Problem

codedb_remote today hits codedb.codegraff.com only. That backend is the WASM-on-Workers indexer with actions tree | outline | search | meta. Its sibling project codedb-cloud / wiki.codes is a Zig-native router on Hetzner with parquet-backed cold + hot tiers, and it offers a superset of useful actions — notably symbol (exact-identifier lookup) and policy (hot-pin size class) — plus more repos indexed and richer result shapes.

Agents calling codedb today have no way to reach wiki.codes. Forcing a separate MCP server for it would double the install footprint and fracture the "codedb_remote" mental model.

Proposal

Add a backend parameter to the existing codedb_remote tool. Default preserves current behavior.

```
codedb_remote repo="rust-lang/rust" action="symbol" query="HashMap" backend="wiki"
codedb_remote repo="vercel/next.js" action="tree" backend="wiki"
codedb_remote repo="justrach/merjs" action="search" query="handleRequest" # still codegraff
```

URL shape

• codegraff: `https://codedb.codegraff.com//` (existing; unchanged)
• wiki: `https://www.wiki.codes/api/query?slug=&endpoint=&q=` via the Vercel proxy (server-side-authed, no client secrets)

Slug derivation: `owner/repo` → `owner-repo` (matches the naming wiki.codes produces on ingest: e.g. `rust-lang/rust` → `rust-lang-rust`, `vercel/next.js` → `vercel-next-js`).

Validation

• `backend` ∈ `{"codegraff","wiki"}`, default `"codegraff"`
• When `backend="wiki"`: reject `action="meta"` with a clear error
• When `backend="codegraff"`: reject `action="symbol"|"policy"`
• Same repo-format + path-traversal validation as today

Why bundle here instead of a separate MCP server

• One `codedb_remote` namespace means agents don't need to know which service a repo is indexed on — they just pick the backend.
• Shares the existing curl + error handling.
• ~80 lines of Zig in `src/mcp.zig`, one new handler branch, no new dependencies.

Out of scope for this issue

• Auto-failover between backends (e.g. codegraff 404 → try wiki). Leave as a follow-up if agents want a single "best effort" mode.
• Writing to wiki (indexing a new repo). wiki exposes `/admin/ingest` but that's authenticated — bundling it would mean exposing a token to the agent. Keep read-only.
• Swapping the default backend. Current callers stay on codegraff unless they opt in.

Test plan

• `codedb_remote repo="rust-lang/rust" action="symbol" query="HashMap" backend="wiki"` → 25 hits, includes `library/std/src/collections/hash/map.rs:247`
• `codedb_remote repo="justrach/merjs" action="search" query="handleRequest"` (codegraff default) → unchanged
• `codedb_remote repo="x" action="meta" backend="wiki"` → clear error "action meta is not supported on the wiki backend"