feat: DTail fork — server/client feature development

Squashed development of the snonux/dtail fork's product code (internal/, cmd/)
since diverging from mimecast/dtail. Major areas:

- Read/output path: the former "turbo" channel-less path is now the single,
  default server-side read/output path for cat/grep/tail and MapReduce; the old
  channel-based path and its config/env toggles were removed.
- MapReduce: single aggregate implementation (server + serverless) fed directly
  by a processor pipeline, with input-exhausted finalization via the shutdown
  coordinator; high-concurrency and data-race fixes.
- Journal source reads (journal:unit.service) via journalctl, Linux-gated behind
  a journal-v1 capability.
- Auth-key fast reconnect: in-memory per-user public-key cache with TTL/max-keys,
  registered over an authenticated session (AUTHKEY), checked before
  authorized_keys.
- Interactive query reload (--interactive-query) with SESSION START/UPDATE
  generation boundaries and capability negotiation.
- Client-side deadlines: --timeout / --shutdownAfter as context deadlines;
  follow shutdown handling.
- Client logging: diagnostics-only daily log by default, opt-in payload tee via
  --log-payload.
- Numerous correctness fixes (buffer-pool double-recycle races, EOF-sentinel
  leaks, glob-expansion cap, TOCTOU in CSV parsing) with accompanying unit tests.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

1 files changed, 104 insertions, 0 deletions

diff --git a/internal/cli/runtime.go b/internal/cli/runtime.go
new file mode 100644
index 0000000..950ed33
--- /dev/null
+++ b/internal/cli/runtime.go
@@ -0,0 +1,104 @@
+package cli
+
+import (
+	"context"
+	"sync"
+	"time"
+
+	"github.com/mimecast/dtail/internal/io/dlog"
+	"github.com/mimecast/dtail/internal/profiling"
+	"github.com/mimecast/dtail/internal/source"
+)
+
+// ClientRuntime owns common client command runtime components.
+type ClientRuntime struct {
+	ctx            context.Context
+	cancel         context.CancelFunc
+	wg             sync.WaitGroup
+	pprofServer    *PProfServer
+	profiler       *profiling.Profiler
+	profileEnabled bool
+}
+
+// NewClientRuntime starts logging and profiling for a client command.
+func NewClientRuntime(parent context.Context, profileFlags profiling.Flags, profileName string) *ClientRuntime {
+	if parent == nil {
+		parent = context.Background()
+	}
+	ctx, cancel := context.WithCancel(parent)
+	runtime := &ClientRuntime{
+		ctx:            ctx,
+		cancel:         cancel,
+		profiler:       profiling.NewProfiler(profileFlags.ToConfig(profileName)),
+		profileEnabled: profileFlags.Enabled(),
+	}
+
+	runtime.wg.Add(1)
+	dlog.Start(ctx, &runtime.wg, source.Client)
+	return runtime
+}
+
+// Context returns the runtime context.
+func (r *ClientRuntime) Context() context.Context {
+	return r.ctx
+}
+
+// Cancel cancels the runtime context.
+func (r *ClientRuntime) Cancel() {
+	r.cancel()
+}
+
+// StartPProf starts the pprof server if an address is provided.
+func (r *ClientRuntime) StartPProf(address string) {
+	if address == "" {
+		return
+	}
+
+	r.stopPProf()
+
+	server, err := NewPProfServer(address)
+	if err != nil {
+		dlog.Client.Error("Unable to start PProf", err)
+		return
+	}
+
+	r.pprofServer = server
+	dlog.Client.Info("Starting PProf", server.Address())
+	server.Start(&r.wg)
+}
+
+// LogStartupMetrics logs startup profiling metrics when enabled.
+func (r *ClientRuntime) LogStartupMetrics() {
+	if r.profileEnabled {
+		r.profiler.LogMetrics("startup")
+	}
+}
+
+// LogShutdownMetrics logs shutdown profiling metrics when enabled.
+func (r *ClientRuntime) LogShutdownMetrics() {
+	if r.profileEnabled {
+		r.profiler.LogMetrics("shutdown")
+	}
+}
+
+// Stop stops profiling and logging runtime goroutines.
+func (r *ClientRuntime) Stop() {
+	r.profiler.Stop()
+	r.stopPProf()
+	r.cancel()
+	r.wg.Wait()
+}
+
+func (r *ClientRuntime) stopPProf() {
+	if r.pprofServer == nil {
+		return
+	}
+
+	ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
+	defer cancel()
+
+	if err := r.pprofServer.Shutdown(ctx); err != nil {
+		dlog.Client.Error("Unable to stop PProf", err)
+	}
+	r.pprofServer = nil
+}