feat: truncate oversized web tool output

[K-Mistele]

Why the change

Large successful web fetches and searches now stay within the model-context budget while their complete serialized output remains available through the existing Read tool.

Special things to note

• The hook matches the dispatched web_fetch and web_search registry keys because their underlying interfaces are named webfetch and websearch.
• Spilled results use AgentLayer's existing anonymous OS-temp agent-tool-output-* directories rather than session-persistent storage.

Change outline

Business logic

postToolUse(web_fetch | web_search)
  if output is not a string, or is within 2,000 lines and 50 KiB
    keep the serialized result unchanged
  otherwise
    keep a head excerpt at whole-line boundaries
    save the complete serialized result to an OS-temp file
    replace history output with the excerpt, saved path, and Read offset
    first line exceeds byte limit -> instruct Read from offset 1

Files

agentlayer/
├── packages/agentlayer-filesystem/
│   ├── src/hooks/output-truncation.ts  # web-specific spill hook and Read guidance
│   ├── src/coding-agent.ts             # canonical filesystem hook chain
│   └── test/                           # boundaries, spill content, hook composition
├── agents/codelayer/
│   ├── src/agent.ts                    # root and RLM hook composition
│   ├── src/coding-subagent-tool.ts     # specialist composition and library Read access
│   └── test/                           # root and specialist coverage
└── packages/docs/content/packages/filesystem/hooks.md
    # public hook behavior and configuration

Call flow

createCodelayerAgent / createCodingSubagentTool
  createAgentFilesystemHooks
    Read -> Bash -> Glob -> Grep -> List -> Web output -> file state -> caller hooks
  standard root, RLM root, and web-capable children share this one chain

Agent executes web_fetch or web_search
  serialized successful result
    -> web output hook
    -> bounded replacement enters the next model request
    -> full result remains readable at the returned temp-file path

[github-actions]

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