WIP feat(T5): MRTR (multi round trip requests) types (#243)

.github/workflows/ci.yml

@@ -48,6 +48,8 @@ jobs:
         run: sbt -v test
       - name: Client conformance tests (2025-11-25)
         run: sbt -v "clientConformance/conformance client --requirements 2025-11-25"
+      - name: Client conformance tests (2026-07-28)
+        run: sbt -v "clientConformance/conformance client --requirements 2026-07-28"
       - name: Server conformance tests (2025-11-25)
         run: sbt -v "serverConformance/conformance server --requirements 2025-11-25"
       - name: Server conformance tests (2026-07-28)

build.sbt

@@ -251,7 +251,7 @@ lazy val serverConformance = (project in file("server-conformance"))
       val baseline = specVersion
         .map(v => rootDir / s"conformance-baseline-$v.yml")
         .filter(_.exists)
-        .getOrElse(rootDir / "conformance-baseline.yml")
+        .getOrElse(rootDir / "conformance-baseline-2025-11-25.yml")
         .getAbsolutePath
       val log = streams.value.log
 
@@ -327,8 +327,23 @@ lazy val clientConformance = (project in file("client-conformance"))
       val baseDir = baseDirectory.value
       val rootDir = (LocalRootProject / baseDirectory).value
       val wrapper = (baseDir / "bin" / "chimp-conformance-client").getAbsolutePath
+      val specVersion = args
+        .sliding(2)
+        .collectFirst {
+          case Seq("--requirements", v) => v
+          case Seq("--spec-version", v) => v
+        }
+        .orElse(args.collectFirst {
+          case a if a.startsWith("--requirements=") => a.stripPrefix("--requirements=")
+          case a if a.startsWith("--spec-version=") => a.stripPrefix("--spec-version=")
+        })
+      val baseline = specVersion
+        .map(v => rootDir / s"conformance-baseline-$v.yml")
+        .filter(_.exists)
+        .getOrElse(rootDir / "conformance-baseline-2025-11-25.yml")
+        .getAbsolutePath
       val cmd = List("npx", s"@modelcontextprotocol/conformance@$conformanceHarnessV") ++ args ++
-        List("--command", wrapper, "--expected-failures", (rootDir / "conformance-baseline.yml").getAbsolutePath)
+        List("--command", wrapper, "--expected-failures", baseline)
       val rc = Process(cmd, rootDir, "CHIMP_CLIENT_CONFORMANCE_JAR" -> jar.getAbsolutePath).!
       if (rc != 0) sys.error(s"conformance harness exited with code $rc")
     }

client-conformance/README.md

@@ -22,17 +22,18 @@ The sbt task pins the harness to the version set in `conformanceHarnessV` in [`b
 
 ## How to run
 
-Run the full requirement set:
+Run a full requirement set (CI runs both revisions):
 
 ```bash
 sbt 'clientConformance/conformance client --requirements 2025-11-25'
+sbt 'clientConformance/conformance client --requirements 2026-07-28'
 ```
 
-Run one scenario during development:
+Run one scenario during development (pass the spec version):
 
 ```bash
 sbt 'clientConformance/conformance client --scenario initialize --spec-version 2025-11-25'
-sbt 'clientConformance/conformance client --scenario tools_call --spec-version 2025-11-25'
+sbt 'clientConformance/conformance client --scenario tools_call --spec-version 2026-07-28'
 ```
 
 The sbt task downloads `@modelcontextprotocol/conformance` with npm; `npx` must be available on the PATH.
@@ -44,8 +45,10 @@ with `McpClient`, return exit code 0 on success. Once it passes, remove the entr
 
 ## The baseline file
 
-[`conformance-baseline.yml`](../conformance-baseline.yml) lists scenarios that are known to fail today. The harness
-uses it like this:
+Each spec revision keeps its own baseline, selected from the run's `--requirements` (or `--spec-version`):
+[`conformance-baseline-2025-11-25.yml`](../conformance-baseline-2025-11-25.yml) and
+[`conformance-baseline-2026-07-28.yml`](../conformance-baseline-2026-07-28.yml). Each file lists the scenarios (in its
+`server:` and `client:` sections) known to fail today. The harness uses the chosen file like this:
 
 | Scenario result | In baseline? | Exit code | Meaning                               |
 |-----------------|--------------|-----------|---------------------------------------|

client-conformance/src/main/scala/chimp/conformance/client/Main.scala

@@ -67,7 +67,11 @@ object Main:
           case "elicitation-sep1034-client-defaults" =>
             supervised:
               val oxTransport = OxClientHttpTransport(backend, serverUrl, protocolVersion)
-              val handler = (req: ElicitRequest) => ElicitResult(ElicitAction.Accept, Some(defaultsFrom(req.params.requestedSchema)))
+              val handler = (req: ElicitRequest) =>
+                val requestedSchema = req.params match
+                  case ElicitParams.Form(_, schema, _, _) => schema
+                  case _: ElicitParams.Url                => Json.obj()
+                ElicitResult(ElicitAction.Accept, Some(defaultsFrom(requestedSchema)))
               val client = McpClient.bidirectional[Identity](
                 oxTransport,
                 clientInfo,

