONE wallet
+      // critical section — hold the slot on success through Submit at end.
+      const claimOutcome = await deps.state.walletMutex.run(async () => {
+        let built;
+        try {
+          built = await buildClaimTx({ chain: deps.chain, supplierKey: deps.supplierKey, escrowRef });
+        } catch (err) {
+          return { kind: "build_failed" as const, err };
+        }
+        try {
+          await deps.chain.awaitTx(built.expectedTxHash, 60_000);
+        } catch (err) {
+          return { kind: "await_failed" as const, err };
+        }
+        return { kind: "ok" as const, built };
+      });
+      if (claimOutcome.kind === "build_failed") {
+        deps.state.release(escrowRefStr);
+        acquiredRef = null;
+        triggerOnFailureConsolidate({ chain: deps.chain, state: deps.state, supplierKey: deps.supplierKey });
+        return jsonError(res, 503, "chain_submit_failed", `Claim tx submit failed: ${(claimOutcome.err as Error).message}`);
+      }
+      if (claimOutcome.kind === "await_failed") {
+        deps.state.release(escrowRefStr);
+        acquiredRef = null;
+        return jsonError(res, 504, "claim_timeout", `Claim awaitTx failed: ${(claimOutcome.err as Error).message}`);
      }

      // ── 10. Create session + arm watchdog ────────────────────────────
-      const claimedRef: OutputReference = { txHash: claimResult.expectedTxHash, index: 0 };
-      const record = deps.chatSessions.create({ escrowRef: escrowRefStr, claimedRef, advert, escrowDatum });
+      const claimedRef: OutputReference = { txHash: claimOutcome.built.expectedTxHash, index: 0 };
+      const record = deps.chatSessions.create({ escrowRef: escrowRefStr, claimedRef, settleMode: "full", advert, escrowDatum });
+      acquiredRef = null; // record owns the slot; endChatSession releases it
      armIdleTimer(record);
      armHardCapTimer(record, nowMs);

      return res.status(200).json({ status: "claimed", escrow_ref: escrowRefStr });
    } catch (err) {
-      try { deps.state.release(); } catch { /* ignore */ }
+      if (acquiredRef) {
+        try { deps.state.release(acquiredRef); } catch { /* ignore */ }
+      }
      next(err);
      return;
    }
@@ -954,6 +1036,11 @@ function makeChatSessionHandlers(deps: ResolvedDeps) {
      if (!record) {
        return jsonError(res, 404, "chat_session_not_found", `no chat session for ${escrowRefStr}`);
      }
+      if (record.settleMode === "ticket") {
+        // No receipt/Submit in ticket mode — the buyer reclaims the escrow.
+        // Idempotent: a re-end returns the same shape.
+        return res.status(200).json({ status: "ended", escrow_ref: escrowRefStr, settle_mode: "ticket" });
+      }
      if (record.endFailure) {
        return jsonError(res, 502, record.endFailure.reason, record.endFailure.message);
      }
--- a/supplier/src/state.ts
+++ b/supplier/src/state.ts
@@ -1,35 +1,68 @@
 /**
- * supplier/src/state.ts — In-process single-slot concurrency lock.
+ * supplier/src/state.ts — In-process session-slot admission + wallet mutex.
 *
- * SupplierState tracks whether the node is free, working, or offline.
+ * SupplierState admits up to `capacity` concurrent sessions (capacity 1 for
+ * one-shot chat/tts kinds; MAX_CHAT_SESSIONS for chat-session kind). Status is
+ * free-until-full: "working" only when every slot is taken, so the indexer
+ * status poller and the buyer SDK's pre-check keep their existing semantics.
 * Cross-process coordination is M1-D; this is purely in-memory.
 *
- * Methods:
- *   tryAcquire(escrowRef): boolean  — atomic test-and-set; returns false unless free
- *   release()                       — transition working → free (no-op from free/offline)
- *   markOffline()                   — transition any state → offline; idempotent
- *   snapshot()                      — current status snapshot (defensive copy)
+ * walletMutex serializes every wallet-spending chain op (Claim/Submit/
+ * consolidate): the wallet holds one working UTxO + one collateral UTxO, so
+ * concurrent txs would double-spend regardless of how many session slots
+ * exist. Hold it across build+awaitTx as one critical section.
 *
 * Invariants:
- *   - currentEscrowRef is set IFF status === "working"
- *   - markOffline() clears currentEscrowRef
- *   - tryAcquire never overwrites a held lock
+ *   - a ref can be held at most once (duplicate tryAcquire returns false)
+ *   - release(ref) frees exactly that ref's slot
+ *   - markOffline() clears all slots and refuses new acquires
+ *   - snapshot.currentEscrowRef is present IFF status === "working" (legacy
+ *     consumers; holds the oldest active ref)
 *   - lastSeenIso updates on every state-changing operation
 */

 export type SupplierStatus = "free" | "working" | "offline";

+/** Tiny promise-chain mutex: run(fn) executes fns strictly one at a time. */
+export class Mutex {
+  private tail: Promise<unknown> = Promise.resolve();
+
+  run<T>(fn: () => Promise<T>): Promise<T> {
+    const result = this.tail.then(fn, fn);
+    // Keep the chain alive even if fn rejects; swallow here so the next
+    // run() isn't poisoned by a prior rejection.
+    this.tail = result.then(
+      () => undefined,
+      () => undefined,
+    );
+    return result;
+  }
+}
+
 export interface SupplierSnapshot {
  status: SupplierStatus;
+  /** Oldest active ref; present ONLY when status === "working" (back-compat). */
  currentEscrowRef?: string;
+  activeEscrowRefs: string[];
+  activeSessions: number;
+  maxSessions: number;
  lastSeenIso: string;
 }

 export class SupplierState {
-  private status: SupplierStatus = "free";
-  private currentEscrowRef: string | undefined = undefined;
+  /** Serializes ALL wallet-spending chain ops (Claim/Submit/consolidate). */
+  readonly walletMutex = new Mutex();
+
+  private readonly active = new Set<string>(); // insertion-ordered
+  private offline = false;
  private lastSeenIso: string = new Date().toISOString();

