Show product usage types in credit ledger

Persist hotword request origin so every reservation lifecycle entry can be classified without mutating the immutable ledger.

src/test/kotlin/com/osglab/account/features/admin/routes/AdminRoutesTest.kt

@@ -214,6 +214,7 @@ class AdminRoutesTest {
                     balanceAfter = 102,
                     referenceId = null,
                     createdAt = "2026-08-19T09:00:00Z",
+                    usageType = "hotword",
                 ),
             ),
             nextCursor = null,
@@ -233,6 +234,7 @@ class AdminRoutesTest {
         assertEquals(HttpStatusCode.OK, response.status)
         response.bodyAsText() shouldContain """"userId":"11111111-1111-4111-8111-111111111111""""
         response.bodyAsText() shouldContain """"reasonCode":"USAGE_SETTLE""""
+        response.bodyAsText() shouldContain """"usageType":"hotword""""
     }
 
     @Test

src/test/kotlin/com/osglab/account/features/gateway/models/TextRequestPolicyTest.kt

@@ -42,4 +42,16 @@ class TextRequestPolicyTest : StringSpec({
             )
         }
     }
+
+    "accepts hotword source only for AI requests" {
+        val request = TextGatewayRequest(
+            input = "latest news",
+            requestSource = GatewayRequestSource.HOTWORD,
+        )
+
+        TextRequestPolicy.validate(request, GatewayCapability.AI)
+        shouldThrow<IllegalArgumentException> {
+            TextRequestPolicy.validate(request, GatewayCapability.POLISH)
+        }
+    }
 })

src/test/kotlin/com/osglab/account/features/gateway/routes/GatewayRequestIdTest.kt

@@ -2,6 +2,7 @@ package com.osglab.account.features.gateway.routes
 
 import com.osglab.account.features.gateway.models.GatewayCapability
 import com.osglab.account.features.gateway.models.GatewayPrincipal
+import com.osglab.account.features.gateway.models.GatewayRequestSource
 import com.osglab.account.features.gateway.models.ProviderDescriptor
 import com.osglab.account.features.gateway.models.ProviderOutput
 import com.osglab.account.features.gateway.models.ProviderRequest
@@ -62,11 +63,12 @@ class GatewayRequestIdTest : StringSpec({
             val response = client.post("/v1/gateway/llm/ai") {
                 header("X-Request-ID", "request-route-123")
                 contentType(ContentType.Application.Json)
-                setBody("""{"input":"hello","maxOutputTokens":8}""")
+                setBody("""{"input":"hello","maxOutputTokens":8,"requestSource":"hotword"}""")
             }
 
             response.status shouldBe HttpStatusCode.OK
             provider.lastRequestId shouldBe "request-route-123"
+            provider.lastRequestSource shouldBe GatewayRequestSource.HOTWORD
         }
     }
 })
@@ -93,6 +95,7 @@ private fun io.ktor.server.application.Application.gatewayTestApplication(provid
 private class RequestIdProvider : GatewayProvider {
     var calls = 0
     var lastRequestId: String? = null
+    var lastRequestSource: GatewayRequestSource? = null
 
     override val descriptor = ProviderDescriptor(
         id = "request-id-provider",
@@ -104,6 +107,7 @@ private class RequestIdProvider : GatewayProvider {
     override suspend fun execute(request: ProviderRequest, output: ProviderOutput): ProviderUsage {
         calls += 1
         lastRequestId = request.requestId
+        lastRequestSource = request.requestSource
         output.emit("""{"result":"ok"}""".encodeToByteArray())
         return ProviderUsage(
             meter = UsageMeter.LLM_TOKEN,

src/test/kotlin/com/osglab/account/features/gateway/services/GatewayServiceBillingTest.kt

@@ -2,6 +2,7 @@ package com.osglab.account.features.gateway.services
 
 import com.osglab.account.features.gateway.models.GatewayCapability
 import com.osglab.account.features.gateway.models.GatewayPrincipal
+import com.osglab.account.features.gateway.models.GatewayRequestSource
 import com.osglab.account.features.gateway.models.ProviderDescriptor
 import com.osglab.account.features.gateway.models.ProviderOutput
 import com.osglab.account.features.gateway.models.ProviderRequest
@@ -66,6 +67,19 @@ class GatewayServiceBillingTest : StringSpec({
         credits.lastEstimate?.outputUnits shouldBe 32L
     }
 
+    "records hotword request source with provider metadata" {
+        val usageRecords = FakeUsageRecords()
+        val service = service(FakeCredits(), FakeProvider(), usageRecords)
+
+        service.execute(
+            PRINCIPAL,
+            request(GatewayRequestSource.HOTWORD),
+            DISCARD_OUTPUT,
+        )
+
+        usageRecords.lastClaim?.requestSource shouldBe GatewayRequestSource.HOTWORD
+    }
+
     "uses one reservation when a buffered DeepSeek empty result succeeds on retry" {
         val credits = FakeCredits()
         var attempts = 0
@@ -203,7 +217,7 @@ private fun service(
     usageRecords = usageRecords,
 )
 
-private fun request() = TextProviderRequest(
+private fun request(requestSource: GatewayRequestSource? = null) = TextProviderRequest(
     requestId = "request-123",
     capability = GatewayCapability.AI,
     input = "hello",
@@ -211,6 +225,7 @@ private fun request() = TextProviderRequest(
     maxOutputTokens = 32,
     temperature = 0.2,
     stream = false,
+    requestSource = requestSource,
 )
 
 private class FakeCredits(
@@ -293,7 +308,11 @@ private class EmptyResultProvider : GatewayProvider {
 private class FakeUsageRecords(
     private val pending: MutableList<PendingSettlement> = mutableListOf(),
 ) : GatewayUsagePort {
-    override suspend fun claim(metadata: ProviderRequestMetadata) = Unit
+    var lastClaim: ProviderRequestMetadata? = null
+
+    override suspend fun claim(metadata: ProviderRequestMetadata) {
+        lastClaim = metadata
+    }
     override suspend fun markStarted(accountId: String, requestId: String) = Unit
     override suspend fun markSettlementPending(
         accountId: String,