Use shared memory for broker pipes

[wdcui]

Each broker connection establishes one sealed memfd after protocol negotiation and reuses it at offset zero for serialized pipe transfers. Pipe requests carry transfer lengths and responses carry byte counts; the host and local adapters stage data through shared memory while BrokerCore remains authoritative for pipe state.

[github-actions]

🤖 SemverChecks 🤖 ⚠️ Potential breaking API changes detected ⚠️

Click for details

--- failure function_parameter_count_changed: pub fn parameter count changed ---

Description:
A publicly-visible function now takes a different number of parameters.
        ref: https://doc.rust-lang.org/cargo/reference/semver.html#fn-change-arity
       impl: https://github.com/obi1kenobi/cargo-semver-checks/tree/v0.49.0/src/lints/function_parameter_count_changed.ron

Failed in:
  litebox_broker_host::serve_connection now takes 5 parameters instead of 3, in /home/runner/work/litebox/litebox/litebox_broker_host/src/lib.rs:51

--- failure auto_trait_impl_removed: auto trait no longer implemented ---

Description:
A public type has stopped implementing one or more auto traits. This can break downstream code that depends on the traits being implemented.
        ref: https://doc.rust-lang.org/reference/special-types-and-traits.html#auto-traits
       impl: https://github.com/obi1kenobi/cargo-semver-checks/tree/v0.49.0/src/lints/auto_trait_impl_removed.ron

Failed in:
  type BrokerLocal is no longer UnwindSafe, in /home/runner/work/litebox/litebox/litebox_broker_local/src/lib.rs:42
  type BrokerLocal is no longer RefUnwindSafe, in /home/runner/work/litebox/litebox/litebox_broker_local/src/lib.rs:42

--- 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/v0.49.0/src/lints/inherent_method_missing.ron

Failed in:
  BrokerLocal::request, previously in file /home/runner/work/litebox/litebox/target/semver-checks/git-ulitebox/62066dddce29519d1489a2508de199b2bf9bf1da/litebox_broker_local/src/lib.rs:95

--- failure method_parameter_count_changed: pub method parameter count changed ---

Description:
A publicly-visible method now takes a different number of parameters, not counting the receiver (self) parameter.
        ref: https://doc.rust-lang.org/cargo/reference/semver.html#fn-change-arity
       impl: https://github.com/obi1kenobi/cargo-semver-checks/tree/v0.49.0/src/lints/method_parameter_count_changed.ron

Failed in:
  litebox_broker_local::BrokerLocal::negotiate takes 1 parameters in /home/runner/work/litebox/litebox/target/semver-checks/git-ulitebox/62066dddce29519d1489a2508de199b2bf9bf1da/litebox_broker_local/src/lib.rs:51, but now takes 2 parameters in /home/runner/work/litebox/litebox/litebox_broker_local/src/lib.rs:61

--- failure constructible_struct_adds_field: externally-constructible struct adds field ---

Description:
A pub struct constructible with a struct literal has a new pub field. Existing struct literals must be updated to include the new field.
        ref: https://doc.rust-lang.org/reference/expressions/struct-expr.html
       impl: https://github.com/obi1kenobi/cargo-semver-checks/tree/v0.49.0/src/lints/constructible_struct_adds_field.ron

Failed in:
  field ReadPipeResponse.read in /home/runner/work/litebox/litebox/litebox_broker_protocol/src/pipe.rs:46
  field WritePipeRequest.length in /home/runner/work/litebox/litebox/litebox_broker_protocol/src/pipe.rs:55

--- failure copy_impl_added: type now implements Copy ---

Description:
A public type now implements Copy, causing non-move closures to capture it by reference instead of moving it.
        ref: https://github.com/rust-lang/rust/issues/100905
       impl: https://github.com/obi1kenobi/cargo-semver-checks/tree/v0.49.0/src/lints/copy_impl_added.ron

Failed in:
  litebox_broker_protocol::pipe::ReadPipeResponse in /home/runner/work/litebox/litebox/litebox_broker_protocol/src/pipe.rs:44
  litebox_broker_protocol::pipe::WritePipeRequest in /home/runner/work/litebox/litebox/litebox_broker_protocol/src/pipe.rs:51

--- failure struct_pub_field_missing: pub struct's pub field removed or renamed ---

Description:
A publicly-visible struct has at least one public field 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/v0.49.0/src/lints/struct_pub_field_missing.ron

Failed in:
  field data of struct ReadPipeResponse, previously in file /home/runner/work/litebox/litebox/target/semver-checks/git-ulitebox/62066dddce29519d1489a2508de199b2bf9bf1da/litebox_broker_protocol/src/pipe.rs:45
  field data of struct WritePipeRequest, previously in file /home/runner/work/litebox/litebox/target/semver-checks/git-ulitebox/62066dddce29519d1489a2508de199b2bf9bf1da/litebox_broker_protocol/src/pipe.rs:54