diff --git a/src/workbench/extensions/agent/AgentPanelRoot.test.ts b/src/workbench/extensions/agent/AgentPanelRoot.test.ts
index 7b8578bdcf..16be4361ef 100644
--- a/src/workbench/extensions/agent/AgentPanelRoot.test.ts
+++ b/src/workbench/extensions/agent/AgentPanelRoot.test.ts
@@ -46,11 +46,17 @@ vi.mock('@/scripts/api', () => {
   }
 })
 
-const appMock = vi.hoisted(() => ({
-  loadGraphData: vi.fn(),
-  graph: { nodes: [] as unknown[] },
-  canvas: undefined as { graph: { nodes: unknown[] } } | undefined
-}))
+const appMock = vi.hoisted(() => {
+  const graph = {
+    nodes: [] as unknown[],
+    serialize: () => ({ version: 0.4, nodes: graph.nodes })
+  }
+  return {
+    loadGraphData: vi.fn(),
+    graph,
+    canvas: undefined as { graph: { nodes: unknown[] } } | undefined
+  }
+})
 
 vi.mock('@/scripts/app', () => ({ app: appMock }))
 
@@ -932,7 +938,7 @@ describe('AgentPanelRoot workflow binding', () => {
   })
 
   it('retries once without the speculative id when the server rejects it', async () => {
-    makeTab('someone-elses-uuid')
+    const tab = makeTab('someone-elses-uuid')
     const bodies: unknown[] = []
     vi.stubGlobal(
       'fetch',
@@ -968,8 +974,8 @@ describe('AgentPanelRoot workflow binding', () => {
     expect(bodies[0]).toMatchObject({ workflow_id: 'someone-elses-uuid' })
     expect(bodies[1]).not.toHaveProperty('workflow_id')
 
-    // The minted id was NOT adopted onto the active tab (it is not the id we
-    // sent), so its first patch takes the new-tab path, not the active tab.
+    // The send uploaded this tab's canvas, so the minted id binds to it and
+    // its first patch applies IN the active tab (the draft mirrors the tab).
     const graph = { version: 0.4, nodes: [{ id: 9 }] }
     socket.emit('message', {
       data: JSON.stringify({
@@ -983,7 +989,7 @@ describe('AgentPanelRoot workflow binding', () => {
       })
     })
     await vi.waitFor(() =>
-      expect(app.loadGraphData).toHaveBeenCalledWith(graph, true, true, null)
+      expect(app.loadGraphData).toHaveBeenCalledWith(graph, true, true, tab)
     )
   })
 
@@ -1062,7 +1068,7 @@ describe('AgentPanelRoot workflow binding', () => {
     await screen.findByRole('button', { name: 'Stop' })
 
     tab.isModified = true
-    patch(1, { version: 0.4, nodes: [] })
+    patch(1, { version: 0.4, nodes: [{ id: 2 }] })
     await screen.findByText(i18n.global.t('agent.conflictTitle'))
     // The X close is a defer, same as Cancel: nothing applies.
     await userEvent.click(
@@ -1098,7 +1104,7 @@ describe('AgentPanelRoot workflow binding', () => {
     await screen.findByRole('button', { name: 'Stop' })
 
     tab.isModified = true
-    patch(1, { version: 0.4, nodes: [] })
+    patch(1, { version: 0.4, nodes: [{ id: 2 }] })
     await screen.findByText(i18n.global.t('agent.conflictTitle'))
     await userEvent.click(
       screen.getByRole('button', { name: i18n.global.t('g.cancel') })
@@ -1174,7 +1180,7 @@ describe('AgentPanelRoot workflow binding', () => {
 
     // The user edited the tab after the turn started: no silent overwrite.
     tab.isModified = true
-    patch(1, { version: 0.4, nodes: [] })
+    patch(1, { version: 0.4, nodes: [{ id: 1 }] })
     expect(
       await screen.findByText(i18n.global.t('agent.conflictTitle'))
     ).toBeInTheDocument()
@@ -1184,7 +1190,7 @@ describe('AgentPanelRoot workflow binding', () => {
     await userEvent.click(
       screen.getByRole('button', { name: i18n.global.t('g.cancel') })
     )
-    patch(2, { version: 0.4, nodes: [] })
+    patch(2, { version: 0.4, nodes: [{ id: 1 }] })
     await nextTick()
     expect(app.loadGraphData).not.toHaveBeenCalled()
     expect(
@@ -1227,7 +1233,7 @@ describe('AgentPanelRoot workflow binding', () => {
     await screen.findByRole('button', { name: 'Stop' })
 
