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, 6 insertions, 5 deletions

diff --git a/internal/mapr/globalgroupset.go b/internal/mapr/globalgroupset.go
index 2b12898..cbee303 100644
--- a/internal/mapr/globalgroupset.go
+++ b/internal/mapr/globalgroupset.go
@@ -33,12 +33,13 @@ func (g *GlobalGroupSet) Merge(query *Query, group *GroupSet) error {
 }
 
 // MergeNoblock merges (non-blocking) a group set into the global group set.
+// The semaphore is released via defer so it is always returned even if
+// g.merge panics, mirroring the guarantee provided by the blocking Merge.
 func (g *GlobalGroupSet) MergeNoblock(query *Query, group *GroupSet) (bool, error) {
 	select {
 	case g.semaphore <- struct{}{}:
-		err := g.merge(query, group)
-		<-g.semaphore
-		return true, err
+		defer func() { <-g.semaphore }()
+		return true, g.merge(query, group)
 	default:
 		return false, nil
 	}
@@ -86,8 +87,8 @@ func (g *GlobalGroupSet) WriteResult(query *Query, finalResult bool) error {
 }
 
 // Result returns the result of the mapreduce aggregation as a string.
-func (g *GlobalGroupSet) Result(query *Query, rowsLimit int) (string, int, error) {
+func (g *GlobalGroupSet) Result(query *Query, rowsLimit int, renderer ResultRenderer) (string, int, error) {
 	g.semaphore <- struct{}{}
 	defer func() { <-g.semaphore }()
-	return g.GroupSet.Result(query, rowsLimit)
+	return g.GroupSet.Result(query, rowsLimit, renderer)
 }