+  constructor(readonly capacity: number = 1) {
+    if (!Number.isInteger(capacity) || capacity < 1) {
+      throw new Error(`SupplierState: capacity must be a positive integer, got ${capacity}`);
+    }
+  }
+
  private touch(): void {
    // ISO 8601 with millisecond resolution. Coarse clocks may produce equal
    // values in tight succession — tests use >= rather than strict greater.
@@ -37,40 +70,45 @@ export class SupplierState {
  }

  tryAcquire(escrowRef: string): boolean {
-    if (this.status !== "free") return false;
-    this.status = "working";
-    this.currentEscrowRef = escrowRef;
+    if (this.offline) return false;
+    if (this.active.has(escrowRef)) return false;
+    if (this.active.size >= this.capacity) return false;
+    this.active.add(escrowRef);
    this.touch();
    return true;
  }

-  release(): void {
-    if (this.status === "working") {
-      this.status = "free";
-      this.currentEscrowRef = undefined;
+  release(escrowRef: string): void {
+    if (this.active.delete(escrowRef)) {
      this.touch();
    }
  }

  markOffline(): void {
-    this.status = "offline";
-    this.currentEscrowRef = undefined;
+    this.offline = true;
+    this.active.clear();
    this.touch();
  }

  snapshot(): SupplierSnapshot {
-    // Omit currentEscrowRef key entirely when not working so
-    // ('currentEscrowRef' in snap) === false (matches test expectation).
-    if (this.status === "working" && this.currentEscrowRef !== undefined) {
-      return {
-        status: this.status,
-        currentEscrowRef: this.currentEscrowRef,
-        lastSeenIso: this.lastSeenIso,
-      };
-    }
-    return {
-      status: this.status,
+    const refs = [...this.active];
+    const status: SupplierStatus = this.offline
+      ? "offline"
+      : refs.length >= this.capacity
+        ? "working"
+        : "free";
+    const snap: SupplierSnapshot = {
+      status,
+      activeEscrowRefs: refs,
+      activeSessions: refs.length,
+      maxSessions: this.capacity,
      lastSeenIso: this.lastSeenIso,
    };
+    // Omit currentEscrowRef key entirely when not working so
+    // ('currentEscrowRef' in snap) === false (matches legacy consumers).
+    if (status === "working" && refs.length > 0) {
+      snap.currentEscrowRef = refs[0];
+    }
+    return snap;
  }
 }
--- a/supplier/src/walletHealth.ts
+++ b/supplier/src/walletHealth.ts
@@ -16,9 +16,10 @@
 *     multiple consolidates. Returns 503 to the buyer for THIS request; the
 *     next buyer retry (~30-60s later) finds the wallet healthy.
 *
- * State-lock discipline: both layers use state.tryAcquire with a synthetic
- * escrowRef so they share the existing single-slot lock with real Claims.
- * If a Claim is in flight, the consolidation skips this tick.
+ * Wallet-lock discipline: consolidation spends EVERY wallet UTxO, so it runs
+ * inside state.walletMutex — the same mutex that serializes Claims/Submits —
+ * queueing behind any in-flight chain op instead of skipping. Session slots
+ * are not consumed: consolidation is a wallet op, not a session.
 */

 import type { ChainProvider } from "@marketplace/shared/chain";
@@ -31,7 +32,6 @@ import {

 import type { SupplierState } from "./state.js";

-const WALLET_HEALTH_LOCK_REF = "__wallet_consolidate__";
 const DEFAULT_COLLATERAL_LOVELACE = 5_000_000n;
 const DEFAULT_AWAIT_TIMEOUT_MS = 90_000;
 const DEFAULT_ON_FAILURE_DEBOUNCE_MS = 5 * 60_000;
@@ -77,20 +77,20 @@ async function consolidateOnce(
    opts.log("skip: another consolidate already in flight");
    return;
  }
-  if (!state.tryAcquire(WALLET_HEALTH_LOCK_REF)) {
-    opts.log("skip: supplier busy");
-    return;
-  }
  inFlight.add(state);
  const consolidate: ConsolidateFn = deps.consolidate ?? runConsolidateWallet;
  try {
-    const result = await consolidate({
-      chain: deps.chain,
-      walletKey: deps.supplierKey,
-      collateralLovelace: opts.collateralLovelace,
-      awaitTimeoutMs: opts.awaitTimeoutMs,
-      log: opts.log,
-    });
+    // Queue behind any in-flight Claim/Submit — consolidation reshapes the
+    // whole wallet and must never race another wallet spend.
+    const result = await state.walletMutex.run(() =>
+      consolidate({
+        chain: deps.chain,
+        walletKey: deps.supplierKey,
+        collateralLovelace: opts.collateralLovelace,
+        awaitTimeoutMs: opts.awaitTimeoutMs,
+        log: opts.log,
+      }),
+    );
    if (result.reason === "already-healthy") {
      opts.log("already-healthy");
    } else {
@@ -100,7 +100,6 @@ async function consolidateOnce(
    opts.log(`consolidate failed: ${(err as Error).message}`);
  } finally {
    inFlight.delete(state);
-    state.release();
  }
 }

