feat(base,app,keys): keys of shared spaces, sealed to each member

Step 3 of ADR 0044 (D3, D18, D19). A shared space's data keys are
sealed on a device to each member's public keys; the instance keeps
what devices sealed and never opens it.

- halkyon_keys: the safety code of two accounts' public keys
  (`safetyCode`), 60 digits, the same on both sides.
- halkyon_base: the register hands out accounts' public keys
  (`public-keys-of`, local and remote); the table `shared_space_key`
  and the endpoint `sharedSpaceKeys` (memberKeys, keysNeeded, seal,
  mine). Only the Owner and Editors seal, the first key sealed to a
  member stays, and a member's keys go with their membership. Every
  host's migration creates the table.
- halkyon_app: `ContentCipher` seals a key to another account and
  opens one sealed by another; `SharedKeys` shares a space's key with
  its members, seals keys to newcomers and opens the person's own,
  holding each member to the public keys `KeyPins` pinned on first
  sight (`key_pins.json` in the person's folder), a change refused
  until trusted anew.

Learn takes them into its `Privacy` in step 4.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Signed-off-by: Tizian 「ティツィアーン」 <raisondetredev@pm.me>

apps/learn/halkyon_learn_server/migrations/20261111100124819-shared-space-keys/migration.json

@@ -0,0 +1,134 @@
+{
+  "__className__": "serverpod.DatabaseMigration",
+  "actions": [
+    {
+      "__className__": "serverpod.DatabaseMigrationAction",
+      "type": "createTable",
+      "createTable": {
+        "__className__": "serverpod.TableDefinition",
+        "name": "shared_space_key",
+        "dartName": "SharedSpaceKey",
+        "module": "halkyon_base",
+        "schema": "public",
+        "columns": [
+          {
+            "__className__": "serverpod.ColumnDefinition",
+            "name": "id",
+            "fieldName": "id",
+            "columnType": 7,
+            "isNullable": false,
+            "columnDefault": "random_v7",
+            "dartType": "UuidValue?"
+          },
+          {
+            "__className__": "serverpod.ColumnDefinition",
+            "name": "sharedSpaceId",
+            "fieldName": "sharedSpaceId",
+            "columnType": 7,
+            "isNullable": false,
+            "dartType": "UuidValue"
+          },
+          {
+            "__className__": "serverpod.ColumnDefinition",
+            "name": "keyId",
+            "fieldName": "keyId",
+            "columnType": 0,
+            "isNullable": false,
+            "dartType": "String"
+          },
+          {
+            "__className__": "serverpod.ColumnDefinition",
+            "name": "recipientId",
+            "fieldName": "recipientId",
+            "columnType": 7,
+            "isNullable": false,
+            "dartType": "UuidValue"
+          },
+          {
+            "__className__": "serverpod.ColumnDefinition",
+            "name": "sealedKey",
+            "fieldName": "sealedKey",
+            "columnType": 5,
+            "isNullable": false,
+            "dartType": "dart:typed_data:ByteData"
+          },
+          {
+            "__className__": "serverpod.ColumnDefinition",
+            "name": "sealedBy",
+            "fieldName": "sealedBy",
+            "columnType": 7,
+            "isNullable": false,
+            "dartType": "UuidValue"
+          },
+          {
+            "__className__": "serverpod.ColumnDefinition",
+            "name": "createdAt",
+            "fieldName": "createdAt",
+            "columnType": 4,
+            "isNullable": false,
+            "dartType": "DateTime"
+          }
+        ],
+        "foreignKeys": [
+          {
+            "__className__": "serverpod.ForeignKeyDefinition",
+            "constraintName": "shared_space_key_fk_0",
+            "columns": [
+              "sharedSpaceId"
+            ],
+            "referenceTable": "shared_space",
+            "referenceTableSchema": "public",
+            "referenceColumns": [
+              "id"
+            ],
+            "onUpdate": 3,
+            "onDelete": 4
+          }
+        ],
+        "indexes": [
+          {
+            "__className__": "serverpod.IndexDefinition",
+            "indexName": "shared_space_key_unique_idx",
+            "elements": [
+              {
+                "__className__": "serverpod.IndexElementDefinition",
+                "type": 0,
+                "definition": "sharedSpaceId"
+              },
+              {
+                "__className__": "serverpod.IndexElementDefinition",
+                "type": 0,
+                "definition": "keyId"
+              },
+              {
+                "__className__": "serverpod.IndexElementDefinition",
+                "type": 0,
+                "definition": "recipientId"
+              }
+            ],
+            "type": "btree",
+            "isUnique": true,
+            "isPrimary": false
+          },
+          {
+            "__className__": "serverpod.IndexDefinition",
+            "indexName": "shared_space_key_recipient_idx",
+            "elements": [
+              {
+                "__className__": "serverpod.IndexElementDefinition",
+                "type": 0,
+                "definition": "recipientId"
+              }
+            ],
+            "type": "btree",
+            "isUnique": false,
+            "isPrimary": false
+          }
+        ],
+        "managed": true
+      }
+    }
+  ],
+  "warnings": [],
+  "migrationApiVersion": 1
+}

apps/learn/halkyon_learn_server/migrations/20261111100124819-shared-space-keys/migration.sql

