Summary

• return status="error" for broken persisted metadata instead of mislabeling it as missing
• make status_from_run_folder() and pipefunc-cli status return JSON errors instead of raising on malformed storage metadata
• keep heartbeat-backed status readable when disk output metadata cannot be merged, and cover the new paths with real run-folder tests

Verification

• uv run pytest tests/test_run_status_cli.py tests/test_mcp.py -q
• uv run pytest -n 0 --cov=pipefunc._run_status --cov=pipefunc._run_status_heartbeat --cov=pipefunc._run_status_cli --cov-report term-missing tests/test_run_status_cli.py
• uv run ruff check pipefunc/_run_status.py tests/test_run_status_cli.py

Notes

• uv run mypy pipefunc/_run_status.py tests/test_run_status_cli.py in the fresh worktree hit unrelated missing-stub baseline errors outside this change (pipefunc/cache.py, pipefunc/_widgets/output_tabs.py), so I did not use it as a gate for this follow-up PR.