--- a/tests/fixtures/supplier-side/sample-config.ts
+++ b/tests/fixtures/supplier-side/sample-config.ts
@@ -31,6 +31,8 @@ export function buildSampleConfig(): SupplierConfig {
    piperUrl: "",
    piperTimeoutMs: 120_000,
    capabilityKind: "chat",
+    maxChatSessions: 1,
+    chatSettleMode: "full",
    liveChain: false,
  };
 }
--- a/tests/unit/buyer-sdk-chat-session.test.ts
+++ b/tests/unit/buyer-sdk-chat-session.test.ts
@@ -0,0 +1,118 @@
+/**
+ * buyer-sdk-chat-session.test.ts — settle-mode handling in startChat/endChat.
+ *
+ * Ticket-mode suppliers answer /v1/chat/start with {status:"ticket"} and
+ * /v1/chat/end with {status:"ended", settle_mode:"ticket"}. The SDK must map
+ * those to settleMode:"ticket" — and, at end, skip receipt verification AND
+ * the Accept tx entirely (zero chain calls). Full-shaped responses keep the
+ * existing behavior.
+ */
+
+import { describe, it, expect, vi } from "vitest";
+import { Marketplace } from "../../buyer/src/sdk/Marketplace.js";
+import { MockChainProvider } from "../../packages/shared/src/chain/MockChainProvider.js";
+import { encodeAdvertDatum } from "../../packages/shared/src/cbor/AdvertDatum.js";
+import type { AdvertDatum } from "../../packages/shared/src/cbor/types.js";
+import { buildBuyerWalletKey } from "../fixtures/buyer-side/wallet-keys.js";
+
+const ADVERT_TX_HASH = "b".repeat(64);
+const ESCROW_REF = { txHash: "f".repeat(64), index: 0 };
+const ESCROW_REF_STR = `${ESCROW_REF.txHash}#0`;
+
+function advertDatum(): AdvertDatum {
+  return {
+    supplier_pkh: "abcdef0123456789abcdef0123456789abcdef0123456789abcdef01",
+    capability_id: "llm.chat.v1",
+    model: "kimi",
+    max_output_tokens: 512,
+    max_processing_ms: 1_800_000,
+    price_lovelace: 200_000n,
+    supplier_bond_lovelace: 1_000_000n,
+    buyer_bond_lovelace: 1_000_000n,
+    endpoint_url: "http://supplier.test",
+    detail_uri: "ipfs://QmTest",
+    detail_hash: "a".repeat(64),
+    advertised_at: 1_745_500_000_000,
+    status: "Active",
+  };
+}
+
+/** fetch stub answering the supplier's /status, /v1/chat/start, /v1/chat/end. */
+function supplierFetch(responses: { start?: unknown; end?: unknown }) {
+  return vi.fn(async (url: RequestInfo | URL) => {
+    const u = String(url);
+    if (u.includes("/status")) {
+      return new Response(JSON.stringify({ status: "free" }), { status: 200 });
+    }
+    if (u.includes("/v1/chat/start")) {
+      return new Response(JSON.stringify(responses.start ?? { status: "claimed" }), { status: 200 });
+    }
+    if (u.includes("/v1/chat/end")) {
+      return new Response(JSON.stringify(responses.end ?? {}), { status: 200 });
+    }
+    if (u.includes("/capability")) {
+      return new Response(JSON.stringify({ supplier_pkh: "", model: "kimi" }), { status: 200 });
+    }
+    return new Response("{}", { status: 200 });
+  }) as unknown as typeof globalThis.fetch;
+}
+
+function makeMp(fetchImpl: typeof globalThis.fetch, chain = new MockChainProvider()) {
+  chain.seed({
+    ref: { txHash: ADVERT_TX_HASH, index: 0 },
+    address: "addr_test1wfakeadvert",
+    lovelace: 2_000_000n,
+    assets: {},
+    datumHex: encodeAdvertDatum(advertDatum()),
+    scriptRef: null,
+  });
+  return { mp: new Marketplace({
+    chain,
+    indexerUrl: "http://indexer.test",
+    walletKey: buildBuyerWalletKey(),
+    networkParams: { networkId: 0 },
+    _fetch: fetchImpl,
+  }), chain };
+}
+
+describe("Marketplace.startChat — settle-mode mapping", () => {
+  it("maps {status:'ticket'} to settleMode ticket", async () => {
+    const { mp } = makeMp(supplierFetch({ start: { status: "ticket", settle_mode: "ticket" } }));
+    const result = await mp.startChat({ advertRef: { txHash: ADVERT_TX_HASH, index: 0 }, payment_lovelace: 200_000n });
+    expect(result.settleMode).toBe("ticket");
+  });
+
+  it("maps {status:'claimed'} (and legacy responses) to settleMode full", async () => {
+    const { mp } = makeMp(supplierFetch({ start: { status: "claimed" } }));
+    const result = await mp.startChat({ advertRef: { txHash: ADVERT_TX_HASH, index: 0 }, payment_lovelace: 200_000n });
+    expect(result.settleMode).toBe("full");
+  });
+});
+
+describe("Marketplace.endChat — ticket branch", () => {
+  it("returns the ticket result with zero chain calls and no receipt verification", async () => {
+    const chain = new MockChainProvider();
+    const submitSpy = vi.spyOn(chain, "submitTx");
+    const { mp } = makeMp(
+      supplierFetch({ end: { status: "ended", escrow_ref: ESCROW_REF_STR, settle_mode: "ticket" } }),
+      chain,
+    );
+
+    const result = await mp.endChat({
+      escrowRef: ESCROW_REF,
+      sessionNonce: "nonce-abc",
+      supplierBaseUrl: "http://supplier.test",
+    });
+
+    expect(result.settleMode).toBe("ticket");
+    expect("receipt" in result).toBe(false);
+    expect(submitSpy).not.toHaveBeenCalled(); // no Accept tx
+  });
+
+  it("still rejects a receipt-less response that does not declare ticket mode", async () => {
+    const { mp } = makeMp(supplierFetch({ end: { status: "submitted" } }));
+    await expect(
+      mp.endChat({ escrowRef: ESCROW_REF, sessionNonce: "nonce-abc", supplierBaseUrl: "http://supplier.test" }),
+    ).rejects.toThrow(/receipt/);
+  });
+});
--- a/tests/unit/supplier-chat-session-ticket.test.ts
+++ b/tests/unit/supplier-chat-session-ticket.test.ts
@@ -0,0 +1,277 @@
+/**
+ * supplier-chat-session-ticket.test.ts — entry-ticket settle mode + N slots.
+ *
+ * Ticket mode (CHAT_SETTLE_MODE=ticket): /v1/chat/start verifies the Open
+ * escrow but never Claims (zero chain txs), arms no hard-cap timer, and
+ * /v1/chat/end returns a receipt-less {status:"ended"}. A used escrow ref can
+ * never open a second session (records are retained). MAX_CHAT_SESSIONS
+ * admits N concurrent sessions and the N+1th start gets 409 supplier_busy.
+ */
+
+import { describe, it, expect, vi, afterEach } from "vitest";
+import request from "supertest";
+import { createHash } from "crypto";
+import type { Application } from "express";
+import { MockChainProvider } from "../../packages/shared/src/chain/MockChainProvider.js";
+import { canonicalize } from "../../packages/shared/src/cbor/canonical.js";