     tab.isModified = true
-    patch(1, { version: 0.4, nodes: [] })
+    patch(1, { version: 0.4, nodes: [{ id: 1 }] })
     await screen.findByText(i18n.global.t('agent.conflictTitle'))
     await userEvent.click(
       screen.getByRole('button', { name: i18n.global.t('agent.keepMine') })
@@ -1318,8 +1324,8 @@ describe('AgentPanelRoot workflow binding', () => {
     })
     expect(vi.mocked(app.loadGraphData).mock.calls[1][3]).toBe(tab)
   })
-  it('parks an empty unbound draft instead of opening a blank tab', async () => {
-    makeTab()
+  it('parks an empty minted draft, then applies the first real patch to the uploading tab', async () => {
+    const tab = makeTab()
     mockMessagesEndpoint('wf-42')
 
     render(AgentPanelRoot, { global: { plugins: [i18n] } })
@@ -1334,11 +1340,12 @@ describe('AgentPanelRoot workflow binding', () => {
     await nextTick()
     expect(app.loadGraphData).not.toHaveBeenCalled()
 
-    // The first patch with real nodes opens the tab as usual.
+    // The send uploaded this tab's canvas, so the minted id is bound to it
+    // and the first patch with real nodes applies in place.
     const graph = { version: 0.4, nodes: [{ id: 1 }] }
     patch(2, graph)
     await vi.waitFor(() =>
-      expect(app.loadGraphData).toHaveBeenCalledWith(graph, true, true, null)
+      expect(app.loadGraphData).toHaveBeenCalledWith(graph, true, true, tab)
     )
   })
 
