Method lookup

server/src/server/disk_prefix_cache.cpp:369–420

            if (nlen < 4 || sname.compare(nlen - 4, 4, ".dkv") != 0) continue;

            // Read the header to get the layout_id.
            std::string fpath = se.path().string();
            FILE * f = std::fopen(fpath.c_str(), "rb");
            if (!f) continue;

            DiskCacheHeader hdr{};
            if (read_header(f, hdr) && std::memcmp(hdr.magic, "DKVC", 4) == 0) {
                std::memcpy(layout_id_.data(), hdr.layout_id, 16);
                layout_known_ = true;
                layout_from_disk_ = true;  // unverified — must be confirmed by learn_layout()
                layout_dir_ = subdir;
                std::fclose(f);
                scan_directory();
                return;
            }
            std::fclose(f);
        }
    }
}

// ─── Lookup ─────────────────────────────────────────────────────────────

bool DiskPrefixCache::lookup(const std::vector<int32_t> & prompt_ids, int slot) {
    if (disabled() || !layout_known_) return false;

    PrefixHash hash = hash_prefix(prompt_ids.data(), (int)prompt_ids.size());

    std::lock_guard<std::mutex> lock(mu_);
    int idx = find_entry(hash);
    if (idx < 0) return false;

    auto & entry = entries_[idx];
    if (!read_file(entry.path, slot)) {
        // File is corrupt or incompatible — remove it.
        std::fprintf(stderr, "[disk-cache] lookup failed, removing %s\n",
                     entry.path.c_str());
        std::remove(entry.path.c_str());
        total_bytes_ -= entry.file_size;
        entries_.erase(entries_.begin() + idx);
        return false;
    }

    if (layout_from_disk_) {
        const std::array<uint8_t, 16> disk_id = layout_id_;
        auto ref = backend_.snapshot_ref(slot);
        if (!ref.ctx) {
            backend_.snapshot_free(slot);
            return false;
        }
        compute_layout_id(ref.ctx);
        if (std::memcmp(disk_id.data(), layout_id_.data(), 16) != 0) {
            std::fprintf(stderr,
                         "[disk-cache] adopted layout mismatch: disk=%s model=%s\n",
                         hex(disk_id.data(), 16).c_str(),
                         hex(layout_id_.data(), 16).c_str());