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transcript.jsonl

The agent's redirected stdout, written as newline-delimited JSON (NDJSON). Every sandbox_agent and sandbox_research run produces one.

Location

Context Path
Inside the sandbox /out/transcript.jsonl
On the host <output_dir>/transcript.jsonl

output_dir is returned in the MCP result of every sandbox_agent / sandbox_research call and corresponds to the sandbox's /out on the host filesystem.

Contents

Each line is a JSON object emitted by the agent CLI with NDJSON / stream-json output enabled.

claude-code: invoked with --output-format stream-json --verbose. Event shapes:

  • {"type":"assistant","message":{...}} — intermediate assistant turn; message.content is an array of content blocks (text, tool_use, etc.).
  • {"type":"result","subtype":"success","result":"...","usage":{...}} — terminal event; result holds the final answer, emitted once at exit.
  • Other event types (tool_result, system, etc.) may appear; unrecognised lines are silently skipped by the parser.

A typical result-event line:

{"type":"result","subtype":"success","result":"Done. Written to /out/report.txt.","usage":{"input_tokens":1234,"output_tokens":56,"cache_read_input_tokens":0,"cache_creation_input_tokens":0}}

For the full event schema see the Claude Code CLI reference or the parser source at internal/agents/anthropic/streamjson.go.

codex (the preferred default when enabled and configured): invoked with --json. The terminal event is {"type":"item.completed","item":{"type":"agent_message","text":"..."}}. Parser source: internal/agents/codex/streamjson.go.

How ResultText extracts the final answer

ResultText in the agent-provider package scans the transcript line by line:

  • claude-code (internal/agents/anthropic/streamjson.go): prefers the result field of the terminal {"type":"result"} event; falls back to concatenating text from all {"type":"assistant"} events if no result event is present (e.g. the run errored).
  • codex (internal/agents/codex/streamjson.go): returns the text of the last item.completed / agent_message event.

Malformed lines are silently skipped in both parsers.

Relationship to the MCP stdout result field

The stdout field in the MCP result is the parsed final answer from ResultText — not the raw transcript. It is bounded by tailStdout to the last 32 KiB. When truncated, the field ends with:

[stdout truncated to last N bytes; full transcript in <output_dir>/transcript.jsonl]

The transcript file is the authoritative full record. Read it when:

  • The stdout field contains the truncation marker.
  • You need intermediate reasoning steps or tool-call traces (e.g. a verifier child needs the full reasoning trail — see Spawning a verifier/judge child).