Zen CLI common server interface (#920)

Introduces a common `ZenServiceClient` RAII wrapper for zen CLI commands that interact with a zenserver instance. CLI operations (admin, builds, cache, exec, hub, info, projectstore, trace, ui, version, vfs, workspaces) automatically register sessions so they become visible in the server's session list, and forward log output to the server's session log endpoint.

All session HTTP I/O (announce, remove, log batches) runs on a single background worker thread, so CLI startup and shutdown never block on server availability.

### Key changes

- **`ZenServiceClient`** — new RAII class that wraps host resolution, HTTP client creation, and session lifecycle (register on connect, remove on exit). Replaces ad-hoc boilerplate across all command files that talk to a server, including the new `trace` subcommands (`start`, `stop`, `status`).
- **Async session I/O** — `SessionsServiceClient` now owns a single worker thread and command queue. `Announce()`, `Remove()`, and `UpdateMetadata()` enqueue commands and return immediately. The worker creates one `HttpClient` with a 5-second total timeout, bounding any individual request. Eliminates main-thread stalls when the server is unreachable.
- **Session log forwarding** — `SessionLogSink` is a thin enqueuer that posts log messages to the same worker queue (no separate thread or HTTP client). Log levels are serialized as integers; the server-side ingest handles both string and integer formats for backwards compatibility, with bounds checking on integer values.
- **Build & projectstore session registration** — Long-running `builds` and projectstore cache (oplog-download) connections register sessions too, making them visible alongside regular CLI command sessions.

### Cleanup

- Extract `SetupCacheSession` helper on `StorageInstance` to reduce duplication.
- Remove unused `HttpClient` reference in ui command.

1 files changed, 27 insertions, 19 deletions

diff --git a/src/zen/cmds/cache_cmd.cpp b/src/zen/cmds/cache_cmd.cpp
index f024ea57e..b6f272ee7 100644
--- a/src/zen/cmds/cache_cmd.cpp
+++ b/src/zen/cmds/cache_cmd.cpp
@@ -2,6 +2,8 @@
 
 #include "cache_cmd.h"
 
+#include "zenserviceclient.h"
+
 #include <zencore/compactbinarybuilder.h>
 #include <zencore/compress.h>
 #include <zencore/except.h>
@@ -169,6 +171,8 @@ void
 CacheDropSubCmd::Run(const ZenCliOptions& /*GlobalOptions*/)
 {
 	ResolveHost();
+	ZenServiceClient Service({.HostSpec = m_HostName, .CommandName = "drop"});
+	HttpClient&		 Http = Service.Http();
 
 	if (m_NamespaceName.empty())
 	{
@@ -180,18 +184,16 @@ CacheDropSubCmd::Run(const ZenCliOptions& /*GlobalOptions*/)
 
 	if (m_BucketName.empty())
 	{
-		DropDescription = fmt::format("cache namespace '{}' from '{}'", m_NamespaceName, m_HostName);
+		DropDescription = fmt::format("cache namespace '{}' from '{}'", m_NamespaceName, Service.HostSpec());
 		Url				= fmt::format("/z$/{}", m_NamespaceName);
 	}
 	else
 	{
-		DropDescription = fmt::format("cache bucket '{}/{}' from '{}'", m_NamespaceName, m_BucketName, m_HostName);
+		DropDescription = fmt::format("cache bucket '{}/{}' from '{}'", m_NamespaceName, m_BucketName, Service.HostSpec());
 		Url				= fmt::format("/z$/{}/{}", m_NamespaceName, m_BucketName);
 	}
 
