fix(mcp): detect Dolt-backed projects in workspace discovery (GH#2997)

[maphew]

Summary

Fixes #2997 — MCP context() tool reported "Database: Not found" for embedded Dolt projects because workspace discovery only globbed for *.db files. Embedded Dolt has no *.db; data lives at .beads/embeddeddolt/ and the backend is declared in .beads/metadata.json.

• Adds _has_beads_project_files() mirroring Go's hasBeadsProjectFiles (checks metadata.json, config.yaml, dolt/, embeddeddolt/, or non-backup *.db)
• _find_beads_db_in_tree() and .beads/redirect validation now recognise SQLite, embedded Dolt, and server Dolt
• New _find_beads_project() + _detect_backend() in server.py; context() reports Project: ... (backend: dolt-embedded) instead of the misleading "Not found" for Dolt projects

Test plan

• 5 new unit tests covering embedded Dolt, server Dolt, metadata-only projects, redirects to Dolt, vc.db exclusion
• All 18 test_workspace_auto_detect.py tests pass
• 0 regressions across 62 related tests (test_workspace_auto_detect, test_multi_project_switching, test_lifecycle, test_tools, test_worktree_separate_dbs)
• End-to-end: context_set() returns correct output for both Dolt-embedded and SQLite workspaces

🤖 Generated with Claude Code

[maphew]

Code Review: fix(mcp): detect Dolt-backed projects in workspace discovery

Good work — _has_beads_project_files correctly mirrors Go's hasBeadsProjectFiles, the tools.py refactoring is clean, and the 5 new tests are thorough. Three bugs to address:

---

1. 🔴 Bug (high) — _detect_backend crashes on malformed metadata.json

File: server.py L290-300

json.load() can return any JSON type ([], "string", 42). The subsequent meta.get("backend") throws AttributeError which is not caught by the except (OSError, ValueError, json.JSONDecodeError) clause, crashing the MCP server.

Fix:

        try:
            with open(metadata_path) as f:
                meta = json.load(f)
            if not isinstance(meta, dict):
                meta = {}
            backend = (meta.get("backend") or meta.get("database") or "").lower()

---

2. 🟡 Bug (medium) — _find_beads_project doesn't follow .beads/redirect

File: server.py L256-278

This function duplicates the upward directory walk from _find_beads_db_in_tree (in tools.py) but skips redirect handling. Worktree setups that rely on .beads/redirect will fail — _context_set won't find the project even though the existing _find_beads_db_in_tree would.

Fix: Remove _find_beads_project entirely. In _context_set, call the already-robust _find_beads_db_in_tree(resolved_root) to get the project root, then derive the backend:

    project_root = _find_beads_db_in_tree(resolved_root)
    if project_root is None:
        # ... "Not found" path ...

    backend = _detect_backend(os.path.join(project_root, ".beads"))

This eliminates the duplicated walk and inherits redirect + symlink support for free.

---

3. 🟡 Bug (medium) — SQLite fallthrough when .db file is missing

File: server.py L703-721

When _detect_backend returns "sqlite" (e.g. metadata.json declares it) but no .db file exists yet, _find_beads_db(project_root) returns None. The code falls out of the if db_path: block and into the Dolt/unknown path, reporting:

Context set successfully:
  Project: /path/.beads (backend: sqlite)

…instead of the expected "Database: Not found (run context(action='init') to create)" message.

Fix: Add an else clause:

    if backend == "sqlite":
        db_path = _find_beads_db(project_root)
        if db_path:
            _workspace_context["BEADS_DB"] = db_path
            os.environ["BEADS_DB"] = db_path
            return (
                f"Context set successfully:\n"
                f"  Workspace root: {resolved_root}\n"
                f"  Database: {db_path}"
            )
        else:
            _workspace_context.pop("BEADS_DB", None)
            os.environ.pop("BEADS_DB", None)
            return (
                f"Context set successfully:\n"
                f"  Workspace root: {resolved_root}\n"
                f"  Database: Not found (run context(action='init') to create)"
            )

---

Note (pre-existing, not from this PR)

test_compaction_config.py has hardcoded macOS paths (/Users/stevey/src/dave/beads/...) that fail on non-macOS environments.

---

Tests and _has_beads_project_files logic look solid. With these three fixes the PR should be good to merge. 👍