Add changelog for #4493

changelog/4493.added.md

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+- Added `pipecat.tasks`, a task-based agent framework folded in from the standalone `pipecat-subagents` package. Tasks inherit from `BaseTask`, share a `TaskBus`, register in a `TaskRegistry`, and exchange typed work via `@job` handlers. `LLMTask` and `LLMContextTask` provide ready-made LLM-driven tasks. `PipelineRunner.spawn(task)` registers fire-and-forget tasks alongside the main pipeline task.

changelog/4493.changed.2.md

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+- ⚠️ `FrameProcessorSetup.pipeline_task` and `FunctionCallParams.pipeline_task` are now mandatory fields, and `FrameProcessor.pipeline_task` raises if read before `setup()` instead of returning `None`. Real-world code (frame processors set up by `PipelineTask`, tool handlers invoked by `LLMService`) is unaffected; only callers that construct these dataclasses by hand (typically tests) now have to supply a `pipeline_task` reference.

changelog/4493.changed.md

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+- `PipelineTask` now inherits from `BaseTask`, so every pipeline task is also a bus participant. It accepts a new optional `bridged=()` parameter that auto-wraps the pipeline with bus edge processors, letting the task exchange frames with other bridged tasks over the shared `TaskBus`. The bus is supplied by `PipelineRunner` via `task.attach(registry=..., bus=...)` instead of through the constructor.