[code-review] knowledge_graph doAdd unconditionally overwrites Tags with nil on update — silent tag data loss

[topcheer]

File: internal/tool/knowledge_graph.go
Lines: 186
Severity: Medium

Problem

Line 186 unconditionally assigns ex.Tags = p.Tags when updating an existing node. If the caller didn't provide tags (p.Tags is nil from JSON unmarshal), existing tags are silently erased. In contrast, Status at line 187-189 is conditionally preserved with if p.Status != "". Tags get no such guard — inconsistent and surprising data loss.

Trigger Scenario

1. Node exists with tags: ["decision", "accepted"] and status: "accepted"
2. User calls knowledge_graph add with the same ID to update only the title (no tags, no status provided)
3. After update: tags becomes nil (erased), status remains "accepted" (preserved)
4. Tags are silently destroyed while status survives

Expected vs Actual

• Expected: Tags are preserved when not provided, just like Status
• Actual: Tags are unconditionally overwritten with nil

Fix

Add a nil-guard for Tags, matching the Status pattern:

if p.Tags != nil {
    ex.Tags = p.Tags
}

[topcheer]

Fixed in ee47559. Tags are now conditionally preserved on update (if p.Tags != nil), matching the existing Status pattern. Updating a node's title without providing tags no longer silently erases existing tags.