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/capture.getRules.json

@@ -0,0 +1,52 @@
+{
+  "name": "capture.getRules \u2014 the extension mirrors the daemon's policy",
+  "description": "Fetched on connect and whenever event.settings.changed names a capture.* key, so the two can never disagree about what should be intercepted.",
+  "request": {
+    "jsonrpc": "2.0",
+    "id": 60,
+    "method": "capture.getRules",
+    "params": {}
+  },
+  "response": {
+    "jsonrpc": "2.0",
+    "id": 60,
+    "result": {
+      "enabled": true,
+      "monitoredExtensions": [
+        "iso",
+        "zip",
+        "tar",
+        "gz",
+        "xz",
+        "7z",
+        "rar",
+        "deb",
+        "rpm",
+        "exe",
+        "msi",
+        "appimage",
+        "mkv",
+        "mp4",
+        "flac",
+        "pdf"
+      ],
+      "monitoredMimeTypes": [
+        "application/octet-stream",
+        "application/x-iso9660-image",
+        "application/zip",
+        "video/x-matroska"
+      ],
+      "minSizeBytes": 1048576,
+      "excludedHosts": [
+        "*.corp.internal",
+        "localhost"
+      ],
+      "bypassModifier": "alt",
+      "rulesVersion": 7
+    }
+  },
+  "assertions": [
+    "if this call fails the extension keeps its last known rules and stays fail-open",
+    "rulesVersion increases on every change so the extension knows when to re-fetch"
+  ]
+}