Cargo by Harness (CbH)

A DeepSeek Harness session mode, That gives everyone the ability to build reliable, efficient Rust software

Select Cargo by Harness when starting a new session in DSH. The Agent prioritizes retrieving crate sources and API signatures from the local Cargo cache rather than relying on memory. Core features:

• Local-cache-first retrieval
• Pure JS macro_rules! expansion (zero external binaries)
• Compile-feedback loop (check → fix → verify)
• Beginner-first guided workflow
• Physical isolation of publish/install commands

Screenshots

Building a full terminal Tetris game from a single prompt.

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Use axum to build a “Hello world” example program that returns JSON.

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Tracklogs During DSH Operation.

How It Works

CbH reuses DSH capability seams instead of reinventing them:

DSH Capability	Plugin Usage
@deepseek-ai/dsh-agent-preset	Declares preset-cbh, exposing "Cargo by Harness" in the new-session mode selector
ctx.tools.register	Registers 4 model tools: cargo_search, cargo_read, cargo, cargo_expand
ctx.commands.register	Registers 6 deterministic slash commands; handlers answer directly without creating model messages
ctx.skills.register	Registers 4 bundled skills: rust-beginner-workflow, rust-compile-fix, rust-crate-choice, rust-daily-loop
File System	Reads local sources and rustdoc JSON under $CARGO_HOME/registry/

Data flow in one sentence: The model uses cargo_search / cargo_read to fetch real APIs from the local cache, cargo to execute toolchain commands with structured diagnostics, and cargo_expand to see through generated code from macro_rules!.

Tools

Tool	Description
cargo_search	Searches local crate caches for crates, symbols, trait impls, or code patterns. Returns up to 20 item summaries without full doc bodies.
cargo_read	Reads exact signatures, docs, sources, implementations, or cache status by precise ID or full Rust path.
cargo	Executes daily toolchain commands (build/check/test/run/fmt/clippy/add/tree, etc.) with exit status and structured diagnostics. Does NOT expose publish, install, or yank.
cargo_expand	Pure JavaScript macro_rules! expander. Parses top-level use aliases and resolves definitions from locally cached crates. No external binaries or Rust builds required.

Installation

If you haven't installed Rust yet, click here and follow the instructions to download and install it.

dsh plugin --profile <profile> add https://github.com/Lavaver/Cargo-by-Harness

After installation, select "Cargo by Harness" in the mode selector of a new DSH session. If you modify the bundle's sub-rows (e.g., adding skills), restart the DSH process to remount the preset composition.

Usage

Once in CbH mode, describe your Rust needs in natural language. The Agent follows a "local cache → minimal implementation → compile verify → fix" rhythm.

Example prompt:

I'm a Rust beginner. Help me write a hello world using axum that returns JSON, and make sure it runs.

The Agent will first use cargo_search to check the local axum version and API, write the code, run cargo check to verify, and automatically apply the rust-compile-fix skill when errors occur.

Retrieval Order

Both tools and commands follow the same non-skippable order:

1. $CARGO_HOME/registry/src/<index>/<crate>-<version>/ — Cargo unpacked source.
2. Workspace's exact version: Cargo.lock first, then manifest version requirements.
3. Cached rustdoc JSON as the structured layer; registry source remains authoritative for declarations, where clauses, and feature-gated code.
4. Only if steps 1–3 miss, perform a single minimal remote completion (crates.io .crate or docs.rs rustdoc JSON), written under $CARGO_HOME/cbh-cache/ before returning.

Commands

Command	Purpose
/cargo-doctor	Diagnose Rust toolchain, workspace, lockfile, and target directory.
/cargo-check [--all-targets] [--clippy] [--offline] [--timeout <s>]	Compile-verify and deterministically summarize diagnostics (error/warning counts, error codes, file:line:col).
/cargo-cache [status|list|prune|verify]	Inspect, list, prune unreferenced cache entries, or verify cached crates.
/cargo-fetch <crate>[@version] [--from crates.io|docs.rs|local]	Perform one minimal remote completion.
/cargo-workspace [deps|features|target]	View current workspace dependency resolution.
/cargo-item <crate::path> [--source]	Read an exact single item, optionally including the source snippet.

Commands perform deterministic, cacheable work only. Anything requiring natural-language judgment of "what to look up" is delegated to cargo_search / cargo_read tools.

Verification

Local check scripts are provided under the ../tools/ directory:

node tools/cbh-smoke.mjs                    # registry, version precedence, all commands
node tools/cbh-command-test.mjs             # command registration and handlers
node tools/cbh-tool-test.mjs                # fallback compiler path
node --import ./tools/register-cbh-stubs.mjs tools/cbh-tool-test.mjs   # host compiler path + schema parity + cargo_expand
node tools/cbh-macro-expander-test.mjs      # pure-JS macro expansion and graceful degradation
node tools/cbh-skills-test.mjs              # bundled skill discovery and registration
node tools/cbh-cargo-run-test.mjs           # cargo runner: whitelist, diagnostics, metadata
node tools/cbh-toolchain-test.mjs           # real cargo doctor / check (fixtures)
node tools/cbh-remote-smoke.mjs             # crates.io completion (throwaway CARGO_HOME)

tools/vendor/dsh-tools is a test-only extraction of @deepseek-ai/dsh-tools from the installed app, used to run the schema compiler outside the Host.

Verified Records: Real run of cargo check --offline on a failure correctly reported error [E0308] src/main.rs:2:22 mismatched types. /cargo-doctor correctly identified cargo 1.99.1 / rustc 1.99.1 / edition 2021.

Known Limitations

• No Procedural Macro Expansion: #[derive], attribute macros, and functional proc-macros are left untouched; cargo_expand returns the original code. Reason: Proc-macros require compilation execution, which pure static analysis cannot cover. Mitigation: The Agent can fall back to cargo_read to inspect the macro crate's source for alternative context.
• No Glob Import Resolution: Imports like use tokio::*; do not establish macro alias mappings. Reason: Static text cannot determine which macros a glob actually imports. Mitigation: When a bare call cannot be resolved, cargo_expand reports it as unresolved, and the Agent can switch to a fully qualified path.
• No Macro Hygiene: Identifier capture checks are skipped during expansion. Reason: Pursuing compiler-level hygiene significantly increases the complexity of a pure JS implementation. Mitigation: Expanded calls are appended with /* <- [original call] */ comments to preserve a trace back to the original invocation.
• Restart Required for Preset Reinstall: Modifying preset sub-rows (skills, tool rows) mounts new compositions at startup; a DSH restart is required to load them. Mitigation: This is inherent to the DSH preset mechanism and is documented.

License

MIT