sessions: persist to disk, prune, track client liveness, accept UE_LOGFMT (#1014)HEADmain

Branch started as a sessions-service overhaul (persistence, client liveness, UE_LOGFMT intake) and grew to pick up adjacent infrastructure work: an early-startup log backlog, a hardened `MemoryArena`, the `zen trace serve` viewer gaining a counter view + compact timeline + tabbed callsite panel, defensive fixes in the third-party `tourist` trace parser, a series of allocation reductions across the HTTP and compact-binary hot paths, and a new `zen sessions` CLI command tree.

## Sessions service

**Persistence.** Each session lives on disk under `<DataRoot>/sessions/<id>/` as `info.cb` (metadata) plus `log.bin` (length-prefixed CbObject log records). On startup the service scans that directory and loads prior sessions as ended sessions, preloading the tail of each log so historical views work after a restart. `SessionLog` is noexcept-constructed and falls back to a disabled state on disk errors, so a bad disk can't take down `RegisterSession`. `GetSession` falls back to the ended-sessions list (fixes historical log fetches over HTTP). `LoadTail` counts only successfully-parsed records.

**Pruning.** Periodic cleanup task drops ended sessions once any of three caps is exceeded: age (default 1 year), count (default 1000), or total on-disk footprint (default 50 MiB). Runs 30 s after startup, hourly thereafter. Active sessions never pruned; disk removal and directory stat happen outside the exclusive lock so a slow filesystem can't stall lookups.

**Client liveness.** Sessions carry a `ProcessHandle` for the client-reported pid, captured at registration time so Windows pid recycling can't produce false positives. A 30 s asio timer probes liveness and ends dead sessions through the normal remove path, producing a synthetic `Session ended: process exited (...)` line persisted to `log.bin`. Windows decodes common NTSTATUS exit codes to human names (Ctrl-C, access violation, stack overflow, ...); POSIX stays at plain `process exited`. Clients auto-fill `ClientPid` only for local targets (unix socket / loopback); the server defensively accepts pids only from `IsLocalMachineRequest()` peers. zenserver also reports its own pid when registering its self-session, so it shows up with a real pid in the dashboard and `zen sessions ls`.

**Synthetic end-of-session line.** `RemoveSession` takes an optional reason; before the session moves to the ended list it appends an Info-level `Session ended[: reason]` entry through the normal log path (released outside `m_Lock`). Current reasons: `client request` (HTTP DELETE), `server shutdown` (self-session), `process exited (...)` (liveness).

**UE_LOGFMT structured entries.** `POST /sessions/{id}/log` now accepts `{level, logger, format, fields}` alongside the existing `{level, logger, message}` shape. New `logtemplate.{h,cpp}` implements UE's `StructuredLog.cpp` template grammar (field paths with `.name` / `[N]`, `{{`/`}}` escapes, `$text` / `$format` / `$locformat` object conventions, bounded recursion). Renders to a displayable message at intake while persisting raw format + fields so a future UI can drill into fields without another schema bump. Hot path is zero-alloc — renders into `ExtendableStringBuilder<256>` using stack-buffered `Oid::ToString` / `IoHash::ToHexString` overloads. UI shows a `{…}` marker with the raw template + JSON-pretty fields on hover.

**Parent sessions.** `SessionInfo` gains `parent_session_id`; hub-managed storage server child processes inherit the hub's session id via `--parent-session=<id>`. `ZEN_SESSIONS_URL` env var becomes a fallback for `--sessions-url` / config when neither is provided. The in-process session log sink is disabled when a remote sessions target is configured (logs flow through `SessionsServiceClient` instead). The sessions UI groups child sessions under their parent (collapsible/expandable, sorts as a unit, supports nesting).

**Platform reporting.** `SessionInfo` gains `Platform`, flowed end-to-end: client auto-fills via `GetRuntimePlatformName()`, server persists in `info.cb` (`plat`) and emits on GET. UI renders as a SimpleIcons-style inline SVG (windows / macOS / iOS / linux / wine / android / playstation / xbox / nintendo) with case-insensitive alias resolution (Win32/Win64, PS4/PS5, XSX/XSS, NintendoSwitch, iPhone/iPad, Darwin/OSX). Unknown values fall back to text; sorting runs on the underlying string.

