Merge branch 'master' into worktree/plan-review-layout

packages/host/apiproxy/src/api/rpc-map.ts

@@ -24,6 +24,7 @@ export interface RpcMethodMap {
   'session.models': SessionsApi['models']
   'session.selectModel': SessionsApi['selectModel']
   'session.rename': SessionsApi['rename']
+  'session.fork': SessionsApi['fork']
   'session.prompt': SessionsApi['prompt']
   'session.updateQueue': SessionsApi['updateQueue']
   'session.cancel': SessionsApi['cancel']

packages/host/apiproxy/src/api/rpc.schema.ts

@@ -51,6 +51,7 @@ export const rpcErrorSchema: z.ZodType<RpcError> = z.discriminatedUnion('code',
   z.object({ code: z.literal('command-error'), message: z.string(), details: z.object({}) }),
   z.object({ code: z.literal('unknown-command'), message: z.string(), details: z.object({}) }),
   z.object({ code: z.literal('title-invalid'), message: z.string(), details: z.object({ sessionId: z.string() }) }),
+  z.object({ code: z.literal('fork-unavailable'), message: z.string(), details: z.object({ sessionId: z.string() }) }),
   z.object({ code: z.literal('internal'), message: z.string(), details: z.object({}) }),
 ]) as unknown as z.ZodType<RpcError>
 

packages/host/apiproxy/src/api/rpc.ts

@@ -51,6 +51,7 @@ export interface RpcErrorDetailsMap {
   /** A leading-/ prompt named no registered command; the message names the token. */
   'unknown-command': {}
   'title-invalid': { sessionId: SessionId }
+  'fork-unavailable': { sessionId: SessionId }
   'internal': {}
 }
 

packages/host/apiproxy/src/api/sessions.schema.ts

@@ -89,6 +89,17 @@ export const sessionRenameValueSchema = z.object({
   seq: z.number().int().nonnegative(),
 }) satisfies z.ZodType<Wire<ResponseValue<'session.rename'>>>
 
+/** session.fork request payload (atSeq anchors the completed-turn cut). */
+export const sessionForkRequestSchema = z.object({
+  sessionId: sessionIdSchema,
+  atSeq: z.number().int().nonnegative().optional(),
+}) satisfies z.ZodType<Wire<RequestPayload<'session.fork'>>>
+
+/** session.fork response value (the child session id). */
+export const sessionForkValueSchema = z.object({
+  sessionId: sessionIdSchema,
+}) satisfies z.ZodType<Wire<ResponseValue<'session.fork'>>>
+
 /** session.history request payload (beforeSeq/maxMessages page backwards from the window tail). */
 export const sessionHistoryRequestSchema = z.object({
   sessionId: sessionIdSchema,

packages/host/apiproxy/src/api/sessions.ts

@@ -238,6 +238,21 @@ export interface SessionsApi {
    * one — carried for future rendering; the state change is the feedback). A usage/state error is an
    * RPC error with code command-error; an unrecognized name is an RPC error with code unknown-command.
    */
+  /**
+   * Forks a new session from a completed-turn prefix of the source. `atSeq`
+   * anchors the cut: the boundary is the first `turn/end` at or after it
+   * (a message's fork button passes the message seq, so the fork includes
+   * that whole turn); a boundary past the log end, or an omitted `atSeq`,
+   * falls back to the source's last completed turn. An in-log anchor whose
+   * turn is still open fails with `fork-unavailable` instead of clipping to
+   * an earlier turn. The child inherits the source cwd, latest logged model
+   * target, workspace attachment, and `parentSessionId` lineage; the seed
+   * prefix carries the source title.
+   */
+  fork(request: RpcRequest<{ sessionId: SessionId; atSeq?: number }>):
+  Promise<RpcResponse<{ sessionId: SessionId }>>
+
+  /** Sends a message. content is core's ContentBlock[] verbatim; mode maps 1:1 — queue→send, steer→steer. */
   prompt(request: RpcRequest<{ sessionId: SessionId; mode: 'queue' | 'steer'; content: ContentBlock[] }>):
   Promise<RpcResponse<{ accepted: true; command?: { kind: 'success'; text?: string } }>>