+import { encodeAdvertDatum } from "../../packages/shared/src/cbor/AdvertDatum.js";
+import { encodeEscrowDatum } from "../../packages/shared/src/cbor/EscrowDatum.js";
+import type { AdvertDatum, EscrowDatum } from "../../packages/shared/src/cbor/types.js";
+import { chatSessionPromptHash } from "../../packages/shared/src/tx/escrow/postChatEscrow.js";
+import type { SupplierConfig } from "../../supplier/src/config.js";
+import { SupplierState } from "../../supplier/src/state.js";
+import { JobStore } from "../../supplier/src/jobs.js";
+import { ChatSessionStore } from "../../supplier/src/chatSession.js";
+import { createApp } from "../../supplier/src/server.js";
+import { buildSampleConfig, SAMPLE_ADVERT_TX_HASH, SAMPLE_ADVERT_INDEX } from "../fixtures/supplier-side/sample-config.js";
+import { buildSupplierWalletKey, SUPPLIER_PKH } from "../fixtures/supplier-side/wallet-keys.js";
+
+const MODEL = "kimi";
+const MAX_TOKENS = 512;
+const CAPABILITY = "llm.chat.v1";
+const NONCE = "nonce-abc";
+const POSTED_AT = 1_745_500_000_000;
+const DELIVER_BY = POSTED_AT + 90_000;
+
+function sha256Hex(s: string): string {
+  return createHash("sha256").update(s, "utf8").digest("hex");
+}
+
+function advertDatum(): AdvertDatum {
+  return {
+    supplier_pkh: SUPPLIER_PKH,
+    capability_id: CAPABILITY,
+    model: MODEL,
+    max_output_tokens: MAX_TOKENS,
+    max_processing_ms: 1_800_000,
+    price_lovelace: 200_000n,
+    supplier_bond_lovelace: 1_000_000n,
+    buyer_bond_lovelace: 1_000_000n,
+    endpoint_url: "http://supplier.example:8080",
+    detail_uri: "ipfs://QmTest",
+    detail_hash: "a".repeat(64),
+    advertised_at: POSTED_AT,
+    status: "Active",
+  };
+}
+
+function escrowDatum(nonce: string): EscrowDatum {
+  return {
+    buyer_pkh: "1234567890abcdef1234567890abcdef1234567890abcdef12345678",
+    supplier_pkh: SUPPLIER_PKH,
+    advert_ref: { txHash: SAMPLE_ADVERT_TX_HASH, index: SAMPLE_ADVERT_INDEX },
+    capability_id: CAPABILITY,
+    request_spec_hash: sha256Hex(canonicalize({ capability_id: CAPABILITY, max_output_tokens: MAX_TOKENS, model: MODEL })),
+    prompt_hash: chatSessionPromptHash({ session_nonce: nonce }),
+    payment_lovelace: 200_000n,
+    buyer_bond_lovelace: 1_000_000n,
+    supplier_bond_lovelace: 1_000_000n,
+    deliver_by: DELIVER_BY,
+    posted_at: POSTED_AT,
+    submitted_at: null,
+    result_receipt_hash: null,
+    state: "Open",
+  };
+}
+
+interface Harness {
+  app: Application;
+  chain: MockChainProvider;
+  state: SupplierState;
+  chatSessions: ChatSessionStore;
+  seedEscrow: (txHashChar: string, nonce?: string) => string;
+}
+
+function makeHarness(overrides?: Partial<SupplierConfig>): Harness {
+  const chain = new MockChainProvider();
+  chain.seed({
+    ref: { txHash: SAMPLE_ADVERT_TX_HASH, index: SAMPLE_ADVERT_INDEX },
+    address: "addr_test1wfakeadvertaddress",
+    lovelace: 2_000_000n,
+    assets: {},
+    datumHex: encodeAdvertDatum(advertDatum()),
+    scriptRef: null,
+  });
+  const config: SupplierConfig = {
+    ...buildSampleConfig(),
+    capabilityKind: "chat-session",
+    llmBackend: "openai",
+    ollamaUrl: "",
+    openaiBaseUrl: "http://up",
+    openaiApiKey: "",
+    openaiTimeoutMs: 5_000,
+    openaiMaxTokens: 0,
+    openaiReasoningDisabled: false,
+    chatIdleTimeoutMs: 60_000,
+    chatSettleMode: "ticket",
+    maxChatSessions: 1,
+    ...overrides,
+  } as SupplierConfig;
+  const state = new SupplierState(config.maxChatSessions);
+  const chatSessions = new ChatSessionStore();
+  const app = createApp({
+    chain,
+    state,
+    config,
+    supplierKey: buildSupplierWalletKey(),
+    jobs: new JobStore(),
+    chatSessions,
+  });
+  const seedEscrow = (txHashChar: string, nonce = NONCE): string => {
+    const txHash = txHashChar.repeat(64);
+    chain.seed({
+      ref: { txHash, index: 0 },
+      address: "addr_test1wfakeescrowaddress",
+      lovelace: 2_200_000n,
+      assets: {},
+      datumHex: encodeEscrowDatum(escrowDatum(nonce)),
+      scriptRef: null,
+    });
+    return `${txHash}#0`;
+  };
+  return { app, chain, state, chatSessions, seedEscrow };
+}
+
+afterEach(() => {
+  vi.restoreAllMocks();
+});
+
+describe("chat-session ticket mode — /v1/chat/start", () => {
+  it("verifies the escrow, skips Claim, and arms no hard-cap timer", async () => {
+    const h = makeHarness();
+    const submitSpy = vi.spyOn(h.chain, "submitTx");
+    const ref = h.seedEscrow("e");
+
+    const res = await request(h.app)
+      .post("/v1/chat/start")
+      .set("X-Escrow-Ref", ref)
+      .send({ session_nonce: NONCE });
+
+    expect(res.status).toBe(200);
+    expect(res.body).toEqual({ status: "ticket", escrow_ref: ref, settle_mode: "ticket" });
+    expect(submitSpy).not.toHaveBeenCalled(); // zero chain txs
+
+    const record = h.chatSessions.get(ref)!;
+    expect(record.settleMode).toBe("ticket");
+    expect(record.claimedRef).toBeUndefined();
+    expect(record.idleTimer).toBeDefined();
+    expect(record.hardCapTimer).toBeUndefined();
+    expect(h.state.snapshot().activeSessions).toBe(1);
+  });
+
+  it("still rejects a foreign-supplier escrow", async () => {
+    const h = makeHarness();
+    const txHash = "c".repeat(64);
+    h.chain.seed({
+      ref: { txHash, index: 0 },
+      address: "addr_test1wfakeescrowaddress",
+      lovelace: 2_200_000n,
+      assets: {},
+      datumHex: encodeEscrowDatum({ ...escrowDatum(NONCE), supplier_pkh: "9".repeat(56) }),
+      scriptRef: null,
+    });
+    const res = await request(h.app)
+      .post("/v1/chat/start")
+      .set("X-Escrow-Ref", `${txHash}#0`)
+      .send({ session_nonce: NONCE });
+    expect(res.status).toBe(403);
+    expect(res.body.reason).toBe("wrong_supplier");
+  });
+
+  it("rejects reusing an escrow ref while the session is active AND after it ended", async () => {
+    const h = makeHarness();
+    const ref = h.seedEscrow("e");
+
+    const first = await request(h.app).post("/v1/chat/start").set("X-Escrow-Ref", ref).send({ session_nonce: NONCE });
+    expect(first.status).toBe(200);
+
+    const whileActive = await request(h.app).post("/v1/chat/start").set("X-Escrow-Ref", ref).send({ session_nonce: NONCE });