 	ZEN_CONSOLE("Dropping {}", DropDescription);
-
-	HttpClient Http = CacheCommand::CreateHttpClient(m_HostName);
 	if (HttpClient::Response Response = Http.Delete(Url))
 	{
 		ZEN_CONSOLE("{}", Response.ToText());
@@ -224,6 +226,8 @@ void
 CacheInfoSubCmd::Run(const ZenCliOptions& /*GlobalOptions*/)
 {
 	ResolveHost();
+	ZenServiceClient Service({.HostSpec = m_HostName, .CommandName = "info"});
+	HttpClient&		 Http = Service.Http();
 
 	std::string Url;
 	if (m_NamespaceName.empty())
@@ -236,7 +240,7 @@ CacheInfoSubCmd::Run(const ZenCliOptions& /*GlobalOptions*/)
 		{
 			throw OptionParseException("'--bucketsize' requires '--namespace' and '--bucket'", m_SubOptions.help());
 		}
-		ZEN_CONSOLE("Info on cache from '{}'", m_HostName);
+		ZEN_CONSOLE("Info on cache from '{}'", Service.HostSpec());
 		Url = "/z$";
 	}
 	else if (m_BucketName.empty())
@@ -246,7 +250,7 @@ CacheInfoSubCmd::Run(const ZenCliOptions& /*GlobalOptions*/)
 			throw OptionParseException(fmt::format("'--bucketsize' requires '--namespace' and '--bucket' ('{}')", m_BucketName),
 									   m_SubOptions.help());
 		}
-		ZEN_CONSOLE("Info on cache namespace '{}' from '{}'", m_NamespaceName, m_HostName);
+		ZEN_CONSOLE("Info on cache namespace '{}' from '{}'", m_NamespaceName, Service.HostSpec());
 		Url = fmt::format("/z$/{}", m_NamespaceName);
 	}
 	else
@@ -255,7 +259,7 @@ CacheInfoSubCmd::Run(const ZenCliOptions& /*GlobalOptions*/)
 		{
 			throw OptionParseException("'--bucketsizes' conflicts with '--bucket'", m_SubOptions.help());
 		}
-		ZEN_CONSOLE("Info on cache bucket '{}/{}' from '{}'", m_NamespaceName, m_BucketName, m_HostName);
+		ZEN_CONSOLE("Info on cache bucket '{}/{}' from '{}'", m_NamespaceName, m_BucketName, Service.HostSpec());
 		Url = fmt::format("/z$/{}/{}", m_NamespaceName, m_BucketName);
 	}
 
@@ -271,7 +275,6 @@ CacheInfoSubCmd::Run(const ZenCliOptions& /*GlobalOptions*/)
 
 	const ZenContentType AcceptType = m_YAML ? ZenContentType::kYAML : ZenContentType::kJSON;
 
-	HttpClient Http = CacheCommand::CreateHttpClient(m_HostName);
 	if (HttpClient::Response Response = Http.Get(Url, HttpClient::Accept(AcceptType), Parameters))
 	{
 		ZEN_CONSOLE("{}", Response.ToText());
@@ -294,10 +297,11 @@ void
 CacheStatsSubCmd::Run(const ZenCliOptions& /*GlobalOptions*/)
 {
 	ResolveHost();
+	ZenServiceClient Service({.HostSpec = m_HostName, .CommandName = "stats"});
+	HttpClient&		 Http = Service.Http();
 
 	const ZenContentType AcceptType = m_YAML ? ZenContentType::kYAML : ZenContentType::kJSON;
 
-	HttpClient Http = CacheCommand::CreateHttpClient(m_HostName);
 	if (HttpClient::Response Response = Http.Get("/stats/z$", HttpClient::Accept(AcceptType)))
 	{
 		ZEN_CONSOLE("{}", Response.ToText());
@@ -331,6 +335,8 @@ void
 CacheDetailsSubCmd::Run(const ZenCliOptions& /*GlobalOptions*/)
 {
 	ResolveHost();
+	ZenServiceClient Service({.HostSpec = m_HostName, .CommandName = "details"});
+	HttpClient&		 Http = Service.Http();
 
 	if (m_CSV && m_YAML)
 	{
@@ -387,7 +393,6 @@ CacheDetailsSubCmd::Run(const ZenCliOptions& /*GlobalOptions*/)
 		Url = "/z$/details$";
 	}
 
