docs: document Pipeline.stream(), remove the AsyncPipeline page, ChatPromptBuilder insert tag, and Toolset run-scoped copies

[julian-risch]

Related Issues

• Resolves four subtasks of deepset-ai/haystack-private#381:
  • feat: expose AsyncPipeline.stream for chunk-by-chunk consumption #11258
  • feat: Extend ChatPromptBuilder with insert tag #11486
  • fix: Fix usage of SearchableToolset with Agent when selecting a subset of tools to be active #11564
  • fix: In AsyncPipeline cancel inflight tasks if a PipelineRuntimeError is raised by another component #11499

Proposed Changes:

• AsyncPipeline page removal + feat: expose AsyncPipeline.stream for chunk-by-chunk consumption #11258 + fix: In AsyncPipeline cancel inflight tasks if a PipelineRuntimeError is raised by another component #11499 — AsyncPipeline was merged into Pipeline in 3.0, so the AsyncPipeline concepts page is removed from the current docs (the 2.x copies live on under versioned_docs/). Its still-relevant content is consolidated into a rewritten "Async Execution and Streaming" section on the Pipelines concepts page:

  • concurrent component execution and the concurrency_limit init parameter,
  • the three async execution methods run_async, run_async_generator, and the new stream() with a runnable example — iterate the returned handle with async for to consume StreamingChunks, read the final output from handle.result, restrict sources via streaming_components, and control abandonment behavior with cancel_on_abandon,
  • an "Error Handling and Task Cancellation" subsection (moved here from docs: document sync streaming callbacks in async contexts #11870): in-flight tasks are cancelled and drained when a component raises, when run_async_generator iteration is abandoned, or when the run is cancelled — plus the caveat that sync components offloaded to a worker thread run to completion with their outputs discarded.

  The sidebar entry is removed and a client redirect from /docs/asyncpipeline to /docs/pipelines is added. No references to AsyncPipeline remain in the current docs.

• feat: Extend ChatPromptBuilder with insert tag #11486 — ChatPromptBuilder docs: new "The insert Tag" subsection under String Templates, documenting {% insert %} with a runnable example, expression/slice/index support, lossless round-tripping of all content types, and multiple-tag usage.

• fix: Fix usage of SearchableToolset with Agent when selecting a subset of tools to be active #11564 — Toolset docs: new "Run-Scoped Copies and Tool Selection" section covering spawn() and get_selectable_tools(), per-run isolation (concurrent runs sharing a Toolset are safe), and runtime name-based selection via Agent.run(tools=[...]) keeping toolsets live. Also updated the SearchableToolset "Reusing the toolset across multiple agent runs" section: discovered tools no longer persist across Agent runs and clear() between runs is not necessary.

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Project	Deployment	Actions	Updated (UTC)
haystack-docs	Error		Jul 9, 2026 12:50pm

[claude]

Code review

No issues found. Checked for bugs and CLAUDE.md compliance.

[davidsbatista]

Removed two mentions of "AsyncPipeline" on docs-website/docs/

[davidsbatista]

Looks good!