fix: a form field's id is not the workflow field's name

Prefill is computed from the record row, so it is keyed the way the data
  is keyed; the form's fields carry the deploy-assigned suffix. Untranslated,
  the draft landed under a key no control reads and then rode into the submit
  payload, where the workflow refuses the whole activity on an unknown key.

  Re-key prefill and seed onto the form's own field ids, and build the submit
  payload by walking fields rather than posting the whole value bag.

  Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

src/components/ActivityForm.tsx

@@ -71,13 +71,51 @@ export function ActivityForm({
 
   const fields = schema.data?.fields ?? [];
 
+  /**
+   * Re-key a values bag onto the form's OWN field ids.
+   *
+   * A form field's id is not the workflow field's name. A mapped activity
+   * field shares its slug with the workflow-level field it maps to, and
+   * deploy resolves that collision by suffixing the activity copy — so the
+   * instance data says `cm_approved_amount` and this form's field is
+   * `cm_approved_amount_2`. Everything we compute from a record row
+   * (prefill.ts, and any seed) is keyed the way the DATA is keyed, so it has
+   * to be translated on the way in.
+   *
+   * Untranslated it fails twice over, and the first failure hides the second:
+   * the drafted value lands under a key no control reads, so the form opens
+   * blank; and it then rides along in the submit payload, where the workflow
+   * rejects it as an unknown field — `validation failed for activity
+   * hdfc-act-cm-approve: cm_approved_amount(unknown), …`.
+   *
+   * Match on the exact id first, then on the id with a trailing `_<n>`
+   * removed. Never hardcode `_2`: the number is deploy-assigned and a slug
+   * used on two activities takes the next one (`firm_name_2` on Capture,
+   * `firm_name_3` on Upload Documents).
+   */
+  const toFieldKeys = (bag: Record<string, unknown> | undefined) => {
+    if (!bag) return {};
+    const byId = new Map(fields.map((f) => [f.id, f]));
+    const bySlug = new Map<string, string>();
+    for (const f of fields) {
+      const slug = f.id.replace(/_\d+$/, '');
+      if (slug !== f.id && !byId.has(slug) && !bySlug.has(slug)) bySlug.set(slug, f.id);
+    }
+    const out: Record<string, unknown> = {};
+    for (const [k, v] of Object.entries(bag)) {
+      const id = byId.has(k) ? k : bySlug.get(k);
+      if (id) out[id] = v;
+    }
+    return out;
+  };
+
   // Precedence, weakest first: the platform's own field defaults, then our
   // computed draft, then the seeded identifiers (which also become read-only).
   const initial = useMemo(
     () => ({
       ...(schema.data?.field_defaults ?? {}),
-      ...(prefill ?? {}),
+      ...toFieldKeys(prefill),
-      ...(seed ?? {}),
+      ...toFieldKeys(seed),
     }),
     // eslint-disable-next-line react-hooks/exhaustive-deps
     [schema.data, JSON.stringify(prefill), JSON.stringify(seed)],
@@ -143,9 +181,19 @@ export function ActivityForm({
     setBusy(true);
     setErr(null);
     try {
+      // Submit ONLY what this form actually has a field for. The workflow
+      // validates every key in the payload and refuses the whole submission
+      // on an unknown one, so a stray key is not ignored — it is fatal. This
+      // is the backstop for the re-keying above: if a translation ever misses,
+      // the field simply arrives empty instead of failing the activity.
+      const payload: Record<string, unknown> = {};
+      for (const f of fields) {
+        if (Object.prototype.hasOwnProperty.call(current, f.id)) payload[f.id] = current[f.id];
+      }
+
       const res = instanceId
-        ? await client.performActivity(WORKFLOW, instanceId, activityUid, current)
+        ? await client.performActivity(WORKFLOW, instanceId, activityUid, payload)
-        : await client.startInstance(WORKFLOW, activityUid, current);
+        : await client.startInstance(WORKFLOW, activityUid, payload);
       reset();
       onDone?.({ instance_id: res.instance_id });
       onClose();
@@ -183,7 +231,7 @@ export function ActivityForm({
                 key={f.id}
                 field={f}
                 value={current[f.id]}
-                readOnly={seed ? Object.prototype.hasOwnProperty.call(seed, f.id) : false}
+                readOnly={Object.prototype.hasOwnProperty.call(toFieldKeys(seed), f.id)}
                 error={touched && missing.includes(f.id) ? 'Required' : null}
                 onChange={(v) => setValues((s) => ({ ...s, [f.id]: v }))}
                 activityUid={activityUid}