Separate editing from running with a draft/publish split

Edits autosave to flow.draft.json and nodes.draft/ instead of the files the
engine reads, so the pipeline keeps running the published version until
someone publishes. Every save carries the version it was based on: a second
client editing the same flow is refused with 409 and offered the choice
between their version and its own, rather than silently overwriting.

Draft saves no longer rebuild the pipeline; validation and node status for a
draft come from a throwaway build that never touches live state.

Also fixes a latent bug where an empty state backend is falsy, so Pipeline
quietly built itself a second, private state and left message history empty.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

frontend/src/client/schemas.gen.ts

@@ -161,12 +161,21 @@ export const FlowDetailSchema = {
             type: 'array',
             title: 'Issues',
             default: []
+        },
+        has_draft: {
+            type: 'boolean',
+            title: 'Has Draft',
+            default: false
         }
     },
     type: 'object',
     required: ['definition'],
     title: 'FlowDetail',
-    description: 'A flow plus how it is currently doing.'
+    description: `A flow plus how it is currently doing.
+
+\`\`definition\`\` is the working copy — the unpublished draft when there is
+one — because that is what the editor shows. \`\`nodes\`\` reports the
+published flow, which is what is actually running.`
 } as const;
 
 export const FlowInput_InputSchema = {
@@ -252,6 +261,11 @@ export const FlowSummarySchema = {
             type: 'integer',
             title: 'Error Count',
             default: 0
+        },
+        has_draft: {
+            type: 'boolean',
+            title: 'Has Draft',
+            default: false
         }
     },
     type: 'object',
@@ -631,6 +645,18 @@ export const PrivateUserCreateSchema = {
     title: 'PrivateUserCreate'
 } as const;
 
+export const PublishRequestSchema = {
+    properties: {
+        version: {
+            type: 'integer',
+            title: 'Version'
+        }
+    },
+    type: 'object',
+    required: ['version'],
+    title: 'PublishRequest'
+} as const;
+
 export const RenameRequestSchema = {
     properties: {
         new_name: {