feat(studio): switch dashboard assistant to remote MCP server (#47479)

## I have read the
[CONTRIBUTING.md](<https://github.com/supabase/supabase/blob/master/CONTRIBUTING.md>)
file.

YES

## What kind of change does this PR introduce?

Feature / refactor.

## What is the current behavior?

The dashboard assistant runs `@supabase/mcp-server-supabase` in-process
over an in-memory transport (`lib/ai/supabase-mcp.ts`).

## What is the new behavior?

The assistant connects to the **remote MCP server** over HTTP
(`@ai-sdk/mcp`), forwarding the dashboard session token as a bearer. URL
comes from `NEXT_PUBLIC_MCP_URL` with a local-dev fallback;
platform-only, and Nimbus works via the same env var.

* **Tool model unchanged:** UI-controlled `execute_sql` (with
`needsApproval`) and `deploy_edge_function` still come from Studio; the
allowlist (`TOOL_CATEGORY_MAP`) remains the gate keeping the remote's
write tools away from the assistant (`read_only` is defense-in-depth).
* **Attribution:** sends `x-source-name: supabase-studio` (+
`x-source-version`) → logged as `source_name`/`client_name`.
* **Connection lifecycle:** the HTTP client is closed via the request's
`AbortSignal` (tools execute later during streaming); `signal` is
required on `getTools`/`getMcpTools`.
* **Resilience:** a remote-MCP failure degrades to the remaining tools
instead of failing the assistant.
* **Drift protection:** relied-upon tools are typed against `keyof
typeof supabaseMcpToolSchemas`, so a package bump that renames/removes
one fails `pnpm typecheck`; a runtime check also warns if the deployed
server returns fewer tools.
* Adds unit tests for the above.

## Additional context

* Verified end-to-end against a local remote MCP server with a dashboard
token: `initialize` 200, tools listed, a tool executed, client closed
cleanly.
* The remote MCP (mgmt-api) already accepts dashboard session tokens
(GoTrue-JWT auth path) — no backend change needed. `NEXT_PUBLIC_MCP_URL`
must point at each env's `/mcp`.
* `@supabase/mcp-server-supabase` is kept — still used by the
self-hosted `/api/mcp` routes.

Closes
[AI-137](https://linear.app/supabase/issue/AI-137/switch-dashboard-assistant-to-remote-mcp)

## Rollout

* **Rollout:** merges with `USE_REMOTE_MCP` off (in-process); flip it to
`true` per environment (staging → prod → Nimbus) once each one's
prerequisites land.
* **Rollback:** unset `USE_REMOTE_MCP` and redeploy to fall back to the
in-process client — no revert needed.

## Summary by CodeRabbit

* **Bug Fixes**
* Improved AI request handling so tool loading and generation clean up
properly when a request is cancelled or the browser connection closes.
* Added safer fallback behavior when remote tool loading fails, so AI
features can continue with available tools instead of stopping entirely.
* Updated remote tool access to use the current project reference and
preserve the correct access headers.

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->

## Summary by CodeRabbit

* **New Features**
* AI tools now connect more reliably to remote services and stop cleanly
when requests end or are canceled.
* Tool loading is more resilient, continuing with available tools if
remote access is unavailable.

* **Bug Fixes**
* Improved cleanup to prevent lingering connections during SQL
generation and policy workflows.
  * Added safer handling for remote tool changes and invalid responses.

* **Tests**
* Expanded automated coverage for remote tool setup, cancellation, and
fallback behavior.


<!-- end of auto-generated comment: release notes by coderabbit.ai -->

---------

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

.github/workflows/braintrust-evals.yml

@@ -15,8 +15,42 @@ permissions:
   contents: read
 
 jobs:
+  # Cheap, always-on gate: verifies the eval harness can reach the MCP server
+  # (its one real tool, search_docs). Runs on every push/PR — no OpenAI, no full
+  # eval suite — so a broken MCP connection is caught early with an actionable
+  # message. The eval job depends on this, so evals never run against a broken
+  # MCP connection.
+  preflight:
+    name: Eval MCP preflight
+    runs-on: ubuntu-latest
+    timeout-minutes: 10
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@08eba0b27e820071cde6df949e0beb9ba4906955 # v4.3.0
+        with:
+          persist-credentials: false
+
+      - name: Install pnpm
+        uses: pnpm/action-setup@41ff72655975bd51cab0327fa583b6e92b6d3061 # v4.2.0
+        with:
+          run_install: false
+
+      - name: Use Node.js
+        uses: actions/setup-node@49933ea5288caeca8642d1e84afbd3f7d6820020 # v4.4.0
+        with:
+          node-version-file: '.nvmrc'
+          cache: 'pnpm'
+
+      - name: Install Dependencies
+        run: pnpm install --frozen-lockfile
+
+      - name: Preflight — MCP connectivity
+        run: cd apps/studio && pnpm evals:preflight
+
   eval:
     name: Run evals
+    needs: preflight
     if: github.event_name == 'push' || (github.event_name == 'pull_request' && contains(github.event.pull_request.labels.*.name, 'run-evals') && github.event.pull_request.head.repo.full_name == github.repository)
     runs-on: ubuntu-latest
     timeout-minutes: 20
@@ -43,8 +77,8 @@ jobs:
       - name: Use Node.js
         uses: actions/setup-node@49933ea5288caeca8642d1e84afbd3f7d6820020 # v4.4.0
         with:
-          node-version-file: ".nvmrc"
-          cache: "pnpm"
+          node-version-file: '.nvmrc'
+          cache: 'pnpm'
 
       - name: Install Dependencies
         run: pnpm install --frozen-lockfile