fix: use map key as fallback SessionID in map-format sessions.json

[bughunt8]

Summary

Fixes #5 — When sessions.json is in map format, the map keys (which are the session IDs) were discarded, causing empty SessionID fields and phantom .jsonl file lookups.

Problem

loadSessions() in collector/token.go parses sessions.json as either a map or an array. In the map path, only the values were used (for _, v := range asMap), throwing away the keys. If the JSON values don't contain a sessionId field (since the ID is the map key), the resulting sessionEntry.SessionID is empty. This causes readSessionUsage() to try to open a file named .jsonl (no basename), which always fails silently — meaning token metrics for those sessions are never reported.

Fix

When iterating the map, use the key as a fallback if v.SessionID is empty:

for k, v := range asMap {
    if v.SessionID == "" {
        v.SessionID = k
    }
    entries = append(entries, v)
}

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Warp conversation

Co-Authored-By: Oz oz-agent@warp.dev