feat(canon): §2.G strip UPGRADE_BASE_VERSION entirely (plausible verified dynamic-base green)

Gate satisfied — live: with the pin removed, plausible's upgrade tier resolves base 3.0.1+v2.0.0 via
the same-version step-back (canonical 3.1.0 == head 3.1.0 → newest-older = 3.0.1, NOT the broken
3.0.0) and passes install+upgrade green (level 5/5). The pin is redundant, so removed everywhere:
- meta.py KEYS entry (RecipeMeta field auto-drops; 15→14 keys).
- run_recipe_ci.resolve_upgrade_base override branch + docstrings.
- tests/unit/test_meta.py (count 15→14, dropped None-assert), test_upgrade_base.py (override test).
- docs/recipe-customization.md (regenerated table + mentions), docs/testing.md.
- tests/plausible/recipe_meta.py (pin removed), tests/bluesky-pds (re-enable note → dynamic base).
294 unit tests pass; lint clean.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

tests/unit/test_meta.py

@@ -58,7 +58,6 @@ def test_missing_meta_yields_spec_baseline(tmp_path):
     assert meta.BACKUP_CAPABLE is None  # None = auto-detect (tri-state, not False)
     assert meta.EXPECTED_NA is None
     assert meta.READY_PROBE is None
-    assert meta.UPGRADE_BASE_VERSION is None
     assert meta.BACKUP_VERIFY is None
     assert meta.UPGRADE_EXTRA_ENV is None
     assert meta.EXTRA_ENV == {}
@@ -74,9 +73,9 @@ def test_registry_field_set_matches_dataclass():
     import dataclasses
 
     assert [f.name for f in dataclasses.fields(RecipeMeta)] == [k.name for k in KEYS]
-    # the 15 final keys, no more (the 3 P2-deleted legacy keys are gone from the registry,
-    # so any recipe_meta still setting them hard-fails the typo gate)
-    assert len(KEYS) == 15
+    # 14 final keys (UPGRADE_BASE_VERSION removed in phase canon §2.G; the 3 P2-deleted legacy keys
+    # are gone too — any recipe_meta still setting a removed key hard-fails the typo gate)
+    assert len(KEYS) == 14
     assert not [k for k in KEYS if k.deprecated]
     for gone in ("CHAOS_BASE_DEPLOY", "OIDC_AT_INSTALL", "SKIP_GENERIC"):
         assert gone not in {k.name for k in KEYS}

tests/unit/test_upgrade_base.py

@@ -1,9 +1,10 @@
 """Unit tests for `run_recipe_ci.resolve_upgrade_base` — the DYNAMIC upgrade-base decision (phase prevb).
 
-Resolution order: upgrade∉stages / EXPECTED_NA[upgrade] (declared skip) → explicit UPGRADE_BASE_VERSION
-override → last-green (warm canonical) → target-branch (`main`) tip → skip (no predecessor). The result
-is a `BasePlan(kind, version, ref, reason)`: kind ∈ {"version", "ref", "skip"}; `.runs` is True for
-version/ref (the upgrade tier runs). Replaces the old static `recipe_versions[-2]` default.
+Resolution order: upgrade∉stages / EXPECTED_NA[upgrade] (declared skip) → last-green (warm canonical,
+with same-version step-back) → target-branch (`main`) tip → skip (no predecessor). The result is a
+`BasePlan(kind, version, ref, reason)`: kind ∈ {"version", "ref", "skip"}; `.runs` is True for
+version/ref (the upgrade tier runs). Replaces the old static `recipe_versions[-2]` default; the old
+explicit `UPGRADE_BASE_VERSION` override knob was removed in phase canon (§2.G).
 """
 
 from __future__ import annotations
@@ -22,8 +23,8 @@ HEAD = "aaaa1111head"
 MAIN = "bbbb2222main"
 
 
-def _meta(expected_na=None, upgrade_base_version=None):
-    return SimpleNamespace(EXPECTED_NA=expected_na, UPGRADE_BASE_VERSION=upgrade_base_version)
+def _meta(expected_na=None):
+    return SimpleNamespace(EXPECTED_NA=expected_na)
 
 
 def _no_canonical(monkeypatch):
@@ -43,33 +44,16 @@ def test_upgrade_not_in_stages_skip(monkeypatch):
     assert plan.kind == "skip" and not plan.runs
 
 
-def test_expected_na_upgrade_skip_even_with_canonical_and_override(monkeypatch):
-    # EXPECTED_NA[upgrade] is the strongest, declared fact — short-circuits before override/canonical.
+def test_expected_na_upgrade_skip_even_with_canonical(monkeypatch):
+    # EXPECTED_NA[upgrade] is the strongest, declared fact — short-circuits before canonical.
     monkeypatch.setattr(
         canonical, "read_registry", lambda r: {"version": "9.9.9", "status": "warm"}
     )
     declared = {"upgrade": "no deployable upgrade base (moving tag republished)"}
-    plan = run_recipe_ci.resolve_upgrade_base(
-        ALL, _meta(expected_na=declared, upgrade_base_version="0.2.0+v0.4"), "bluesky-pds"
-    )
+    plan = run_recipe_ci.resolve_upgrade_base(ALL, _meta(expected_na=declared), "bluesky-pds")
     assert plan.kind == "skip" and "EXPECTED_NA" in plan.reason
 
 
-def test_explicit_override_wins_over_canonical(monkeypatch):
-    monkeypatch.setattr(
-        canonical, "read_registry", lambda r: {"version": "9.9.9", "status": "warm"}
-    )
-    monkeypatch.setattr(
-        lifecycle,
-        "recipe_branch_commit",
-        lambda r, b="main": (_ for _ in ()).throw(AssertionError("not consulted")),
-    )
-    plan = run_recipe_ci.resolve_upgrade_base(
-        ALL, _meta(upgrade_base_version="0.7.0+3.3.1"), "discourse"
-    )
-    assert plan.kind == "version" and plan.version == "0.7.0+3.3.1" and plan.runs
-
-
 def test_last_green_warm_canonical_is_primary(monkeypatch):
     # no override → last-green (warm canonical version) is the PRIMARY base; main is not consulted.
     monkeypatch.setattr(