[bbdu3]

Fixes #583 - adds Builder::setFiberContext() and FiberContextInterface, so an integration can carry execution context, e.g. the active OpenTelemetry context, into handler fibers in both protocol eras.

• wrap() runs in the context of the caller, the returned closure runs in the fiber - the SDK keeps creating the fiber itself
• No OpenTelemetry dependency, and nothing changes without a fiber context
• Under an event loop the application needs to activate a context in the request fiber first, and fibers a handler starts itself don't get it - both documented
• Also frees a discarded handler fiber right away - since [Server] Let an event loop drive the fibers request handlers run in #616 its finally only ran on the next GC run

[Copilot]

🟢 Approval recommended

No active review issues are recorded for the optional handler-fiber context-propagation hook.

No open issues 🎉

What changed in this PR

Adds an optional context-propagation hook for SDK-managed handler fibers, addressing #583 without introducing an OpenTelemetry dependency or changing fiber scheduling.

Changes:

• Introduces FiberFactoryInterface and Builder::setFiberFactory() for both protocol eras, including buildStateless().
• Documents explicit OpenTelemetry context propagation while preserving default behavior.
• Adds regression coverage for context isolation, suspension/resumption, errors, and cleanup.

File	Description
tests/​Unit/​Server/​FiberFactoryTest.php	Tests context propagation and cleanup across HTTP and stdio.
tests/​Unit/​Fixtures/​ContextFiberFactory.php	Provides a context-tracking factory for tests.
src/​Server/​Stateless/​StatelessProtocol.php	Uses the optional factory for modern-era handler fibers.
src/​Server/​Protocol.php	Uses the optional factory for handshake-era handler fibers.
src/​Server/​FiberFactoryInterface.php	Defines the factory contract and callback-preservation requirements.
src/​Server/​Builder.php	Adds factory configuration and passes it to both protocols.
docs/​run/​server-builder.md	Explains factory usage with an OpenTelemetry example.
CHANGELOG.md	Records the new server integration hook.

_{Review effort: Balanced}

[chr-hertel]

Thanks @bbdu3 - approach works nicely, tested it with real OTel & Revolt 👍 I took over to land it on top of #616: rebased your commit and narrowed the factory to a wrap() of the handler closure, so the SDK keeps creating the fiber. Hope that is fine for you!

[Copilot]

🟢 Approval recommended

No active review issues block approval of the optional fiber context-propagation change.

No open issues 🎉

_{Review effort: Balanced}

[chr-hertel]

Thanks @bbdu3!