betterbird: lock the ask to be the default mail client off, so it never shows at a start (hq issue 345)

Betterbird's own default asks at every start with a window to become the default for mail, news, feeds and
calendar files. The policy locks mail.shell.checkDefaultClient off, which wins over a profile's own value, and
betterbird_check says when a node would still ask.

modules/betterbird/cmd/betterbird-tools/install.go

@@ -30,6 +30,10 @@ const (
 	// owlFile is Owl's xpi as the mesh placed it, and the URL the policy installs it from.
 	owlFile = installDir + "/owl/owl.xpi"
 	owlID   = "owl@beonex.com"
+	// defaultClientPref is Betterbird's ask at its start to be the default mail, news, feed and calendar
+	// client (Thunderbird's all-thunderbird.js: pref("mail.shell.checkDefaultClient", true); messenger.js opens
+	// systemIntegrationDialog.xhtml while it is true). The module's policy locks it off (novox/hq issue 345).
+	defaultClientPref = "mail.shell.checkDefaultClient"
 	// preparation is the tools' program as the module places it for its start (betterbird-tools prepare).
 	preparation = "/usr/local/lib/mesh-betterbird/betterbird-tools"
 	// versionsURL is where Betterbird publishes its newest build per major version: what its own updater
@@ -167,7 +171,8 @@ func (m *Machine) policyState() string {
 	if why := policyProblem(raw); why != "" {
 		return "placed, and " + why
 	}
-	return "placed: Betterbird's updater off, Owl installed into every profile from the mesh's xpi, its updates off"
+	return "placed: Betterbird's updater off, Owl installed into every profile from the mesh's xpi, its updates off, " +
+		"and the ask to be the default mail client locked off"
 }
 
 // policyProblem is what the policy fails to say of what ADR 0316 asks, or "".
@@ -180,6 +185,10 @@ func policyProblem(raw []byte) string {
 				URL      string `json:"install_url"`
 				Disabled bool   `json:"updates_disabled"`
 			} `json:"ExtensionSettings"`
+			Preferences map[string]struct {
+				Value  any    `json:"Value"`
+				Status string `json:"Status"`
+			} `json:"Preferences"`
 		} `json:"policies"`
 	}
 	if err := json.Unmarshal(raw, &p); err != nil {
@@ -196,9 +205,37 @@ func policyProblem(raw []byte) string {
 	case !owl.Disabled:
 		return "it leaves Owl's updates on"
 	}
+	if pr, ok := p.Policies.Preferences[defaultClientPref]; !ok || pr.Value != false || pr.Status != "locked" {
+		return "it does not lock Betterbird's ask to be the default mail client off (Preferences " + defaultClientPref + ": false, locked)"
+	}
 	return ""
 }
 
+// defaultClientAsk says why Betterbird asks at its start to be the default mail client, or "" when it does
+// not: the module's policy locks the ask off, else the profile's user.js (which wins at the start) or prefs.js
+// turns it off. Betterbird's own default is to ask.
+func (m *Machine) defaultClientAsk(profile string) string {
+	raw, err := readBounded(m.path(policyFile))
+	if err == nil && !strings.Contains(policyProblem(raw), defaultClientPref) {
+		return ""
+	}
+	if profile != "" {
+		for _, f := range []string{"user.js", "prefs.js"} {
+			b, err := readBounded(filepath.Join(profile, f))
+			if err != nil {
+				continue
+			}
+			if v, ok := readPrefs(b)[defaultClientPref]; ok {
+				if v == "false" {
+					return ""
+				}
+				return "the profile's " + f + " sets " + defaultClientPref + " to " + v + " and no policy locks it off"
+			}
+		}
+	}
+	return "no policy locks " + defaultClientPref + " off and Betterbird's default is to ask"
+}
+
 // xpiVersion is the version an add-on's manifest.json says, or "" when it cannot be read.
 func xpiVersion(path string) string {
 	r, err := zip.OpenReader(path)