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, 113 insertions, 0 deletions

diff --git a/internal/ssh/ssh_test.go b/internal/ssh/ssh_test.go
new file mode 100644
index 0000000..f413145
--- /dev/null
+++ b/internal/ssh/ssh_test.go
@@ -0,0 +1,113 @@
+package ssh
+
+import (
+	"crypto/rand"
+	"crypto/rsa"
+	"encoding/pem"
+	"errors"
+	"os"
+	"path/filepath"
+	"testing"
+
+	gossh "golang.org/x/crypto/ssh"
+)
+
+func TestPrivateKeySignerLoadsUnencryptedKey(t *testing.T) {
+	keyFile := filepath.Join(t.TempDir(), "id_rsa")
+	privateKey, err := rsa.GenerateKey(rand.Reader, 1024)
+	if err != nil {
+		t.Fatalf("GenerateKey failed: %v", err)
+	}
+
+	if err := os.WriteFile(keyFile, EncodePrivateKeyToPEM(privateKey), 0o600); err != nil {
+		t.Fatalf("WriteFile failed: %v", err)
+	}
+
+	signer, err := PrivateKeySigner(keyFile)
+	if err != nil {
+		t.Fatalf("PrivateKeySigner failed: %v", err)
+	}
+	if signer == nil {
+		t.Fatalf("PrivateKeySigner returned nil signer")
+	}
+}
+
+func TestPrivateKeySignerLoadsEncryptedKeyWithEnvPassphrase(t *testing.T) {
+	keyFile := filepath.Join(t.TempDir(), "id_rsa")
+	privateKey, err := rsa.GenerateKey(rand.Reader, 1024)
+	if err != nil {
+		t.Fatalf("GenerateKey failed: %v", err)
+	}
+
+	block, err := gossh.MarshalPrivateKeyWithPassphrase(privateKey, "", []byte("secret-passphrase"))
+	if err != nil {
+		t.Fatalf("MarshalPrivateKeyWithPassphrase failed: %v", err)
+	}
+	if err := os.WriteFile(keyFile, pem.EncodeToMemory(block), 0o600); err != nil {
+		t.Fatalf("WriteFile failed: %v", err)
+	}
+
+	t.Setenv("DTAIL_KEY_PASSPHRASE", "secret-passphrase")
+
+	signer, err := PrivateKeySigner(keyFile)
+	if err != nil {
+		t.Fatalf("PrivateKeySigner failed: %v", err)
+	}
+	if signer == nil {
+		t.Fatalf("PrivateKeySigner returned nil signer")
+	}
+}
+
+func TestPrivateKeySignerReturnsPassphraseMissingWithoutEnv(t *testing.T) {
+	keyFile := filepath.Join(t.TempDir(), "id_rsa")
+	privateKey, err := rsa.GenerateKey(rand.Reader, 1024)
+	if err != nil {
+		t.Fatalf("GenerateKey failed: %v", err)
+	}
+
+	block, err := gossh.MarshalPrivateKeyWithPassphrase(privateKey, "", []byte("secret-passphrase"))
+	if err != nil {
+		t.Fatalf("MarshalPrivateKeyWithPassphrase failed: %v", err)
+	}
+	if err := os.WriteFile(keyFile, pem.EncodeToMemory(block), 0o600); err != nil {
+		t.Fatalf("WriteFile failed: %v", err)
+	}
+
+	_, err = PrivateKeySigner(keyFile)
+	if err == nil {
+		t.Fatalf("PrivateKeySigner succeeded without passphrase env")
+	}
+
+	var passphraseMissingErr *gossh.PassphraseMissingError
+	if !errors.As(err, &passphraseMissingErr) {
+		t.Fatalf("PrivateKeySigner returned %T, want PassphraseMissingError", err)
+	}
+}
+
+func TestPrivateKeySignerRejectsIncorrectEnvPassphrase(t *testing.T) {
+	keyFile := filepath.Join(t.TempDir(), "id_rsa")
+	privateKey, err := rsa.GenerateKey(rand.Reader, 1024)
+	if err != nil {
+		t.Fatalf("GenerateKey failed: %v", err)
+	}
+
+	block, err := gossh.MarshalPrivateKeyWithPassphrase(privateKey, "", []byte("secret-passphrase"))
+	if err != nil {
+		t.Fatalf("MarshalPrivateKeyWithPassphrase failed: %v", err)
+	}
+	if err := os.WriteFile(keyFile, pem.EncodeToMemory(block), 0o600); err != nil {
+		t.Fatalf("WriteFile failed: %v", err)
+	}
+
+	t.Setenv("DTAIL_KEY_PASSPHRASE", "wrong-passphrase")
+
+	_, err = PrivateKeySigner(keyFile)
+	if err == nil {
+		t.Fatalf("PrivateKeySigner succeeded with wrong passphrase env")
+	}
+
+	var passphraseMissingErr *gossh.PassphraseMissingError
+	if errors.As(err, &passphraseMissingErr) {
+		t.Fatalf("PrivateKeySigner returned PassphraseMissingError instead of parse failure")
+	}
+}