Migrating from 1.x to 2.0.0rc1

This release candidate changes execution boundaries. Test your integration before upgrading production workloads.

1.x behavior	2.x behavior / action
Docker errors silently select local execution	Docker errors raise; use Runtime(use_docker=False), --no-docker, or PYGENT_USE_DOCKER=0 only for trusted local use
Python 3.9 advertised	Python 3.10+ supported; newer Python no longer depends on removed imghdr
Workspace methods accept absolute/escaping paths	Supply workspace-relative paths; symlinks in file/copy paths are rejected
A disabled tool is only hidden from the model	Agent now blocks it at dispatch too
Unbounded command output capture	Runtime.bash retains up to 64,000 characters by default; max_output_chars configures it
Local timeout kills only the shell	On POSIX, the process group is killed; background children do not survive ordinary command completion
First agent sets a process-wide log-file default	Each agent selects its own log path; explicit PYGENT_LOG_FILE still applies
History rewrites can leave partial JSON; restored tool IDs are lost	Atomic replacement and preserved tool-call IDs; interrupted/incomplete turns are not automatically recovered

Agent.step, its mixed legacy history representation, run_until_stop, and CLI commands remain available. Harness is the recommended API for new integrations: its tools are explicit, it has no interactive terminal behavior, and it returns RunResult with a termination reason.

Harness does not reuse global register_tool entries. Construct Tool objects explicitly. Tool functions take validated keyword arguments, with no automatically injected Runtime parameter; use bound runtime methods or closures.

The legacy autonomous loop still has its older stop-tool semantics and cooperative post-step timeout checks. Do not confuse it with the new harness's final-answer termination and per-batch budgeting.