Tau agentic search

Standalone Rust Tau extension for the opt-in search_code tool.

Build and test

cargo test
cargo build --bin tau-ext-search-code

Opt-in Tau configuration

Keep the extension disabled unless explicitly opted in. Example harness.json5 entry:

{
  extensions: {
    search_code: {
      enable: false,
      command: ["/absolute/path/to/tau-ext-search-code"],
    },
  },
}

When enabled, the extension registers search_code beside Tau's existing grep; it does not replace or override grep.

See docs/opt-in-rollout.md for full opt-in rollout guidance, MVP request defaults, the result contract, limitations, fixture-based validation, and the evidence required before any default-on rollout.

Relationship to pgr

pgr is strong prior art for ranked, agent-oriented code search. However, it is exposed as an MCP server, while Tau currently uses its own extension protocol and does not consume MCP tools directly.

This project therefore implements a Tau-native search_code extension rather than depending on pgr in the MVP. The goal is not to replace pgr, but to bring the same class of ranked, file-level agentic search into Tau's existing extension model.