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, 209 insertions, 0 deletions

diff --git a/src/zen/trace/trace_model.cpp b/src/zen/trace/trace_model.cpp
index ac81161a1..c11e2c47c 100644
--- a/src/zen/trace/trace_model.cpp
+++ b/src/zen/trace/trace_model.cpp
@@ -387,6 +387,26 @@ begin_outline(CsvProfiler, Metadata)
 	field(uint8[], Key)
 	field(uint8[], Value)
 end_outline()
+
+// Counters trace events (UE CountersTrace / zen ZEN_TRACE_INT_VALUE).
+begin_outline(Counters, Spec)
+	field(uint16, Id)
+	field(uint8, Type)
+	field(uint8, DisplayHint)
+	field(uint8[], Name)
+end_outline()
+
+begin_outline(Counters, SetValueInt)
+	field(uint64, Cycle)
+	field(int64, Value)
+	field(uint16, CounterId)
+end_outline()
+
+begin_outline(Counters, SetValueFloat)
+	field(uint64, Cycle)
+	field(double, Value)
+	field(uint16, CounterId)
+end_outline()
 	// clang-format on
 
 	//////////////////////////////////////////////////////////////////////////////
@@ -1471,6 +1491,138 @@ private:
 };
 
 //////////////////////////////////////////////////////////////////////////////
+// Counters analyzer -- consumes Counters.Spec / SetValueInt / SetValueFloat
+// (UE TRACE_INT_VALUE / TRACE_FLOAT_VALUE / zen ZEN_TRACE_INT_VALUE etc.).
+// Spec events register a counter id; SetValue events emit a sample. We keep
+// per-counter time series for the viewer / report to render.
+
+class CountersAnalyzer : public Analyzer
+{
+public:
+	explicit CountersAnalyzer(const TraceTiming* Timing = nullptr) : m_Timing(Timing) {}
+
+	void subscribe(Vector<Subscription>& Subs) override
+	{
+		Subs.emplace_back(this, &CountersAnalyzer::OnSpec);
+		Subs.emplace_back(this, &CountersAnalyzer::OnSetValueInt);
+		Subs.emplace_back(this, &CountersAnalyzer::OnSetValueFloat);
+	}
+
+	struct EditableSeries
+	{
+		zen::trace_detail::TraceModel::CounterSeries Series;
+		bool										 HasMin = false;
+	};
+
+	const eastl::hash_map<uint16_t, zen::trace_detail::TraceModel::CounterDef>& Defs() const { return m_Defs; }
+	eastl::hash_map<uint16_t, EditableSeries>&									MutableSeriesMap() { return m_Series; }
+
+private:
+	uint32_t CycleToTimeUs(uint64_t Cycle) const
+	{
+		if (!m_Timing || m_Timing->Freq == 0)
+		{
+			return 0;
+		}
+		uint64_t Elapsed = (Cycle >= m_Timing->Base) ? (Cycle - m_Timing->Base) : 0;
+		return uint32_t(Elapsed * 1'000'000 / m_Timing->Freq);
+	}
+
+	static std::string DecodeAnsiName(const Array<uint8[]>& Data)
+	{
+		const uint8_t* P	= Data.get();
+		size_t		   Size = Data.get_size();
+		if (!P || Size == 0)
+		{
+			return {};
+		}
+		return std::string(reinterpret_cast<const char*>(P), Size);
+	}
+
+	void OnSpec(const Counters_Spec& Ev)
+	{
+		uint16_t Id = uint16_t(Ev.Id());
+		if (Id == 0)
+		{
+			return;
+		}
+		zen::trace_detail::TraceModel::CounterDef Def;
+		Def.Id			= Id;
+		Def.Type		= uint8_t(Ev.Type());
+		Def.DisplayHint = uint8_t(Ev.DisplayHint());
+		Def.Name		= DecodeAnsiName(Ev.Name());
+		if (Def.Name.empty())
+		{
+			Def.Name = fmt::format("counter_{}", Id);
+		}
+		m_Defs[Id] = std::move(Def);
+	}
+
+	EditableSeries& EnsureSeries(uint16_t Id, uint8_t Type)
+	{
+		auto It = m_Series.find(Id);
+		if (It == m_Series.end())
+		{
+			EditableSeries E;
+			E.Series.Id	  = Id;
+			E.Series.Type = Type;
+			It			  = m_Series.emplace(Id, std::move(E)).first;
+		}
+		return It->second;
+	}
+
+	void OnSetValueInt(const Counters_SetValueInt& Ev)
+	{
+		uint16_t Id = uint16_t(Ev.CounterId());
+		if (Id == 0)
+		{
+			return;
+		}
+		EditableSeries& E	   = EnsureSeries(Id, /*Int*/ 0);
+		double			Value  = double(int64_t(Ev.Value()));
+		uint32_t		TimeUs = CycleToTimeUs(Ev.Cycle());
+		E.Series.Samples.push_back({TimeUs, Value});
+		++E.Series.Count;
+		if (!E.HasMin || Value < E.Series.Min)
+		{
+			E.Series.Min = Value;
+			E.HasMin	 = true;
+		}
+		if (Value > E.Series.Max)
+		{
+			E.Series.Max = Value;
+		}
+	}
+
+	void OnSetValueFloat(const Counters_SetValueFloat& Ev)
+	{
+		uint16_t Id = uint16_t(Ev.CounterId());
+		if (Id == 0)
+		{
+			return;
+		}
+		EditableSeries& E	   = EnsureSeries(Id, /*Float*/ 1);
+		double			Value  = double(Ev.Value());
+		uint32_t		TimeUs = CycleToTimeUs(Ev.Cycle());
+		E.Series.Samples.push_back({TimeUs, Value});
+		++E.Series.Count;
+		if (!E.HasMin || Value < E.Series.Min)
+		{
+			E.Series.Min = Value;
+			E.HasMin	 = true;
+		}
+		if (Value > E.Series.Max)
+		{
+			E.Series.Max = Value;
+		}
+	}
+
+	const TraceTiming*													 m_Timing = nullptr;
+	eastl::hash_map<uint16_t, zen::trace_detail::TraceModel::CounterDef> m_Defs;
+	eastl::hash_map<uint16_t, EditableSeries>							 m_Series;
+};
+
+//////////////////////////////////////////////////////////////////////////////
 // Analyzers
 