**WebSocket log streaming.** Sessions UI moves from 2 s polling to a WebSocket push model. New `WsSubscriber` has a stable id + helper methods. UI caps the log-line DOM at 5 000 entries with a shared cursor-regression helper, factored out of two call sites. Per-broadcast allocations trimmed on the push path; fixed a stack overrun in the WS log broadcast hex-id buffer.

**Log memory.** `LogEntry::Level` is now `logging::LogLevel` (1 byte) instead of `std::string` (~32 B) — saves ~310 KB per full 10 k-entry deque and eliminates a per-message allocation in the in-proc sink. On-disk format writes an int32 and accepts either int or legacy string on read. `LogEntry` strings now live in a `MemoryArena`; logger names are interned across the deque. `SessionLog::Append` and `WriteSessionInfoFile` drop their `UniqueBuffer` round-trip and write `CbObject::GetView()` straight through `BasicFile` / `SafeWriteFile`. Multi-entry `POST /log` batched under one lock + one push.

**In-proc log timestamps.** `InProcSessionLogSink::TimePointToDateTime` previously preserved only whole seconds, so every in-proc entry rendered at `.000` ms in the dashboard and `zen sessions tail`. It now adds the sub-second part (nanoseconds → 100 ns ticks) to keep ms precision end-to-end.

**UI.** Side "Session Details" panel is gone — its info is inline in the table (appname, mode, platform, id, timestamps, this/log pills, active dot). Bottom panel is a tabbed `Log | Metadata` view with a right-side "Session Information" panel beside metadata; log-only controls (filter, newest-first, follow, log-level filter, expand/collapse) hide when Metadata is active, polling keeps running across tab switches. Wide-mode toggle fills the viewport edge-to-edge. Log lines show the logger category; timestamps render in 24 h with zero-padded fields regardless of locale. Sessions list defaults to All / 10 per page / created-desc, gains click-to-sort headers on the full dataset, a header filter box, and a pager aligned to the table's right edge. Duplicate auto-injected `<h1>Sessions</h1>` removed.

## `zen sessions` CLI

New command tree on the `zen` client for inspecting the sessions service from the terminal:

- **`zen sessions ls`** — lists sessions (active first, ended next; newest-first within each group) with id, status, app/mode, pid, created, duration, and log count. Supports `--status active|ended|all` (default `all`).
- **`zen sessions status`** — prints the sessions service summary: self id, active / ended counts, and the read/write/delete/list/request/bad-request counters from `/stats/sessions`.
- **`zen sessions tail [session]`** — tails a session's log. With no argument it tails zenserver's own session (resolved via `/sessions/list`'s `self_id`); an explicit 24-hex id targets any session, including ended ones (historical replay). `--lines N` (default 50, 0 = all buffered) trims the initial dump client-side. `--follow` prefers a WebSocket push subscription on `/sessions/ws` for sub-second latency; on upgrade failure (older server, blocked port, unix-socket transport) it falls back to HTTP cursor polling at `--interval-ms` (default 500), with sleeps chunked to 50 ms so Ctrl-C reacts quickly. Output matches `zen::logging::FullFormatter` (`[YY-MM-DD HH:MM:SS.mmm] [lvl] [logger] message`); on a TTY the level is colored and the logger is bold, with continuation lines indented under the message column using the *visible* prefix width. 404 surfaces as `(session ended)` and connection errors as `(server gone)` — both clean exits, so stopping the server mid-tail no longer prints a stack trace.
- **`zen sessions ui`** — opens `<host>/dashboard/?page=sessions` in the user's default browser. Rejects unix-socket hosts.

A small `ZenServiceClient::IsUnixSocket()` helper now wraps the unix-socket check used by `ui`, `sessions tail` (WS path), and `sessions ui`.

## Logging

`BacklogSink` captures early-startup log entries in a fixed-capacity ring so late-attached sinks (session sink, file sink) can replay them. Detaches from the broadcast list when disabled; backed by destructor-only cleanup (no `unique_ptr` indirection per entry). Tuned defaults so the backlog covers typical bring-up without unbounded growth.

