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, 16 insertions, 3 deletions

diff --git a/internal/server/handlers/mapcommand.go b/internal/server/handlers/mapcommand.go
index 65e0ed8..bd83b46 100644
--- a/internal/server/handlers/mapcommand.go
+++ b/internal/server/handlers/mapcommand.go
@@ -4,6 +4,7 @@ import (
 	"context"
 	"strings"
 
+	"github.com/mimecast/dtail/internal/io/dlog"
 	"github.com/mimecast/dtail/internal/mapr/server"
 )
 
@@ -13,13 +14,25 @@ type mapCommand struct {
 	server    *ServerHandler
 }
 
-// NewMapCommand returns a new server side mapreduce command.
+// newMapCommand returns a new server side mapreduce command.
+//
+// The Aggregate is the one and only aggregate path for BOTH server mode and
+// serverless: an Aggregate is always built, and the read commands feed it
+// directly via AggregateProcessor (no aggregate line-channel). The former
+// regular server.Aggregate has been deleted (task hv0), so there is no
+// fallback branch.
 func newMapCommand(serverHandler *ServerHandler, argc int,
 	args []string) (mapCommand, *server.Aggregate, error) {
 
 	m := mapCommand{server: serverHandler}
 	queryStr := strings.Join(args[1:], " ")
-	aggregate, err := server.NewAggregate(queryStr)
+	defaultLogFormat := ""
+	if serverHandler.serverCfg != nil {
+		defaultLogFormat = serverHandler.serverCfg.MapreduceLogFormat
+	}
+
+	dlog.Server.Info("Creating turbo aggregate for MapReduce", "query", queryStr)
+	aggregate, err := server.NewAggregate(queryStr, defaultLogFormat)
 	if err != nil {
 		return m, nil, err
 	}
@@ -27,6 +40,6 @@ func newMapCommand(serverHandler *ServerHandler, argc int,
 	return m, aggregate, nil
 }
 
-func (m mapCommand) Start(ctx context.Context, aggregatedMessages chan<- string) {
+func (m *mapCommand) Start(ctx context.Context, aggregatedMessages chan<- string) {
 	m.aggregate.Start(ctx, aggregatedMessages)
 }