feat(mcp): add project cost confirmation elicitation by barryroodt · Pull Request #391 · supabase/mcp

barryroodt · 2026-08-28T19:41:07Z

What kind of change does this PR introduce?

Feature.

Implements the create_project slice of AI-1091.

What is the current behavior?

create_project requires a valid confirm_cost_id before execution. Clients without elicitation capability keep this flow.

What is the new behavior?

When costConfirmation is configured with enabledTools: ['create_project'], form-capable clients can confirm the quoted cost inside create_project through the SDK-native inputRequired and inputResponse flow. The signed request state binds the method and authenticated principal, and carries tool: 'create_project', the project name, region, organization, and quoted cost.

The form has no properties. Consent lives in the elicitation action, so clients use their native accept, decline, and cancel controls. Accept creates the project. Decline or cancel returns a normal result without creating anything.

Argument mismatches are rejected, and cost drift starts confirmation again. A state signed for the wrong tool fails before argument or acceptance checks. Empty elicitation mode maps count as form-capable; URL-only or absent elicitation uses the legacy confirm_cost flow. A precomputed legacy ID cannot bypass confirmation for a form-capable request.

This PR covers create_project only. It does not change stdio, and there is no create_branch implementation in this PR.

How to Review

Server setup
- packages/mcp-server-supabase/src/server.ts
- Inspect how costConfirmation, its enabledTools, and request state enter the server.
Confirmation flow and executor seam
- packages/mcp-server-supabase/src/tools/cost-confirmation.ts, packages/mcp-server-supabase/src/tools/account-tools.ts, packages/mcp-server-supabase/src/tools/util.ts, and packages/mcp-utils/src/server.ts
- Inspect the private module that owns the project state discriminator, action-only schema, and capability helper, plus signed state, project creation behavior, request-state verification, and SDK result passthrough.
Behavioral coverage
- packages/mcp-server-supabase/src/server.test.ts
- Inspect the modern and legacy paths.

Does capability detection select the right lane?
Is signed state bound to the right request, tool, and principal?
Do decline and cancel avoid project creation?
Does the legacy flow remain strict?

Verification

pnpm --filter @supabase/mcp-server-supabase test src/server.test.ts -t "create_project cost confirmation via elicitation" passed 8 tests.
pnpm --filter @supabase/mcp-server-supabase build passed.
pnpm test:packed-platform-consumer passed all 3 public-surface assertions.
biome ci . passed.

Additional context

This is a fresh, project-only implementation separate from the earlier draft in #389.

When confirmation is configured, the public schema makes confirm_cost_id optional so form-capable clients can call create_project directly. Capability-free execution still requires a valid ID.

Known limits remain: signed state has no single-use replay prevention, and the existing final cost-check concurrency race remains.

The platform PR will first pin the pkg.pr.new preview, then switch to the released npm version.

This implementation was AI-assisted. The verification evidence is above, and human review is required before merge.

pkg-pr-new · 2026-08-28T19:42:37Z

Open in StackBlitz

pnpm add https://pkg.pr.new/@supabase/mcp-server-postgrest@d1e46fd

pnpm add https://pkg.pr.new/@supabase/mcp-server-supabase@d1e46fd

pnpm add https://pkg.pr.new/@supabase/mcp-utils@d1e46fd

commit: d1e46fd

coveralls · 2026-08-28T19:43:40Z

Coverage Report for CI Build 33395048111

Coverage decreased (-0.3%) to 96.269%

Details

Coverage decreased (-0.3%) from the base build.
Patch coverage: 15 uncovered changes across 2 files (158 of 173 lines covered, 91.33%).
No coverage regressions found.

Uncovered Changes

File	Changed	Covered	%
packages/mcp-server-supabase/src/tools/account-tools.ts	127	114	89.76%
packages/mcp-server-supabase/src/tools/cost-confirmation.ts	18	16	88.89%
Total (4 files)	173	158	91.33%

Coverage Regressions

No coverage regressions found.

