fix(ai-builder): Handle data table name conflict gracefully instead of looping (no-changelog)

[JoseBra]

Summary

• Fix create-data-table tool throwing DataTableNameConflictError when the table already exists during the builder's rebuild cycle, causing the agent to waste iterations retrying
• Return denied: true with guidance to use the existing table, which the agent handles gracefully
• Add unit tests for the create-data-table tool (8 tests covering all tool states)

Before / After

	Before	After
Build	1/3 succeeded (parallel runs)	3/3 succeeded

Context

Reported independently by product team — a user spent 45 min trying to build a workflow with a data table before giving up. The data table conflict during the builder's rebuild cycle wastes agent iterations and context, making it more likely to hit proxy timeouts.

Related Linear ticket

https://linear.app/n8n/issue/AI-2358

Review checklist

• I have seen this code, I have run this code, and I take responsibility for this code.

Test plan

• Unit tests: 8/8 passing (create, conflict handling, suspension, permission blocked, non-conflict errors)
• Typecheck clean
• Manual before/after testing: without fix 1/3 builds succeed, with fix 3/3 builds succeed

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

📢 Thoughts on this report? Let us know!

[cubic-dev-ai]

1 issue found across 2 files

Prompt for AI agents (unresolved issues)

Check if these issues are valid — if so, understand the root cause of each and fix them. If appropriate, use sub-agents to investigate and fix each issue separately.


<file name="packages/@n8n/instance-ai/src/tools/data-tables/create-data-table.tool.ts">

<violation number="1" location="packages/@n8n/instance-ai/src/tools/data-tables/create-data-table.tool.ts:117">
P1: Convert `DataTableNameConflictError` to `denied: true` unconditionally. The extra `list()` check can still rethrow the conflict and recreate the retry loop described in AI-2358.</violation>
</file>

Architecture diagram

sequenceDiagram
    participant Agent as AI Agent (Mastra)
    participant Tool as Tool: create-data-table
    participant Service as DataTableService
    participant DB as Database

    Note over Agent, DB: Request Flow: Data Table Creation

    Agent->>Tool: execute(name, columns)
    
    alt Permission: require_approval
        Tool->>Agent: suspend(message)
        Note over Agent, Tool: User approves action
        Agent->>Tool: resume(approved: true)
    else Permission: blocked
        Tool-->>Agent: { denied: true, reason: "Action blocked" }
    end

    Note over Tool, Service: Execution Phase (CHANGED)

    Tool->>Service: create(name, columns)
    Service->>DB: INSERT INTO data_tables ...
    
    alt Table Name Unique
        DB-->>Service: Table Record
        Service-->>Tool: table
        Tool-->>Agent: { table }
    else Table Name Conflict
        DB-->>Service: Error (Unique Constraint)
        Service-->>Tool: throw DataTableNameConflictError
        
        Note over Tool: NEW: Handle conflict to prevent retry loop
        
        Tool->>Service: list({ projectId })
        Service->>DB: SELECT * FROM data_tables
        DB-->>Service: existing tables
        Service-->>Tool: tables
        
        opt Table found in list
            Tool-->>Agent: CHANGED: { denied: true, reason: "Table already exists..." }
            Note right of Agent: Agent continues gracefully<br/>instead of retrying
        end
    else Other Error
        Service-->>Tool: throw Error
        Tool-->>Agent: Exception (Agent may retry)
    end

Loading

_{Reply with feedback, questions, or to request a fix. Tag @cubic-dev-ai to re-run a review, or fix all with cubic.}

[OlegIvaniv]

That's neat!