simplify: dedup stage-content accessor + hoist the forward-source map

Two cleanups from the post-implementation review:

- Export stageContentOf from textStages.js and reuse it in storyBuilder's
  collectIssueSourceText, which was re-inlining the same
  "edited input wins over raw output" precedence expression.

- Move the client's DEFAULT_FORWARD_SOURCE into apiPipeline.js as
  PIPELINE_DEFAULT_FORWARD_SOURCE, next to PIPELINE_TEXT_STAGES /
  PIPELINE_STAGE_LABELS, matching the established client/server stage-constant
  mirror convention instead of a second private copy in TextStagePanel.

Author: atomantic

client/src/components/pipeline/stages/TextStagePanel.jsx

@@ -12,22 +12,13 @@ import {
   generatePipelineStage, updatePipelineIssue,
   PIPELINE_STAGE_LABELS,
   PIPELINE_TEXT_STAGES,
+  PIPELINE_DEFAULT_FORWARD_SOURCE as DEFAULT_FORWARD_SOURCE,
   PIPELINE_STAGE_STATUS_LABEL as STATUS_LABEL,
   PIPELINE_STAGE_STATUS_COLOR as STATUS_COLOR,
 } from '../../../services/api';
 import { useAsyncAction } from '../../../hooks/useAsyncAction';
 import StageHistoryModal from './StageHistoryModal';
 
-// The stage that conventionally feeds each target — mirrors the server's
-// DEFAULT_FORWARD_SOURCE. Used to pre-check the source picker so the common
-// forward flow needs no clicks, while still allowing any populated stage to be
-// chosen as a backport source.
-const DEFAULT_FORWARD_SOURCE = {
-  prose: ['idea'],
-  comicScript: ['prose'],
-  teleplay: ['prose'],
-};
-
 const stageHasContent = (stage) => Boolean(stage?.input?.trim() || stage?.output?.trim());
 
 export default function TextStagePanel({

client/src/services/apiPipeline.js

@@ -38,6 +38,16 @@ export const PIPELINE_STAGE_LABELS = Object.freeze({
   audio: 'Audio',
 });
 
+// The stage that conventionally feeds each text-stage target — mirrors the
+// server's DEFAULT_FORWARD_SOURCE (server/services/pipeline/textStages.js).
+// The text-stage source picker pre-checks these so the common forward flow
+// needs no clicks, while still letting any populated stage be a backport source.
+export const PIPELINE_DEFAULT_FORWARD_SOURCE = Object.freeze({
+  prose: ['idea'],
+  comicScript: ['prose'],
+  teleplay: ['prose'],
+});
+
 export const PIPELINE_TARGET_FORMATS = Object.freeze(['comic', 'tv', 'comic+tv']);
 
 export const PIPELINE_STAGE_STATUS_LABEL = Object.freeze({

server/services/storyBuilder.js

@@ -40,6 +40,7 @@ import {
   generateArcOverview, generateArcFromSource, generateReaderMap, refineReaderMap, commitSeasonsWithRemap,
 } from './pipeline/arcPlanner.js';
 import { listIssues } from './pipeline/issues.js';
+import { stageContentOf } from './pipeline/textStages.js';
 
 const TYPE_SCHEMA_VERSION = 1;
 
@@ -440,7 +441,7 @@ async function collectIssueSourceText(seriesId) {
   for (const iss of ordered) {
     const st = iss.stages || {};
     const pick = ['comicScript', 'teleplay', 'prose', 'idea']
-      .map((sid) => ({ sid, content: (st[sid]?.input?.trim() || st[sid]?.output?.trim() || '') }))
+      .map((sid) => ({ sid, content: stageContentOf(st[sid]) }))
       .find((x) => x.content);
     if (!pick) continue;
     parts.push(`# Issue ${iss.number}${iss.title ? ` — ${iss.title}` : ''} (${pick.sid})\n\n${pick.content}`);