v0.8.0

feat(codex): read a Block from turn.failed's error message
feat(codex): claim BlockReporter for exhausted and rejected reasons
test(codex): add derived exhausted-block fixtures and testdata provenance
test(codex): assert BlockReporter behavior and its rejection boundary
test(codex): guard the installed binary against a stale usage-limit phrase
docs: record ADR 0007 and bring 0006, CONTEXT.md, README.md into agreement
feat(codex): classify a spent usage limit as a block, not an ordinary failure (#13)

Full changelog: v0.7.0...v0.8.0