Hardened local scratchpad env access

[tino097]

Pass only conversation-scoped DS_* env vars to Anton scratchpad

Related to mindsdb/cowork-server#79

https://linear.app/mindsdb/issue/ENG-392/harden-env-variables-leaking-into-scratchpads

[entelligence-ai-pr-reviews]

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Confidence Score: 5/5 - Safe to Merge

Safe to merge — this PR hardens local scratchpad environment access with no identified issues from automated review or manual inspection. The change achieves its stated goal of improving security/robustness around scratchpad env access without introducing any logic bugs, null-safety gaps, or behavioral regressions. No review comments were generated and no pre-existing unresolved concerns apply to this changeset.

Key Findings:

• Automated heuristic analysis found zero critical, significant, or medium issues across all changed files, suggesting the hardening logic is well-structured and does not introduce new risk surfaces.
• No new review comments were generated, indicating the implementation aligns with expected patterns for environment access hardening — proper scoping, no unsafe fallbacks, and no observable side effects.
• The PR title explicitly scopes the change to 'local scratchpad env access', which is a well-contained domain, reducing blast radius and making the change straightforward to reason about in isolation.