+    expect(whileActive.status).toBe(409);
+    expect(whileActive.body.reason).toBe("session_exists");
+
+    await request(h.app).post("/v1/chat/end").set("X-Escrow-Ref", ref).send({});
+    // The escrow is still Open on-chain (never Claimed) — the retained record
+    // is the only thing standing between a used ticket and a free session.
+    const afterEnd = await request(h.app).post("/v1/chat/start").set("X-Escrow-Ref", ref).send({ session_nonce: NONCE });
+    expect(afterEnd.status).toBe(409);
+    expect(afterEnd.body.reason).toBe("session_exists");
+  });
+});
+
+describe("chat-session ticket mode — /v1/chat/end", () => {
+  it("ends without a receipt, frees the slot, and is idempotent", async () => {
+    const h = makeHarness();
+    const submitSpy = vi.spyOn(h.chain, "submitTx");
+    const ref = h.seedEscrow("e");
+    await request(h.app).post("/v1/chat/start").set("X-Escrow-Ref", ref).send({ session_nonce: NONCE });
+
+    const end = await request(h.app).post("/v1/chat/end").set("X-Escrow-Ref", ref).send({});
+    expect(end.status).toBe(200);
+    expect(end.body).toEqual({ status: "ended", escrow_ref: ref, settle_mode: "ticket" });
+    expect(end.body.receipt).toBeUndefined();
+    expect(submitSpy).not.toHaveBeenCalled();
+    expect(h.state.snapshot().activeSessions).toBe(0);
+
+    const again = await request(h.app).post("/v1/chat/end").set("X-Escrow-Ref", ref).send({});
+    expect(again.status).toBe(200);
+    expect(again.body.status).toBe("ended");
+  });
+});
+
+describe("chat-session slots — MAX_CHAT_SESSIONS", () => {
+  it("admits N concurrent sessions and 409s the N+1th", async () => {
+    const h = makeHarness({ maxChatSessions: 2 });
+    // NB: "b".repeat(64) is the advert tx hash — do not reuse it for escrows.
+    const refA = h.seedEscrow("d");
+    const refB = h.seedEscrow("e");
+    const refC = h.seedEscrow("f");
+
+    const a = await request(h.app).post("/v1/chat/start").set("X-Escrow-Ref", refA).send({ session_nonce: NONCE });
+    const b = await request(h.app).post("/v1/chat/start").set("X-Escrow-Ref", refB).send({ session_nonce: NONCE });
+    expect(a.status).toBe(200);
+    expect(b.status).toBe(200);
+
+    const status = await request(h.app).get("/status");
+    expect(status.body.status).toBe("working");
+    expect(status.body.active_sessions).toBe(2);
+    expect(status.body.max_sessions).toBe(2);
+
+    const c = await request(h.app).post("/v1/chat/start").set("X-Escrow-Ref", refC).send({ session_nonce: NONCE });
+    expect(c.status).toBe(409);
+    expect(c.body.reason).toBe("supplier_busy");
+
+    // Ending one session readmits the third.
+    await request(h.app).post("/v1/chat/end").set("X-Escrow-Ref", refA).send({});
+    const retry = await request(h.app).post("/v1/chat/start").set("X-Escrow-Ref", refC).send({ session_nonce: NONCE });
+    expect(retry.status).toBe(200);
+  });
+
+  it("serves concurrent message turns on distinct sessions", async () => {
+    const h = makeHarness({ maxChatSessions: 2 });
+    const refA = h.seedEscrow("d");
+    const refB = h.seedEscrow("e");
+    await request(h.app).post("/v1/chat/start").set("X-Escrow-Ref", refA).send({ session_nonce: NONCE });
+    await request(h.app).post("/v1/chat/start").set("X-Escrow-Ref", refB).send({ session_nonce: NONCE });
+
+    const stream = [
+      `data: ${JSON.stringify({ choices: [{ delta: { content: "Hello" }, finish_reason: null }] })}\n\n`,
+      `data: ${JSON.stringify({ choices: [{ delta: {}, finish_reason: "stop" }], usage: { prompt_tokens: 3, completion_tokens: 2 } })}\n\n`,
+      "data: [DONE]\n\n",
+    ].join("");
+    vi.stubGlobal(
+      "fetch",
+      vi.fn().mockImplementation(async () =>
+        new Response(stream, { status: 200, headers: { "content-type": "text/event-stream" } })),
+    );
+
+    const [ta, tb] = await Promise.all([
+      request(h.app).post("/v1/chat/message").set("X-Escrow-Ref", refA).send({ messages: [{ role: "user", content: "hi" }] }),
+      request(h.app).post("/v1/chat/message").set("X-Escrow-Ref", refB).send({ messages: [{ role: "user", content: "yo" }] }),
+    ]);
+    expect(ta.text).toContain('"type":"done"');
+    expect(tb.text).toContain('"type":"done"');
+    expect(h.chatSessions.get(refA)!.transcript).toHaveLength(2);
+    expect(h.chatSessions.get(refB)!.transcript).toHaveLength(2);
+    vi.unstubAllGlobals();
+  });
+});
--- a/tests/unit/supplier-config.test.ts
+++ b/tests/unit/supplier-config.test.ts
@@ -218,3 +218,39 @@ describe("parseAdvertRef()", () => {
    expect(() => parseAdvertRef(`${"a".repeat(64)}#-1`)).toThrow();
  });
 });
+
+// ─── loadConfig — chat-session concurrency + settle mode ─────────────────────
+
+describe("loadConfig() — MAX_CHAT_SESSIONS / CHAT_SETTLE_MODE", () => {
+  const chatSessionEnv = () => ({
+    ...buildSampleEnv(),
+    CAPABILITY_KIND: "chat-session",
+    LLM_BACKEND: "openai",
+    OPENAI_BASE_URL: "http://up",
+  });
+
+  it("defaults to 1 slot and full settle mode", () => {
+    const cfg = loadConfig(buildSampleEnv());
+    expect(cfg.maxChatSessions).toBe(1);
+    expect(cfg.chatSettleMode).toBe("full");
+  });
+
+  it("parses MAX_CHAT_SESSIONS and CHAT_SETTLE_MODE for chat-session kind", () => {
+    const cfg = loadConfig({ ...chatSessionEnv(), MAX_CHAT_SESSIONS: "8", CHAT_SETTLE_MODE: "ticket" });
+    expect(cfg.maxChatSessions).toBe(8);
+    expect(cfg.chatSettleMode).toBe("ticket");
+  });
+
+  it("rejects MAX_CHAT_SESSIONS > 1 for non-chat-session kinds", () => {
+    expect(() => loadConfig({ ...buildSampleEnv(), MAX_CHAT_SESSIONS: "4" })).toThrow();
+  });
+
+  it("rejects CHAT_SETTLE_MODE=ticket for non-chat-session kinds", () => {
+    expect(() => loadConfig({ ...buildSampleEnv(), CHAT_SETTLE_MODE: "ticket" })).toThrow();
+  });
+
+  it("rejects invalid values", () => {
+    expect(() => loadConfig({ ...chatSessionEnv(), MAX_CHAT_SESSIONS: "0" })).toThrow();
+    expect(() => loadConfig({ ...chatSessionEnv(), CHAT_SETTLE_MODE: "nope" })).toThrow();
+  });
+});
--- a/tests/unit/supplier-routes-status.test.ts
+++ b/tests/unit/supplier-routes-status.test.ts
@@ -117,6 +117,25 @@ describe("GET /status — response body when offline", () => {
  });
 });

