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fix(mcp): serve tools without a root index + make the front-load hook monorepo-aware (#964) (#966)

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The MCP server gated tool availability on whether the server root had a
.codegraph/ index, so in a monorepo where only sub-projects are indexed the
agent saw zero tools — and couldn't reach an indexed sub-project even by
projectPath. A session started before `codegraph init` also never surfaced the
tools afterward. The Claude front-load hook had the mirror gap: it only walked
UP for an index, so it stayed silent at a monorepo root.

MCP server:
- Always expose the tool surface; when the root isn't indexed, send a
  per-project instructions variant (pass projectPath) instead of the
  "inactive" note. Safety comes from response SHAPE (success-shaped guidance,
  never isError), not from hiding tools.
- Reword the no-default-project guidance to be per-project, not per-session,
  and sharpen the projectPath schema description.

Front-load hook (UserPromptSubmit):
- Scan DOWN (bounded depth, workspace-root-gated) for indexed sub-projects and
  shape the injection by topology: front-load the one the prompt names, nudge
  about the rest, or list them when ambiguous.

Verified: full suite (1703 passed); a live two-package monorepo run confirms the
hook front-loads the correct sub-project with no cross-package leakage. The
front-load's net speed effect is the existing multi-file-vs-single-file
tradeoff, unchanged by this work.

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
This commit is contained in:
Colby Mchenry
2026-06-23 12:57:47 -05:00
committed by GitHub
co-authored by Claude Opus 4.8
parent 0a91d0f512
commit 85a8f32fd9
10 changed files with 431 additions and 87 deletions
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README.md
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@@ -426,7 +426,7 @@ CodeGraph's MCP server delivers its usage guidance to your agent **automatically
- **Answer structural questions directly with CodeGraph** — it *is* the pre-built index, so a grep/read loop just repeats work it already did. Treat the returned source as already read.
- **Reach for `codegraph_explore` for almost anything** — "how does X work", a flow/"how does X reach Y", or surveying an area. One call returns the relevant symbols' verbatim source grouped by file, the call paths between them (dynamic-dispatch hops included), and a blast-radius summary. Name a file or symbol in the query to read its current line-numbered source.
- **Trust the results — don't re-verify with grep**, and check the staleness banner after edits.
- In a workspace with no index, CodeGraph announces itself inactive and serves no tools — indexing stays your decision.
- Works **per project**: query any project that has a `.codegraph/` index by passing `projectPath` — so a monorepo where only some services are indexed, or a second repo, works in one session. A path with no index returns clean guidance to use built-in tools; indexing stays your decision.
The exact text is `src/mcp/server-instructions.ts` — the single source of truth for the main agent. Because subagents and non-MCP harnesses never see the MCP guidance, the installer also writes a short marker-fenced section into the agent's instructions file pointing at the `codegraph explore` CLI equivalent.
@@ -534,7 +534,7 @@ When running as an MCP server, CodeGraph exposes a **single tool** — `codegrap
The other tools (`codegraph_node`, `codegraph_search`, `codegraph_callers`, `codegraph_callees`, `codegraph_impact`, `codegraph_files`, `codegraph_status`) stay fully functional but **unlisted by default** — everything they return already arrives inline on `codegraph_explore` (its blast-radius section, the relationship map, a symbol's body as its callee list). Re-enable any of them for the MCP surface with the `CODEGRAPH_MCP_TOOLS` environment variable (e.g. `CODEGRAPH_MCP_TOOLS=explore,node,search,callers`), or use their CLI equivalents (`codegraph node` / `query` / `callers` / `callees` / `impact` / `files` / `status`).
In a workspace with no `.codegraph/` index, the server announces itself inactive and lists **no** tools — agents work normally with their built-in tools, and indexing stays your decision.
Even when the server's own root has no `.codegraph/` index, the tools stay available: pass `projectPath` to query any indexed project — a sub-service in a monorepo, or a second repo — in the same session. A path that has no index returns clean guidance to use built-in tools instead, so nothing fails loudly, and indexing stays your decision.
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