fix(tags): only show start block upstream if is ancestor

[Sg312]

Summary

Only shows start block in the tag dropdown if it is an ancestor of the block

Type of Change

• Bug fix

Testing

Manual

Checklist

• Code follows project style guidelines
• Self-reviewed my changes
• Tests added/updated and passing
• No new warnings introduced
• I confirm that I have read and agree to the terms outlined in the Contributor License Agreement (CLA)

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1 Skipped Deployment

Project	Deployment	Preview	Comments	Updated (UTC)
docs	Skipped			Nov 15, 2025 8:24pm

[greptile-apps]

Greptile Overview

Greptile Summary

Fixed the tag dropdown to only show the start block when it's actually upstream in the workflow graph, preventing incorrect references to disconnected start blocks.

Key changes:

• Modified three locations where starter block accessibility is determined: use-accessible-reference-prefixes hook, BlockPathCalculator, and Serializer
• Added conditional check ancestorIds.includes(starterBlock.id) before adding starter block to accessible blocks
• Previously, the starter block was always added if it existed on the canvas, regardless of whether it was connected upstream
• Now ensures consistent behavior across frontend (UI) and backend (serialization) by only allowing references to blocks that are actually connected in the execution path

Impact:
This fix prevents users from accidentally referencing a start block that isn't in the current block's execution path, which would cause runtime errors or unexpected behavior.

Confidence Score: 5/5

• This PR is safe to merge with minimal risk - it's a focused bug fix with consistent changes across three related files
• The changes are straightforward, consistent, and follow the same pattern across all three files. The fix addresses a clear logical issue where the starter block was being made accessible regardless of whether it was upstream in the workflow graph. The implementation correctly uses the already-computed ancestorIds/pathNodes to check connectivity before adding the starter block. No new dependencies, no complex logic, and the changes maintain consistency between frontend and backend code paths.
• No files require special attention

Important Files Changed

File Analysis

Filename	Score	Overview
apps/sim/app/workspace/[workspaceId]/w/[workflowId]/hooks/use-accessible-reference-prefixes.ts	5/5	Added check to only include starter block if it's an ancestor of the current block
apps/sim/lib/block-path-calculator.ts	5/5	Added check to only include starter block if it's already in pathNodes (upstream)
apps/sim/serializer/index.ts	5/5	Added check to only include starter block if it's in ancestorIds (actually upstream)

Sequence Diagram

sequenceDiagram
    participant User
    participant Block
    participant Calculator as BlockPathCalculator
    participant Serializer
    participant Hook as useAccessibleReferencePrefixes
    
    User->>Block: Open tag dropdown for Block B
    Block->>Hook: Request accessible references
    Hook->>Calculator: findAllPathNodes(edges, blockId)
    Calculator-->>Hook: ancestorIds (upstream blocks)
    
    alt Starter block exists
        Hook->>Hook: Check if starterBlock.id in ancestorIds
        alt Starter is upstream
            Hook->>Hook: Add starter to accessibleIds ✓
        else Starter is NOT upstream
            Hook->>Hook: Skip starter (FIX) ✗
        end
    end
    
    Hook-->>Block: Return accessible prefixes
    Block-->>User: Show only upstream blocks in dropdown
    
    Note over User,Hook: Same logic applies in Serializer<br/>and BlockPathCalculator for consistency

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[greptile-apps]

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