fix(core): record selected catalog model identity on assistant steps (#34911)

packages/core/src/session/compaction.ts

@@ -321,12 +321,12 @@ export const layer = Layer.effect(
       compactIfNeeded: compaction.compactIfNeeded,
       compactAfterOverflow: compaction.compactAfterOverflow,
       compactManual: Effect.fn("SessionCompaction.compactManual")(function* (input) {
-        const model = yield* models.resolve(input.session).pipe(Effect.catch(() => Effect.succeed(undefined)))
-        if (!model) return false
+        const resolved = yield* models.resolve(input.session).pipe(Effect.catch(() => Effect.succeed(undefined)))
+        if (!resolved) return false
         return yield* compaction.compactManual({
           sessionID: input.session.id,
           messages: input.messages,
-          model,
+          model: resolved.model,
         })
       }),
     })

packages/core/src/session/runner/llm.ts

@@ -14,8 +14,6 @@ import { Config } from "../../config"
 import { Database } from "../../database/database"
 import { EventV2 } from "../../event"
 import { Location } from "../../location"
-import { ModelV2 } from "../../model"
-import { ProviderV2 } from "../../provider"
 import { QuestionV2 } from "../../question"
 import { SystemContext } from "../../system-context/index"
 import { SystemContextBuiltIns } from "../../system-context/builtins"
@@ -217,7 +215,8 @@ const layer = Layer.effect(
         }
         if (promoted > 0) currentStep = 1
       }
-      const model = yield* models.resolve(session)
+      const resolved = yield* models.resolve(session)
+      const model = resolved.model
       const entries = yield* SessionHistory.entriesForRunner(db, session.id, checkpoint.baselineSeq)
       const context = entries.map((entry) => entry.message)
       const isLastStep = agent.info?.steps !== undefined && currentStep >= agent.info.steps
@@ -244,11 +243,9 @@ const layer = Layer.effect(
       const publisher = createLLMEventPublisher(events, {
         sessionID: session.id,
         agent: agent.id,
-        model: {
-          id: ModelV2.ID.make(model.id),
-          providerID: ProviderV2.ID.make(model.provider),
-          ...(session.model?.variant === undefined ? {} : { variant: session.model.variant }),
-        },
+        // The selected catalog identity, not model.id: route-level ids are provider API
+        // model ids (for example gpt-5.5-fast resolves to api id gpt-5.5).
+        model: resolved.ref,
         snapshot: startSnapshot,
       })
       const publication = Semaphore.makeUnsafe(1)

packages/core/src/session/runner/model.ts

@@ -72,8 +72,15 @@ export type Error =
   | UnsupportedApiError
   | Integration.AuthorizationError
 
+export interface Resolved {
+  /** Route-level model for provider requests; its id is the provider API model id, which may differ from the catalog id. */
+  readonly model: Model
+  /** Selected catalog identity. Durable records and displays must use this, never the API model id. */
+  readonly ref: ModelV2.Ref
+}
+
 export interface Interface {
-  readonly resolve: (session: SessionSchema.Info) => Effect.Effect<Model, Error>
+  readonly resolve: (session: SessionSchema.Info) => Effect.Effect<Resolved, Error>
 }
 
 export class Service extends Context.Service<Service, Interface>()("@opencode/v2/SessionRunnerModel") {}
@@ -81,6 +88,16 @@ export class Service extends Context.Service<Service, Interface>()("@opencode/v2
 /** Test or embedding seam for supplying a model resolver directly. */
 export const layerWith = (resolve: Interface["resolve"]) => Layer.succeed(Service, Service.of({ resolve }))
 
+/** Builds a Resolved whose catalog identity mirrors the route model. Test or embedding seam. */
+export const resolved = (model: Model, variant?: ModelV2.VariantID): Resolved => ({
+  model,
+  ref: ModelV2.Ref.make({
+    id: ModelV2.ID.make(model.id),
+    providerID: ProviderV2.ID.make(model.provider),
+    ...(variant === undefined ? {} : { variant }),
+  }),
+})
+
 const apiKey = (model: ModelV2.Info, credential?: Credential.Value) => {
   if (credential?.type === "key") return Auth.value(credential.key)
   if (credential?.type === "oauth") return Auth.value(credential.access)
@@ -233,11 +250,19 @@ const layer = Layer.effect(
         const connection = yield* integrations.connection.active(
           provider?.integrationID ?? Integration.ID.make(selected.providerID),
         )
-        return yield* resolve(
+        const model = yield* resolve(
           session,
           selected,
           connection ? yield* integrations.connection.resolve(connection) : undefined,
         )
+        return {
+          model,
+          ref: ModelV2.Ref.make({
+            id: selected.id,
+            providerID: selected.providerID,
+            ...(session.model?.variant === undefined ? {} : { variant: session.model.variant }),
+          }),
+        }
       }),
     })
   }),

packages/core/src/session/title.ts

@@ -42,17 +42,17 @@ const make = (dependencies: Dependencies) => {
     if (!firstUser) return
     const agent = yield* dependencies.agents.get(AgentV2.ID.make("title"))
     if (!agent) return
-    const model = yield* (agent.model
+    const resolved = yield* (agent.model
       ? dependencies.models.resolve({ ...session, model: agent.model })
       : dependencies.models.resolve(session)
     ).pipe(Effect.catch(() => Effect.succeed(undefined)))
-    if (!model) return
+    if (!resolved) return
     const chunks: string[] = []
     let failed = false
     const streamed = yield* dependencies.llm
       .stream(
         LLM.request({
-          model,
+          model: resolved.model,
           system: agent.system,
           messages: [Message.user(firstUser.text)],
           tools: [],