Summary of Changes

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This pull request enhances the vfox runtime by exposing the detected libc environment type (glibc or musl) to Lua plugins via a new RUNTIME.envType field. This enables plugins to dynamically adapt their behavior, such as downloading appropriate binaries, based on the underlying Linux system's libc implementation. The change involves adding a new detection mechanism, integrating it into the runtime, and updating relevant documentation and tests.

Highlights

• New RUNTIME.envType for Libc Detection: Introduced RUNTIME.envType to vfox Lua plugins, allowing detection of the libc variant (glibc or musl) on Linux systems. This enables plugins to adapt their behavior based on the underlying libc implementation.
• Libc Detection Logic: Implemented a new env_type() function in crates/vfox/src/config.rs for runtime libc detection. This function identifies glibc or musl by checking for the presence of specific dynamic linker files (ld-linux-* or ld-musl-*).
• Documentation Updates: Updated documentation for both backend-plugin-development.md and tool-plugin-development.md to reflect the new RUNTIME.envType field. Additionally, RUNTIME.version and RUNTIME.pluginDirPath were added to tool-plugin-development.md for consistency.
• Platform Override Handling: Added a regression test to verify that RUNTIME.envType is correctly set to nil when using platform overrides, ensuring that libc detection is not applied in cross-platform contexts where it is not applicable.

Greptile Summary

This PR exposes the libc variant detection introduced in #8490 to vfox Lua plugins via a new RUNTIME.envType field ("gnu", "musl", or nil). The implementation is clean and the design decision to duplicate the detection logic within the vfox crate boundary (rather than sharing it with src/platform.rs) is explicitly documented and justified.

Key changes:

• env_type() is added to crates/vfox/src/config.rs, mirroring the is_musl_system() logic in src/platform.rs with cross-reference sync-notes in both files.
• Runtime gains an env_type: Option<String> field, initialised from env_type() on startup and forced to None in Runtime::with_platform() (correct, since target libc is unknown for platform overrides).
• RUNTIME.envType is exposed via mlua::UserData, with Option<String> naturally mapping to string|nil in Lua.
• LuaCATS types, and both plugin-development doc pages are updated, including back-filling previously missing RUNTIME.version and RUNTIME.pluginDirPath entries in tool-plugin-development.md.
• Tests correctly accept None as a valid env_type return on Linux (fixing the brittle assertion noted in prior review threads) and a new integration test verifies the with_platform() nil contract.

Minor style observations:

• config.rs uses once_cell::sync::Lazy while the mirrored src/platform.rs uses std::sync::LazyLock; aligning on the stdlib type would make the "keep in sync" comment easier to follow.
• The new integration test (and existing tests) mutate the global RUNTIME singleton without panic-safe cleanup; a scopeguard defer or similar would make resets unconditional.

Confidence Score: 4/5

• This PR is safe to merge; all identified issues are style-level with no functional or correctness impact.
• The logic is small and self-contained, mirrors an already-reviewed implementation, tests cover the main behavioural contract (including the cross-platform override nil case), and documentation is complete. The two minor points — inconsistent lazy-init primitive and non-panic-safe test teardown — are stylistic and consistent with the rest of the codebase.
• No files require special attention; the two style observations are in crates/vfox/src/config.rs and crates/vfox/src/hooks/pre_install.rs.

Important Files Changed

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A[env_type called] --> B{target_os = linux?}
    B -- No --> C[return None]
    B -- Yes --> D{/lib or /lib64 contains ld-linux-* ?}
    D -- Yes --> E[return Some-gnu]
    D -- No --> F{/lib contains ld-musl-* ?}
    F -- Yes --> G[return Some-musl]
    F -- No --> H[return None]

    subgraph Runtime Initialisation
        I[Runtime::new] --> J[env_type = env_type]
        K[Runtime::with_platform] --> L[env_type = None\ntarget libc unknown]
    end

    subgraph Lua Exposure
        M[RUNTIME.envType] --> N{env_type value}
        N -- Some-gnu --> O[Lua string 'gnu']
        N -- Some-musl --> P[Lua string 'musl']
        N -- None --> Q[Lua nil]
    end

_{Last reviewed commit: 118ebf4}