feat(mcp): surface project root in codegraph_status + actionable errors

[mschreib28]

🔗 Stacked on colbymchenry#117 (MCP tool registry). Until that lands, this PR's diff transitively includes the refactor commit. The intrinsic addition for this PR is just the changes in src/mcp/tools.ts (handler + error surface), src/mcp/tools/status.ts (description), and the new tests — see "Files changed" below. After colbymchenry#117 lands, the diff auto-cleans.\n\n## Summary\n\nCloses a real ergonomics gap I hit running the MCP server in an agentic flow: when the server's default project doesn't match the codebase the agent wants to query, every tool call has to pass projectPath, but the agent has no way of knowing whether to do that — no tool surfaces the default. The agent guesses, gets back CodeGraph not initialized, guesses again. The error even pointed at the wrong remediation (codegraph init instead of pass projectPath).\n\n## What changes\n\n**codegraph_status now leads with the project identity:\n\n\n## CodeGraph Status\n\n**Project root:** `/Users/foo/projects/codegraph` (default — server CWD at startup)\n**Files indexed:** 153\n...\n\n### Other projects this server has open\n- `/Users/foo/projects/some-other-repo`\n\nPass `projectPath` to query any of these (or any other directory containing `.codegraph/`).\n\n\nThe label is (default — server CWD at startup) or (from \\projectPath\ argument). One look at status answers "do I need to start passing projectPath?" — which previously required an unrelated tool call to fail first.\n\nErrors are rewritten with concrete next steps:\n\n| Situation | Old | New |\n|---|---|---|\n| No default, no projectPath | CodeGraph not initialized for this project. Run 'codegraph init' first. | Three-way: restart server / codegraph init / pass projectPath |\n| projectPath supplied, no .codegraph/ found | CodeGraph not initialized in {path}. Run 'codegraph init' in that project first. | No .codegraph/ found at or above {path}. Run \\codegraph init\ in that project first, or pass a different projectPath. |\n\nSTATUS_TOOL description nudges agents to call status FIRST** in unfamiliar sessions, so the project-identity check is the natural opening move.\n\n## Independent reviewer pass\n\nCaught and fixed three issues before opening:\n\n1. The third '(resolved from cache)' sourceLabel branch was unreachable — getCodeGraph(undefined) always returns this.cg or throws, so when args.projectPath is undefined the project IS the default. Collapsed to a binary ternary with a comment explaining why.\n2. The new test file leaked SQLite handles — handler.closeAll() was never called, leaving cached project connections open across tests. Fixed via afterEach cleanup + idempotent double-close handling.\n3. macOS/Windows case-insensitive-FS edge case — path.resolve doesn't normalise case, so a client-supplied rootUri with different capitalisation than process.cwd() could compare unequal under strict-string equality. Documented as a comment; deferred a realpath-based fix until someone actually hits it.\n\n## Test plan\n\n- [x] npx tsc --noEmit clean\n- [x] npx vitest run — 799/799 tests pass\n- [x] New tests in __tests__/mcp-status.test.ts (5 cases):\n - Default-project label\n - projectPath-argument label\n - "Other projects this server has open" list when cache has multiple entries\n - Actionable error when no default and no projectPath\n - Actionable error pointing at the supplied path when .codegraph/ is missing there\n- [x] Updated __tests__/mcp-tool-registry.test.ts regex for the new error wording\n- [x] Live smoke test against codegraph's own indexed tree — all four user-facing strings render correctly\n\n## Files changed\n\n| File | Change |\n|---|---|\n| src/mcp/tools.ts | handleStatus rewrite + getCodeGraph error rewrite |\n| src/mcp/tools/status.ts | Tool description nudges agents to call status FIRST |\n| __tests__/mcp-status.test.ts | New: 5 focused tests |\n| __tests__/mcp-tool-registry.test.ts | Updated regex for new error wording |\n\n## Pairs naturally with colbymchenry#121\n\nThe MCP-instructions playbook from colbymchenry#121 tells the agent which tool to call for each intent. This PR makes sure the answer to "is the project root what I expect?" is always one tool call away and self-explanatory — exactly the kind of "tier-1 first" check the playbook recommends.\n\n🤖 Generated with Claude Code\n

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Copied from colbymchenry/codegraph#126