create_branch uncallable in project-scoped mode — confirm_cost not exposed

[ocean-views-228]

Bug report

Describe the bug

When using the Supabase MCP server in project-scoped mode (recommended security configuration), the branching tools are fully non-functional:

1. create_branch requires a confirm_cost_id parameter, which can only be obtained from confirm_cost. But confirm_cost (and get_cost) are in the Account Management feature group, which is disabled in project-scoped mode. This makes create_branch uncallable.

2. list_branches returns the error: "Project reference is missing when validating permissions." This makes the entire branching surface non-functional — even if a branch were created via the dashboard, the MCP cannot see or manage it.merge_branch is presumed to fail the same way.

The branching tools are listed in the Branching feature group, which is documented as available in project-scoped mode. The bug
is that they depend on an account-scoped prerequisite (confirm_cost) that is unavailable in the same mode.

To Reproduce

1. Connect the Supabase MCP server in project-scoped mode (passing project_ref parameter)
2. Call list_branches → error: "Project reference is missing when validating permissions"
3. Attempt to call create_branch → cannot provide required confirm_cost_id parameter because confirm_cost tool is
   not available in project-scoped mode
4. All branching operations are blocked

Expected behavior

Branching tools should be fully functional in project-scoped mode. Either:

• Expose get_cost / confirm_cost in project-scoped mode (scoped to the connected project), or
• Allow create_branch without confirm_cost_id in project-scoped mode (project is already identified, cost is deterministic), or
• Fix project reference resolution for list_branches / merge_branch in project-scoped connections

Screenshots

N/A — MCP tool calls, not browser UI.

System information

• OS: N/A (cloud-hosted MCP via Claude.ai)
• Browser: N/A
• Version of supabase-js: N/A
• Version of Node.js: N/A
• MCP access method: Claude.ai MCP integration
• Supabase plan: Pro
• MCP connection mode: project-scoped
• Region: us-west-2

Additional context

This blocks the staging-branch workflow for MCP-managed migrations. The intended workflow is create_branch → apply_migration on dev branch → verify → merge_branch to production. Without functional branching, migrations must be applied directly to production with no staging validation.

[kayalopez]

This looks like a good regression target for project-scoped MCP mode because the broken path is not just create_branch; it is the whole migration-staging contract.

The acceptance checks I would want before marking this fixed:

• In a project-scoped connection, tools/list exposes only branching tools that are actually callable in that same scope, or the blocked prerequisite is documented in the tool description.
• list_branches succeeds without a Project reference is missing when validating permissions error.
• create_branch either does not require confirm_cost_id in project-scoped mode, or a project-scoped get_cost / confirm_cost path is visible and callable.
• The create branch -> apply migration on dev branch -> verify -> merge branch workflow is covered by one regression test using the same scoped connection.
• If branching cannot be used, apply_migration should not be treated as a safe fallback to production without an explicit approval gate.

I made a small client-side checker for this exact shape of failure if it helps people triage their own redacted MCP notes: https://ai-launch-risk-check-public.vercel.app/supabase-mcp-branching-readiness.html

It does not ask for credentials or call Supabase; it just flags the project-scoped confirm_cost gap, list_branches project-ref errors, and production-migration fallback risk from pasted redacted notes.