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# Tool Execution Pipeline

This graph shows where policy, hooks, sandboxing, filesystem guards, result rewriting, and UI rendering fit without changing the loop. The key extension points are the `tools/pre-execute`, `tools/execute`, and `tools/post-execute` waterfalls.

```mermaid
flowchart TD
  model["Assistant message contains tool-call block"]
  toolCall["Session event: <code>tool/call</code><br/>logged before execution"]
  presentCall["UI pending card<br/>presentCall(args)"]
  pre["<code>tools/pre-execute</code> waterfall<br/>hooks, permission, sandbox"]
  denied["denied<br/>tool body skipped"]
  approval["<code>ctx.approval</code> one-shot prompt<br/>absent or unanswerable: deny"]
  around["<code>tools/execute</code> waterfall<br/>timeout, retry, metrics (around dispatch)"]
  toolBody["Registered tool execute() body"]
  fsGate["<code>fs/write-intent</code> or <code>fs/edit-intent</code><br/>tool-fs mutations only"]
  owned["Tool-owned session events<br/><code>todo/write</code>, <code>fs/observed</code>, <code>hook/invoked</code>, <code>hook/result</code>, <code>tool/code-dispatch</code>"]
  post["<code>tools/post-execute</code> waterfall<br/>accept, block, replace, add context"]
  context["Buffered additionalContext<br/>context/message after all tool results"]
  toolResult["Session event: <code>tool/result</code><br/>single model-facing outcome"]
  presentResult["UI completed card<br/>presentResult(args, result)"]
  model --> toolCall
  toolCall --> presentCall
  toolCall --> pre
  pre -->|allow| around
  around --> toolBody
  pre -->|deny| denied
  pre -->|ask| approval
  approval -->|allowed-once| around
  approval -->|rejected, cancelled, unavailable| denied
  denied --> post
  toolBody --> fsGate
  fsGate --> toolBody
  toolBody --> owned
  toolBody --> around
  around --> post
  post --> context
  post --> toolResult
  toolResult --> presentResult
```

Filesystem read-before-edit checks live below `tool-fs` on the `fs/*` event gate; hook bridges and the approval seam's permission prompts live on the generic pre/post tool waterfalls; and around-dispatch concerns like the tool-call timeout policy (`@deepseek-ai/dsh-timeout-policy`) wrap core dispatch on `tools/execute`. That split lets the same hooks observe bash, fs, web, todo, and subagent calls without coupling those tools to one policy service.

Maintenance mode: curated Mermaid flow; exact tool schemas and event signatures live in generated catalogs.
