fix(mcp): adopt a single indexed sub-project below the server root + say when no project resolves (#1606, #1607) (#1614)

Fixes #1606 and #1607 together — the MCP server's root resolution never got the sub-project down-scan `planFrontload` gained in #964, and the resulting no-default state was completely silent.

## What changed

**Adoption (#1606).** A new `resolveServerRoot()` in `src/directory.ts` is the single resolution every server entry point now uses: up-walk first (`findNearestCodeGraphRoot`, the common case, unchanged), and when that misses, the existing bounded down-scan (`findIndexedSubprojectRoots` — depth 4, max 64, heavy dirs skipped). **Exactly one** indexed sub-project is unambiguous and is adopted as the default project — `open` → `startWatching` → `catchUpSync` → query pool, the full normal path. Zero or several candidates → no default, never a guess. Wired into:

- `MCPEngine.doInitialize()` and `retryInitializeSync()` — the retry path also picks up a child indexed *after* the server started (its down-scan is throttled to once per 5s so the persistent no-default state doesn't pay a directory walk per tool call; the up-walk still runs every time).
- `resolveDaemonRoot()` — the adopted root gets the shared daemon (one watcher, one writer, socket keyed on the child) instead of a direct-mode server per host, exactly as the issue suggested.
- `MCPSession.handleInitialize()` — the instructions variant is picked with the same resolution, so a workspace whose single child becomes the default gets the full single-project playbook. Race-free by construction: handshake and engine compute it independently, no ordering assumed.

**Workspace-root gate (the open question in #1606).** Decided deliberately: the down-scan runs only when the base has a workspace manifest (`looksLikeProjectRoot`, unchanged list) **or a `.git` entry** — the exact container shape that motivated the report — and never when the base is `$HOME` or the filesystem root. The gate lives in the new helper only; `planFrontload` and the prompt-hook are untouched, so #1454's surface is not widened.

**Diagnostics (#1607).** The no-root branch is no longer silent:

```
[CodeGraph MCP] No .codegraph/ at or above <searchFrom>: no default project, live sync disabled.
[CodeGraph MCP] Indexed sub-projects found: service-a, service-b. Pass `projectPath` per call, or launch with --path.
```

(second line only when the scan found candidates), plus one line naming the adopted child when adoption happens. The same fact is protocol-reachable: the "No CodeGraph project is loaded" tool response now lists the discovered sub-projects with `projectPath` guidance. The list is engine-maintained (initial resolve + throttled retry) — tool calls never scan — and the response stays SUCCESS-shaped (`NotIndexedError` → `textResult`, never `isError`).

## Tested

- New `__tests__/mcp-subproject-adoption.test.ts` (real spawned server over stdio, same harness as `mcp-roots.test.ts`): single child → tool call answers from it, full instructions, adoption stderr; two children → no default, both listed in the tool response and stderr, per-project instructions; no manifest/no `.git` → gate holds, no scan, plain one-line message.
- `mcp-subproject-adoption` + `mcp-roots` + `mcp-initialize` + `daemon-bind-failure`: **13/13 pass**.
- End-to-end repro harness against the built `dist/` on an unmodified-main build first (confirmed: empty stderr, no adoption, NO_ROOT instructions even with one adoptable child), then on this branch (all three shapes behave as above; catch-up sync runs on the adopted child).

🤖 Generated with [Claude Code](https://claude.com/claude-code)

https://claude.ai/code/session_01LxZj6W6Y1SHXwvpT3uwJpK

CHANGELOG.md

@@ -27,6 +27,10 @@ and adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
 ### Fixes
 
+- The MCP server now finds your project when it's launched from a workspace folder above it: if the launch directory has no index of its own but exactly one indexed project sits below it (a repo container, an agent workspace, a monorepo root), that project becomes the session's default — live file watching and the shared daemon included — instead of every tool call failing until a `projectPath` or `--path` is supplied. Thanks @nakisen. (#1606)
+
+- When no project can be resolved at all, the MCP server now says so instead of starting silently: a startup log line names the directory it searched, and tool calls list the indexed sub-projects it can see nearby so you can pass one as `projectPath`. Previously the server looked healthy from the outside while every tool quietly had no project to answer from. Thanks @nakisen. (#1607)
+
 - Indexing no longer hangs on a Swift Vapor project containing a call with a long argument list. A single `.get(...)`-style call with many labeled arguments and no `use:` handler — the shape generated request builders produce — could stall `codegraph index`, `codegraph sync`, and the MCP server indefinitely. Route detection now handles such files in milliseconds, and every previously-recognized route shape still parses exactly as before. Thanks @maxmilian. (#1544) (Swift)
 
 - `codegraph status` now sees new files inside brand-new directories. Git reports an entirely-untracked directory as a single collapsed entry, so source files created there — a freshly scaffolded `frontend/`, for example — were missing from the pending-changes report, which could claim everything was up to date while those files had not yet been indexed. Thanks @maxmilian. (#1213)