@@ -1398,4 +1405,117 @@ describe('AgentPanelRoot workflow binding', () => {
       selection: { node_ids: ['12'], nodes: [serialized] }
     })
   })
+
+  it('uploads the canvas once per change and binds the minted id for in-place applies', async () => {
+    const tab = makeTab()
+    const bodies = mockMessagesEndpoint('wf-mint')
+    appMock.graph.nodes = [{ id: 1 }]
+
+    render(AgentPanelRoot, { global: { plugins: [i18n] } })
+
+    await userEvent.type(screen.getByRole('textbox'), 'help me')
+    await userEvent.click(screen.getByRole('button', { name: 'Send' }))
+    await screen.findByRole('button', { name: 'Stop' })
+
+    // First send carries the serialized canvas; the tab is unsaved, so no id.
+    expect(bodies[0]).toMatchObject({
+      workflow: {
+        content: { version: 0.4, nodes: [{ id: 1 }] },
+        base_version: null
+      }
+    })
+    expect(bodies[0]).not.toHaveProperty('workflow_id')
+
+    socket.emit('message', {
+      data: JSON.stringify({
+        type: 'agent_message_done',
+        data: { message_id: 'm-1', thread_id: 'th-1' }
+      })
+    })
+    await screen.findByRole('button', { name: 'Send' })
+
+    // Unchanged graph: the second send skips the upload.
+    await userEvent.type(screen.getByRole('textbox'), 'and more')
+    await userEvent.click(screen.getByRole('button', { name: 'Send' }))
+    await vi.waitFor(() => expect(bodies).toHaveLength(2))
+    expect(bodies[1]).not.toHaveProperty('workflow')
+
+    // The uploaded draft mirrors the tab, so the minted id applies in place.
+    const graph = { version: 0.4, nodes: [{ id: 2 }] }
+    socket.emit('message', {
+      data: JSON.stringify({
+        type: 'draft_patch',
+        data: {
+          workflow_id: 'wf-mint',
+          base_version: 0,
+          version: 1,
+          content: graph
+        }
+      })
+    })
+    await vi.waitFor(() =>
+      expect(app.loadGraphData).toHaveBeenCalledWith(graph, true, true, tab)
+    )
+  })
+
+  it('parks an empty draft even for the bound tab', async () => {
+    const tab = makeTab('wf-42')
+    mockMessagesEndpoint('wf-42')
+
+    render(AgentPanelRoot, { global: { plugins: [i18n] } })
+
+    await userEvent.type(screen.getByRole('textbox'), 'help me')
+    await userEvent.click(screen.getByRole('button', { name: 'Send' }))
+    await screen.findByRole('button', { name: 'Stop' })
+
+    // The server's initial empty draft must neither blank the bound tab nor
+    // raise the conflict dialog against a user-edited one.
+    tab.isModified = true
+    patch(1, { version: 0.4, nodes: [] })
+    await nextTick()
+    await nextTick()
+    expect(app.loadGraphData).not.toHaveBeenCalled()
+    expect(
+      screen.queryByText(i18n.global.t('agent.conflictTitle'))
+    ).not.toBeInTheDocument()
+  })
+
+  it('re-uploads the canvas after a failed send', async () => {
+    makeTab()
+    appMock.graph.nodes = [{ id: 1 }]
+    const bodies: unknown[] = []
+    let calls = 0
+    vi.stubGlobal(
+      'fetch',
+      vi.fn(async (url: string, init?: RequestInit) => {
+        if (!url.includes('/messages') || init?.method !== 'POST')
+          return new Response('{}', { status: 200 })
+        calls += 1
+        bodies.push(JSON.parse(String(init?.body)))
+        if (calls === 1) return new Response('{}', { status: 500 })
+        return new Response(
+          JSON.stringify({
+            thread_id: 'th-1',
+            message_id: 'm-1',
+            workflow_id: 'wf-mint'
+          }),
+          { status: 202, headers: { 'Content-Type': 'application/json' } }
+        )
+      })
+    )
+
+    render(AgentPanelRoot, { global: { plugins: [i18n] } })
+
+    await userEvent.type(screen.getByRole('textbox'), 'one')
+    await userEvent.click(screen.getByRole('button', { name: 'Send' }))
+    await vi.waitFor(() => expect(bodies).toHaveLength(1))
+
+    // The failed send consumed the guard without reaching the server; the
+    // retry must carry the canvas again.
+    await userEvent.type(screen.getByRole('textbox'), 'two')
+    await userEvent.click(screen.getByRole('button', { name: 'Send' }))
+    await vi.waitFor(() => expect(bodies).toHaveLength(2))
+    expect(bodies[0]).toHaveProperty('workflow')
+    expect(bodies[1]).toHaveProperty('workflow')
+  })
 })
diff --git a/src/workbench/extensions/agent/AgentPanelRoot.vue b/src/workbench/extensions/agent/AgentPanelRoot.vue
index 9fb9273b3f..e16442b596 100644
--- a/src/workbench/extensions/agent/AgentPanelRoot.vue
+++ b/src/workbench/extensions/agent/AgentPanelRoot.vue
@@ -35,6 +35,7 @@ import { useAgentDraftStore } from './stores/agent/agentDraftStore'
 import { useAgentWorkflowTabBindingStore } from './stores/agent/agentWorkflowTabBindingStore'
 import { buildTranscriptMarkdown } from './services/agent/agentTranscript'
 import { createAgentRestClient } from './services/agent/agentRestClient'
+import type { WorkflowUpload } from './services/agent/agentRestClient'
 import { createReconnectingEventSource } from './services/agent/agentEventSource'
 import { useAgentChatHistoryStore } from './stores/agent/agentChatHistoryStore'
 import { useAgentPanelStore } from './stores/agent/agentPanelStore'
@@ -114,14 +115,46 @@ const activeTab = computed<ActiveTab | null>(() => {
   return active ? { name: active.filename } : null
 })
 
-// Bind only when the server confirmed the id we sent for that tab; a freshly
-// minted id stays unbound so its first patch opens (and binds) its own tab.
+// The turn runs against the canvas as of the send: upload the serialized
+// graph when it changed since the last upload so the server can seed the
+// thread's draft from it (cloud postMessage.workflow contract; servers
+// without the field ignore it). Oversized graphs are skipped, matching the
+// server's 413 limit.
+const MAX_UPLOAD_CHARS = 2_000_000
+let lastSentGraph: string | null = null
+let snapshotTabPath: string | null = null
+
+function takeWorkflowSnapshot(): WorkflowUpload | undefined {
+  const graph = app.graph?.serialize()
+  if (!graph) return undefined
+  const serialized = JSON.stringify(graph)
+  if (serialized === lastSentGraph || serialized.length > MAX_UPLOAD_CHARS)
+    return undefined
+  lastSentGraph = serialized
+  snapshotTabPath = workflowStore.activeWorkflow?.path ?? null
+  return { content: graph, base_version: draftStore.version }
+}
+
+// A fresh thread gets a fresh draft on the server: re-upload on next send.
+function resetSnapshotGuard(): void {
+  lastSentGraph = null
+  snapshotTabPath = null
+}
+
+// Bind when the server confirmed the id we sent for that tab, or when the
+// send uploaded this tab's canvas: the draft then mirrors the tab, so even a
+// freshly minted id applies in place instead of opening a new tab.
 function onWorkflowAdopted(
   workflowId: string,
-  sent: WorkflowTurnContext | undefined
+  sent: WorkflowTurnContext | undefined,
+  uploaded: boolean
 ): void {
-  if (sent !== undefined && sent.id === workflowId)
+  if (sent !== undefined && sent.id === workflowId) {
     bindingStore.bind(workflowId, sent.tabPath)
+    return
+  }
+  if (uploaded && snapshotTabPath !== null)
+    bindingStore.bind(workflowId, snapshotTabPath)
 }
 