## `zen trace serve` viewer

- Compact timeline mode for high-density views.
- New `TRACE_INT_VALUE` / `TRACE_FLOAT_VALUE` counter trace points + a counters page in the viewer.
- Callsite tables collapsed into a single tabbed panel.
- Lossless `Oid <-> Guid` bridge for trace session ids; trace `SessionId` plumbed through.
- `tourist` parser hardening: bounds-check `BufferStream::read`, validate `Type::info_size` before `patch()`, convert `parse_important_aux` to a loop (avoids deep recursion), widen `ParserPool` index to `uint32`, bounds-check field offsets in the dispatcher, pin `Types::parse` buffer up-front.

## `MemoryArena`

Configurable chunk size, inline chunk list, oversize requests routed to truly-dedicated chunks (no slack waste, no fragmentation when one allocation is much larger than the chunk).

## Allocation cleanups across hot paths

- `zenhttp::HttpRequestRouter::HandleRequest` and `FormatPackageMessageInternal`: drop heap allocations.
- Compact-binary validation: `eastl::fixed_vector` + `eastl::sort`; eliminate `std::vector` churn.
- `zenserverprocess`: trim transient allocations in spawn paths.
- Sessions HTTP intake / broadcast: drop transient `std::string` allocs.

1 files changed, 61 insertions, 0 deletions

diff --git a/src/zenserver/frontend/html/pages/platform_icons.js b/src/zenserver/frontend/html/pages/platform_icons.js
new file mode 100644
index 000000000..65a04c840
--- /dev/null
+++ b/src/zenserver/frontend/html/pages/platform_icons.js
@@ -0,0 +1,61 @@
+// Copyright Epic Games, Inc. All Rights Reserved.
+
+// SimpleIcons-style platform glyphs (viewBox 0 0 24 24, fill: currentColor)
+// used by the sessions table to render a recognizable icon instead of a raw
+// platform label. Lives in its own module because the data table is bulky and
+// other pages may want to reuse the resolver.
+
+"use strict";
+
+// Path data is intentionally one-line per entry to keep the icon table dense.
+// Unknown platforms fall through to a text cell at the call site.
+export const PLATFORM_ICONS = {
+	windows:     { label: "Windows",     path: "M0 3.449L9.75 2.1v9.451H0m10.949-9.602L24 0v11.4H10.949M0 12.6h9.75v9.451L0 20.699M10.949 12.6H24V24l-13.051-1.351" },
+	macos:       { label: "macOS",       path: "M17.05 20.28c-.98.95-2.05.8-3.08.35-1.09-.46-2.09-.48-3.24 0-1.44.62-2.2.44-3.06-.35C2.79 15.25 3.51 7.59 9.05 7.31c1.35.07 2.29.74 3.08.8 1.18-.24 2.31-.93 3.57-.84 1.51.12 2.65.72 3.4 1.8-3.12 1.87-2.38 5.98.48 7.13-.57 1.5-1.31 2.99-2.54 4.09l.01-.01zM12.03 7.25c-.15-2.23 1.66-4.07 3.74-4.25.29 2.58-2.34 4.5-3.74 4.25z" },
+	ios:         { label: "iOS",         path: "M17.05 20.28c-.98.95-2.05.8-3.08.35-1.09-.46-2.09-.48-3.24 0-1.44.62-2.2.44-3.06-.35C2.79 15.25 3.51 7.59 9.05 7.31c1.35.07 2.29.74 3.08.8 1.18-.24 2.31-.93 3.57-.84 1.51.12 2.65.72 3.4 1.8-3.12 1.87-2.38 5.98.48 7.13-.57 1.5-1.31 2.99-2.54 4.09l.01-.01zM12.03 7.25c-.15-2.23 1.66-4.07 3.74-4.25.29 2.58-2.34 4.5-3.74 4.25z" },