conformance-baseline-2026-07-28.yml

@@ -1,6 +1,6 @@
-# Expected server-conformance failures for spec version 2026-07-28.
+# Expected conformance failures for spec version 2026-07-28 (server and client).
 # These need protocol features that land in later tickets; remove each entry once its
-# scenario passes. See server-conformance/README.md for how the baseline is used.
+# scenario passes. See server-conformance/README.md and client-conformance/README.md.
 server:
   # multi-round-trip requests (tasks) — T5, https://github.com/softwaremill/chimp/issues/243
   - tasks-capability-negotiation
@@ -31,3 +31,43 @@ server:
   - sep-2164-resource-not-found
   - input-required-result-missing-input-response
   - input-required-result-ignore-extra-params
+client:
+  # OAuth client flows — chimp's client has no full OAuth support yet
+  - auth/authorization-server-migration
+  - auth/basic-cimd
+  - auth/client-credentials-basic
+  - auth/client-credentials-jwt
+  - auth/dpop
+  - auth/dpop-nonce
+  - auth/enterprise-managed-authorization
+  - auth/iss-normalized
+  - auth/iss-not-advertised
+  - auth/iss-supported
+  - auth/iss-supported-missing
+  - auth/iss-unexpected
+  - auth/iss-wrong-issuer
+  - auth/metadata-default
+  - auth/metadata-issuer-mismatch
+  - auth/metadata-var1
+  - auth/metadata-var2
+  - auth/metadata-var3
+  - auth/offline-access-not-supported
+  - auth/offline-access-scope
+  - auth/pre-registration
+  - auth/scope-from-scopes-supported
+  - auth/scope-from-www-authenticate
+  - auth/scope-omitted-when-undefined
+  - auth/scope-retry-limit
+  - auth/scope-step-up
+  - auth/token-endpoint-auth-basic
+  - auth/token-endpoint-auth-none
+  - auth/token-endpoint-auth-post
+  - auth/wif-jwt-bearer
+  # modern (2026-07-28) client era: stateless lifecycle, request _meta, HTTP headers — T10-T12, #248/#249/#250
+  - tools_call
+  - http-custom-headers
+  - http-invalid-tool-headers
+  - json-schema-2020-12-preservation
+  - json-schema-ref-no-deref
+  - request-metadata
+  - sep-2322-client-request-state

core/src/main/scala/chimp/protocol/Elicitation.scala

@@ -1,5 +1,6 @@
 package chimp.protocol
 
+import io.circe.syntax.*
 import io.circe.{Codec, Decoder, Encoder, Json}
 
 enum ElicitAction:
@@ -16,11 +17,50 @@ object ElicitAction:
     case "cancel"  => Right(ElicitAction.Cancel)
     case other     => Left(s"Unknown elicitation action: $other")
 
-final case class ElicitParams(
-    message: String,
-    requestedSchema: Json,
-    _meta: Option[Map[String, Json]] = None
-) derives Codec
+/** Params of an `elicitation/create` request (2026-07-28): either a `Form` (a JSON schema to fill in) or a `Url` (open a URL to complete
+  * the interaction out of band). `mode` distinguishes them on the wire; it is optional on `Form` for backward compatibility with
+  * 2025-11-25.
+  */
+enum ElicitParams:
+  case Form(message: String, requestedSchema: Json, mode: Option[String] = None, _meta: Option[Map[String, Json]] = None)
+  case Url(message: String, url: String, mode: String = "url", _meta: Option[Map[String, Json]] = None)
+
+object ElicitParams:
+  given Encoder[ElicitParams] = Encoder.instance:
+    case Form(message, requestedSchema, mode, meta) =>
+      Json
+        .obj(
+          "message" -> Json.fromString(message),
+          "requestedSchema" -> requestedSchema,
+          "mode" -> mode.asJson,
+          "_meta" -> meta.asJson
+        )
+        .dropNullValues
+    case Url(message, url, mode, meta) =>
+      Json
+        .obj(
+          "message" -> Json.fromString(message),
+          "url" -> Json.fromString(url),
+          "mode" -> Json.fromString(mode),
+          "_meta" -> meta.asJson
+        )
+        .dropNullValues
+
+  given Decoder[ElicitParams] = Decoder.instance: c =>
+    if c.downField("url").succeeded then
+      for
+        message <- c.downField("message").as[String]
+        url <- c.downField("url").as[String]
+        mode <- c.downField("mode").as[Option[String]]
+        meta <- c.downField("_meta").as[Option[Map[String, Json]]]
+      yield Url(message, url, mode.getOrElse("url"), meta)
+    else
+      for
+        message <- c.downField("message").as[String]
+        requestedSchema <- c.downField("requestedSchema").as[Json]
+        mode <- c.downField("mode").as[Option[String]]
+        meta <- c.downField("_meta").as[Option[Map[String, Json]]]
+      yield Form(message, requestedSchema, mode, meta)
 
