Workaround Leaf Route

WORKAROUND = BRANCH AT LEAF (Deterministic Liminal, 2026-09-08). Body: {tree, leaf_id, value, source_ref?, caller?}. tree is a reduce tree OR a decide frame; leaf_id a leaf key ('leaf-<16hex>'), the exact leaf text, a child-index path ('root.0.2'), or a decide address ('candidate:<name>.<criterion>' / 'criterion:<name>.weight' / an ask_user need). The original is NEVER edited: the answer is a named pivot leaf and BOTH branches — main (untouched) and the branch with the asserted value applied and downstream re-derived (tree: ancestors marked stale; decide: scores/ranked recomputed from the frozen criteria). The assertion is persisted as a PRIVATE fact on its own branch for the caller resolved SERVER-SIDE (_pref_caller: bound identity wins; explicit override only off the sell plane). Zero model calls. Coded failures: 404 E_WA_LEAF_NOT_FOUND / 409 E_WA_AMBIGUOUS (body echoes code + candidates) — never a silent pick.