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_identity.go

@@ -0,0 +1,106 @@
+// 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.
+
+package update
+
+import (
+	"fmt"
+	"strings"
+)
+
+// codeSigningIdentity is the Apple code-signing identity fields that
+// Background Task Management uses to key a background item.
+type codeSigningIdentity struct {
+	Team       string
+	Identifier string
+}
+
+// codeSigningIdentitiesCompatible refuses an update that would change
+// the BTM identity of a Developer ID-signed agent. Both Team ID and
+// signing Identifier must match. Machines already running an unsigned
+// (ad-hoc) binary are allowed to upgrade onto a signed release.
+func codeSigningIdentitiesCompatible(
+	current codeSigningIdentity,
+	candidate codeSigningIdentity,
+) error {
+	if current.Team == "" {
+		return nil
+	}
+
+	if candidate.Team == "" {
+		return fmt.Errorf(
+			"candidate binary has no Apple Team ID (current Team ID %s); refusing signature downgrade",
+			current.Team,
+		)
+	}
+
+	if candidate.Team != current.Team {
+		return fmt.Errorf(
+			"candidate Team ID %s does not match current Team ID %s",
+			candidate.Team,
+			current.Team,
+		)
+	}
+
+	if candidate.Identifier != current.Identifier {
+		return fmt.Errorf(
+			"candidate Identifier %q does not match current Identifier %q",
+			candidate.Identifier,
+			current.Identifier,
+		)
+	}
+
+	return nil
+}
+
+func parseCodeSigningIdentity(codesignOutput string) codeSigningIdentity {
+	return codeSigningIdentity{
+		Team:       parseCodesignField(codesignOutput, "TeamIdentifier="),
+		Identifier: parseCodesignField(codesignOutput, "Identifier="),
+	}
+}
+
+func parseCodesignField(codesignOutput string, prefix string) string {
+	for line := range strings.SplitSeq(codesignOutput, "\n") {
+		line = strings.TrimSpace(line)
+
+		after, ok := strings.CutPrefix(line, prefix)
+		if !ok {
+			continue
+		}
+
+		after = strings.TrimSpace(after)
+		if after == "" || after == "not set" {
+			return ""
+		}
+
+		return after
+	}
+
+	return ""
+}
+
+func isUnsignedCodesignOutput(output string) bool {
+	lower := strings.ToLower(output)
+
+	return strings.Contains(lower, "code object is not signed") ||
+		strings.Contains(lower, "not signed at all") ||
+		strings.Contains(lower, "teamidentifier=not set")
+}