diff --git a/.sisyphus/notepads/rebase-v146/decisions.md b/.sisyphus/notepads/rebase-v146/decisions.md
new file mode 100644
index 000000000000..e6f8c870a065
--- /dev/null
+++ b/.sisyphus/notepads/rebase-v146/decisions.md
@@ -0,0 +1 @@
+- Kept upstream Effect-native `session/index.ts`/middleware shapes, added `DuplicateIDError` support via shared import paths and `CreateInput.id`, and squashed the resolution into `pyyluxzz` so the workspace no longer reports conflicts.
diff --git a/.sisyphus/notepads/rebase-v146/issues.md b/.sisyphus/notepads/rebase-v146/issues.md
new file mode 100644
index 000000000000..5578253377e2
--- /dev/null
+++ b/.sisyphus/notepads/rebase-v146/issues.md
@@ -0,0 +1 @@
+- `bun typecheck` initially failed because this workspace had no installed dependencies (`tsgo` missing); running `bun install` in the workspace restored the toolchain.
diff --git a/.sisyphus/notepads/rebase-v146/learnings.md b/.sisyphus/notepads/rebase-v146/learnings.md
new file mode 100644
index 000000000000..2f9160ed2791
--- /dev/null
+++ b/.sisyphus/notepads/rebase-v146/learnings.md
@@ -0,0 +1 @@
+- Branch 8 resolves by keeping upstream route migration in `server/instance/session.ts` and deleting `server/routes/session.ts`; only the create route needs `...errors(400, 409)` ported.
diff --git a/packages/app/public/ort-wasm-simd-threaded.wasm b/packages/app/public/ort-wasm-simd-threaded.wasm
new file mode 100644
index 000000000000..f21ee10a4c63
Binary files /dev/null and b/packages/app/public/ort-wasm-simd-threaded.wasm differ
diff --git a/packages/app/public/silero_vad_legacy.onnx b/packages/app/public/silero_vad_legacy.onnx
new file mode 100644
index 000000000000..e6db48d6e2a0
Binary files /dev/null and b/packages/app/public/silero_vad_legacy.onnx differ
diff --git a/packages/opencode/src/server/error.ts b/packages/opencode/src/server/error.ts
index cc5fa961877a..9907bd70adc3 100644
--- a/packages/opencode/src/server/error.ts
+++ b/packages/opencode/src/server/error.ts
@@ -29,6 +29,25 @@ export const ERRORS = {
       },
     },
   },
+  409: {
+    description: "Conflict",
+    content: {
+      "application/json": {
+        schema: resolver(
+          z
+            .object({
+              name: z.literal("DuplicateIDError"),
+              data: z.object({
+                id: z.string(),
+              }),
+            })
+            .meta({
+              ref: "DuplicateIDError",
+            }),
+        ),
+      },
+    },
+  },
 } as const
 
 export function errors(...codes: number[]) {
diff --git a/packages/opencode/src/server/instance/session.ts b/packages/opencode/src/server/instance/session.ts
index a011c32f9b2d..e791c87b70e5 100644
--- a/packages/opencode/src/server/instance/session.ts
+++ b/packages/opencode/src/server/instance/session.ts
@@ -198,7 +198,7 @@ export const SessionRoutes = lazy(() =>
         description: "Create a new OpenCode session for interacting with AI assistants and managing conversations.",
         operationId: "session.create",
         responses: {
-          ...errors(400),
+          ...errors(400, 409),
           200: {
             description: "Successfully created session",
             content: {
diff --git a/packages/opencode/src/server/middleware.ts b/packages/opencode/src/server/middleware.ts
index 6e916518669c..ff1e3f863ced 100644
--- a/packages/opencode/src/server/middleware.ts
+++ b/packages/opencode/src/server/middleware.ts
@@ -23,6 +23,7 @@ export const ErrorMiddleware: ErrorHandler = (err, c) => {
     else if (err instanceof Provider.ModelNotFoundError) status = 400
     else if (err.name === "ProviderAuthValidationFailed") status = 400
     else if (err.name.startsWith("Worktree")) status = 400
+    else if (err.name === "DuplicateIDError") status = 409
     else status = 500
     return c.json(err.toObject(), { status })
   }
diff --git a/packages/opencode/src/session/index.ts b/packages/opencode/src/session/index.ts
index d8ab812349c7..531d96725711 100644
--- a/packages/opencode/src/session/index.ts
+++ b/packages/opencode/src/session/index.ts
@@ -1,4 +1,5 @@
 import { Slug } from "@opencode-ai/shared/util/slug"
+import { NamedError } from "@opencode-ai/shared/util/error"
 import path from "path"
 import { BusEvent } from "@/bus/bus-event"
 import { Bus } from "@/bus"
@@ -32,6 +33,13 @@ import { Effect, Layer, Option, Context } from "effect"
 export namespace Session {
   const log = Log.create({ service: "session" })
 