 final case class ElicitRequest(method: String = "elicitation/create", params: ElicitParams) derives Codec
 

core/src/main/scala/chimp/protocol/Lifecycle.scala

@@ -2,7 +2,14 @@ package chimp.protocol
 
 import io.circe.{Codec, Json}
 
-final case class Implementation(name: String, version: String, title: Option[String] = None) derives Codec
+final case class Implementation(
+    name: String,
+    version: String,
+    title: Option[String] = None,
+    icons: Option[List[Icon]] = None,
+    websiteUrl: Option[String] = None,
+    description: Option[String] = None
+) derives Codec
 
 final case class ClientRootsCapability(listChanged: Option[Boolean] = None) derives Codec
 

core/src/main/scala/chimp/protocol/Metadata.scala

@@ -0,0 +1,22 @@
+package chimp.protocol
+
+import io.circe.Codec
+
+/** An icon for a resource, tool, prompt, or implementation (2026-07-28). `src` is a URI (http(s) or data:); the other fields are optional
+  * hints. Present on `icons` fields across the shared types.
+  */
+final case class Icon(
+    src: String,
+    mimeType: Option[String] = None,
+    sizes: Option[List[String]] = None,
+    theme: Option[String] = None
+) derives Codec
+
+/** Optional annotations describing how an object or content should be used (2026-07-28): its intended `audience`, a `priority` (0.0-1.0),
+  * and a `lastModified` ISO-8601 timestamp.
+  */
+final case class Annotations(
+    audience: Option[List[Role]] = None,
+    lastModified: Option[String] = None,
+    priority: Option[Double] = None
+) derives Codec

core/src/main/scala/chimp/protocol/Mrtr.scala

@@ -0,0 +1,56 @@
+package chimp.protocol
+
+import io.circe.syntax.*
+import io.circe.{Decoder, DecodingFailure, Encoder, HCursor, Json}
+
+/** A server-to-client request embedded in an `input_required` tool result (MRTR, 2026-07-28): a sampling, roots or elicitation request. On
+  * the wire it is the bare request object, discriminated by its `method`.
+  */
+enum InputRequest:
+  case Sampling(request: CreateMessageRequest)
+  case Roots(request: ListRootsRequest)
+  case Elicit(request: ElicitRequest)
+
+object InputRequest:
+  given Encoder[InputRequest] = Encoder.instance:
+    case Sampling(request) => request.asJson
+    case Roots(request)    => request.asJson
+    case Elicit(request)   => request.asJson
+
+  given Decoder[InputRequest] = Decoder.instance: (c: HCursor) =>
+    c.downField("method")
+      .as[String]
+      .flatMap:
+        case "sampling/createMessage" => c.as[CreateMessageRequest].map(Sampling(_))
+        case "roots/list"             => c.as[ListRootsRequest].map(Roots(_))
+        case "elicitation/create"     => c.as[ElicitRequest].map(Elicit(_))
+        case other                    => Left(DecodingFailure(s"Unknown InputRequest method: $other", c.history))
+
+/** A client-to-server response to an [[InputRequest]] (MRTR): a sampling, roots or elicitation result. Discriminated structurally
+  * (elicitation by `action`, roots by `roots`, otherwise sampling).
+  */
+enum InputResponse:
+  case Sampling(result: CreateMessageResult)
+  case Roots(result: ListRootsResult)
+  case Elicit(result: ElicitResult)
+
+object InputResponse:
+  given Encoder[InputResponse] = Encoder.instance:
+    case Sampling(result) => result.asJson
+    case Roots(result)    => result.asJson
+    case Elicit(result)   => result.asJson
+
+  given Decoder[InputResponse] = Decoder.instance: (c: HCursor) =>
+    if c.downField("action").succeeded then c.as[ElicitResult].map(Elicit(_))
+    else if c.downField("roots").succeeded then c.as[ListRootsResult].map(Roots(_))
+    else c.as[CreateMessageResult].map(Sampling(_))
+
+/** Result of a tool call that needs client input before it can finish (MRTR): the pending [[InputRequest]]s keyed by an opaque key, the
+  * opaque `requestState` the client echoes back on its response, and the modern result envelope fields.
+  */
+final case class InputRequiredResult(
+    inputRequests: Map[String, InputRequest],
+    requestState: Option[String] = None,
+    resultType: ResultType = ResultType.Incomplete,
+    _meta: Option[Map[String, Json]] = None
+) derives io.circe.Codec

core/src/main/scala/chimp/protocol/Prompts.scala

@@ -26,6 +26,7 @@ final case class Prompt(
     title: Option[String] = None,
     description: Option[String] = None,
     arguments: Option[List[PromptArgument]] = None,
+    icons: Option[List[Icon]] = None,
     _meta: Option[Map[String, Json]] = None
 ) derives Codec
 
