[zuudevs]

Summary

Implements the v0.6 roadmap milestone: single-slot HTTP/1.1 connection reuse for the stateful Client.

Behavior

• retain one eligible TCP connection inside Client
• reuse only for the same effective host + port
• skip DNS resolution and TCP connect when reuse is valid
• close the retained connection before switching origin
• retain only fully framed responses that the parser marks reusable
• never retain connections with parser pending bytes
• honor response Connection: close
• never reuse close-delimited responses or protocol upgrades
• honor request Connection: close
• discard the connection after write/read/protocol failure
• preserve zero-copy request-body transmission

Ownership design

The public Client remains no-PImpl. Reusable connection state is stored inline as an opaque std::uintptr_t socket token plus owned host/port identity; native Winsock/POSIX socket types remain internal. During request execution the token is adopted back into the existing RAII TcpConnection, and an eligible live handle is released back into the Client slot only after the response is complete.

Client is now explicitly move-only, matching its resource-owning semantics.

Stale keep-alive policy

This PR does not add automatic retries. If a peer has closed an apparently reusable connection, the next request may fail with the normal transport/protocol error; that stale slot is discarded, and the following request reconnects normally. This avoids silently replaying non-idempotent requests and keeps automatic retry policy outside v1 scope.

Tests

Adds dedicated loopback integration coverage for:

• two sequential requests over one accepted socket
• Connection: close forcing a reconnect
• close-delimited response forcing a reconnect
• port/origin change replacing the retained connection
• stale keep-alive failure being discarded without hidden retry

All tests are local-only and use bounded accept/read waits to avoid hanging CI.

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Ensure the worker is joined before a fatal assertion

If the initial request fails—for example because of a loopback or transport regression—ASSERT_TRUE(first) returns from the test while worker is still joinable. Destroying that std::thread invokes std::terminate, aborting the entire test executable instead of reporting this test failure and continuing; use RAII joining or a nonfatal check with an explicit cleanup path.

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