zen trace analysis support (#945)

Integrates the **tourist** trace analysis library and builds a full `zen trace` command suite for working with Unreal Engine `.utrace` files.

### Trace analysis library (`thirdparty/tourist/`)
- Adds the tourist library as a third-party dependency with three modules: **foundation** (platform primitives, memory, scheduling), **trace** (UE Trace protocol decoding), and **analysis** (event dispatching and analyzer framework).
- Cross-platform support for Windows, Linux, and macOS.

### `zen trace` CLI commands (`src/zen/cmds/`, `src/zen/trace/`)
- **`zen trace analyze`** — Summarize a `.utrace` file: session metadata, thread inventory, command line + build configuration, CPU profiling scopes, timing, event rates, log messages, and (with symbols) memory allocation metrics including live-allocs dumps, callstack-keyed aggregation, and allocation churn. Optional HTML output for memory reports.
- **`zen trace inspect`** — Dump the event schema (declared types, fields, sizes) from a trace file.
- **`zen trace trim`** — Extract a time-window from a trace into a new `.utrace` file.
- **`zen trace serve`** — Launch a local HTTP server hosting an interactive trace viewer; opens in the default browser.

### Symbolication (`src/zen/trace/symbol_resolver.*`, `thirdparty/raw_pdb/`)
- Pluggable resolver with multiple backends: `pdb` (in-tree raw_pdb), `dbghelp` (Windows), `llvm-symbolizer` (all platforms), `atos` (macOS). An `auto` backend picks the best available tool per platform.
- Microsoft Symbol Server support: downloads PDBs on demand using a redirect-aware HTTP client.
- Local PDB cache keyed by image GUID preserves symbols across binary recompilation.
- Callstack trimming heuristic strips UE internal noise from reports.
- Binary analysis cache (`.ucache_z`) avoids re-resolving the same trace.

### Interactive trace viewer (`src/zen/frontend/html/`, `src/zen/trace/trace_viewer_service.*`)
- Timeline: scope-level detail, horizontal zoom/pan, vertical scrolling, viewport-driven loading with pre-computed LOD for responsive navigation of large traces.
- Thread grouping (collapsible sidebar sections) synthesized from name suffixes, natural sort order, visual distinction between lane threads and OS threads.
- Bookmark and region annotations; region categories with per-category toggles; bookmark marker toggle in the toolbar.
- Filterable Logs tab showing captured `UE_LOG` output.
- Stats tab with per-scope aggregate statistics.
- Memory tab with interactive allocation analysis and an allocation size histogram.
- CsvProfiler event parsing and chart UI.

### Other in-branch supporting changes
- **Cross-platform browser launcher** (`browser_launcher.{h,cpp}`) used by `trace serve`.
- **`ReciprocalU64`** fast 64-bit integer division (zencore/intmath) for trace analyzers.
- **`parallelsort`** cross-platform parallel sort helper (zenutil).
- Frontend zip build rule so the viewer's HTML assets are bundled into `zen.exe`.
- `/Zo` flag for better optimized debug info on Windows release builds.
- `trace-tests.cpp` in the `zen-test` harness (harness itself landed on main via #985).

