symfony/mercure 0.8.0 (2026-08-11) added getProtocolVersion() and getCookieName() to HubInterface.
The TestHub decorator did not implement them, so every CI job died at container warmup before a
single test ran -- 20 jobs red on 4.3, with no green run since 2026-07-08.

symfony/mercure-bundle was declared as "*" in all four composer.json files, which let a breaking
0.x release land unannounced. Constrain it to ^0.4.3|^0.5 so both majors stay covered: 0.4.3
resolves mercure ^0.6.1|^0.7 for the lowest jobs, 0.5.0 resolves ^0.8.

ProtocolVersion does not exist before 0.8, but PHP resolves return types lazily and nothing calls
these methods on older versions. Verified: cache warmup and the Mercure functional tests pass under
both 0.7.2 and 0.8.0.