+	linux:       { label: "Linux",       path: "M12.504 0c-.155 0-.315.008-.48.021-4.226.333-3.105 4.807-3.17 6.298-.076 1.092-.3 1.953-1.05 3.02-.885 1.051-2.127 2.75-2.716 4.521-.278.832-.41 1.684-.287 2.489a.424.424 0 00-.11.135c-.26.268-.45.6-.663.839-.2.271-.53.4-.953.58-.42.17-.94.33-1.31.84-.5.84-.33 1.83.03 2.72.39.89.95 1.64.89 2.13-.06.72.21 1.24.59 1.48.38.24.83.24 1.17.24.34 0 .57-.01.67-.06.19-.1.38-.25.55-.26.22-.02.43.11.72.26.67.35 1.3.43 1.88.3.57-.13 1.08-.44 1.52-.78.9-.74 1.7-1.5 2.6-1.63.24-.03.5-.05.78-.05.13 0 .25 0 .39.02.11.01.26.1.5.26.25.17.6.4 1 .59.4.17.87.32 1.4.3.59-.02 1.18-.22 1.73-.63 1.57-1.19 4.21-.97 5.13-2.08.11-.14.18-.3.2-.48.02-.18 0-.36-.07-.54-.06-.19-.17-.38-.32-.57-.15-.19-.35-.38-.56-.55-.38-.31-.58-.67-.57-1.11.01-.28.14-.58.28-.85.11-.28.24-.54.24-.81-.02-.28-.13-.55-.36-.77-.23-.23-.55-.42-1.01-.51a.424.424 0 00-.14-.02c-.3-.04-.57-.04-.87-.04-.13-.31-.28-.62-.43-.91-.9-1.72-2.23-3.13-3.27-4.31-.92-1.02-1.55-2-1.62-3.07-.12-.9-.07-1.94-.1-2.93-.02-.92-.15-1.81-.67-2.5-.49-.7-1.32-1.22-2.73-1.22z" },
+	wine:        { label: "Wine",        path: "M8 2h8l-1 7a4 4 0 01-3 4v5h3v2H9v-2h3v-5a4 4 0 01-3-4L8 2z" },
+	android:     { label: "Android",     path: "M17.523 15.3414c-.5511 0-.9993-.4486-.9993-.9997s.4482-.9993.9993-.9993c.5511 0 .9993.4482.9993.9993.0001.5511-.4482.9997-.9993.9997m-11.046 0c-.5511 0-.9993-.4486-.9993-.9997s.4482-.9993.9993-.9993c.5511 0 .9993.4482.9993.9993 0 .5511-.4482.9997-.9993.9997m11.4045-6.02l1.9973-3.4592a.416.416 0 00-.1521-.5676.416.416 0 00-.5677.1521l-2.0223 3.503C15.5902 8.2439 13.8533 7.8508 12 7.8508s-3.5902.3931-5.1367 1.0989L4.841 5.4467a.4161.4161 0 00-.5677-.1521.4157.4157 0 00-.1521.5676l1.9973 3.4592C2.6889 11.1867.3432 14.6589 0 18.761h24c-.3432-4.1021-2.6889-7.5743-6.1185-9.4396" },
+	playstation: { label: "PlayStation", path: "M8.985 2.596v17.548l3.915 1.261V6.688c0-.69.304-1.151.794-.991.636.181.76.814.76 1.505v5.875c2.441 1.193 4.362 0 4.362-3.118 0-3.198-1.13-4.63-4.442-5.76-1.313-.444-3.697-1.203-5.389-1.603zM0 17.81c.069.24.213.489.487.728C4.024 21.22 9.45 22.395 15.03 22.395c.58 0 1.142-.034 1.725-.08-5.423-1.39-9.33-3.77-15.203-4.87a5.78 5.78 0 01-1.55-.364v.728zm18.7-8.97c.057-.035.114-.057.194-.08.695-.148 1.15.217 1.15.908 0 .706-.478 1.283-1.162 1.486-.08.023-.137.034-.194.057v4.74c.079-.023.148-.034.228-.057 3.426-1.193 4.374-2.796 4.374-5.502 0-2.637-1.37-4.063-3.357-4.748-.387-.137-.764-.228-1.162-.32l-.068-.023v3.54l-.003-.001z" },
+	xbox:        { label: "Xbox",        path: "M4.102 21.033C6.211 22.881 8.977 24 12 24c3.026 0 5.789-1.119 7.902-2.965 1.16-1.016-4.553-6.929-7.902-9.518-3.349 2.589-9.063 8.499-7.898 9.516zm11.08-18.52c2.699-1.159 5.062-1.169 6.52-.546l.025.033c-1.377-2.152-3.624-4.001-7.004-3.978-2.049 0-4.062.826-5.725 2.208 1.964.468 4.114 1.404 6.184 2.283zM2.27 1.976l.025-.033c1.458-.623 3.82-.613 6.519.546 2.07-.879 4.22-1.815 6.184-2.283C13.335.824 11.32-.002 9.272 0 5.891-.02 3.646 1.828 2.27 1.976zM1.62 19.46l-.012.003C.597 17.8 0 15.838 0 13.749c0-1.749.425-3.399 1.157-4.85.9-1.784 4.126-5.59 5.73-7.37.118-.131-4.425 1.976-5.267 9.931-.025.221-.025.442-.025.663 0 2.586.741 5 2.025 7.017zm20.763 0l-.011-.003c1.283-2.017 2.025-4.431 2.025-7.017 0-.22 0-.442-.025-.663-.842-7.955-5.386-10.062-5.267-9.93 1.604 1.779 4.83 5.585 5.73 7.37.732 1.45 1.157 3.1 1.157 4.849 0 2.09-.596 4.051-1.609 5.714l.013.003-.014-.324z" },
