Method ensureActive

packages/runtime/src/runtime-kernel.ts:2802–2852

(
    sessionId: string,
    header: SessionHeader,
    execution: PendingExecutionClaim,
  )

  }

  private async ensureActive(
    sessionId: string,
    header: SessionHeader,
    execution: PendingExecutionClaim,
  ): Promise<BackendGeneration> {
    await this.clearBackendQuarantineForActivation(sessionId, execution);
    let existing = this.active.get(sessionId);
    if (existing) {
      existing.cachedHeader = header;
      return existing;
    }
    await this.waitForBackendDisposal(sessionId);
    existing = this.active.get(sessionId);
    if (existing) {
      existing.cachedHeader = header;
      return existing;
    }
    const entry = await this.shareBackendActivation(`parent:${sessionId}`, async () => {
      const current = this.active.get(sessionId);
      if (current) return current;
      const subagent = this.resolveSubagentActivation(header);
      const backend = await this.deps.backends.build(header.backend, {
        sessionId,
        workspaceRoot: header.workspaceRoot,
        header,
        store: this.deps.store,
        abortSignal: execution.abortController.signal,
        ...(subagent
          ? {
              systemPrompt: subagent.systemPrompt,
              tools: subagent.tools,
            }
          : {}),
        ...this.buildBackendRecorderHooks({
          resolveActive: () => this.active.get(sessionId),
          sessionId,
        }),
        allowMidTurnHistoryCompaction: Boolean(this.deps.runtimeEventStore),
        shellRunContextSummary: () =>
          this.deps.shellRuns?.buildContextSummary(sessionId) ?? Promise.resolve(undefined),
      });
      await this.rejectCancelledBackendActivation(backend, header, { kind: 'parent' }, execution);
      const generation = this.createBackendGeneration(sessionId, backend, header, {
        kind: 'parent',
      });
      this.active.set(sessionId, generation);
      return generation;
    });
    entry.cachedHeader = header;
    return entry;
  }

  private async shareBackendActivation(
    activationKey: string,