+describe("GET /status — session slot fields", () => {
+  it("reports active_sessions/max_sessions when free", async () => {
+    const state = new SupplierState();
+    const res = await request(makeApp(state)).get("/status");
+    expect(res.body.active_sessions).toBe(0);
+    expect(res.body.max_sessions).toBe(1);
+  });
+
+  it("stays free with slots remaining and reports the active count", async () => {
+    const state = new SupplierState(3);
+    state.tryAcquire(ESCROW_REF);
+    const res = await request(makeApp(state)).get("/status");
+    expect(res.body.status).toBe("free");
+    expect(res.body.active_sessions).toBe(1);
+    expect(res.body.max_sessions).toBe(3);
+    expect(res.body.current_escrow_ref).toBeUndefined();
+  });
+});
+
 describe("GET /status — does not touch chain", () => {
  it("returns 200 even when chain has no UTxOs seeded", async () => {
    // If the handler incorrectly touches chain, it would throw because
--- a/tests/unit/supplier-state.test.ts
+++ b/tests/unit/supplier-state.test.ts
@@ -1,11 +1,13 @@
 /**
- * supplier-state.test.ts — RED phase tests for supplier/src/state.ts
+ * supplier-state.test.ts — tests for supplier/src/state.ts
 *
- * Tests the SupplierState in-process slot lock:
- *   - tryAcquire(escrowRef): boolean — atomic test-and-set
- *   - release()
+ * Tests the SupplierState session-slot admission (capacity-aware) + the
+ * wallet mutex:
+ *   - tryAcquire(escrowRef): boolean — slot admission (default capacity 1)
+ *   - release(escrowRef) — frees exactly that ref's slot
 *   - markOffline()
- *   - snapshot(): { status, currentEscrowRef?, lastSeenIso }
+ *   - snapshot(): { status, currentEscrowRef?, activeSessions, maxSessions, ... }
+ *   - walletMutex.run — strict serialization of wallet chain ops
 */

