betterbird: own Betterbird's whole configuration as settings, shown without a credential (hq issue 586, ADR 0329)

The module owned only the accounts' server fields, so identities, signatures,
calendars, address books, filters and tags could differ between desktop nodes
unseen, and the operator's own preferences were shipped in the catalogue.

prefs becomes one entry per preference (a node's layer overrides one key) and the
defaults file keeps no value of the operator's; identities, calendars,
address-books, filters and tags become settings, adopted like accounts, filters
owned whole per account, and what Betterbird rewrites written only while it is
closed. New tools list each kind, derive the layers from every desktop node and
propose one at a time, and show drift; every answer passes a credential check.

modules/betterbird/module.json

@@ -9,15 +9,11 @@
     "x11-display"
   ],
   "invokes": [
-    "seat:mesh-controller.settings"
+    "seat:mesh-controller.settings",
+    "seat:mesh-controller.nodes",
+    "seat:mesh-controller.node",
+    "betterbird.betterbird_derive"
   ],
-  "settings": {
-    "prefs": {
-      "kind": "preference",
-      "default": "// none",
-      "why": "Betterbird runs with its own defaults until a machine's assignment names a preference: one line of user_pref(\"name\", value); statements, which the module's user.js holds and Betterbird reads at its start (novox/hq issue 345). An account's preferences (mail.account., mail.identity., mail.server., mail.smtpserver. and the account lists) are refused here: an account is declared in the setting accounts, so it has one owner (novox/hq ADR 0316 §11)"
-    }
-  },
   "tools": [
     "betterbird_status",
     "betterbird_prefs",
@@ -28,6 +24,13 @@
     "betterbird_restart",
     "betterbird_check",
     "betterbird_accounts",
+    "betterbird_identities",
+    "betterbird_calendars",
+    "betterbird_address_books",
+    "betterbird_filters",
+    "betterbird_tags",
+    "betterbird_derive",
+    "betterbird_drift",
     "betterbird_reminder_test"
   ],
   "resources": [
@@ -39,12 +42,16 @@
       "mode": "0755"
     },
     {
-      "id": "user-js",
+      "id": "prefs",
       "type": "file",
-      "path": "${machine:account-home}/.config/betterbird/user.js",
+      "path": "${machine:account-home}/.config/betterbird/prefs.json",
       "owner": "${machine:account}",
       "mode": "0644",
-      "content": "// Betterbird's user.js (module betterbird, novox/hq issue 345). Owned by the mesh: the node-engine\n// writes it here at every push, and the module's tools copy it whole into Betterbird's profile\n// (betterbird_user_js with apply, betterbird_restart), where Betterbird reads it at its start and lets it\n// win over the preferences Betterbird saves itself. Change the module's setting prefs, never this file or the profile's copy.\n//\n// Only comments and user_pref(\"name\", value); statements; the tools refuse anything else, and any\n// preference whose name can hold a credential.\n${setting:prefs}\n",
+      "merge": "json",
+      "takes-settings": [
+        "prefs"
+      ],
+      "content": "{\n  \"prefs\": {}\n}\n",
       "trusted": true
     },
     {
@@ -60,6 +67,35 @@
       "content": "{\n  \"accounts\": {}\n}\n",
       "trusted": true
     },
+    {
+      "id": "configuration",
+      "type": "file",
+      "path": "${machine:account-home}/.config/betterbird/configuration.json",
+      "owner": "${machine:account}",
+      "mode": "0600",
+      "merge": "json",
+      "takes-settings": [
+        "identities",
+        "calendars",
+        "address-books",
+        "filters"
+      ],
+      "content": "{\n  \"identities\": {},\n  \"calendars\": {},\n  \"address-books\": {},\n  \"filters\": {}\n}\n",
+      "trusted": true
+    },
+    {
+      "id": "tags",
+      "type": "file",
+      "path": "${machine:account-home}/.config/betterbird/tags.json",
+      "owner": "${machine:account}",
+      "mode": "0644",
+      "merge": "json",
+      "takes-settings": [
+        "tags"
+      ],
+      "content": "{\n  \"tags\": {}\n}\n",
+      "trusted": false
+    },
     {
       "id": "community-package",
       "type": "package",
@@ -101,7 +137,7 @@
       "type": "file",
       "path": "/usr/local/bin/betterbird",
       "mode": "0755",
-      "content": "#!/bin/sh\n# Betterbird's start, written by the mesh (module betterbird, novox/hq ADR 0316). Replaced at every push.\n#\n# Before Betterbird starts, the module's tools place its user.js in the profile (the setting prefs, and the\n# accounts the setting accounts declares) and add the declared accounts to the profile's account list. They do\n# it only while no Betterbird of this account runs, because Betterbird rewrites its saved preferences when it quits; a\n# second start while one runs only hands over to it. What the preparation could not do it says here, and\n# betterbird_check says it too. Betterbird starts either way: its configuration never holds the mail back.\n/usr/local/lib/mesh-betterbird/betterbird-tools prepare || echo \"betterbird: the mesh's preparation did not complete; betterbird_check says why\" >&2\nexec /opt/betterbird/betterbird \"$@\"\n"
+      "content": "#!/bin/sh\n# Betterbird's start, written by the mesh (module betterbird, novox/hq ADR 0316). Replaced at every push.\n#\n# Before Betterbird starts, the module's tools place its user.js in the profile (the settings prefs, accounts, identities, calendars,\n# address-books and tags) and write what Betterbird rewrites itself: the account lists and each declared account's filters. They do\n# it only while no Betterbird of this account runs, because Betterbird rewrites its saved preferences when it quits; a\n# second start while one runs only hands over to it. What the preparation could not do it says here, and\n# betterbird_check says it too. Betterbird starts either way: its configuration never holds the mail back.\n/usr/local/lib/mesh-betterbird/betterbird-tools prepare || echo \"betterbird: the mesh's preparation did not complete; betterbird_check says why\" >&2\nexec /opt/betterbird/betterbird \"$@\"\n"
     },
     {
       "id": "launcher",