FN-6035: align builtin coding workflow registry with canonical IR

Keep builtin:coding anchored to the canonical coding workflow IR across registry, resolver, and docs.

- add regression coverage that builtin:coding reuses BUILTIN_CODING_WORKFLOW_IR and preserves canonical columns, traits, settings, and enabled ordering
- extend workflow IR resolver/settings tests to pin canonical builtin fallback behavior for explicit and missing built-in selections
- document builtin:coding as the canonical default/fallback workflow and add a patch changeset for @runfusion/fusion

Files changed:
 .../FN-6035-builtin-coding-workflow-parity.md      |  5 ++
 docs/workflow-steps.md                             |  4 +-
 .../core/src/__tests__/builtin-workflows.test.ts   | 65 +++++++++++++++++++++-
 .../src/__tests__/workflow-ir-resolver.test.ts     | 18 +++++-
 .../src/__tests__/workflow-ir-settings.test.ts     |  3 +
 5 files changed, 92 insertions(+), 3 deletions(-)

Fusion-Task-Id: FN-6035

Fusion-Task-Lineage: ece0c8c6-810f-44b1-afb3-6545d3156459

docs/workflow-steps.md

@@ -36,10 +36,12 @@ FN-5766 adds a **flagged-off** interpreter scaffold in `@fusion/engine` (`Workfl
 - Default: **OFF**
 - OFF behavior is strict no-op (no task mutations, no session/git side effects), so the legacy imperative pipeline remains authoritative.
 
-Built-in coding IR currently encodes the legacy lifecycle path as graph stages:
+The default built-in catalog entry `builtin:coding` is backed by the canonical `BUILTIN_CODING_WORKFLOW_IR`, which is also the resolver/runtime fallback for tasks with no workflow selection, an explicit default selection, or a missing/corrupt custom selection. That IR currently encodes the legacy lifecycle path as graph stages:
 
 - `triage` → `execute` → `review` → `merge` → `end`
 
+`builtin:stepwise-coding` is a separate opt-in graph-mode variant backed by `BUILTIN_STEPWISE_CODING_WORKFLOW_IR`; it keeps the same lifecycle columns/traits while modeling per-step parse/execute/review as authored graph structure, and requires the `workflowGraphExecutor` flag at runtime.
+
 #### Interpreter-parity gating criterion
 
 Interpreter authority is gated on parity: interpreter-driven coding runs must match legacy behavior for observable task transitions and reliability invariants (file-scope guards including `FileScopeViolationError`, squash/merge contract, self-healing expectations, `autoMerge:false` terminal-until-merged, and `moveTask(in-progress→todo)` hard-cancel semantics).