Establish the 0.9.0 HTTP behavior contract

[Mattsface]

Establish the 0.9.0 HTTP behavior contract

Why

Version 0.9.0 will add configurable HTTP behavior on top of the transport work completed in version 0.8.0.

The compatibility and strict-mode behavior should be protected by deterministic tests before production behavior changes.

Parent release issue: #265

Scope

Add offline contract tests covering:

• Library-created Session retry configuration
• Caller-injected Session behavior
• Existing 4xx compatibility behavior
• Existing endpoint-specific 404 behavior
• Existing MlbHttpError attributes
• User-Agent behavior
• Public retry-policy imports
• Planned strict-mode behavior

This issue should document the baseline and expected new contract without intentionally changing production behavior.

Required coverage

• Library-created Sessions receive the default retry policy
• Injected Sessions are not automatically reconfigured
• Injected Sessions are not closed by the library
• Final 404 responses preserve endpoint-specific behavior
• Final non-404 4xx responses preserve compatibility behavior by default
• Final 5xx responses raise MlbHttpError
• Existing exception inheritance remains unchanged
• Existing constructor usage remains valid
• Existing timeout forwarding remains unchanged

Add failing or skipped contract tests for planned behavior only where that clearly improves the implementation sequence.

Suggested branch

test/v0.9-http-contract

The branch should start from and target:

release/0.9.0

Acceptance criteria

• HTTP behavior is covered without contacting the live MLB API
• Existing version 0.8.0 behavior is explicitly protected
• New strict-mode expectations are documented in tests
• New retry-policy expectations are documented in tests
• No intentional production behavior changes occur
• Offline tests pass

Not included

• Public retry helpers
• Strict mode implementation
• New warning classes
• User-Agent changes
• Error-context changes
• Documentation changes