`src/middleware.rs` — the pipeline core

The middleware trait, the dispatch context/result carriers, and the pipeline builder. The layers themselves live in middleware/*.rs.

Key items

• ToolMiddleware — name() + dispatch(ctx, next) (boxed async); pre-process, call next, post-process — or short-circuit.
• ToolDispatchContext { tool_name, input, call_id, turn_number, cancel, permission, tool_context } — everything a layer may read or rewrite.
• ToolPipeline — cursor-based chain; registration order = execution order, first registered outermost; invoke(ctx), dispatch_all (all-or-nothing on cancel), middleware_names().
• ToolPipelineBuilder — with_middleware, with_middleware_arc, with_core(registry), build(); PipelineError { Empty, MissingCore }.
• Re-exports every shipped layer and ToolDispatchResult (defined in tool.rs).

Behavior notes

• The core (ToolCallMiddleware, in tool_call.rs) is always innermost — the registry lookup and the actual tool call.
• The engine path: agent.set_pipeline(builder) injects the loop’s registry as the core — don’t call with_core yourself there.
• Ordering guidance: permission outermost (deny before work), redaction before verifiers, the shield inside renamers and outside memoize.

Deep dive: Middleware.