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

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>

CLAUDE.md

@@ -104,7 +104,7 @@ CodeGraph's only channels to influence the agent are low-salience: the MCP `init
 What works is meeting the agent where it already is:
 - **explore-flow** — `codegraph_explore` is the PRIMARY tool the agent reliably calls; its query is a precise bag of symbol names (incl. qualified `Class.method`) spanning the flow the agent is after; explore finds the call path _among those named symbols_ (riding synthesized edges) and leads its output with it. (`buildFlowFromNamedSymbols`: segment/co-naming disambiguation; ≤1 unnamed bridge so it never wanders a god-function's fan-out. Overload-aware: a PascalCase type token in the query biases an overloaded name to that type's own def — `DataRequest task` → DataRequest's `task`, not the abstract base; named-symbol files sort first.)
 - **Sufficiency** — make the tool's output complete enough that the agent stops. `codegraph_node` returns the full body + the caller/callee trail, and for an AMBIGUOUS name returns **every overload's body in one call** (so the agent never Reads a file to find the right overload — validated on Alamofire/gin). This is the after-explore depth tool (labeled SECONDARY).
-- **Errors teach abandonment** — one or two `isError: true` responses early in a session and the agent stops calling codegraph entirely (maintainer-observed, repeatedly). `isError` is reserved for genuine "stop trying" cases: security refusals (`PathRefusalError`) and real malfunctions (which carry a retry-once note). Every expected/recoverable condition — project not indexed, symbol not found, file not in the index — returns a **SUCCESS-shaped response carrying the guidance** (`NotIndexedError` → `textResult`, see `ToolHandler.execute`'s catch). The same principle session-wide: an **unindexed workspace serves an empty `tools/list` + a 2-line "inactive" instructions variant** instead of 8 tools that all fail — absence is the one signal an agent can't misread, and indexing is deliberately the user's call, never the agent's.
+- **Errors teach abandonment** — one or two `isError: true` responses early in a session and the agent stops calling codegraph entirely (maintainer-observed, repeatedly). `isError` is reserved for genuine "stop trying" cases: security refusals (`PathRefusalError`) and real malfunctions (which carry a retry-once note). Every expected/recoverable condition — project not indexed, symbol not found, file not in the index — returns a **SUCCESS-shaped response carrying the guidance** (`NotIndexedError` → `textResult`, see `ToolHandler.execute`'s catch). The same principle is why the tool surface is **always exposed, even at an un-indexed root** (the old empty-`tools/list` gate was removed in #964 — it broke monorepos where only sub-projects carry a `.codegraph/`, and hid the tools from a session that started before `codegraph init`): safety comes from the response SHAPE (success-shaped guidance, never `isError`), not from hiding tools. An un-indexed root's `initialize` sends a per-project variant (`SERVER_INSTRUCTIONS_NO_ROOT_INDEX` — "pass `projectPath` to a project that has a `.codegraph/`"), not an "inactive" note; indexing is still deliberately the user's call, never the agent's.
 
 What fails is the inverse — folding a precise answer into a **fuzzy-input** tool: the now-removed `codegraph_context` took a description, not symbols, so it couldn't disambiguate a flow's endpoints and surfaced the _wrong feature_ (which is why it was cut). Precise output needs precise input — explore takes a symbol bag for exactly this reason. (`codegraph_trace` was likewise removed: explore-flow does its job and the agent under-picked it.)