proto: freeze the wire contract at 1.0.0

Schemas for the whole v1 surface: 38 methods, 9 events, 25 named types and the
JSON-RPC envelope, with x-privileged / x-transports / x-deadlineMs / x-errors
annotations that both generators emit as data rather than prose.

Four generators over one IR (contracts/codegen/schema_ir.py), so the C++ structs,
the TypeScript types and the OpenRPC document cannot disagree about what the
contract says:

  gen_cpp.py             -> core/generated/velox_proto.{hpp,cpp}
  gen_ts.py              -> extension/src/shared/protocol/
  gen_openrpc.py         -> contracts/openrpc.json
  gen_cpp_conformance.py -> tests/conformance/cpp/fixture_dispatcher.hpp

Inbound parsing never throws: parse<T>() returns std::expected<T, ParseError> and
nlohmann's throwing ADL from_json is deliberately not emitted. Schema constraints
(minimum, maxLength, pattern, ...) become real runtime checks in both languages —
the daemon does not trust the extension and the extension does not trust the
daemon.

59 golden fixtures: a success case per method, 12 error cases, 9 events. Replayed
by tests/conformance/ against both the generated C++ and a live server over both
transports. tools/mockd serves the same fixtures with unhappy-path flags so the
GUI and EXT lanes never wait for veloxd.

run.sh also proves capture.offer fails open: with a daemon answering slower than
750 ms the client gives up and lets Firefox take the download.

core/generated/ is libveloxproto, a separate target from libveloxcore, which
still never sees JSON — see docs/adr/0009.

Co-Authored-By: Claude Opus 5 <[email protected]>
Claude-Session: https://claude.ai/code/session_012fgjnqFCS5h5L7gZTZo3rV

contracts/fixtures/events/event.task.progress.json

@@ -0,0 +1,43 @@
+{
+  "name": "event.task.progress \u2014 one batched tick for two tasks",
+  "description": "A single array at no more than 4 Hz, never one notification per task. At twenty active downloads that is four messages a second instead of eighty.",
+  "notification": {
+    "jsonrpc": "2.0",
+    "method": "event.task.progress",
+    "params": {
+      "tasks": [
+        {
+          "taskId": "3f7a2b1c-5d6e-4f80-9a1b-2c3d4e5f6071",
+          "downloadedBytes": 2941190144,
+          "speedBps": 29796556,
+          "etaSeconds": 110,
+          "segments": [
+            {
+              "index": 0,
+              "downloadedBytes": 402653184,
+              "speedBps": 4089446
+            },
+            {
+              "index": 1,
+              "downloadedBytes": 356515840,
+              "speedBps": 3565158
+            }
+          ]
+        },
+        {
+          "taskId": "8c1d4e5f-6a7b-4c8d-9e0f-1a2b3c4d5e6f",
+          "downloadedBytes": 402653184,
+          "speedBps": 0,
+          "etaSeconds": null,
+          "segments": []
+        }
+      ],
+      "at": "$isoDate"
+    }
+  },
+  "assertions": [
+    "emitted at no more than 4 Hz regardless of how many tasks are active",
+    "clients apply a row patch; rebuilding the model on this event is a bug",
+    "a task with no segment detail still reports its byte counter"
+  ]
+}