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, 15 insertions, 9 deletions

diff --git a/internal/clients/catclient.go b/internal/clients/catclient.go
index bd65560..e2e247e 100644
--- a/internal/clients/catclient.go
+++ b/internal/clients/catclient.go
@@ -2,9 +2,7 @@ package clients
 
 import (
 	"errors"
-	"fmt"
 	"runtime"
-	"strings"
 
 	"github.com/mimecast/dtail/internal/clients/handlers"
 	"github.com/mimecast/dtail/internal/config"
@@ -26,14 +24,18 @@ func NewCatClient(args config.Args) (*CatClient, error) {
 
 	c := CatClient{
 		baseClient: baseClient{
+			mu:         newBaseClientMu(),
 			Args:       args,
 			throttleCh: make(chan struct{}, args.ConnectionsPerCPU*runtime.NumCPU()),
 			retry:      false,
+			runtime:    newClientRuntimeBoundary(config.CurrentRuntime()),
 		},
 	}
 
 	c.init()
-	c.makeConnections(c)
+	if err := c.makeConnections(c); err != nil {
+		return nil, err
+	}
 	return &c, nil
 }
 
@@ -41,14 +43,18 @@ func (c CatClient) makeHandler(server string) handlers.Handler {
 	return handlers.NewClientHandler(server)
 }
 
+func (c CatClient) makeSessionSpec() (SessionSpec, error) {
+	return NewSessionSpec(c.Args), nil
+}
+
 func (c CatClient) makeCommands() (commands []string) {
-	regex, err := c.Regex.Serialize()
+	sessionSpec, err := c.makeSessionSpec()
 	if err != nil {
-		dlog.Client.FatalPanic(err)
+		dlog.Client.FatalPanic("unable to build cat session spec", err)
 	}
-	for _, file := range strings.Split(c.What, ",") {
-		commands = append(commands, fmt.Sprintf("%s:%s %s %s",
-			c.Mode.String(), c.Args.SerializeOptions(), file, regex))
+	commands, err = sessionSpec.Commands()
+	if err != nil {
+		dlog.Client.FatalPanic("unable to build cat commands from session spec", err)
 	}
-	return
+	return commands
 }