Honor client_no_context_takeover offer

[jhugard]

Problem (#1193)

In the default WebSocket++ permessage-deflate client configuration, the client offer generated by generate_offer() advertises client_no_context_takeover, but client-side compression behavior only honors that setting when the server echoes the parameter in its response. If the server accepts permessage-deflate and omits client_no_context_takeover, the client still reuses compressor context across messages.

This means the offer string and the actual outbound behavior can diverge.

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Branch and commit series

• Branch: permessage-deflate-client-no-context-takeover
• Base: origin/develop

This branch contains two commits:

1. b8e4b6f — Add client_no_context_takeover regression test
2. 6ed4712 — Honor client_no_context_takeover offer

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Overview of changes

The fix keeps track of whether the client advertised client_no_context_takeover in generate_offer() and carries that offer-side state into the client init(false) path.

With that state available at initialization time, the client uses no-context-takeover compression behavior for outbound messages even when the server omits client_no_context_takeover from the negotiated response parameters.

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Tests

Added coverage in test/extension/permessage_deflate.cpp for the case where:

• the client offer includes client_no_context_takeover
• the server response attribute list is empty
• the client compresses the same deterministic message twice
• each compressed output is decompressed independently by a fresh server-side extension instance

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Validation

Reviewer flow:

1. check out b8e4b6f and run the new regression (expected to fail)
2. apply 6ed4712 and rerun (expected to pass)

Observed behavior:

• before the fix, the second compressed message depends on prior context and fails the fresh-receiver model
• with the fix, both messages decompress successfully and match the original input

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Files touched

• test/extension/permessage_deflate.cpp
• websocketpp/extensions/permessage_deflate/enabled.hpp

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Target branch

Per repository guidance in readme.md, this series is based on and intended for develop.