fix(agent): guard against nil user message in knowledgeBaseLookup (nil-pointer panic)

[Osamaali313]

Problem

knowledgeBaseLookup (core/agent/knowledgebase.go) dereferences the result of GetLatestUserMessage() before checking it for nil:

userMessage := conv.GetLatestUserMessage().Content   // line 44 — panics when nil

xlog.Info("[Knowledge Base Lookup] Last user message", ..., "lastMessage", conv.GetLatestUserMessage())

if userMessage == "" {                                // intended "no user message" handler
    ...
    return conv
}

Messages.GetLatestUserMessage() (core/agent/actions.go) returns nil when the conversation has no user-role message:

func (m Messages) GetLatestUserMessage() *openai.ChatCompletionMessage {
    for i := len(m) - 1; i >= 0; i-- {
        if m[i].Role == UserRole { msg := m[i]; return &msg }
    }
    return nil
}

So line 44 panics with a nil pointer dereference. The function's own if userMessage == "" branch is meant to handle exactly this "no user message" case — but it's unreachable, because the crash happens first. A non-empty conversation with no user message is a real, anticipated state (e.g. previous_response_id continuations that end with an assistant message, or system/assistant-only history). knowledgeBaseLookup runs for every job when KB auto-search is enabled (agent.go:986).

Reproduction

conv = [{system,...}, {assistant,...}] (no user message):

• Before: runtime error: invalid memory address or nil pointer dereference
• After: reaches the existing "No user message found in conversation" branch and returns cleanly.

(Verified with go1.26 on a standalone reproduction of GetLatestUserMessage + the line-44 pattern.)

Fix

Nil-check before dereferencing so the existing guard runs (and drop the redundant second GetLatestUserMessage() call in the log):

lastUser := conv.GetLatestUserMessage()
if lastUser == nil || lastUser.Content == "" {
    xlog.Info("[Knowledge Base Lookup] No user message found in conversation", "agent", a.Character.Name)
    if obs != nil {
        obs.Completion = &types.Completion{Error: "No user message found in conversation"}
        a.observer.Update(*obs)
    }
    return conv
}
userMessage := lastUser.Content

go build ./core/agent/ passes. (The core/agent suite expects a live LLM endpoint, so I verified the crash/fix via the standalone repro rather than the full suite.)

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