fix(index): compile in-process when the serving image has no guest rootfs

[philocalyst]

Summary

The Linux serving image has no Smolvm guest rootfs, so every package failed in the cage and stayed unindexed. Compile strategy now follows whether NUDOX_GUEST_ROOTFS is provisioned:

• unset or empty: run the in-process language producer on the materialized tree
• non-empty on Linux: keep the cage, and still fail the job if the cage fails

The image entrypoint creates /tmp before the first tempfile, and now also puts cargo, rustc, and the gcc cc wrapper on PATH with a writable CARGO_HOME. In-process Rust indexing runs cargo metadata and build-script cargo check. Without the linker, serde failed in Compiling with linker cc not found.

tests/docker/lib_rs_indexed.sh ingests serde, waits until it is Stored, and requires a package card plus a Serialize symbol hit.

Tests

RUSTC_BOOTSTRAP=1 cargo test -p index --features server --lib select_compile_strategy — 3 passed.

Against a container with cargo, rustc, and cc on PATH, tests/docker/lib_rs_indexed.sh passed: serde Stored, description "A generic serialization/deserialization framework", keywords, license mit or apache-2.0, downloads present, and a Serialize symbol hit. The image rebuild bakes those tools in so the container no longer depends on a host mount.

  

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