 import { describe, it, expect, beforeEach } from "vitest";
@@ -13,6 +15,7 @@ import { SupplierState } from "../../supplier/src/state.js";

 const ESCROW_REF_A = `${"f".repeat(64)}#0`;
 const ESCROW_REF_B = `${"e".repeat(64)}#1`;
+const ESCROW_REF_C = `${"d".repeat(64)}#2`;

 describe("SupplierState — initial state", () => {
  it("starts in free state", () => {
@@ -102,25 +105,25 @@ describe("SupplierState.release()", () => {

  it("transitions working → free", () => {
    state.tryAcquire(ESCROW_REF_A);
-    state.release();
+    state.release(ESCROW_REF_A);
    expect(state.snapshot().status).toBe("free");
  });

  it("clears currentEscrowRef on release", () => {
    state.tryAcquire(ESCROW_REF_A);
-    state.release();
+    state.release(ESCROW_REF_A);
    expect(state.snapshot().currentEscrowRef).toBeUndefined();
  });

  it("allows re-acquire after release", () => {
    state.tryAcquire(ESCROW_REF_A);
-    state.release();
+    state.release(ESCROW_REF_A);
    expect(state.tryAcquire(ESCROW_REF_B)).toBe(true);
  });

  it("re-acquire after release sets new currentEscrowRef", () => {
    state.tryAcquire(ESCROW_REF_A);
-    state.release();
+    state.release(ESCROW_REF_A);
    state.tryAcquire(ESCROW_REF_B);
    expect(state.snapshot().currentEscrowRef).toBe(ESCROW_REF_B);
  });
@@ -128,7 +131,7 @@ describe("SupplierState.release()", () => {
  it("updates lastSeenIso on release", () => {
    state.tryAcquire(ESCROW_REF_A);
    const beforeRelease = state.snapshot().lastSeenIso;
-    state.release();
+    state.release(ESCROW_REF_A);
    const afterRelease = state.snapshot().lastSeenIso;
    expect(new Date(afterRelease).getTime()).not.toBeNaN();
    expect(afterRelease >= beforeRelease).toBe(true);
@@ -199,4 +202,94 @@ describe("SupplierState.snapshot()", () => {
    // State must remain working
    expect(state.snapshot().status).toBe("working");
  });
+
+  it("reports active/max session counts", () => {
+    const state = new SupplierState();
+    expect(state.snapshot().activeSessions).toBe(0);
+    expect(state.snapshot().maxSessions).toBe(1);
+    state.tryAcquire(ESCROW_REF_A);
+    expect(state.snapshot().activeSessions).toBe(1);
+    expect(state.snapshot().activeEscrowRefs).toEqual([ESCROW_REF_A]);
+  });
+});
+
+describe("SupplierState — capacity > 1", () => {
+  let state: SupplierState;
+
+  beforeEach(() => {
+    state = new SupplierState(2);
+  });
+
+  it("stays free until every slot is taken (free-until-full)", () => {
+    expect(state.tryAcquire(ESCROW_REF_A)).toBe(true);
+    expect(state.snapshot().status).toBe("free");
+    expect(state.snapshot().activeSessions).toBe(1);
+    expect("currentEscrowRef" in state.snapshot()).toBe(false);
+
+    expect(state.tryAcquire(ESCROW_REF_B)).toBe(true);
+    expect(state.snapshot().status).toBe("working");
+    expect(state.snapshot().currentEscrowRef).toBe(ESCROW_REF_A); // oldest
+  });
+
+  it("rejects the N+1th acquire", () => {
+    state.tryAcquire(ESCROW_REF_A);
+    state.tryAcquire(ESCROW_REF_B);
+    expect(state.tryAcquire(ESCROW_REF_C)).toBe(false);
+  });
+
+  it("rejects a duplicate ref while held", () => {
+    state.tryAcquire(ESCROW_REF_A);
+    expect(state.tryAcquire(ESCROW_REF_A)).toBe(false);
+  });
+
+  it("release frees exactly that ref's slot", () => {
+    state.tryAcquire(ESCROW_REF_A);
+    state.tryAcquire(ESCROW_REF_B);
+    state.release(ESCROW_REF_A);
+    expect(state.snapshot().status).toBe("free");
+    expect(state.snapshot().activeEscrowRefs).toEqual([ESCROW_REF_B]);
+    expect(state.tryAcquire(ESCROW_REF_C)).toBe(true);
+  });
+
+  it("release of an unheld ref is a no-op", () => {
+    state.tryAcquire(ESCROW_REF_A);
+    state.release(ESCROW_REF_B);
+    expect(state.snapshot().activeSessions).toBe(1);
+  });
+
+  it("markOffline clears all slots and refuses new acquires", () => {
+    state.tryAcquire(ESCROW_REF_A);
+    state.tryAcquire(ESCROW_REF_B);
+    state.markOffline();
+    expect(state.snapshot().status).toBe("offline");
+    expect(state.snapshot().activeSessions).toBe(0);
+    expect(state.tryAcquire(ESCROW_REF_C)).toBe(false);
+  });
+
+  it("rejects a non-positive capacity", () => {
+    expect(() => new SupplierState(0)).toThrow();
+  });
+});
+
+describe("SupplierState.walletMutex", () => {
+  it("serializes runs in submission order and survives rejection", async () => {
+    const state = new SupplierState(4);
+    const order: number[] = [];
+    const p1 = state.walletMutex.run(async () => {
+      await new Promise((r) => setTimeout(r, 20));
+      order.push(1);
+    });
+    const p2 = state.walletMutex.run(async () => {
+      order.push(2);
+    });
+    await Promise.all([p1, p2]);
+    expect(order).toEqual([1, 2]);
+
+    await state.walletMutex
+      .run(async () => {
+        throw new Error("boom");
+      })
+      .catch(() => undefined);
+    expect(await state.walletMutex.run(async () => 42)).toBe(42);
+  });
 });
--- a/tests/unit/supplier-walletHealth.test.ts
+++ b/tests/unit/supplier-walletHealth.test.ts
@@ -4,11 +4,11 @@
 *
 * Coverage:
 *   - Ticker calls consolidate when idle, logs already-healthy
- *   - Ticker skips when the supplier state is busy
- *   - Ticker releases the lock around runConsolidateWallet (success + failure)
+ *   - Consolidation runs even while session slots are held (wallet ops don't
+ *     consume session slots) but queues behind a held walletMutex
+ *   - Failure paths never leave the walletMutex poisoned
 *   - On-failure trigger fires consolidate the first time
 *   - On-failure trigger debounces back-to-back invocations
- *   - On-failure trigger respects the state lock
 *
 * The consolidate function is injected via deps so the test never touches
 * a real Ogmios.
@@ -91,7 +91,7 @@ describe("walletHealth — ticker", () => {
    ticker.stop();
  });

