feat(runtime): add workspace-aware run foundations

[wendeus0]

Summary

• add runtime boundaries for tool specs, workspace providers and run context
• persist workspace-aware run metadata and enrich local runtime observability events
• sync PENDING_LOG.md to the post-F53 backlog state

Commits

• feat(runtime): add workspace-aware run foundations
• docs(backlog): sync post-F53 pending log

Validation

• F51 spec validation, targeted pytest, ruff, mypy
• F52 spec validation, targeted pytest, ruff, mypy
• F53 spec validation, targeted pytest, expanded pytest, ruff, mypy