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/schema/methods/download.list.schema.json

@@ -0,0 +1,31 @@
+{
+  "$schema": "https://json-schema.org/draft/2020-12/schema",
+  "$id": "https://velox.dev/schema/methods/download.list.schema.json",
+  "title": "download.list",
+  "description": "The main table. Filtering, sorting and paging all happen in the daemon so the GUI never materializes 100k rows to show 40. Called once on connect; after that the table is maintained from events, never re-fetched on a progress tick.",
+  "x-privileged": false,
+  "x-transports": ["uds", "ws"],
+  "x-deadlineMs": 5000,
+  "type": "object",
+  "properties": {
+    "params": {
+      "type": "object",
+      "additionalProperties": false,
+      "properties": {
+        "filter": { "oneOf": [{ "$ref": "https://velox.dev/schema/types/TaskFilter.schema.json" }, { "type": "null" }] },
+        "sort":   { "oneOf": [{ "$ref": "https://velox.dev/schema/types/TaskSort.schema.json" }, { "type": "null" }] },
+        "offset": { "type": ["integer", "null"], "minimum": 0 },
+        "limit":  { "type": ["integer", "null"], "minimum": 1, "maximum": 5000, "description": "Defaults to 500. The GUI pages; the extension popup asks for far fewer." }
+      }
+    },
+    "result": {
+      "type": "object",
+      "additionalProperties": false,
+      "required": ["total", "items"],
+      "properties": {
+        "total": { "type": "integer", "minimum": 0, "description": "Rows matching the filter, ignoring offset and limit." },
+        "items": { "type": "array", "items": { "$ref": "https://velox.dev/schema/types/TaskSummary.schema.json" } }
+      }
+    }
+  }
+}