diff --git a/packages/core/src/plugin/host.ts b/packages/core/src/plugin/host.ts
index e002d4452b4..02927d583d0 100644
--- a/packages/core/src/plugin/host.ts
+++ b/packages/core/src/plugin/host.ts
@@ -425,6 +425,7 @@ export const make = Effect.fn("PluginHost.make")(function* (plugin: PluginV2.Int
       get: (input) => runtime.session.get(input.sessionID),
       prompt: runtime.session.prompt,
       command: runtime.session.command,
+      synthetic: runtime.session.synthetic,
       interrupt: (input) => runtime.session.interrupt(input.sessionID),
     },
   } satisfies Plugin.Context
diff --git a/packages/core/src/plugin/promise.ts b/packages/core/src/plugin/promise.ts
index 57bac546e01..ad9cfc3bf12 100644
--- a/packages/core/src/plugin/promise.ts
+++ b/packages/core/src/plugin/promise.ts
@@ -244,6 +244,17 @@ export function fromPromise(plugin: Plugin) {
                   resume: input.resume ?? undefined,
                 }),
               ),
+            synthetic: (input) =>
+              run(
+                host.session.synthetic({
+                  ...input,
+                  sessionID: Session.ID.make(input.sessionID),
+                  id: input.id == null ? undefined : SessionMessage.ID.make(input.id),
+                  description: input.description ?? undefined,
+                  delivery: input.delivery ?? undefined,
+                  resume: input.resume ?? undefined,
+                }),
+              ),
             interrupt: (input) => run(host.session.interrupt({ sessionID: Session.ID.make(input.sessionID) })),
           },
         }
diff --git a/packages/core/test/plugin/host.ts b/packages/core/test/plugin/host.ts
index b999e462528..07a06e7744e 100644
--- a/packages/core/test/plugin/host.ts
+++ b/packages/core/test/plugin/host.ts
@@ -97,6 +97,7 @@ export function host(overrides: Overrides = {}): PluginContext {
       get: overrides.session?.get ?? (() => Effect.die("unused session.get")),
       prompt: overrides.session?.prompt ?? (() => Effect.die("unused session.prompt")),
       command: overrides.session?.command ?? (() => Effect.die("unused session.command")),
+      synthetic: overrides.session?.synthetic ?? (() => Effect.die("unused session.synthetic")),
       interrupt: overrides.session?.interrupt ?? (() => Effect.die("unused session.interrupt")),
     },
   }
diff --git a/packages/core/test/plugin/promise.test.ts b/packages/core/test/plugin/promise.test.ts
index 8619b0e39ca..34d8e1f975f 100644
--- a/packages/core/test/plugin/promise.test.ts
+++ b/packages/core/test/plugin/promise.test.ts
@@ -1,6 +1,6 @@
 import { describe, expect } from "bun:test"
 import { Message, SystemPart } from "@opencode-ai/ai"
-import { Effect, Schema } from "effect"
+import { DateTime, Effect, Schema } from "effect"
 import { AgentV2 } from "@opencode-ai/core/agent"
 import { Catalog } from "@opencode-ai/core/catalog"
 import { ModelV2 } from "@opencode-ai/core/model"
@@ -10,6 +10,7 @@ import { PluginHost } from "@opencode-ai/core/plugin/host"
 import { PluginPromise } from "@opencode-ai/core/plugin/promise"
 import { SessionV2 } from "@opencode-ai/core/session"
 import { SessionMessage } from "@opencode-ai/core/session/message"
+import { SessionPending } from "@opencode-ai/core/session/pending"
 import { ToolRegistry } from "@opencode-ai/core/tool/registry"
 import { ProviderV2 } from "@opencode-ai/core/provider"
 import { Plugin } from "@opencode-ai/plugin/v2"
@@ -18,10 +19,63 @@ import { Model } from "@opencode-ai/schema/model"
 import { Provider } from "@opencode-ai/schema/provider"
 import { testEffect } from "../lib/effect"
 import { PluginTestLayer } from "./fixture"
+import { host as testHost } from "./host"
 
 const it = testEffect(PluginTestLayer)
 
