feat(http): support persistent sessions via X-GoClaw-User-Id header

[olbboy]

Summary

HTTP /v1/chat/completions endpoint now supports persistent sessions when X-GoClaw-User-Id header is provided. Without the header, behavior is unchanged (stateless, random session per request).

Problem

Every HTTP API request creates a new session (random UUID in session key), even when the same user sends multiple messages. The agent always responds as if it was a new conversation — no memory of previous messages.

Root cause: Session key includes runID[:8] (random UUID per request):

// Before: always random
sessionSuffix = "http-" + userID + "-" + runID[:8]
sessionKey = SessionKey(agentID, sessionSuffix)

This is the only channel without persistent sessions — Telegram, Discord, Slack, Zalo all use stable session keys.

Solution

When X-GoClaw-User-Id is present, build a stable session key using the canonical BuildSessionKey() — same pattern as all other channels:

// After: stable per user
if userID != "" {
    sessionKey = sessions.BuildSessionKey(agentID, "http", sessions.PeerDirect, userID)
    // → "agent:{id}:http:direct:{userId}" — same format as telegram/slack/discord
} else {
    sessionKey = sessions.SessionKey(agentID, "http-"+runID[:8])
    // → unchanged stateless behavior
}

Impact

• Backward compatible: No X-GoClaw-User-Id header → behavior unchanged
• No key collision: http:direct: prefix is unique among all channels
• No cross-channel interference: Telegram/Slack/Discord sessions unaffected
• Session lifecycle: Same as Telegram — compaction, history limits, token tracking all work

Test Plan

• HTTP with X-GoClaw-User-Id: user1 → send "I'm Alice" → send "What's my name?" → agent remembers
• HTTP without header → each request independent (existing behavior)
• Different userIDs → different sessions (isolation)
• Telegram/Slack sessions unaffected
• Concurrent requests from same user → same session

Use Case

Enables integration with Microsoft Teams (and any HTTP client) where a bridge bot sends X-GoClaw-User-Id header with the Teams user ID, maintaining conversation history across messages.