test(api-discovery-test): add 3 assertions for tier=engine

Covers the new engine-tier validate_readme_structure behavior:
complete engine README, missing-API detection, and the relaxed Badges
pattern that accepts arbitrary bold key:value lines (engine has no
Lib-ID prefix).

Total assertion-count grows from 52 to 55. Coverage table updated.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

init.lua

@@ -321,6 +321,54 @@ Sig.
         -- Tier community: lockerer
         local r3 = api.validate_readme_structure(missing_api, "community")
         engine.test.equals(#r3.missing_sections, 0, "validate: tier=community -> no enforcement")
+
+        -- Tier engine: same structure as core but flexible Badges
+        local engine_md = [[
+# sporel-engine
+
+**Version:** 0.1.0
+**License:** Proprietary
+
+## Topology
+<!-- topology:start -->
+<!-- topology:end -->
+
+## API
+text
+
+## References
+- spec
+]]
+        local r_engine = api.validate_readme_structure(engine_md, "engine")
+        engine.test.equals(#r_engine.missing_sections, 0, "validate: engine README -> no missing")
+
+        -- Missing API in engine README -> still detected
+        local engine_no_api = [[
+# sporel-engine
+
+**Version:** 0.1.0
+
+## Topology
+<!-- topology:start -->
+<!-- topology:end -->
+
+## References
+]]
+        local r_engine_no_api = api.validate_readme_structure(engine_no_api, "engine")
+        engine.test.assert(#r_engine_no_api.missing_sections > 0, "validate: engine without API -> reports missing")
+
+        -- Naked Badges line (no Lib-ID prefix) accepted in engine tier
+        local engine_naked = [[
+# sporel-engine
+**Anything:** value
+]]
+        local r_engine_naked = api.validate_readme_structure(engine_naked, "engine")
+        -- Just verify Badges-check doesn't fail because of missing "Lib-ID:" prefix
+        local badges_missing = false
+        for _, s in ipairs(r_engine_naked.missing_sections) do
+            if s == "Badges" then badges_missing = true end
+        end
+        engine.test.assert(not badges_missing, "validate: engine tier accepts naked badges")
     end
 
     engine.exit(engine.test.failures())