 class CpuAnalyzer : public Analyzer
@@ -3165,6 +3317,7 @@ BuildTraceModel(const std::filesystem::path& FilePath, WorkerThreadPool& ThreadP
 	LogAnalyzer			LogAn(&Timing);
 	BookmarksAnalyzer	BookmarkAn(&Timing);
 	CsvProfilerAnalyzer CsvAn(&Timing);
+	CountersAnalyzer	CountersAn(&Timing);
 	AllocationAnalyzer	AllocAn(&Timing);
 	CallstackAnalyzer	CallstackAn;
 
@@ -3182,6 +3335,7 @@ BuildTraceModel(const std::filesystem::path& FilePath, WorkerThreadPool& ThreadP
 	Dispatch.add_analyzer(LogAn);
 	Dispatch.add_analyzer(BookmarkAn);
 	Dispatch.add_analyzer(CsvAn);
+	Dispatch.add_analyzer(CountersAn);
 	Dispatch.add_analyzer(AllocAn);
 	Dispatch.add_analyzer(CallstackAn);
 
@@ -3434,6 +3588,61 @@ BuildTraceModel(const std::filesystem::path& FilePath, WorkerThreadPool& ThreadP
 				 Model.CsvEvents.size());
 	}
 
+	// Counters (TRACE_INT_VALUE / TRACE_FLOAT_VALUE)
+	{
+		using CounterDefT	 = zen::trace_detail::TraceModel::CounterDef;
+		using CounterSeriesT = zen::trace_detail::TraceModel::CounterSeries;
+		using CounterSampleT = zen::trace_detail::TraceModel::CounterSample;
+
+		Model.CounterDefs.reserve(CountersAn.Defs().size());
+		for (const auto& [Id, Def] : CountersAn.Defs())
+		{
+			Model.CounterDefs.push_back(Def);
+		}
+
+		auto& SeriesMap = CountersAn.MutableSeriesMap();
+		Model.CounterTimeSeries.reserve(SeriesMap.size());
+		for (auto& [Id, Editable] : SeriesMap)
+		{
+			// Each counter's samples were appended in stream order. Tourist
+			// guarantees per-thread monotonicity but counters can be set from
+			// any thread, so a final sort by TimeUs is required.
+			eastl::sort(Editable.Series.Samples.begin(),
+						Editable.Series.Samples.end(),
+						[](const CounterSampleT& A, const CounterSampleT& B) { return A.TimeUs < B.TimeUs; });
+			// If the counter never produced a Spec event we still want the
+			// series visible. Synthesize a default def so the viewer has a name.
+			if (CountersAn.Defs().find(Id) == CountersAn.Defs().end())
+			{
+				CounterDefT Synth;
+				Synth.Id   = Id;
+				Synth.Type = Editable.Series.Type;
+				Synth.Name = fmt::format("counter_{}", Id);
+				Model.CounterDefs.push_back(std::move(Synth));
+			}
+			Model.CounterTimeSeries.push_back(std::move(Editable.Series));
+		}
+		eastl::sort(Model.CounterDefs.begin(), Model.CounterDefs.end(), [](const CounterDefT& A, const CounterDefT& B) {
+			return A.Id < B.Id;
+		});
+		eastl::sort(Model.CounterTimeSeries.begin(), Model.CounterTimeSeries.end(), [](const CounterSeriesT& A, const CounterSeriesT& B) {
+			return A.Id < B.Id;
+		});
+
+		size_t TotalSamples = 0;
+		for (const CounterSeriesT& S : Model.CounterTimeSeries)
+		{
+			TotalSamples += S.Samples.size();
+		}
+		if (!Model.CounterDefs.empty() || !Model.CounterTimeSeries.empty())
+		{
+			ZEN_INFO("Counters: {} defined, {} with samples ({} samples total)",
+					 Model.CounterDefs.size(),
+					 Model.CounterTimeSeries.size(),
+					 zen::ThousandsNum(TotalSamples));
+		}
+	}
+
 	// Memory allocation data
 	{
 		AllocAn.EmitFinalSample(Model.TraceEndUs);