Stop macOS agent updates from spawning BTM entries

Unsigned darwin release tarballs replaced the Developer ID
binary on each auto-update, so Background Task Management
treated every release as a new identity and showed the generic
executable icon. Sign those archives with a stable identifier,
refuse signature downgrades, and attribute daemon/tray jobs to
Probo Agent.app via AssociatedBundleIdentifiers.

Signed-off-by: Ludovic Vielle <ludovic@probo.com>

pkg/deviceagent/update/install_signature_darwin.go

@@ -0,0 +1,93 @@
+// Copyright (c) 2026 Probo Inc <hello@probo.com>.
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in
+// all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+//go:build darwin
+
+package update
+
+import (
+	"context"
+	"fmt"
+	"os/exec"
+	"strings"
+
+	"go.gearno.de/kit/log"
+)
+
+// ensureSignatureCompatible refuses an update that would replace a
+// Developer ID-signed agent with a binary that lacks the same Apple
+// Team ID and code-signing Identifier. A mismatch on either field
+// creates a fresh Background Task Management identity.
+//
+// Machines already running an unsigned (ad-hoc) binary are allowed to
+// upgrade so they can recover onto a signed release.
+func ensureSignatureCompatible(
+	ctx context.Context,
+	logger *log.Logger,
+	currentPath string,
+	candidatePath string,
+) error {
+	current, err := readCodeSigningIdentity(currentPath)
+	if err != nil {
+		return fmt.Errorf("cannot read current binary code signature: %w", err)
+	}
+
+	candidate, err := readCodeSigningIdentity(candidatePath)
+	if err != nil {
+		return fmt.Errorf("cannot read candidate binary code signature: %w", err)
+	}
+
+	if current.Team == "" {
+		logger.InfoCtx(
+			ctx,
+			"current agent binary has no Apple Team ID; allowing update",
+			log.String("candidate_team_id", candidate.Team),
+			log.String("candidate_identifier", candidate.Identifier),
+		)
+
+		return nil
+	}
+
+	return codeSigningIdentitiesCompatible(current, candidate)
+}
+
+func readCodeSigningIdentity(path string) (codeSigningIdentity, error) {
+	cmd := exec.Command("/usr/bin/codesign", "-d", "--verbose=4", path)
+	out, err := cmd.CombinedOutput()
+	output := string(out)
+
+	identity := parseCodeSigningIdentity(output)
+	if identity.Team != "" {
+		return identity, nil
+	}
+
+	// Unsigned and ad-hoc binaries exit non-zero and report no Team ID.
+	// Treat those as empty rather than failing the update path.
+	if err != nil && !isUnsignedCodesignOutput(output) {
+		return codeSigningIdentity{}, fmt.Errorf(
+			"codesign -d %s: %w: %s",
+			path,
+			err,
+			strings.TrimSpace(output),
+		)
+	}
+
+	return identity, nil
+}