Merged headers not served/enabled by default

[0w3n-d]

Status

Two tests are currently broken on develop (discovered while re-enabling CI's unit-test job): local_cache::tests::test_serve_merged_headers (crates/common/src/local_cache.rs) panics "Merged headers should be served by default"; api::admin_service::test::test_admin_service_merged_headers (crates/relay/src/api/admin_service.rs) panics "should be enabled by default".

Why

Both assert that merged-header serving is on by default; both currently fail, suggesting a shared regression in a default-config value (or the tests' expectation is stale relative to an intentional default change — needs investigation to know which).

Affected surface

• crates/common/src/local_cache.rs
• crates/relay/src/api/admin_service.rs

Steps

• Determine whether the default should be "on" (fix the config default) or the tests are asserting a stale expectation (fix the tests)
• Un-ignore both tests