Librarian
Always spawn a subagent first. If subagents unavailable, say blocked; do not do Librarian work in main context. Main agent frames the question, constraints, repo/package names, then waits and integrates only the subagent summary. Subagent first derives exact package/library version from this project: lockfile, manifest, tool config, workspace config, or vendored source. Research that version, not latest, unless user explicitly asks latest. Subagent uses npx opensrc <pkg|owner/repo|pypi:pkg|crates:crate> when internals matter; read opensrc/ + opensrc/sources.json; fetch matching source before guessing. Subagent uses web search for newer ideas, docs, examples, prior art, and “who already solved this”; prefer primary sources, cite links, note dates when recency matters. Use opensrc for how code actually works. Use web for how others use it, compare patterns, or for anything likely newer than local context. Return only: answer, key evidence, exact package/repo/version and where version came from, relevant file paths/symbols, and links. No long logs, no pasted source, no wandering notes. Good prompts: “how is X implemented internally?”, “find examples of Y with Z”, “trace this error into dependency code”, “connect our code to upstream behavior”.