+	nintendo:    { label: "Nintendo",    path: "M14.176 24h3.674c3.376 0 6.15-2.774 6.15-6.15V6.15C24 2.775 21.226 0 17.85 0H14.16c-.205 0-.38.174-.38.38v23.24c0 .206.19.38.396.38zM8.252 24c.212 0 .39-.174.39-.384V.374c0-.21-.178-.374-.39-.374h-2.1A6.167 6.167 0 0 0 0 6.15v11.7C0 21.224 2.775 24 6.152 24h2.1zm-4.59-15.763a2.578 2.578 0 0 1 2.58-2.58 2.577 2.577 0 0 1 2.578 2.58 2.579 2.579 0 1 1-5.157 0zm12.556 11.928a3.063 3.063 0 0 1 3.067-3.065 3.063 3.063 0 0 1 3.065 3.065 3.067 3.067 0 0 1-3.065 3.07 3.065 3.065 0 0 1-3.067-3.07z" },
+};
+
+// Resolve a platform string (as reported by the client) to an icon entry.
+// Intentionally liberal so UE-style variants like "Win64", "PS5", "XSX",
+// "NintendoSwitch" all land on the right icon.
+export function resolve_platform_icon(platform)
+{
+	const p = platform.toLowerCase();
+	if (p.includes("windows") || p === "win32" || p === "win64" || p === "win") return PLATFORM_ICONS.windows;
+	if (p === "wine")                                                           return PLATFORM_ICONS.wine;
+	if (p.includes("android"))                                                  return PLATFORM_ICONS.android;
+	if (p === "ios" || p === "iphone" || p === "ipad" || p === "ipados" || p === "tvos") return PLATFORM_ICONS.ios;
+	if (p === "mac" || p === "macos" || p === "osx" || p === "darwin")          return PLATFORM_ICONS.macos;
+	if (p === "linux")                                                          return PLATFORM_ICONS.linux;
+	if (p.includes("playstation") || /^ps\d/.test(p) || p === "psvita")         return PLATFORM_ICONS.playstation;
+	if (p.includes("xbox") || p === "xsx" || p === "xss")                       return PLATFORM_ICONS.xbox;
+	if (p.includes("nintendo") || p === "switch")                               return PLATFORM_ICONS.nintendo;
+	return null;
+}
+
+// Build a <span> element representing the platform — either an inline SVG
+// glyph (when the platform resolves) or a plain text fallback.
+export function make_platform_cell(platform)
+{
+	const el = document.createElement("span");
+	if (!platform) { return el; }
+	const icon = resolve_platform_icon(platform);
+	if (!icon)
+	{
+		// Unknown platform — fall back to the raw label.
+		el.textContent = platform;
+		return el;
+	}
+	el.className = "platform-icon";
+	el.title = icon.label;
+	el.setAttribute("aria-label", icon.label);
+	// Paths are hard-coded (no user-controlled input), so innerHTML is safe.
+	el.innerHTML = `<svg viewBox="0 0 24 24" role="img" focusable="false"><path d="${icon.path}"/></svg>`;
+	return el;
+}