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, 81 insertions, 0 deletions

diff --git a/internal/mapr/client/session_state_test.go b/internal/mapr/client/session_state_test.go
new file mode 100644
index 0000000..f43ca70
--- /dev/null
+++ b/internal/mapr/client/session_state_test.go
@@ -0,0 +1,81 @@
+package client
+
+import (
+	"testing"
+
+	"github.com/mimecast/dtail/internal/mapr"
+)
+
+func TestSessionStateCommitQueryResetsGenerationAndResults(t *testing.T) {
+	query := mustSessionStateQuery(t, "select count(status) from stats group by status")
+	state := NewSessionState(query)
+
+	initial := state.Snapshot()
+	group := mapr.NewGroupSet()
+	set := group.GetSet("ERROR")
+	set.Samples = 1
+	set.FValues[query.Select[0].FieldStorage] = 1
+	if err := initial.GlobalGroup.Merge(query, group); err != nil {
+		t.Fatalf("Merge() error = %v", err)
+	}
+	if changed, ok := state.CommitRenderedResult(initial.Generation, "old-result"); !ok || !changed {
+		t.Fatalf("CommitRenderedResult() = changed:%v ok:%v, want changed and ok", changed, ok)
+	}
+
+	rawQuery := "select count(status) from warnings group by status"
+	updatedQuery, err := state.CommitQuery(rawQuery, 3)
+	if err != nil {
+		t.Fatalf("CommitQuery() error = %v", err)
+	}
+	if updatedQuery == nil || updatedQuery.RawQuery != rawQuery {
+		t.Fatalf("unexpected updated query: %#v", updatedQuery)
+	}
+
+	select {
+	case <-state.Changes():
+	default:
+		t.Fatalf("expected change notification after CommitQuery")
+	}
+
+	updated := state.Snapshot()
+	if updated.Generation != 3 {
+		t.Fatalf("generation = %d, want 3", updated.Generation)
+	}
+	if updated.Query == nil || updated.Query.RawQuery != rawQuery {
+		t.Fatalf("unexpected query after commit: %#v", updated.Query)
+	}
+	if !updated.GlobalGroup.IsEmpty() {
+		t.Fatalf("expected committed global group to be reset")
+	}
+	if updated.LastResult != "" {
+		t.Fatalf("last result = %q, want empty", updated.LastResult)
+	}
+}
+
+func TestSessionStateCommitQueryRejectsInvalidQuery(t *testing.T) {
+	query := mustSessionStateQuery(t, "select count(status) from stats group by status")
+	state := NewSessionState(query)
+	before := state.Snapshot()
+
+	if _, err := state.CommitQuery("select from", 5); err == nil {
+		t.Fatalf("expected CommitQuery() to reject invalid query")
+	}
+
+	after := state.Snapshot()
+	if after.Generation != before.Generation {
+		t.Fatalf("generation changed on invalid query: got %d want %d", after.Generation, before.Generation)
+	}
+	if after.Query == nil || after.Query.RawQuery != before.Query.RawQuery {
+		t.Fatalf("query changed on invalid query: before=%#v after=%#v", before.Query, after.Query)
+	}
+}
+
+func mustSessionStateQuery(t *testing.T, queryStr string) *mapr.Query {
+	t.Helper()
+
+	query, err := mapr.NewQuery(queryStr)
+	if err != nil {
+		t.Fatalf("NewQuery(%q) error = %v", queryStr, err)
+	}
+	return query
+}