 const {
@@ -142,7 +175,8 @@ const {
   events,
   workflow: {
     current: activeWorkflowTurnContext,
-    adopted: onWorkflowAdopted
+    adopted: onWorkflowAdopted,
+    snapshot: takeWorkflowSnapshot
   }
 })
 
@@ -250,6 +284,11 @@ async function applyDraft(): Promise<void> {
       lastApplied.version >= version
     )
       return
+    // An agent draft with no nodes is noise (the server's freshly minted
+    // draft starts empty): applying it would blank a bound tab or conjure an
+    // empty one. Park until a patch carries actual nodes.
+    const nodes = (content as { nodes?: unknown }).nodes
+    if (!Array.isArray(nodes) || nodes.length === 0) return
     const boundTab = boundTabFor(workflowId)
     if (boundTab) {
       if (workflowStore.activeWorkflow?.path !== boundTab.path) return
@@ -260,10 +299,6 @@ async function applyDraft(): Promise<void> {
       await loadDraft(workflowId, version, content, boundTab)
       return
     }
-    // The server's freshly minted draft starts empty; conjuring a blank tab
-    // for it only confuses. Park until a patch carries actual nodes.
-    const nodes = (content as { nodes?: unknown }).nodes
-    if (!Array.isArray(nodes) || nodes.length === 0) return
     await loadDraft(workflowId, version, content, null)
   } finally {
     applying = false
@@ -359,6 +394,7 @@ watch(threadId, (id) => history.setActive(id), { immediate: true })
 void refreshHistory()
 
 async function onSelectHistory(id: string): Promise<void> {
+  resetSnapshotGuard()
   await loadThread(id)
   void refreshHistory()
 }
@@ -394,7 +430,15 @@ function onSend(text: string, attachments: ComposerAttachment[]): void {
   // its version may never advance, so the version watch alone cannot re-drive.
   applySuppressed = false
   void applyDraft()
-  void sendMessage(text, attachments, tagsWithNodeData(consumeSelection()))
+  void sendMessage(
+    text,
+    attachments,
+    tagsWithNodeData(consumeSelection())
+  ).then((ok) => {
+    // A failed send consumed the snapshot guard without reaching the
+    // server; drop it so the next send re-uploads.
+    if (!ok) resetSnapshotGuard()
+  })
 }
 
 function onStop(): void {
@@ -402,6 +446,7 @@ function onStop(): void {
 }
 
 function onNewChat(): void {
+  resetSnapshotGuard()
   newChat()
 }
 
diff --git a/src/workbench/extensions/agent/composables/agent/useAgentSession.test.ts b/src/workbench/extensions/agent/composables/agent/useAgentSession.test.ts
index 12363ed436..eef3ff272f 100644
--- a/src/workbench/extensions/agent/composables/agent/useAgentSession.test.ts
+++ b/src/workbench/extensions/agent/composables/agent/useAgentSession.test.ts
@@ -409,6 +409,29 @@ describe('useAgentSession (v1 composition root)', () => {
     expect(sightedBody.selection?.context).not.toContain('ask them to save')
   })
 
