feat(core): workflowColumns integrity pass, graduation report, server-side trait validation, plugin post-commit hooks, docs + changeset (U12)

docs/workflow-steps.md

@@ -57,6 +57,10 @@ Current reconciliation in v1:
 
 FN-5769 evaluated whether those conventions required a `1.1.0` schema bump and recorded the answer as **no**: the current `prompt` + `config` and canonical `edge.condition` token conventions are sufficient for the parity-critical interpreter rollout, so they remain the canonical v1 contract until a future consumer needs stronger schema-level validation or discoverability.
 
+### Workflow IR v2 — columns, traits, hold & split/join nodes
+
+The `workflowColumns` track introduces **IR v2** (`version: "v2"`), where a workflow additionally defines its own **columns** (`{ id, name, traits: [{ trait, config }] }`), places nodes in columns (`node.column`), and gains `hold`, `split`, and `join` node kinds. Columns become first-class, workflow-defined task state carrying composable **traits** (declarative flags + lifecycle hooks); this generalizes the fixed pipeline + the `gateMode` semantics documented below into per-column trait configuration. v1 graphs still parse and upgrade by synthesizing default-workflow columns. The column/trait model — the trait vocabulary, the substrate/policy line, the transition authority, and the graduation gate — is documented in **`docs/architecture.md` § 9 "Workflow-defined columns & traits"** and the **Concepts** glossary (column, trait, lane, hold node, split/join, default workflow, `transitionPending`). The whole v2 model is gated behind `experimentalFeatures.workflowColumns`; with the flag off, the v1 IR and the quality-gate `WorkflowStep` model below are unchanged.
+
 ## What They Are
 
 A workflow step is a reusable check (AI prompt or script) that can be enabled on tasks.