Exchange endpoint userPortfolioMargin, info endpoint exchangeStatus

[TuxedoFish]

Summary

• Adds exchangeStatus - a no-argument /info endpoint returning operational status (RestApi::exchangeStatus, WebsocketApi::exchangeStatus).
• Adds userPortfolioMargin - an EIP-712 user-signed /exchange action toggling portfolio margin mode (RestApi::userPortfolioMargin, WebsocketApi::userPortfolioMargin).
• Follows CONTRIBUTING.md's repeatable patterns for both endpoint kinds (request/response types, builder, parser, listener callbacks, RestApi/WebsocketApi methods, tests, README coverage tables, examples).

Closes #128
Closes #129

Verification notes - both endpoints now confirmed live

exchangeStatus: ran curl -X POST .../info -d '{"type":"exchangeStatus"}' against both api.hyperliquid-testnet.xyz and api.hyperliquid.xyz. Both returned the identical shape:

{"specialStatuses":null,"time":1788859210259}

specialStatuses was null in both captures. Its element shape when non-null is inferred, not confirmed - assumed to be an array of strings by analogy with every other "list of status/message" field in this API (e.g. ApprovedBuildersResponse). time is a raw (non-string-encoded) millisecond timestamp, parsed via get_uint64().

userPortfolioMargin: ran both directions live against testnet with a real signed request from this repo's test wallet:

action: {"type":"userPortfolioMargin","user":"0x6829Fdea522a6Fc3697311d2Ab93414BAd4b0C55","enabled":true,...}
response: status=err, error="Portfolio margin requires account value of $10000 or total volume of $5000000."

action: {"type":"userPortfolioMargin","user":"0x6829Fdea522a6Fc3697311d2Ab93414BAd4b0C55","enabled":false,...}
response: status=ok, type=default

The enabled=true request was accepted and parsed by the server, then rejected on a genuine business rule (this wallet's account value/volume) - not a schema error, confirming the EIP-712 action shape (type/user/enabled, HyperliquidTransaction:UserPortfolioMargin) is correct. The enabled=false request (disabling an already-disabled setting, a no-op) actually succeeded end-to-end - a full confirmed round trip, not just a business-rule rejection. tests/user_portfolio_margin_test.cpp's success/error fixtures now use these real captures instead of the TS-SDK-inferred ones (the success shape happened to already match exactly; the error message did not, and has been corrected to the real wording).

Test plan

• cmake -S . -B build -DHYPERLIQUID_WARNINGS_AS_ERRORS=ON -DHYPERLIQUID_BUILD_TESTS=ON -DHYPERLIQUID_BUILD_EXAMPLES=ON -DCMAKE_TOOLCHAIN_FILE="$VCPKG_ROOT/scripts/buildsystems/vcpkg.cmake" - clean configure
• cmake --build build -j"$(nproc)" - zero warnings/errors (warnings-as-errors on), examples included
• ctest --test-dir build - 100% pass, 29/29 test binaries
• Rebased onto latest main (post-Exchange endpoint: createSubAccount, subAccountTransfer #153/Info endpoints: userBorrowLendInterest, liquidatable #154/Info endpoints: twapHistory, userTwapSliceFillsByTime, activeAssetData #157) - README coverage counts and an example-file conflict resolved (both were "keep both" adjacent insertions, not real conflicts of intent), full clean rebuild/retest after rebasing
• Ran both endpoints live against testnet/mainnet with real signed requests (see "Verification notes" above)
• build/ removed before committing

🤖 Generated with Claude Code

https://claude.ai/code/session_018Le73N2EZjGLsCqmCScAse

[codecov]

Codecov Report

❌ Patch coverage is 79.57746% with 29 lines in your changes missing coverage. Please review.
✅ Project coverage is 70.17%. Comparing base (cec0144) to head (6ee2f81).

Files with missing lines	Patch %	Lines
src/rest/RestApi.cpp	0.00%	12 Missing ⚠️
src/websocket/WebsocketApi.cpp	0.00%	7 Missing ⚠️
src/rest/RestApiMessageParser.cpp	85.00%	3 Missing ⚠️
src/websocket/PostResponseDispatch.cpp	0.00%	3 Missing ⚠️
include/hyperliquid/types/RequestTypes.h	50.00%	2 Missing ⚠️
include/hyperliquid/rest/RestEndpointListener.h	0.00%	1 Missing ⚠️
...clude/hyperliquid/websocket/WebsocketApiListener.h	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #155      +/-   ##
==========================================
+ Coverage   70.02%   70.17%   +0.15%     
==========================================
  Files          53       54       +1     
  Lines        8640     8782     +142     
  Branches      533      534       +1     
==========================================
+ Hits         6050     6163     +113     
- Misses       2587     2616      +29     
  Partials        3        3              

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