Support multiple artifact directories per invocation

[jackcbrown89]

Summary

• Add artifacts_dirs: string[] to InvocationMessage and CommandExecutionMessage so a single invocation/command-execution can declare multiple artifact directories. The underlying ArtifactManager already supported multiple watched directories per session — this change just opens up the wire.
• TS runtime accepts both fields during a transition: the legacy singular artifacts_dir is kept and marked @deprecated, with a one-line logger.warn when it's used. collectArtifactDirs() in session.ts merges and dedupes.
• Python client cuts over cleanly to artifacts_dirs: list[str] | None on QueryOptions and ExecuteCommandsOptions. Pairing rule with on_artifact_upload_request is preserved (empty list = None). The duplicated __post_init__ validation across the two dataclasses is extracted to _validate_artifact_pairing.
• Docs updated: python-client.mdx, both package READMEs.

Test plan

• vitest run in packages/runtimeuse — 149 tests pass, including 4 new tests covering multi-dir, the deprecated singular field, and dedup of overlapping fields.
• pytest test/test_client.py in packages/runtimeuse-client-python — 58 tests pass, including new tests asserting that artifacts_dirs is forwarded to both invocation_message and command_execution_message and that artifacts_dir is no longer sent.
• pytest test/e2e/ — 37 tests pass, including a new test_multiple_artifacts_dirs_in_single_invocation that has a pre-agent command write to one directory and the agent write to another within a single invocation, then asserts both files upload.
• Run advanced LLM tests against live providers if you want to verify there too — kwarg renamed, no behavioral change.

---

Note

Medium Risk
Touches the cross-language wire format for artifact uploads and changes the Python public API from artifacts_dir to artifacts_dirs, so mismatched client/runtime versions could break artifact watching despite runtime backward compatibility.

Overview
Adds multi-directory artifact watching by introducing artifacts_dirs on both InvocationMessage and CommandExecutionMessage, and updating the TypeScript runtime to merge/dedupe artifacts_dirs with the deprecated legacy artifacts_dir (emitting a warning when the old field is used).

Updates the Python client API to replace artifacts_dir with artifacts_dirs: list[str] | None for QueryOptions/ExecuteCommandsOptions, forwards the new field on the wire, and refactors the “artifacts + callback must be paired” validation into a shared helper (treating [] as disabled). Docs and tests are updated, including new coverage for multi-dir uploads and deprecated-field compatibility; versions are bumped to 0.14.2.

^{Reviewed by Cursor Bugbot for commit c4af077. Bugbot is set up for automated code reviews on this repo. Configure here.}