Fix: Tools: atomic commit splitting — order unrelated changes by dependency

[goransh-walia]

This PR addresses #3999.

Tools: atomic commit splitting — order unrelated changes by dependency, reject cycles

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file before submission (syntax check + change-scope check).
Please review carefully — happy to adjust based on feedback.

[github-actions]

Thanks @goransh-walia for taking the time to contribute.

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[Hmbown]

Kind: request-changes. The issue #3999 ask is legitimate, but this can't merge as-is. Blocking: (1) ApprovalRequirement::Manual (your git.rs:254) doesn't exist — the enum is Auto/Suggest/Required (crates/tools/src/lib.rs:44-52), so this doesn't compile; the PR's CI never ran the build. (2) This adds a second commit authority: a model-visible tool that heuristically groups changes and directly runs git apply --cached + git commit -m with generated messages (git.rs:918, :923-1008). Please make it propose-only (return the split plan + messages) and let commits flow through existing write paths, or route via git_tool.rs like status/diff. (3) It declares only Sandboxable, no WritesFiles — every write tool declares it, and the execution envelope fail-closes on under-declared tools (execution_envelope.rs:310-341). (4) Data safety: no git reset before git apply --cached (user-staged hunks get swept in), no rollback on partial failure, and git add -N runs before the dry_run check so dry-run mutates the index (git.rs:276-295). (5) No DCO sign-off. Happy to re-review a plan-only redesign — the cycle-rejection tests are a good start.