+  export const DuplicateIDError = NamedError.create(
+    "DuplicateIDError",
+    z.object({
+      id: z.string(),
+    }),
+  )
+
   const parentTitlePrefix = "New session - "
   const childTitlePrefix = "Child session - "
 
@@ -179,6 +187,7 @@ export namespace Session {
 
   export const CreateInput = z
     .object({
+      id: SessionID.zod.optional(),
       parentID: SessionID.zod.optional(),
       title: z.string().optional(),
       permission: Info.shape.permission,
@@ -334,6 +343,7 @@ export namespace Session {
 
   export interface Interface {
     readonly create: (input?: {
+      id?: SessionID
       parentID?: SessionID
       title?: string
       permission?: Permission.Ruleset
@@ -521,6 +531,7 @@ export namespace Session {
       })
 
       const create = Effect.fn("Session.create")(function* (input?: {
+        id?: SessionID
         parentID?: SessionID
         title?: string
         permission?: Permission.Ruleset
@@ -528,6 +539,7 @@ export namespace Session {
       }) {
         const directory = yield* InstanceState.directory
         return yield* createNext({
+          id: input?.id,
           parentID: input?.parentID,
           directory,
           title: input?.title,
diff --git a/packages/opencode/src/session/projectors.ts b/packages/opencode/src/session/projectors.ts
index 460f0a41c596..6f347c529a3b 100644
--- a/packages/opencode/src/session/projectors.ts
+++ b/packages/opencode/src/session/projectors.ts
@@ -15,6 +15,12 @@ function foreign(err: unknown) {
   return "message" in err && typeof err.message === "string" && err.message.includes("FOREIGN KEY constraint failed")
 }
 
+function duplicate(err: unknown, table: string) {
+  if (typeof err !== "object" || err === null) return false
+  if (!("message" in err) || typeof err.message !== "string") return false
+  return err.message.includes(`UNIQUE constraint failed: ${table}.id`)
+}
+
 export type DeepPartial<T> = T extends object ? { [K in keyof T]?: DeepPartial<T[K]> | null } : T
 
 function grab<T extends object, K1 extends keyof T, X>(
@@ -64,7 +70,12 @@ export function toPartialRow(info: DeepPartial<Session.Info>) {
 
 export default [
   SyncEvent.project(Session.Event.Created, (db, data) => {
-    db.insert(SessionTable).values(Session.toRow(data.info)).run()
+    try {
+      db.insert(SessionTable).values(Session.toRow(data.info)).run()
+    } catch (err) {
+      if (duplicate(err, "session")) throw new Session.DuplicateIDError({ id: data.info.id })
+      throw err
+    }
   }),
 