1 files changed, 211 insertions, 0 deletions

diff --git a/thirdparty/tourist/foundation/src/malloc.cpp b/thirdparty/tourist/foundation/src/malloc.cpp
new file mode 100644
index 000000000..c8d4c5d66
--- /dev/null
+++ b/thirdparty/tourist/foundation/src/malloc.cpp
@@ -0,0 +1,211 @@
+#include <foundation/types.h>
+#include <foundation/malloc.h>
+#include <foundation/platform.h>
+
+//------------------------------------------------------------------------------
+struct Header
+{
+    enum : uint32 { Magic = 0xaa55aa55 };
+    size_t  size;
+    uint32  bias;
+    uint32  canary;
+    uint8   ptr[];
+};
+static bool g_add_canaries = false;
+
+//------------------------------------------------------------------------------
+#ifdef _WIN32
+
+template <typename T=uint8>
+static T* tt_malloc_norm(size_t size, size_t alignment)
+{
+    alignment = uint32(std::max(alignment, alignof(std::max_align_t)));
+    if (!g_add_canaries)
+        return (T*)_aligned_malloc(size, alignment);
+
+    uint32 lead_size = uint32(sizeof(Header) + alignment - 1) & ~uint32(alignment - 1);
+    size_t alloc_size = lead_size + size + sizeof(uint32);
+    auto* alloc_ptr = (uint8*)_aligned_malloc(alloc_size, alignment);
+
+    auto* header = (Header*)(alloc_ptr + lead_size - sizeof(Header));
+    header->bias = lead_size;
+    header->size = size;
+    header->canary = Header::Magic;
+
+    std::memcpy(header->ptr + size, &header->canary, sizeof(uint32));
+
+    return header->ptr;
+}
+
+static void tt_free_norm(void* address)
+{
+    if (address == nullptr)
+        return;
+
+    if (!g_add_canaries)
+        return _aligned_free(address);
+
+    auto* header = (Header*)address - 1;
+
+    auto is_canary = [] (void* ptr) {
+        uint32 canary = Header::Magic;
+        return !std::memcmp(ptr, &canary, sizeof(uint32));
+    };
+    if (!is_canary(&header->canary))            __debugbreak();
+    if (!is_canary(header->ptr + header->size)) __debugbreak();
+
+    _aligned_free(header->ptr - header->bias);
+}
+
+#else // POSIX
+
+template <typename T=uint8>
+static T* tt_malloc_norm(size_t size, size_t alignment)
+{
+    alignment = std::max(alignment, alignof(std::max_align_t));
+    // std::aligned_alloc requires size to be a multiple of alignment
+    size_t aligned_size = (size + alignment - 1) & ~(alignment - 1);
+    if (aligned_size == 0)
+        aligned_size = alignment;
+
+    if (!g_add_canaries)
+        return (T*)std::aligned_alloc(alignment, aligned_size);
+
+    uint32 lead_size = uint32(sizeof(Header) + alignment - 1) & ~uint32(alignment - 1);
+    size_t alloc_size = lead_size + size + sizeof(uint32);
+    size_t alloc_aligned = (alloc_size + alignment - 1) & ~(alignment - 1);
+    auto* alloc_ptr = (uint8*)std::aligned_alloc(alignment, alloc_aligned);
+
+    auto* header = (Header*)(alloc_ptr + lead_size - sizeof(Header));
+    header->bias = lead_size;
+    header->size = size;
+    header->canary = Header::Magic;
+
+    std::memcpy(header->ptr + size, &header->canary, sizeof(uint32));
+
+    return header->ptr;
+}
+
+static void tt_free_norm(void* address)
+{
+    if (address == nullptr)
+        return;
+
+    if (!g_add_canaries)
+        return std::free(address);
+
+    auto* header = (Header*)address - 1;
+
+    auto is_canary = [] (void* ptr) {
+        uint32 canary = Header::Magic;
+        return !std::memcmp(ptr, &canary, sizeof(uint32));
+    };
+    if (!is_canary(&header->canary))            __builtin_trap();
+    if (!is_canary(header->ptr + header->size)) __builtin_trap();
+
+    std::free(header->ptr - header->bias);
+}
+
+#endif
+
+//------------------------------------------------------------------------------
+void tt_memory_canaries_on()
+{
+    g_add_canaries = true;
+}
+
+
+//------------------------------------------------------------------------------
+void*    (*tt_malloc_impl)(size_t, size_t)  = tt_malloc_norm;
+void     (*tt_free)(void*)                  = tt_free_norm;
+
+
+
+//------------------------------------------------------------------------------
+#ifdef _WIN32
+
+template <typename T=uint8>
+static T* tt_malloc_stomp(size_t size, size_t alignment)
+{
+    enum { PAGE_SIZE = 64 << 10 };
+    size = (size + (alignment - 1)) & ~(alignment - 1);
+    size_t alloc_size = (size + (2 * PAGE_SIZE)) & ~(PAGE_SIZE - 1);
+    auto* ptr = (uint8*)VirtualAlloc(nullptr, alloc_size, MEM_COMMIT, PAGE_READWRITE);
+    ptr += alloc_size - PAGE_SIZE;
+    DWORD unused;
+    VirtualProtect(ptr, PAGE_SIZE, PAGE_NOACCESS, &unused);
+
+    return (T*)(ptr - size);
+}
+
+static void tt_free_stomp(void* address)
+{
+    if (address == nullptr)
+        return;
+
+    *(uint32*)address = 0x30493049;
+
+    MEMORY_BASIC_INFORMATION info;
+    VirtualQuery(address, &info, sizeof(info));
+    DWORD unused;
+    VirtualProtect(info.AllocationBase, info.RegionSize, PAGE_NOACCESS, &unused);
+}
+
+#else // POSIX
+
+static size_t tt_get_page_size()
+{
+    static size_t page_size = size_t(sysconf(_SC_PAGESIZE));
+    return page_size;
+}
+
+struct StompHeader
+{
+    void*  base;
+    size_t total_size;
+};
+
+template <typename T=uint8>
+static T* tt_malloc_stomp(size_t size, size_t alignment)
+{
+    size_t page_size = tt_get_page_size();
+    size = (size + (alignment - 1)) & ~(alignment - 1);
+    size_t needed = sizeof(StompHeader) + size + page_size;
+    size_t alloc_size = (needed + (page_size - 1)) & ~(page_size - 1);
+    auto* base = (uint8*)mmap(nullptr, alloc_size, PROT_READ | PROT_WRITE,
+                              MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+    if (base == MAP_FAILED)
+        return nullptr;
+
+    // Guard page at the end
+    uint8* guard = base + alloc_size - page_size;
+    mprotect(guard, page_size, PROT_NONE);
+
+    // User allocation right before the guard, header right before that
+    T* user_ptr = (T*)(guard - size);
+    auto* hdr = (StompHeader*)((uint8*)user_ptr - sizeof(StompHeader));
+    hdr->base = base;
+    hdr->total_size = alloc_size;
+
+    return user_ptr;
+}
+
+static void tt_free_stomp(void* address)
+{
+    if (address == nullptr)
+        return;
+
+    *(uint32*)address = 0x30493049;
+
+    auto* hdr = (StompHeader*)((uint8*)address - sizeof(StompHeader));
+    mprotect(hdr->base, hdr->total_size, PROT_NONE);
+}
+
+#endif
+
+//------------------------------------------------------------------------------
+void tt_memory_stomp_on()
+{
+    tt_malloc_impl = tt_malloc_stomp;
+    tt_free = tt_free_stomp;
+}