-  it("skips when supplier state is busy", async () => {
+  it("runs even while a session slot is held (wallet ops don't consume slots)", async () => {
    state.tryAcquire(ESCROW_REF);
    consolidate.mockResolvedValue(healthyResult);

@@ -101,16 +101,39 @@ describe("walletHealth — ticker", () => {
    );

    await vi.advanceTimersByTimeAsync(1_000);
-    await vi.advanceTimersByTimeAsync(0);
+    await vi.waitFor(() => expect(consolidate).toHaveBeenCalledTimes(1));

-    expect(consolidate).not.toHaveBeenCalled();
-    expect(logLines).toContain("skip: supplier busy");
+    // The held session slot is untouched.
    expect(state.snapshot().status).toBe("working");
+    expect(state.snapshot().activeEscrowRefs).toEqual([ESCROW_REF]);

    ticker.stop();
  });

-  it("releases the lock after a successful consolidate", async () => {
+  it("queues behind a held walletMutex instead of racing it", async () => {
+    consolidate.mockResolvedValue(healthyResult);
+    let releaseChainOp: () => void = () => undefined;
+    const chainOp = state.walletMutex.run(
+      () => new Promise<void>((resolve) => { releaseChainOp = resolve; }),
+    );
+
+    const ticker = startWalletHealthTicker(
+      { chain: FAKE_CHAIN, state, supplierKey: FAKE_KEY, consolidate },
+      { intervalMs: 1_000, log },
+    );
+
+    await vi.advanceTimersByTimeAsync(1_000);
+    // The mutex is held by the fake chain op — consolidate must wait.
+    expect(consolidate).not.toHaveBeenCalled();
+
+    releaseChainOp();
+    await chainOp;
+    await vi.waitFor(() => expect(consolidate).toHaveBeenCalledTimes(1));
+
+    ticker.stop();
+  });
+
+  it("logs success after a real consolidate", async () => {
    consolidate.mockResolvedValue(consolidatedResult);

    const ticker = startWalletHealthTicker(
@@ -127,7 +150,7 @@ describe("walletHealth — ticker", () => {
    ticker.stop();
  });

-  it("releases the lock when consolidate throws", async () => {
+  it("does not poison the walletMutex when consolidate throws", async () => {
    consolidate.mockRejectedValue(new Error("ogmios unreachable"));

    const ticker = startWalletHealthTicker(
@@ -138,8 +161,9 @@ describe("walletHealth — ticker", () => {
    await vi.advanceTimersByTimeAsync(1_000);
    await vi.waitFor(() => expect(consolidate).toHaveBeenCalledTimes(1));

-    expect(state.snapshot().status).toBe("free");
    expect(logLines.some((l) => l.includes("consolidate failed"))).toBe(true);
+    // The mutex still serves the next wallet op.
+    expect(await state.walletMutex.run(async () => "ok")).toBe("ok");

    ticker.stop();
  });
@@ -202,7 +226,7 @@ describe("walletHealth — triggerOnFailureConsolidate", () => {
    expect(consolidate).toHaveBeenCalledTimes(1);
  });

-  it("does not throw when supplier is busy — just skips", async () => {
+  it("runs even when session slots are held (queues on the wallet mutex)", async () => {
    state.tryAcquire(ESCROW_REF);
    consolidate.mockResolvedValue(healthyResult);

@@ -213,9 +237,8 @@ describe("walletHealth — triggerOnFailureConsolidate", () => {
      ),
    ).not.toThrow();

-    await Promise.resolve();
-    expect(consolidate).not.toHaveBeenCalled();
-    expect(logLines).toContain("skip: supplier busy");
+    await vi.waitFor(() => expect(consolidate).toHaveBeenCalledTimes(1));
+    // The held session slot is untouched.
    expect(state.snapshot().status).toBe("working");
  });
 });