[TEST] Add dedicated unit tests for RequestContext (689 lines, only tested indirectly)

[jeromesinolanka]

Priority: 🟡 Medium

Description

src/Fetch/Support/RequestContext.php is 689 lines and serves as the immutable per-request state container. Every single HTTP request flows through it, yet it has no dedicated test file — it is only exercised indirectly when integration tests make full requests.

Testing it in isolation is valuable because:

• It is immutable (readonly properties), so constructor argument handling is the only path to test
• It has a complex set of constructor parameters with defaults, and it's easy for a refactor to change a default silently
• Any bug here affects every request made by the library

Current gap

No RequestContextTest.php in tests/Unit/.

Recommended Fix

Create tests/Unit/RequestContextTest.php covering:

1. All constructor arguments — verify each property is set correctly when explicitly passed
2. Default values — verify each optional parameter's default matches documented behavior
3. Immutability — verify attempting to assign to a readonly property throws an Error
4. Type correctness — verify that passing invalid types (e.g., a negative timeout) surfaces an error at construction time (or document that it doesn't, so the behavior is explicit)
5. Accessor methods — if any exist, verify they return the constructed values

Impact

Without these tests, a change to a constructor default (e.g., changing the default timeout from 30 to 0) is invisible until a production request times out immediately.