Add get_concept tool for exact ID lookup

[mikaelj]

Problem
The list_roots tool returns concept IDs, and the workflow expects agents to use these IDs to navigate the graph. However, there's no way to look up a concept by its ID — the only retrieval tool is understand, which embeds the query string as a 384-dim vector and performs cosine similarity search. When an agent passes a concept ID through understand, the embedding model treats it as arbitrary text, not as a key. The resulting vector may have low similarity to the concept's own embedding, causing lookups to fail.

Motivation
My tool Fuska (https://github.com/mikaelj/fuska) stores chapter plans and task definitions as megamemory concepts with well-defined slug IDs, agents are given slugs during execution and need to retrieve the exact plan concept to follow implementation steps. Semantic search is unreliable for this — a slug like chapter-03-main-c-god-object-split embeds poorly and may not match its own concept. A direct ID lookup is the only reliable path.

Solution
Add get_concept — a lightweight exact-ID lookup tool that calls the existing db.getNode(id) and buildNodeWithContext() helpers. Returns the same NodeWithContext format as understand, with children, edges, incoming edges, and parent.

What this is

• A missing accessor for the primary key, complementary to semantic search
• Follows the exact same patterns as all existing tools (handler, Zod schema, timeline logging)
• ~50 lines, zero new dependencies, no existing behavior changed

What this is not

• A replacement for understand — semantic search remains the primary discovery mechanism
• A text search or fuzzy matching tool — it's a simple PK lookup

[Copilot]

Pull request overview

Adds an exact-ID retrieval path for knowledge graph concepts so agents can reliably fetch a node when they already have its concept ID (complementing understand’s semantic search).

Changes:

• Introduce getConcept tool handler backed by db.getNode(id) + buildNodeWithContext().
• Register new MCP tool get_concept with timeline logging + error formatting.
• Add dedicated getConcept test suite and document the new tool in the README.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
src/types.ts	Adds GetConceptInput type used by the new tool.
src/tools.ts	Implements getConcept exact-ID lookup returning NodeWithContext.
src/index.ts	Registers the get_concept MCP tool and logs it to the timeline.
src/tests/get-concept.test.ts	Adds coverage for success, missing ID, soft-deleted nodes, and context fields.
README.md	Documents get_concept and updates workflow/tool counts.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.