   SyncEvent.project(Session.Event.Updated, (db, data) => {
diff --git a/packages/opencode/test/server/session-messages.test.ts b/packages/opencode/test/server/session-messages.test.ts
index 24ee6a1b436f..e9a7212b05dc 100644
--- a/packages/opencode/test/server/session-messages.test.ts
+++ b/packages/opencode/test/server/session-messages.test.ts
@@ -166,6 +166,7 @@ describe("session messages endpoint", () => {
   })
 })
 
+
 describe("session.prompt_async error handling", () => {
   test("prompt_async route has error handler for detached prompt call", async () => {
     const src = await Bun.file(new URL("../../src/server/instance/session.ts", import.meta.url)).text()
diff --git a/packages/opencode/test/session/session.test.ts b/packages/opencode/test/session/session.test.ts
index 15132a270125..3f3d0f0138ec 100644
--- a/packages/opencode/test/session/session.test.ts
+++ b/packages/opencode/test/session/session.test.ts
@@ -8,6 +8,7 @@ import { MessageV2 } from "../../src/session/message-v2"
 import { MessageID, PartID, type SessionID } from "../../src/session/schema"
 import { AppRuntime } from "../../src/effect/app-runtime"
 import { tmpdir } from "../fixture/fixture"
+import { SyncEvent } from "../../src/sync"
 
 const projectRoot = path.join(__dirname, "../..")
 Log.init({ print: false })
@@ -179,3 +180,19 @@ describe("Session", () => {
     expect(missing).toBe(true)
   })
 })
+
+describe("DuplicateIDError", () => {
+  test("projector throws on duplicate session ID", async () => {
+    await using tmp = await tmpdir({ git: true })
+    await Instance.provide({
+      directory: tmp.path,
+      fn: async () => {
+        const session = await create({})
+        expect(() => {
+          SyncEvent.run(SessionNs.Event.Created, { sessionID: session.id, info: session as any })
+        }).toThrow()
+        await remove(session.id)
+      },
+    })
+  })
+})
diff --git a/packages/sdk/js/src/v2/gen/sdk.gen.ts b/packages/sdk/js/src/v2/gen/sdk.gen.ts
index d7bf43f506f8..6b2f76e5105b 100644
--- a/packages/sdk/js/src/v2/gen/sdk.gen.ts
+++ b/packages/sdk/js/src/v2/gen/sdk.gen.ts
@@ -1653,6 +1653,7 @@ export class Session2 extends HeyApiClient {
     parameters?: {
       directory?: string
       workspace?: string
+      id?: string
       parentID?: string
       title?: string
       permission?: PermissionRuleset
@@ -1667,6 +1668,7 @@ export class Session2 extends HeyApiClient {
           args: [
             { in: "query", key: "directory" },
             { in: "query", key: "workspace" },
+            { in: "body", key: "id" },
             { in: "body", key: "parentID" },
             { in: "body", key: "title" },
             { in: "body", key: "permission" },
diff --git a/packages/sdk/js/src/v2/gen/types.gen.ts b/packages/sdk/js/src/v2/gen/types.gen.ts
index 24c1d53bf749..e0f85a319862 100644
--- a/packages/sdk/js/src/v2/gen/types.gen.ts
+++ b/packages/sdk/js/src/v2/gen/types.gen.ts
@@ -1888,6 +1888,13 @@ export type McpResource = {
   client: string
 }
 
+export type DuplicateIdError = {
+  name: "DuplicateIDError"
+  data: {
+    id: string
+  }
+}
+
 export type TextPartInput = {
   id?: string
   type: "text"
@@ -3265,6 +3272,7 @@ export type SessionListResponse = SessionListResponses[keyof SessionListResponse
 
 export type SessionCreateData = {
   body?: {
+    id?: string
     parentID?: string
     title?: string
     permission?: PermissionRuleset
@@ -3283,6 +3291,10 @@ export type SessionCreateErrors = {
    * Bad request
    */
   400: BadRequestError
+  /**
+   * Conflict
+   */
+  409: DuplicateIdError
 }
 
 export type SessionCreateError = SessionCreateErrors[keyof SessionCreateErrors]