feat: unify MCP slug availability across toolsets and mcp_endpoints

[daviddanialy]

AIM-22

Summary

• Adds a single slug-availability check, mcpendpoints.CheckSlugAvailable, backed by a new CheckUnifiedSlugAvailability query that answers "is (custom_domain_id, slug) taken" against both mcp_endpoints.slug and toolsets.mcp_slug in the same address scope (platform vs custom domain). The endpoint-only CheckSlugAvailability query is deleted.
• Two owner exclusions keep self-validation honest while both representations coexist: a toolset does not collide with its own row or its wrapper's endpoints, and a server does not collide with its own backing toolset.
• Callers switched: both uniqueness branches in updateToolset, the toolsets availability handler (now platform-scoped rather than a cross-namespace global EXISTS; wire contract unchanged), and mcpendpoints create/update/check. Create checks inside the transaction after locks; update only re-checks when the (slug, domain) address actually changes.
• Dashboard: useMcpEndpointSlugValidation drops its second RPC to toolsets.checkMCPSlugAvailability.

Motivation

toolsets.mcp_slug and mcp_endpoints.slug each had their own partial unique indexes and their own availability query, and neither saw the other table — while every public entry point resolves mcp_endpoints first and falls back to toolsets.mcp_slug. An endpoint created with a live hosted server's slug would silently take over that address. This makes availability a single namespace per scope for as long as the two representations coexist, and is the first step of the toolsets-under-mcp_servers migration (the toolset-side query is removed later with the runtime fallback).

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https://claude.ai/code/session_01TCzhsvUYz5VMieXYaQUC2Z

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Summary by cubic

Unifies MCP slug availability across toolsets.mcp_slug and mcp_endpoints.slug into one namespace per address scope (AIM-22). Previously each table checked only itself, so an endpoint could take over a slug a live hosted server still resolved under; now a slug held by either table blocks the other.

Refactors

• Replaces the endpoint-only CheckSlugAvailability query with CheckUnifiedSlugAvailability, probing both tables in the same address scope, and adds a pg_advisory_xact_lock on write paths that serializes competing claims the per-table unique indexes can't catch.
• Owner exclusions let a hosted server's mirrored address validate against itself; updateToolset re-probes on any effective (slug, domain) change and skips the domain-liveness guard so a rename under a soft-deleted domain still works.
• mcpEndpoints create/update, SetRootMcpEndpoint, and toolset create/clone now take the lock and shared check; generated toolset slugs regenerate on collision. The dashboard drops its second RPC, while toolsets.checkMCPSlugAvailability stays for the inline editor — now deprecated, auth-gated, and faulting on endpoint slugs too.

^{Written for commit a5c0993. Summary will update on new commits.}

[linear-code]

AIM-22

[changeset-bot]

🦋 Changeset detected

Latest commit: a5c0993

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 2 packages

Name	Type
server	Patch
dashboard	Patch

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[cubic-dev-ai]

Running ultrareview automatically — This change unifies MCP slug availability across two tables with a complex cross-table SQL query and owner-exclusion logic; a subtle bug could silently break runtime address resolution or block legitimate operations, warranting deep review.. I'll post findings when complete.

[cubic-dev-ai]

Ultrareview completed in 7m 47s

All reported issues were addressed across 9 files

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[cubic-dev-ai]

All reported issues were addressed across 8 files (changes from recent commits).

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[daviddanialy]

End-to-end verification (this PR's changes)

Context: all three Phase-1 branches (#5917, #5918, #5919) were merged into a scratch tree (zero conflicts), the full server suite ran on the merged tree — 14,334 tests, 1 failure: a pre-existing skills-subsystem clock flake, passes in isolation, unrelated to these PRs — and a local stack was booted from the merged tree with simulated backfill rows (a toolset-backed mcp_servers wrapper + mcp_endpoints row) to exercise the dormant paths over real HTTP.

Scenarios exercising this PR:

Scenario	Result	Evidence
RPC endpoint-create claiming a live toolset's mcp_slug	PASS	409 conflict — on main this silently succeeds and the endpoint shadows the toolset at serve time
RPC toolset mcp_slug update into an existing endpoint's slug	PASS	409 "this slug is already taken"; control update to a free slug → 200
Org-prefix rule (incidental)	PASS	un-prefixed platform slug → 422

No panics or unexpected errors in server logs. All test rows and flag changes were reverted after the run (verified by query).

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