RUST-REF-005: Decompose oversized Rust modules

[itlezy]

Objective

Decompose mixed-responsibility Rust source and test modules by subsystem and stable boundary, beginning with emulebb-core/src/lib.rs, while preserving public APIs, REST contracts, protocol behavior, persistence, and VPN fail-closed enforcement.

Source length is an advisory maintainability signal, not a validation limit. Cohesive files do not need allowlist entries or written size exceptions.

Delivery

• Move code in small behavior-preserving commits.
• Add focused modules when a change introduces an independently nameable responsibility.
• Keep small white-box tests beside private helpers when proximity helps; move substantial suites to sibling test modules or integration-test trees.
• Use non-failing checker advisories to focus responsibility reviews.
• Remove only compiler-proven private dead code and unused dependencies.
• Do not require broad prerequisite refactors for focused behavior changes.

Acceptance

• emulebb-core/src/lib.rs becomes a thin crate root with stable re-exports.
• Substantial tests are grouped outside production modules without changing assertions or coverage.
• Static IPv4 and P2P binding audits follow moved boundaries.
• No source or test file fails policy solely because of line count.
• Workspace format, Clippy, tests, Kad swarm, and VPN leak gates remain green.
• Each coherent extraction is committed and pushed independently.

[itlezy]

2026-07-10 implementation wave

Completed and pushed 23 granular RUST-REF-005 commits.

• Reduced crates/emulebb-core/src/lib.rs from 13,711 to 6,132 lines.
• Split the 4,974-line inline test module into nine responsibility-focused files; largest is 717 lines.
• Extracted application, server, search, category, friend, transfer creation/control/state, shared-file, upload, network lifecycle, and direct-download runtime modules.
• Ratcheted the lib.rs hard limit to 6,132 and removed the temporary core-test allowlist.
• Extended the P2P fail-closed scanner to cover the relocated network_api.rs boundary.
• Removed compiler-proven redundant diagnostics conversions; all-target Clippy is green with -D warnings.

Evidence:

• Rust policy and rustfmt checks pass.
• cargo test --workspace --locked -- --skip local_kad_swarm passes.
• 302 core library tests pass.
• VPN egress-audit suite: 3/3 pass serially.
• Orchestrated Release client build: 0 warnings.
• Orchestrated diagnostics Release client build: 0 warnings.
• No repository-local target directory exists.

The workspace-wide validate --include-product-family entrypoint remains blocked before product checks by 67 pre-existing virtual-environment binaries under other managed repositories; no unrelated environments were deleted.

Next wave: split the remaining Kad publish/runtime and core download orchestration blocks, then address kad_store/mod.rs, the Slint UI client, and upload queue hotspots.

[itlezy]

Additional responsibility-based decomposition landed in granular commits: fcd6f36 (thin UI binary), 86b64da (presentation), 4a94087 (models), 8caaef7 (REST client), 5087dab (worker), 8a326e2 (rendering), and 50070b3 (kad_store sibling tests). The UI app wiring is now 495 lines with cohesive modules; kad_store production is 539 lines and its 41-test suite is separate. cf380fd also replaces permanent lint allows with checked reasoned expectations. Focused tests and all-target Clippy pass.