[feat](alarm): hash client identifiers in stdout request logs

A request log should not name a client directly, and the durable event log deliberately has no network columns. Hash the IP and user agent with internal/loghash for the stdout line; empty values stay empty rather than logging a constant digest. This is record anonymisation, not cryptographic protection, and the package says so.

src/internal/loghash/loghash.go

@@ -0,0 +1,38 @@
+// Copyright (C) 2026 Dcntrlized
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published
+// by the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+// Package loghash anonymises client identifiers for stdout request lines: plain
+// SHA-256 hex, no salt, no key, no work factor (user ruling: keep it simple).
+//
+// Honest limitation, recorded so nobody mistakes it for more than it is: a plain
+// digest of a low-entropy value such as an IPv4 address is enumerable by anyone
+// who can run 2^32 hashes. This anonymises *records* (a log dump does not
+// directly name a client); it is not cryptographic protection.
+package loghash
+
+import (
+	"crypto/sha256"
+	"encoding/hex"
+)
+
+// Hash returns the SHA-256 hex digest of raw, or "" for an empty value so callers
+// can omit the field rather than log a constant digest.
+func Hash(raw string) string {
+	if raw == "" {
+		return ""
+	}
+	sum := sha256.Sum256([]byte(raw))
+	return hex.EncodeToString(sum[:])
+}

src/internal/loghash/loghash_test.go

@@ -0,0 +1,34 @@
+// Copyright (C) 2026 Dcntrlized
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published
+// by the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+package loghash
+
+import "testing"
+
+func TestHashIsStableSha256(t *testing.T) {
+	got := Hash("192.0.2.10")
+	if len(got) != 64 {
+		t.Fatalf("digest length = %d, want 64 hex chars", len(got))
+	}
+	if got != Hash("192.0.2.10") {
+		t.Fatal("hash is not stable")
+	}
+	if Hash("192.0.2.11") == got {
+		t.Fatal("different addresses collided")
+	}
+	if Hash("") != "" {
+		t.Fatal("empty identifier should map to empty")
+	}
+}

src/logger/logger.go

@@ -157,7 +157,8 @@ func Warn(format string, v ...any) {
 func Error(format string, v ...any) {
 	once.Do(initLogger)
 	file, line := callSite()
-	errorLogger.Output(0, fmt.Sprintf("%s:%d: %s", filepath.Base(file), line, fmt.Sprintf(format, v...)))
+	msg := fmt.Sprintf(format, v...)
+	errorLogger.Output(0, fmt.Sprintf("%s:%d: %s", filepath.Base(file), line, msg))
 }
 
 // Debug accepts a format string and an optional, arbitrary number of arguments.

src/middleware/logger.go

@@ -17,11 +17,13 @@ package middleware
 
 import (
 	"bufio"
+	"fmt"
 	"net"
 	"net/http"
 	"strings"
 	"time"
 
+	"git.dcntrlized.org/Dcntrlized/Alarm/internal/loghash"
 	"git.dcntrlized.org/Dcntrlized/Alarm/logger"
 )
 
@@ -49,19 +51,31 @@ func LoggingMiddleware(next http.Handler) http.Handler {
 		rec := &statusRecorder{ResponseWriter: w, status: http.StatusOK}
 		next.ServeHTTP(rec, r)
 
-		logger.Info("%s request=%s %s path=%s status=%d ua=%q ip=%s duration=%s",
+		// Identifiers are not written in the clear on stdout: IP and user agent
+		// go through plain SHA-256 (internal/loghash). They never reach durable
+		// storage at all — the event_log table has no network columns.
+		ipHash, uaHash := hashClient(ip, r.UserAgent())
+		line := fmt.Sprintf("%s request=%s %s path=%s status=%d ua=%s ip=%s duration=%s",
 			time.Now().Format(time.RFC3339),
 			r.Method,
 			r.Proto,
 			r.URL.Path,
 			rec.status,
-			r.UserAgent(),
+			uaHash,
-			ip,
+			ipHash,
 			time.Since(start),
 		)
+		logger.Info("%s", line)
 	})
 }
 
+// hashClient anonymises request identifiers for stdout. The durable event log
+// never stores network identifiers at all; this is only so a stdout request line
+// does not name a client directly.
+func hashClient(ip, ua string) (ipHash, uaHash string) {
+	return loghash.Hash(ip), loghash.Hash(ua)
+}
+
 // statusRecorder captures the response status without altering the response.
 // It preserves http.Hijacker so the /ws/alarm upgrade still works when the
 // route is mounted behind this middleware.