fix(web): address session fork review findings

packages/client/runtime/src/client/contract/sessions.ts

@@ -33,7 +33,8 @@ export interface ISessions {
    * Fork a session from a completed-turn prefix of the source; on resolution
    * the child is in the list store and `open()` can target it.
    * @param opts - source session id and the optional event seq anchoring the
-   *   cut (the boundary is the first turn/end at or after it).
+   *   cut (the boundary is the first turn/end at or after it; an in-log
+   *   anchor in an open turn is unavailable rather than clipped backward).
    * @returns the child session id.
    */
   fork(opts: { sessionId: SessionId; atSeq?: number }): Promise<SessionId>

packages/client/runtime/src/client/sessions/manager.ts

@@ -293,7 +293,8 @@ export class SessionManager {
    * Contract session.fork; on success merge the child into summaries
    * immediately (same synchronous-addressability guarantee as create). The
    * child carries the source's history, so it is never blank; lineage rides
-   * parentSessionId so the list nests it under its source.
+   * parentSessionId so the list nests it under its source. A child published
+   * before Workspace attachment fails is also reconciled into the list.
    * @param opts - source session and the optional seq anchoring the cut.
    * @returns the fork result (the child session id).
    */
@@ -306,9 +307,12 @@ export class SessionManager {
         sessionId: opts.sessionId,
         ...opts.atSeq === undefined ? {} : { atSeq: opts.atSeq },
       })
-      if (result.ok) {
+      const childId = result.ok
+        ? result.value.sessionId
+        : workspaceAttachSessionId(result.error)
+      if (childId !== undefined) {
         this.recordMutation({ kind: 'upsert', summary: {
-          sessionId: result.value.sessionId, updatedAt: Date.now(), running: false, blank: false,
+          sessionId: childId, updatedAt: Date.now(), running: false, blank: false,
           parentSessionId: opts.sessionId,
           ...(source?.cwd !== undefined ? { cwd: source.cwd } : {}),
         } })

packages/client/runtime/src/client/sessions/service.ts

@@ -338,7 +338,8 @@ export class SessionsService implements ISessions {
    * synchronous-addressability guarantee as {@link SessionsService.create}:
    * on resolution the child is in the list store and open() can target it).
    * @param opts - source session id and the optional event seq anchoring the
-   *   cut (the boundary is the first turn/end at or after it).
+   *   cut (the boundary is the first turn/end at or after it; an in-log
+   *   anchor in an open turn is unavailable rather than clipped backward).
    * @returns the child session id.
    * @throws {SessionForkError} with the source id.
    */