diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index a311798..a7410cd 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -51,7 +51,7 @@ jobs:
         # /#447 rotations needed for agentic_hosting#26 (trader:v0.2 image
         # rebuild). Keep the docker-publish.yml pin aligned on every bump.
         env:
-          SPHERE_SDK_SHA: 550114c75e0b47151488d0c5d656475fd5a5077b
+          SPHERE_SDK_SHA: b2fd028fdf8dc86a598e7bf34c069dce50442b59
         run: |
           git clone https://github.com/unicity-sphere/sphere-sdk.git ../sphere-sdk
           git -C ../sphere-sdk checkout --detach "$SPHERE_SDK_SHA"
diff --git a/.github/workflows/docker-publish.yml b/.github/workflows/docker-publish.yml
index ee9edef..c9e7e68 100644
--- a/.github/workflows/docker-publish.yml
+++ b/.github/workflows/docker-publish.yml
@@ -31,7 +31,7 @@ jobs:
         # counterparty transport pubkey), #464 PR #465 (MuxAdapter dispatch
         # awaits async handler), #447 PR #461 (terminal swap visibility).
         env:
-          SPHERE_SDK_SHA: 550114c75e0b47151488d0c5d656475fd5a5077b
+          SPHERE_SDK_SHA: b2fd028fdf8dc86a598e7bf34c069dce50442b59
         run: |
           git clone https://github.com/unicity-sphere/sphere-sdk.git sphere-sdk
           git -C sphere-sdk checkout --detach "$SPHERE_SDK_SHA"
diff --git a/src/trader/intent-engine.ts b/src/trader/intent-engine.ts
index cbf5d4c..c362cef 100644
--- a/src/trader/intent-engine.ts
+++ b/src/trader/intent-engine.ts
@@ -893,7 +893,16 @@ export function createIntentEngine(deps: IntentEngineDeps): IntentEngine {
       // Transition DRAFT → ACTIVE (validates transition)
       // Build description for market posting
       const description = encodeDescription(tradingIntent);
-      const midpointRate = Number((rateMin + rateMax) / 2n);
+      // Bigint midpoint of the rate band, serialized to a decimal
+      // string for the wire. NEVER cast to Number — for a typical
+      // 18-decimal quote asset, the midpoint of a 0.08–0.12 band is
+      // 1e17 which is past Number.MAX_SAFE_INTEGER (≈9e15). Coercing
+      // loses precision, the market-api server rejects with HTTP 500,
+      // and the trader logs only an opaque status code. The SDK's
+      // PostIntentRequest.price field is `string` for exactly this
+      // reason (see sphere-sdk PR #483); pass `.toString()` through
+      // and the JSON serialization is correct end-to-end.
+      const midpointRate = (rateMin + rateMax) / 2n;
       const expiresInDays = Math.max(
         1,
         Math.ceil((expiryMs - nowMs()) / 86_400_000),
@@ -905,7 +914,7 @@ export function createIntentEngine(deps: IntentEngineDeps): IntentEngine {
           description,
           intentType: params.direction,
           category: `${params.base_asset}/${params.quote_asset}`,
-          price: midpointRate,
+          price: midpointRate.toString(),
           currency: params.quote_asset,
           // Prefer @nametag for contactHandle — it resolves faster than DIRECT://
           // which requires a binding event lookup that may not have propagated yet.
diff --git a/src/trader/types.ts b/src/trader/types.ts
index 9473fac..008548e 100644
--- a/src/trader/types.ts
+++ b/src/trader/types.ts
@@ -268,7 +268,16 @@ export interface MarketPostRequest {
   readonly description: string;
   readonly intentType: 'buy' | 'sell';
   readonly category: string;
-  readonly price: number;
+  /**
+   * Price as a decimal-string bigint in the quote currency's smallest
+   * units. Same convention as token amounts in sphere-sdk (TXF amount
+   * fields, transfer payloads): internally bigint, over the wire
+   * decimal-string. Avoids JavaScript's `Number` precision loss for
+   * values above 2^53 (an 18-decimal coin hits that ceiling around
+   * 0.09 in human units). See sphere-sdk PR #483 for the SDK-side
+   * type that aligns with this.
+   */
+  readonly price: string;
   readonly currency: string;
   readonly contactHandle: string;
   readonly expiresInDays: number;
@@ -282,8 +291,10 @@ export interface MarketSearchOptions {
 export interface MarketSearchFilters {
   readonly intentType?: 'buy' | 'sell';
   readonly category?: string;
-  readonly minPrice?: number;
-  readonly maxPrice?: number;
+  /** Decimal-string bigint — see {@link MarketPostRequest.price}. */
+  readonly minPrice?: string;
+  /** Decimal-string bigint — see {@link MarketPostRequest.price}. */
+  readonly maxPrice?: string;
   readonly minScore?: number;
 }
 
@@ -295,7 +306,8 @@ export interface MarketSearchResult {
   readonly description: string;
   readonly intentType: 'buy' | 'sell';
   readonly category?: string;
-  readonly price?: number;
+  /** Decimal-string bigint — see {@link MarketPostRequest.price}. */
+  readonly price?: string;
   readonly currency: string;
   readonly contactHandle?: string;
   readonly createdAt: string;
diff --git a/test/e2e/trader-intent-lifecycle.e2e.test.ts b/test/e2e/trader-intent-lifecycle.e2e.test.ts
index 135436e..a15f29c 100644
--- a/test/e2e/trader-intent-lifecycle.e2e.test.ts
+++ b/test/e2e/trader-intent-lifecycle.e2e.test.ts
@@ -249,8 +249,10 @@ describe('E2E: Trader Intent Lifecycle (T1 + T10)', () => {
       expect(postCall.category).toBe('ALPHA/USDC');
       expect(postCall.currency).toBe('USDC');
       expect(postCall.contactHandle).toBe(AGENT_ADDRESS);
-      // Midpoint of 450-500 = 475
-      expect(postCall.price).toBe(475);
+      // Midpoint of 450-500 = 475, serialized as decimal-string bigint
+      // per sphere-sdk PostIntentRequest.price convention (no Number
+      // cast — see trader/intent-engine.ts comment block).
+      expect(postCall.price).toBe('475');
       // Description must match canonical format
       expect(postCall.description).toContain('Selling 100-1000 ALPHA for USDC');
       expect(postCall.description).toContain('Rate: 450-500 USDC per ALPHA');