@@ -42,6 +43,8 @@ final case class ListPromptsResult(
 final case class GetPromptParams(
     name: String,
     arguments: Option[Map[String, String]] = None,
+    inputResponses: Option[Map[String, InputResponse]] = None,
+    requestState: Option[String] = None,
     _meta: Option[Map[String, Json]] = None
 ) derives Codec
 final case class GetPromptRequest(method: String = "prompts/get", params: GetPromptParams) derives Codec
@@ -53,4 +56,4 @@ final case class GetPromptResult(
 
 final case class PromptListChangedNotification(method: String = "notifications/prompts/list_changed") derives Codec
 
-final case class PromptReference(`type`: String = "ref/prompt", name: String) derives Codec
+final case class PromptReference(`type`: String = "ref/prompt", name: String, title: Option[String] = None) derives Codec

core/src/main/scala/chimp/protocol/Resources.scala

@@ -10,6 +10,8 @@ final case class Resource(
     description: Option[String] = None,
     mimeType: Option[String] = None,
     size: Option[Long] = None,
+    icons: Option[List[Icon]] = None,
+    annotations: Option[Annotations] = None,
     _meta: Option[Map[String, Json]] = None
 ) derives Codec
 
@@ -19,6 +21,8 @@ final case class ResourceTemplate(
     title: Option[String] = None,
     description: Option[String] = None,
     mimeType: Option[String] = None,
+    icons: Option[List[Icon]] = None,
+    annotations: Option[Annotations] = None,
     _meta: Option[Map[String, Json]] = None
 ) derives Codec
 
@@ -84,7 +88,12 @@ final case class ListResourceTemplatesResult(
     _meta: Option[Map[String, Json]] = None
 ) derives Codec
 
-final case class ReadResourceParams(uri: String, _meta: Option[Map[String, Json]] = None) derives Codec
+final case class ReadResourceParams(
+    uri: String,
+    inputResponses: Option[Map[String, InputResponse]] = None,
+    requestState: Option[String] = None,
+    _meta: Option[Map[String, Json]] = None
+) derives Codec
 final case class ReadResourceRequest(method: String = "resources/read", params: ReadResourceParams) derives Codec
 final case class ReadResourceResult(contents: List[ResourceContents], _meta: Option[Map[String, Json]] = None) derives Codec
 

core/src/main/scala/chimp/protocol/Subscriptions.scala

@@ -0,0 +1,34 @@
+package chimp.protocol
+
+import io.circe.{Codec, Json}
+
+/** The notification types a client opts into on a `subscriptions/listen` stream (2026-07-28). Each type is opt-in: the server MUST NOT send
+  * a type the client has not requested. `resourceSubscriptions` replaces the former `resources/subscribe` RPC.
+  */
+final case class SubscriptionFilter(
+    promptsListChanged: Option[Boolean] = None,
+    resourceSubscriptions: Option[List[String]] = None,
+    resourcesListChanged: Option[Boolean] = None,
+    toolsListChanged: Option[Boolean] = None
+) derives Codec
+
+/** Params of a `subscriptions/listen` request: the notification filter the client opts into on the stream. */
+final case class SubscriptionsListenParams(notifications: SubscriptionFilter, _meta: Option[Map[String, Json]] = None) derives Codec
+
+final case class SubscriptionsListenRequest(method: String = "subscriptions/listen", params: SubscriptionsListenParams) derives Codec
+
+/** Result of `subscriptions/listen`, sent only when the server tears the subscription down gracefully (e.g. on shutdown); the body is
+  * otherwise empty. The subscription id travels in `_meta` under `io.modelcontextprotocol/subscriptionId`.
+  */
+final case class SubscriptionsListenResult(resultType: ResultType = ResultType.Complete, _meta: Option[Map[String, Json]] = None)
+    derives Codec
+
+/** Params of the `notifications/subscriptions/acknowledged` notification: the subset of requested notification types the server will honor.
+  */
+final case class SubscriptionsAcknowledgedParams(notifications: SubscriptionFilter, _meta: Option[Map[String, Json]] = None) derives Codec
+
+/** The `notifications/subscriptions/acknowledged` notification the server sends first on a listen stream. */
+final case class SubscriptionsAcknowledgedNotification(
+    method: String = "notifications/subscriptions/acknowledged",
+    params: SubscriptionsAcknowledgedParams
+) derives Codec