docs: clarify draft bind input behavior

docs/current_roadmap.md

@@ -100,6 +100,9 @@ clear operator feedback before adding more architecture.
   project missing top-level output schema fields from declared `input.*` and
   `state.*` sources, and challenge prompt templates now always include
   `ux_issues_found: []` so debug-profile reports do not fail by omission.
+- Completed: `wf draft bind` now reuses existing workflow input/state schema
+  fields when binding to step-local inputs, avoiding redundant-schema failures
+  found by debug challenge runs.
 - Keep status read-only; do not mutate registry, auth, config, or stores.
 
 ## Priority 2: Durable Run/Resume Hardening

docs/wf_cli.md

@@ -361,6 +361,10 @@ wf draft bind concat_ws --revision 9 --step call --from local.result --to output
 wf draft validate concat_ws
 ```
 
+If the workflow schema field already exists, `bind` reuses it and only updates
+the step binding. Use `set-input --merge` for pure input-map edits when no
+schema projection is needed.
+
 When validation gives a `repair_hint` with an exact focused `wf draft bind`
 command, run it before falling back to JSON Patch.