 describe("fromPromise", () => {
+  it.effect("forwards synthetic session input", () =>
+    Effect.gen(function* () {
+      const input = {
+        sessionID: "ses_synthetic",
+        id: "msg_synthetic",
+        text: "Background work completed",
+        description: null,
+        metadata: { shellID: "shell_1" },
+        delivery: null,
+        resume: null,
+      }
+      let seen: unknown
+      const host = testHost({
+        session: {
+          synthetic: (value) => {
+            seen = value
+            return Effect.succeed(
+              SessionPending.Synthetic.make({
+                admittedSeq: 1,
+                id: SessionMessage.ID.make(input.id),
+                sessionID: SessionV2.ID.make(input.sessionID),
+                timeCreated: DateTime.makeUnsafe(0),
+                type: "synthetic",
+                data: {
+                  text: input.text,
+                  metadata: input.metadata,
+                },
+                delivery: "queue",
+              }),
+            )
+          },
+        },
+      })
+
+      yield* PluginPromise.fromPromise(
+        Plugin.define({
+          id: "promise-session-synthetic",
+          setup: async (ctx) => {
+            await ctx.session.synthetic(input)
+          },
+        }),
+      ).effect(host)
+
+      expect(seen).toEqual({
+        ...input,
+        description: undefined,
+        delivery: undefined,
+        resume: undefined,
+      })
+    }),
+  )
+
   it.effect("forwards standard client reads", () =>
     Effect.gen(function* () {
       const plugin = yield* PluginV2.Service
diff --git a/packages/docs/build/plugins.mdx b/packages/docs/build/plugins.mdx
index 0a8c1c7d0f6..01a8b5746b9 100644
--- a/packages/docs/build/plugins.mdx
+++ b/packages/docs/build/plugins.mdx
@@ -177,7 +177,7 @@ and plugin options.
 | `ctx.integration`      | `list`, `get`, `connect`, `attempt`, `transform`, `reload`, and connection lookup/resolution |
 | `ctx.plugin`           | `list` currently active plugin IDs                                                           |
 | `ctx.reference`        | `list`, `transform`, `reload`                                                                |
-| `ctx.session`          | `create`, `get`, `prompt`, `command`, `interrupt`, and `hook`                                |
+| `ctx.session`          | `create`, `get`, `prompt`, `command`, `synthetic`, `interrupt`, and `hook`                   |
 | `ctx.skill`            | `list`, `transform`, `reload`                                                                |
 | `ctx.tool`             | `transform` and `hook`                                                                       |
 | `ctx.aisdk`            | `hook`                                                                                       |
diff --git a/packages/plugin/src/v2/effect/session.ts b/packages/plugin/src/v2/effect/session.ts
index 541a8da28c6..836f4431c6b 100644
--- a/packages/plugin/src/v2/effect/session.ts
+++ b/packages/plugin/src/v2/effect/session.ts
@@ -19,6 +19,9 @@ export interface SessionHooks {
   readonly context: SessionContext
 }
 
-export type SessionDomain = Pick<SessionApi<unknown>, "create" | "get" | "prompt" | "command" | "interrupt"> & {
+export type SessionDomain = Pick<
+  SessionApi<unknown>,
+  "create" | "get" | "prompt" | "command" | "synthetic" | "interrupt"
+> & {
   readonly hook: Hooks<SessionHooks>
 }
diff --git a/packages/plugin/src/v2/promise/session.ts b/packages/plugin/src/v2/promise/session.ts
index b2f35c867bc..387d6fe0073 100644
--- a/packages/plugin/src/v2/promise/session.ts
+++ b/packages/plugin/src/v2/promise/session.ts
@@ -19,6 +19,6 @@ export interface SessionHooks {
   readonly context: SessionContext
 }
 
-export type SessionDomain = Pick<SessionApi, "create" | "get" | "prompt" | "command" | "interrupt"> & {
+export type SessionDomain = Pick<SessionApi, "create" | "get" | "prompt" | "command" | "synthetic" | "interrupt"> & {
   readonly hook: Hooks<SessionHooks>
 }