feat(harness): intentional skips + custom-html-tiny functional test; 4-rung ladder (#6)

Declare intentional skips + custom-html-tiny functional test; 4-rung level ladder

- recipe_meta.EXPECTED_NA = {rung: reason} lists intentionally-skipped rungs; any
  essential rung skipped and not listed is unintentional. Skips still cap the level
  (never inflate). results.json: skips:{intentional,unintentional} + level_cap_rung.
- Level ladder = the four essential rungs (install, upgrade, backup/restore,
  functional; top = L4). integration & recipe-local are optional, not leveled
  (SSO still enforced for the run verdict, unchanged).
- Card shows skipped rungs as INTENTIONAL SKIP (green, reason below) / UNINTENTIONAL
  SKIP (amber); level badge gains an expected/gap? third segment.
- custom-html-tiny: functional serve test (exact-byte round-trip + 404); declares
  backup_restore intentionally skipped (stateless static server).

Independently verified by the adversary: 138 unit tests pass cold; live full-stage
run on custom-html-tiny green (upgrade tier ran; level 2; correct skips/badge);
clean teardown.

tests/unit/test_level.py

@@ -19,33 +19,23 @@ def _rungs(
     upgrade="pass",
     backup_restore="pass",
     functional="pass",
-    integration="pass",
-    recipe_local="pass",
 ):
     return {
         "install": install,
         "upgrade": upgrade,
         "backup_restore": backup_restore,
         "functional": functional,
-        "integration": integration,
-        "recipe_local": recipe_local,
     }
 
 
-# ---- the U0 gate: L4-pass and L2-cap ----
+# ---- the ladder: four essential rungs, top is L4 (functional) ----
 
 
-def test_full_clean_climb_to_L6():
+def test_full_clean_climb_to_L4():
+    # All four essential rungs pass → L4 (the top; integration/recipe-local are optional, not leveled).
     lvl, reason = L.compute_level(_rungs())
-    assert lvl == 6
-    assert reason == ""
-
-
-def test_climbs_through_L4_then_no_integration_surface_caps_at_L4():
-    # GATE: a recipe whose functional tests pass but has no SSO/integration surface caps at L4.
-    lvl, reason = L.compute_level(_rungs(integration="na", recipe_local="na"))
     assert lvl == 4
-    assert "L5" in reason and "N/A" in reason
+    assert reason == ""
 
 
 def test_fails_at_L2_capped_at_L1():
@@ -69,34 +59,27 @@ def test_install_fail_is_L0():
 
 def test_higher_pass_does_not_rescue_lower_na():
     # backup/restore N/A (stateless app) caps at L2 even though functional would pass.
-    lvl, reason = L.compute_level(_rungs(backup_restore="na", functional="pass", integration="na"))
+    lvl, reason = L.compute_level(_rungs(backup_restore="na", functional="pass"))
     assert lvl == 2
     assert "L3" in reason and "N/A" in reason
 
 
 def test_upgrade_na_caps_at_L1():
-    # only one published version → no upgrade possible → N/A caps at L1.
+    # only one published version → no upgrade possible → N/A caps at L1 (upgrade is essential).
     lvl, reason = L.compute_level(_rungs(upgrade="na"))
     assert lvl == 1
     assert "L2" in reason and "N/A" in reason
 
 
-def test_integration_fail_caps_at_L4():
-    # SSO declared but unverified (failed) → integration rung fails → cap at L4.
-    lvl, reason = L.compute_level(_rungs(integration="fail", recipe_local="na"))
-    assert lvl == 4
-    assert "L5" in reason and "FAILED" in reason
-
-
-def test_recipe_local_na_caps_at_L5():
-    # SSO passes but no recipe-local tests → cap at L5 (L6 N/A).
-    lvl, reason = L.compute_level(_rungs(recipe_local="na"))
-    assert lvl == 5
-    assert "L6" in reason and "N/A" in reason
+def test_functional_na_caps_at_L3():
+    # no recipe-specific functional tests → functional N/A caps at L3.
+    lvl, reason = L.compute_level(_rungs(functional="na"))
+    assert lvl == 3
+    assert "L4" in reason and "N/A" in reason
 
 
 def test_functional_fail_caps_at_L3():
-    lvl, reason = L.compute_level(_rungs(functional="fail", integration="na"))
+    lvl, reason = L.compute_level(_rungs(functional="fail"))
     assert lvl == 3
     assert "L4" in reason and "FAILED" in reason