Coverage Stats


Relevant Lines:	3201
Covered Lines:	3101
Line Coverage:	96.88%
Relevant Branches:	417
Covered Branches:	382
Branch Coverage:	91.61%
Branches in Coverage %:	Yes
Coverage Strength:	53.49 hits per line

💛 - Coveralls

Rodriguespn · 2026-08-31T16:45:59Z

+  return (
+    typeof value === 'object' &&
+    value !== null &&
+    Array.isArray((value as { content?: unknown }).content)


Any tool returning { content: [...] } as ordinary data gets passed through raw here. I tried it with a { title, content: [...] } payload and the client rejected the whole result (Invalid tools/call result: invalid_union). The data never arrives.
Since this is published and shared, it hits every consumer. Could we use an explicit discriminant like isInputRequiredResult does, rather than the shape check?

Rodriguespn · 2026-08-31T16:47:08Z

+            };
+          }
+
+          if (


This drift check sits above the decline/cancel checks, so a decline gets dropped and re-prompted whenever the quote moved between rounds. Confirmed this locally: declining after a price shift returns input_required instead of {status:'declined'}.
Moving the two action checks above this block should do it.

Rodriguespn · 2026-08-31T16:48:50Z

+                confirm_cost: inputRequired.elicit({
+                  mode: 'form',
+                  message: [
+                    `Creating this project costs $${cost.amount}/month.`,


/month is hardcoded here (and on line 330), but cost.recurrence already tells us 'monthly' vs 'hourly'. Correct today since only create_project is enabled, but nothing type-checks the string, so whenever enabledTools widens to create_branch, this will quietly render an hourly amount as /month. Cheap to read it from cost.recurrence now.

Rodriguespn · 2026-08-31T16:52:07Z

+            };
+          }
+
+          return await account.createProject({


Replaying the same requestState + accept creates a project each time: The user gets 2 projects from one consent locally. I see replay prevention is called out as out of scope, so mostly wanted to check that's a deliberate call for Stage A given it's a billable action, and whether the platform PR handles it.

Rodriguespn · 2026-08-31T16:53:04Z

          throw new Error('Cannot create a project in read-only mode.');
        }

+        if (costConfirmation && isFormCapable(ctx)) {


We elicit even when the cost is $0, so free-tier creates get a round-trip and a "costs $0/month" prompt. Matches the legacy flow's behaviour, so no regression, but since the point here is smoothing the UX, is skipping the prompt at amount === 0 on the table, or is confirming-regardless intentional?

Rodriguespn · 2026-08-31T17:02:04Z

+  }
+
+  const modes = Object.keys(elicitation);
+  return modes.length === 0 || modes.includes('form');


Checked this against the 2026-07-28 spec and it's exactly right (spec):

For backwards compatibility, an empty capabilities object is equivalent to declaring support for form mode only:
"elicitation": {}, // Equivalent to { "form": {} }

Clients declaring the elicitation capability MUST support at least one mode (form or url).

Servers MUST NOT send elicitation requests with modes that are not supported by the client.

An empty map is spec'd as { form: {} }.

Only footnote: the reference client's getSupportedElicitationModes treats any map without form/url as form-capable, so { someFutureMode: {} } differs here. We fall back to the legacy path, which is the safer side, and such a client is non-conforming anyway. Fine as-is IMO.

Rodriguespn

Left some comments

barryroodt requested a review from a team as a code owner August 28, 2026 19:41

barryroodt added the publish-preview Runs `publish-preview` workflow to publish preview packages via https://pkg.pr.new/ label Aug 28, 2026

barryroodt self-assigned this Aug 28, 2026

barryroodt added 3 commits August 31, 2026 10:15

feat(mcp): add project cost confirmation elicitation

b4d48f8

style(mcp-utils): format request state verifier

2f25c84

refactor(mcp): generalize cost confirmation config

29f25db

barryroodt force-pushed the feat/hosted-project-cost-elicitation branch from 619ef97 to 29f25db Compare August 31, 2026 08:15

Rodriguespn reviewed Aug 31, 2026

View reviewed changes

Comment thread packages/mcp-server-supabase/src/tools/account-tools.ts

fix(mcp): require explicit cost acceptance

d1e46fd

Rodriguespn reviewed Aug 31, 2026

View reviewed changes

Rodriguespn requested changes Aug 31, 2026

View reviewed changes

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feat(mcp): add project cost confirmation elicitation - #391

feat(mcp): add project cost confirmation elicitation#391
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What kind of change does this PR introduce?

What is the current behavior?

What is the new behavior?

How to Review

Verification

Additional context

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