-	HttpClient Http = CacheCommand::CreateHttpClient(m_HostName);
 	if (HttpClient::Response Response = Http.Get(Url, Headers, Parameters))
 	{
 		ZEN_CONSOLE("{}", Response.ToText());
@@ -429,6 +434,8 @@ void
 CacheGenSubCmd::Run(const ZenCliOptions& /*GlobalOptions*/)
 {
 	ResolveHost();
+	ZenServiceClient Service({.HostSpec = m_HostName, .CommandName = "gen"});
+	HttpClient&		 Http = Service.Http();
 
 	if (m_MaxSize == 0 && m_MinSize == 0)
 	{
@@ -486,8 +493,6 @@ CacheGenSubCmd::Run(const ZenCliOptions& /*GlobalOptions*/)
 
 	std::uniform_int_distribution<uint64_t> KeyDistribution;
 
-	HttpClient Http = CacheCommand::CreateHttpClient(m_HostName);
-
 	auto GeneratePutCacheValueRequest(
 		[this, &KeyDistribution, &Generator](std::span<std::uint64_t> BatchSizes, uint64_t RequestIndex) -> CbPackage {
 			CbPackage Package;
@@ -663,7 +668,11 @@ CacheGetSubCmd::CacheGetSubCmd() : CacheSubCmdBase("get", "Get cache values/reco
 void
 CacheGetSubCmd::Run(const ZenCliOptions& /*GlobalOptions*/)
 {
+	using namespace std::literals;
+
 	ResolveHost();
+	ZenServiceClient Service({.HostSpec = m_HostName, .CommandName = "get"});
+	HttpClient&		 Http = Service.Http();
 
 	if (m_Namespace.empty())
 	{
@@ -695,8 +704,6 @@ CacheGetSubCmd::Run(const ZenCliOptions& /*GlobalOptions*/)
 		}
 	}
 
-	HttpClient Http = CacheCommand::CreateHttpClient(m_HostName);
-
 	if (!m_OutputPath.empty())
 	{
 		if (IsDir(m_OutputPath))
@@ -774,8 +781,8 @@ void
 CacheRecordSubCmd::Run(const ZenCliOptions& /*GlobalOptions*/)
 {
 	ResolveHost();
-
-	HttpClient Http = CacheCommand::CreateHttpClient(m_HostName);
+	ZenServiceClient Service({.HostSpec = m_HostName, .CommandName = "record"});
+	HttpClient&		 Http = Service.Http();
 
 	if (m_Path == "stop")
 	{
@@ -877,8 +884,6 @@ CacheReplaySubCmd::CacheReplaySubCmd() : CacheSubCmdBase("replay", "Replays a pr
 void
 CacheReplaySubCmd::Run(const ZenCliOptions& /*GlobalOptions*/)
 {
-	ResolveHost();
-
 	if (m_RecordingPath.empty())
 	{
 		throw OptionParseException("'--path' is required", m_SubOptions.help());
@@ -896,6 +901,9 @@ CacheReplaySubCmd::Run(const ZenCliOptions& /*GlobalOptions*/)
 
 	m_ThreadCount = Max(m_ThreadCount, 1);
 
+	ZenServiceClient Service({.HostSpec = m_HostName, .CommandName = "replay"});
+	m_HostName = Service.HostSpec();
+
 	ZEN_CONSOLE("Replay '{}' (start offset {}, stride {}) to '{}', {} threads",
 				m_RecordingPath,
 				m_Offset,
@@ -907,7 +915,7 @@ CacheReplaySubCmd::Run(const ZenCliOptions& /*GlobalOptions*/)
 
 	if (m_OnHost)
 	{
-		HttpClient Http = CacheCommand::CreateHttpClient(m_HostName);
+		HttpClient& Http = Service.Http();
 		if (HttpClient::Response Response =
 				Http.Post("/z$/exec$/replay-recording"sv,
 						  HttpClient::KeyValueMap{},