+  it('(h4) attaches the workflow snapshot and reports the upload to adopted', async () => {
+    const rest = fakeRest()
+    const adopted = vi.fn()
+    const session = useAgentSession({
+      rest,
+      events: fakeEvents().source,
+      workflow: {
+        current: () => undefined,
+        adopted,
+        snapshot: () => ({
+          content: { nodes: [{ id: 1 }] },
+          base_version: null
+        })
+      }
+    })
+    session.start()
+    await session.sendMessage('hi')
+    expect(vi.mocked(rest.postMessage).mock.calls[0][1]).toMatchObject({
+      workflow: { content: { nodes: [{ id: 1 }] }, base_version: null }
+    })
+    expect(adopted).toHaveBeenCalledWith('wf-1', undefined, true)
+  })
+
   it('(h3) a selection whose definitions all dropped does not claim they are included', async () => {
     const rest = fakeRest()
     const session = useAgentSession({ rest, events: fakeEvents().source })
diff --git a/src/workbench/extensions/agent/composables/agent/useAgentSession.ts b/src/workbench/extensions/agent/composables/agent/useAgentSession.ts
index 595fdc8851..4e0a08caeb 100644
--- a/src/workbench/extensions/agent/composables/agent/useAgentSession.ts
+++ b/src/workbench/extensions/agent/composables/agent/useAgentSession.ts
@@ -4,7 +4,10 @@ import { i18n } from '@/i18n'
 import type { TurnId } from '../../schemas/agentApiSchema'
 import { isAgentEvent, parseAgentWsEvent } from '../../schemas/agentApiSchema'
 import { AgentApiError } from '../../services/agent/agentRestClient'
-import type { AgentRestClient } from '../../services/agent/agentRestClient'
+import type {
+  AgentRestClient,
+  WorkflowUpload
+} from '../../services/agent/agentRestClient'
 import { useAgentConversationStore } from '../../stores/agent/agentConversationStore'
 import { useAgentDraftStore } from '../../stores/agent/agentDraftStore'
 
@@ -76,7 +79,14 @@ export interface AgentSessionDeps {
   events: AgentEventSource
   workflow?: {
     current(): WorkflowTurnContext | undefined
-    adopted(workflowId: string, sent: WorkflowTurnContext | undefined): void
+    adopted(
+      workflowId: string,
+      sent: WorkflowTurnContext | undefined,
+      uploaded: boolean
+    ): void
+    // The canvas snapshot to seed the server draft with, or undefined when
+    // unchanged since the last upload.
+    snapshot?(): WorkflowUpload | undefined
   }
 }
 
@@ -187,13 +197,15 @@ export function useAgentSession(deps: AgentSessionDeps) {
     }
     sending.value = true
     const wfContext = workflow?.current()
+    const upload = workflow?.snapshot?.()
     const input = {
       content: text,
       selection:
         tags !== undefined && tags.length > 0
           ? selectionPayload(tags, wfContext !== undefined)
           : undefined,
-      attachments: attachments?.map((attachment) => attachment.ref)
+      attachments: attachments?.map((attachment) => attachment.ref),
+      workflow: upload
     }
     async function postTurn(threadId: string) {
       try {
@@ -216,7 +228,7 @@ export function useAgentSession(deps: AgentSessionDeps) {
       localStorage.setItem(THREAD_STORAGE_KEY, ack.thread_id)
       if (ack.workflow_id !== undefined) {
         draftStore.bind(ack.workflow_id)
-        workflow?.adopted(ack.workflow_id, wfContext)
+        workflow?.adopted(ack.workflow_id, wfContext, upload !== undefined)
       }
       // The ONE branding seam: the server-minted message_id becomes the TurnId.
       const turnId = ack.message_id as TurnId
diff --git a/src/workbench/extensions/agent/services/agent/agentRestClient.ts b/src/workbench/extensions/agent/services/agent/agentRestClient.ts
index 490cb8bd9c..e2c0a87d4b 100644
--- a/src/workbench/extensions/agent/services/agent/agentRestClient.ts
+++ b/src/workbench/extensions/agent/services/agent/agentRestClient.ts
@@ -41,11 +41,20 @@ export interface AgentRestClientDeps {
   fetchImpl?: typeof fetch
 }
 
+// The client's canvas, uploaded with a turn so the server seeds the thread's
+// draft from it before the agent runs. base_version null force-seeds; a
+// non-null value guards against clobbering an agent write (server 409s).
+export interface WorkflowUpload {
+  content: unknown
+  base_version: number | null
+}
+
 export interface PostMessageInput {
   content: string
   workflowId?: string
   selection?: Record<string, unknown>
   attachments?: string[]
+  workflow?: WorkflowUpload
 }
 
 interface IngestErrorBody {
@@ -129,6 +138,7 @@ export function createAgentRestClient(deps: AgentRestClientDeps) {
     if (req.workflowId !== undefined) body.workflow_id = req.workflowId
     if (req.selection !== undefined) body.selection = req.selection
     if (req.attachments !== undefined) body.attachments = req.attachments
+    if (req.workflow !== undefined) body.workflow = req.workflow
     return request(
       `/api/agent/threads/${threadId}/messages`,
       await jsonInit('POST', body),