@@ -0,0 +1,117 @@
+BEGIN;
+
+--
+-- Function: gen_random_uuid_v7()
+-- Source: https://gist.github.com/kjmph/5bd772b2c2df145aa645b837da7eca74
+-- License: MIT (copyright notice included on the generator source code).
+--
+create or replace function gen_random_uuid_v7()
+returns uuid
+as $$
+begin
+  -- use random v4 uuid as starting point (which has the same variant we need)
+  -- then overlay timestamp
+  -- then set version 7 by flipping the 2 and 1 bit in the version 4 string
+  return encode(
+    set_bit(
+      set_bit(
+        overlay(uuid_send(gen_random_uuid())
+                placing substring(int8send(floor(extract(epoch from clock_timestamp()) * 1000)::bigint) from 3)
+                from 1 for 6
+        ),
+        52, 1
+      ),
+      53, 1
+    ),
+    'hex')::uuid;
+end
+$$
+language plpgsql
+volatile;
+
+--
+-- ACTION CREATE TABLE
+--
+CREATE TABLE "shared_space_key" (
+    "id" uuid PRIMARY KEY DEFAULT gen_random_uuid_v7(),
+    "sharedSpaceId" uuid NOT NULL,
+    "keyId" text NOT NULL,
+    "recipientId" uuid NOT NULL,
+    "sealedKey" bytea NOT NULL,
+    "sealedBy" uuid NOT NULL,
+    "createdAt" timestamp without time zone NOT NULL
+);
+
+-- Indexes
+CREATE UNIQUE INDEX "shared_space_key_unique_idx" ON "shared_space_key" USING btree ("sharedSpaceId", "keyId", "recipientId");
+CREATE INDEX "shared_space_key_recipient_idx" ON "shared_space_key" USING btree ("recipientId");
+
+--
+-- ACTION CREATE FOREIGN KEY
+--
+ALTER TABLE ONLY "shared_space_key"
+    ADD CONSTRAINT "shared_space_key_fk_0"
+    FOREIGN KEY("sharedSpaceId")
+    REFERENCES "shared_space"("id")
+    ON DELETE CASCADE
+    ON UPDATE NO ACTION;
+
+
+--
+-- MIGRATION VERSION FOR halkyon_learn
+--
+INSERT INTO "serverpod_migrations" ("module", "version", "timestamp")
+    VALUES ('halkyon_learn', '20261111100124819-shared-space-keys', now())
+    ON CONFLICT ("module")
+    DO UPDATE SET "version" = '20261111100124819-shared-space-keys', "timestamp" = now();
+
+--
+-- MIGRATION VERSION FOR halkyon_base
+--
+INSERT INTO "serverpod_migrations" ("module", "version", "timestamp")
+    VALUES ('halkyon_base', '20261111100053843-shared-space-keys', now())
+    ON CONFLICT ("module")
+    DO UPDATE SET "version" = '20261111100053843-shared-space-keys', "timestamp" = now();
+
+--
+-- MIGRATION VERSION FOR serverpod
+--
+INSERT INTO "serverpod_migrations" ("module", "version", "timestamp")
+    VALUES ('serverpod', '20260824182259319', now())
+    ON CONFLICT ("module")
+    DO UPDATE SET "version" = '20260824182259319', "timestamp" = now();
+
+--
+-- MIGRATION VERSION FOR serverpod_auth_idp
+--
+INSERT INTO "serverpod_migrations" ("module", "version", "timestamp")
+    VALUES ('serverpod_auth_idp', '20260924105404509', now())
+    ON CONFLICT ("module")
+    DO UPDATE SET "version" = '20260924105404509', "timestamp" = now();
+
+--
+-- MIGRATION VERSION FOR serverpod_offline_sync
+--
+INSERT INTO "serverpod_migrations" ("module", "version", "timestamp")
+    VALUES ('serverpod_offline_sync', '20260914143806119', now())
+    ON CONFLICT ("module")
+    DO UPDATE SET "version" = '20260914143806119', "timestamp" = now();
+
+--
+-- MIGRATION VERSION FOR halkyon_oidc
+--
+INSERT INTO "serverpod_migrations" ("module", "version", "timestamp")
+    VALUES ('halkyon_oidc', '20261023180644988', now())
+    ON CONFLICT ("module")
+    DO UPDATE SET "version" = '20261023180644988', "timestamp" = now();
+
+--
+-- MIGRATION VERSION FOR serverpod_auth_core
+--
+INSERT INTO "serverpod_migrations" ("module", "version", "timestamp")
+    VALUES ('serverpod_auth_core', '20260924105232991', now())
+    ON CONFLICT ("module")
+    DO UPDATE SET "version" = '20260924105232991', "timestamp" = now();
+
+
+COMMIT;

apps/learn/halkyon_learn_server/migrations/migration_registry.txt

@@ -54,3 +54,4 @@
 20261026140329810-assistant-budgets
 20261110225358224-file-store-in-halkyon-base
 20261111091720823-shared-spaces
+20261111100124819-shared-space-keys