chore: release v0.4.0

[github-actions]

🤖 New release

• socketeer: 0.3.0 -> 0.4.0 (⚠ API breaking changes)

⚠ socketeer breaking changes

--- failure enum_variant_added: enum variant added on exhaustive enum ---

Description:
A publicly-visible enum without #[non_exhaustive] has a new variant.
        ref: https://doc.rust-lang.org/cargo/reference/semver.html#enum-variant-new
       impl: https://github.com/obi1kenobi/cargo-semver-checks/tree/v0.46.0/src/lints/enum_variant_added.ron

Failed in:
  variant Error:Codec in /tmp/.tmpxAjlZS/socketeer/src/error.rs:29

--- failure enum_variant_missing: pub enum variant removed or renamed ---

Description:
A publicly-visible enum has at least one variant that is no longer available under its prior name. It may have been renamed or removed entirely.
        ref: https://doc.rust-lang.org/cargo/reference/semver.html#item-remove
       impl: https://github.com/obi1kenobi/cargo-semver-checks/tree/v0.46.0/src/lints/enum_variant_missing.ron

Failed in:
  variant Error::SerializationError, previously in file /tmp/.tmprrnVSn/socketeer/src/error.rs:29

--- failure inherent_method_missing: pub method removed or renamed ---

Description:
A publicly-visible method or associated fn is no longer available under its prior name. It may have been renamed or removed entirely.
        ref: https://doc.rust-lang.org/cargo/reference/semver.html#item-remove
       impl: https://github.com/obi1kenobi/cargo-semver-checks/tree/v0.46.0/src/lints/inherent_method_missing.ron

Failed in:
  HandshakeContext::send_json, previously in file /tmp/.tmprrnVSn/socketeer/src/handler.rs:59
  HandshakeContext::recv_json, previously in file /tmp/.tmprrnVSn/socketeer/src/handler.rs:68
  Socketeer::connect_with_handler, previously in file /tmp/.tmprrnVSn/socketeer/src/lib.rs:115

--- failure trait_requires_more_generic_type_params: trait now requires more generic type parameters ---

Description:
A trait now requires more generic type parameters than it used to. Uses of this trait that supplied the previously-required number of generic types will be broken. To fix this, consider supplying default values for newly-added generic types.
        ref: https://doc.rust-lang.org/cargo/reference/semver.html#trait-new-parameter-no-default
       impl: https://github.com/obi1kenobi/cargo-semver-checks/tree/v0.46.0/src/lints/trait_requires_more_generic_type_params.ron

Failed in:
  trait HandshakeContext (0 -> 1 required generic types) in /tmp/.tmpxAjlZS/socketeer/src/handler.rs:17

--- failure type_allows_fewer_generic_type_params: type now allows fewer generic type parameters ---

Description:
A type now allows fewer generic type parameters than it used to. Uses of this type that supplied all previously-supported generic types will be broken.
        ref: https://doc.rust-lang.org/cargo/reference/semver.html#trait-new-parameter-no-default
       impl: https://github.com/obi1kenobi/cargo-semver-checks/tree/v0.46.0/src/lints/type_allows_fewer_generic_type_params.ron

Failed in:
  Struct Socketeer allows 3 -> 2 generic types in /tmp/.tmpxAjlZS/socketeer/src/lib.rs:58

--- failure type_requires_more_generic_type_params: type now requires more generic type parameters ---

Description:
A type now requires more generic type parameters than it used to. Uses of this type that supplied the previously-required number of generic types will be broken. To fix this, consider supplying default values for newly-added generic types.
        ref: https://doc.rust-lang.org/cargo/reference/semver.html#trait-new-parameter-no-default
       impl: https://github.com/obi1kenobi/cargo-semver-checks/tree/v0.46.0/src/lints/type_requires_more_generic_type_params.ron

Failed in:
  Struct HandshakeContext (0 -> 1 required generic types) in /tmp/.tmpxAjlZS/socketeer/src/handler.rs:17

Changelog

[0.4.0] - 2026-05-08

Features

• [breaking] Add Codec abstraction with JSON, MessagePack, and Raw codecs(efc1d5a)

Bug Fixes

• Mark Error::Codec inner as #source
• Surface peer close as WebsocketClosed in HandshakeContext::recv(cd67288)

Testing

• Add coverage for Codec trait and new HandshakeContext paths(aeb3c89)
• Push coverage to 98% lines / 96% regions(09d7364)
• Clarify raw-API test names and cover send_raw directly(b10d987)

---

This PR was generated with release-plz.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.52%. Comparing base (405dc1c) to head (c9bf4e4).

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #17   +/-   ##
=======================================
  Coverage   98.52%   98.52%           
=======================================
  Files           5        5           
  Lines         811      811           
=======================================
  Hits          799      799           
  Misses         12       12           

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