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, 14 insertions, 1 deletions

diff --git a/internal/discovery/comma.go b/internal/discovery/comma.go
index 9bea89c..126cbec 100644
--- a/internal/discovery/comma.go
+++ b/internal/discovery/comma.go
@@ -9,5 +9,18 @@ import (
 // ServerListFromCOMMA retrieves a list of servers from comma separated input list.
 func (d *Discovery) ServerListFromCOMMA() []string {
 	dlog.Common.Debug("Retrieving server list from comma separated list", d.server)
-	return strings.Split(d.server, ",")
+
+	rawServers := strings.Split(d.server, ",")
+	servers := make([]string, 0, len(rawServers))
+	for _, server := range rawServers {
+		if server == "" {
+			continue
+		}
+		servers = append(servers, server)
+	}
+	if len(servers) == 0 && d.server == "" {
+		return rawServers
+	}
+
+	return servers
 }