fix(vfox): use selected install path for env keys

[risu729]

Summary

• pass the resolved ToolVersion install path into traditional vfox EnvKeys hooks
• key/cache vfox exec env by install path so shared/system installs do not reuse user-path cache entries
• add e2e coverage for a fake system-installed vfox poetry tool

Fixes part of #9857.

Testing

• cargo fmt --check
• git diff --check
• CARGO_TARGET_DIR=/tmp/mise-m7-vfox-test /home/risu/.rustup/toolchains/1.95.0-x86_64-unknown-linux-gnu/bin/cargo test -p vfox test_env_keys_for_install_dir
• CARGO_TARGET_DIR=/tmp/mise-m7-e2e-target mise run test:e2e e2e/backend/test_vfox_system_bin_paths

[gemini-code-assist]

Code Review

This pull request refactors the vfox backend to support explicit installation directories when retrieving environment keys. Key changes include the introduction of env_keys_for_install_dir in the vfox crate, updating the VfoxBackend to incorporate the installation path into its cache key and cache freshness checks, and adding an end-to-end test for system binary paths. I have no feedback to provide as there were no review comments to evaluate.

[greptile-apps]

Greptile Summary

This PR fixes vfox env key resolution for system-installed tools by threading the resolved tv.install_path() through to the plugin's EnvKeys hook, and keys the exec-env cache on both options and install path so that system and user installs no longer share cache entries.

• crates/vfox/src/vfox.rs: New env_keys_for_install_dir public method accepts an explicit install dir; both public variants delegate to a shared private env_keys_for_sdk_install_dir helper. A unit test verifies the custom path is forwarded correctly.
• src/backend/vfox.rs: _exec_env now captures tv.install_path() upfront, includes it in the opts_hash used for both the in-memory cache key and the on-disk cache file name, and replaces the coarse installs_path freshness watch with the specific install_path.
• e2e/backend/test_vfox_system_bin_paths: New e2e script sets up a fake system-installed poetry plugin and asserts mise bin-paths returns the system install dir rather than the user install dir.

Confidence Score: 5/5

Safe to merge — changes are narrowly scoped to the vfox env-key path and cache logic, with no regressions on the existing code path.

The fix is well-targeted: the root cause (hardcoded install-dir construction in the hook call and the cache hash) is corrected at both layers, the existing env_keys public API is preserved unchanged by delegating to the new shared helper, and the e2e test validates the system-install scenario end-to-end.

No files require special attention.

Important Files Changed

Filename	Overview
src/backend/vfox.rs	Uses the resolved install_path from tv.install_path() for both the env-key computation and the cache key/freshness file, ensuring system-installed tools get their own cache entries and correct path passed to the plugin hook.
crates/vfox/src/vfox.rs	Adds env_keys_for_install_dir public API and a shared private helper, refactoring env_keys to delegate into the same code path; a unit test validates custom install-dir resolution.
e2e/backend/test_vfox_system_bin_paths	New e2e test that sets up a fake system-installed vfox poetry tool and asserts mise bin-paths reports the system install path rather than the user install path.

_{Reviews (2): Last reviewed commit: "test(vfox): use platform separator in en..." | Re-trigger Greptile}