diff --git a/src/frontend/web/von_interface/static/js/chatTab.js b/src/frontend/web/von_interface/static/js/chatTab.js
index ec4e1bfc..2da77749 100644
--- a/src/frontend/web/von_interface/static/js/chatTab.js
+++ b/src/frontend/web/von_interface/static/js/chatTab.js
@@ -34342,6 +34342,7 @@ export function initializeChatTab() {
 
     // Add event listeners
     const submitComposer = (event) => {
+        if (isComposerDraftSubmissionInFlight()) return;
         updateSendButtonForCurrentChatState();
         if (!chatSteeringControls?.activate(event)) void handleSendPrompt();
     };
@@ -37208,7 +37209,46 @@ function getQueuedChatPromptHeadsBySession() {
     return heads;
 }
 
+const composerSubmissionsInFlight = new Set();
+
+function isComposerDraftSubmissionInFlight(input = getPromptInputElement()) {
+    return input && [...composerSubmissionsInFlight].some(claim => (
+        claim.sessionId === activeChatSessionId
+        && claim.generation === chatOrganisationGeneration
+        && claim.text === input.value
+    ));
+}
+
 async function handleSendPrompt(options = {}) {
+    const input = getPromptInputElement();
+    const direct = input && !options.fromQueue && !options.observeServerDispatch
+        && typeof options.promptOverride !== 'string'
+        && !getSelectedChatPromptQueueEntryForSend();
+    if (!direct) return performSendPrompt(options);
+
+    // Claim the draft before session creation or dictation can yield. A live
+    // request alone is insufficient: a repeated activation would queue the
+    // same draft (including text retained for attachment recovery).
+    const sessionId = activeChatSessionId;
+    const generation = chatOrganisationGeneration;
+    if (isComposerDraftSubmissionInFlight(input)) return;
+    const claim = { sessionId, generation, text: input.value };
+    composerSubmissionsInFlight.add(claim);
+    const releaseEditedDraft = () => {
+        if (activeChatSessionId === claim.sessionId && input.value !== claim.text) {
+            composerSubmissionsInFlight.delete(claim);
+        }
+    };
+    input.addEventListener('input', releaseEditedDraft);
+    try {
+        return await performSendPrompt(options, claim);
+    } finally {
+        input.removeEventListener('input', releaseEditedDraft);
+        composerSubmissionsInFlight.delete(claim);
+    }
+}
+
+async function performSendPrompt(options = {}, composerClaim = null) {
     if (!options?.fromQueue && !options?.observeServerDispatch && chatSteeringControls?.isSending()) return;
     if (pendingChatOrganisationSwitchId !== null) {
         return;
@@ -37357,6 +37397,12 @@ async function handleSendPrompt(options = {}) {
         return;
     }
 
+    if (composerClaim) {
+        composerClaim.sessionId = targetSessionId;
+        composerClaim.text = promptRaw;
+        composerSubmissionsInFlight.add(composerClaim);
+    }
+
     if (
         !observeServerDispatch
         && isChatPromptSessionBusy(targetSessionId, { includeQueued: !fromQueue })
@@ -42087,6 +42133,7 @@ export function __testOnly_resetChatRequestState() {
     chatPromptQueuePollInFlight = false;
     queuedChatPromptClaimsInFlight.clear();
     queuedChatPromptSubmissionsInFlight.clear();
+    composerSubmissionsInFlight.clear();
     serverDispatchedRetryObserversInFlight.clear();
     voicePromptQueueIds.clear();
     chatPromptQueueAdmissionServerInstanceId = null;
diff --git a/tests/browser/chatDuplicateSubmission.cjs b/tests/browser/chatDuplicateSubmission.cjs
new file mode 100644
index 00000000..487e3862
--- /dev/null
+++ b/tests/browser/chatDuplicateSubmission.cjs
@@ -0,0 +1,72 @@
+// Real chat send and composer modules, isolated HTTP fixtures; no provider calls.
+// PLAYWRIGHT_BROWSERS_PATH=/tmp/von-playwright node tests/browser/chatDuplicateSubmission.cjs
+const assert = require('node:assert/strict');
+const fs = require('node:fs');
+const http = require('node:http');
+const path = require('node:path');
+const { chromium } = require('@playwright/test');
+const root = path.resolve(__dirname, '../../src/frontend/web/von_interface');
+const output = process.argv[2] || '.run/duplicate-send/browser';
+fs.mkdirSync(output, { recursive: true });
+const markup = fs.readFileSync(path.join(root, 'templates/chat_tab.html'), 'utf8').replace(/{%[\s\S]*?%}/g, '').replace(/{{[\s\S]*?}}/g, '');
+const server = http.createServer((req, res) => {
+    if (req.url === '/') return res.end(`<!doctype html><meta charset="utf-8"><meta name="viewport" content="width=device-width,initial-scale=1"><link rel="stylesheet" href="/static/styles.css">${markup}`);
+    const file = path.resolve(root, `.${req.url.split('?')[0]}`);
+    if (!file.startsWith(`${root}/static/`) || !fs.existsSync(file)) return res.writeHead(404).end();
+    res.setHeader('Content-Type', file.endsWith('.css') ? 'text/css' : 'text/javascript');
+    res.end(fs.readFileSync(file));
+});
+(async () => {
+    await new Promise(resolve => server.listen(0, '127.0.0.1', resolve));
+    const browser = await chromium.launch();
+    const evidence = [];
+    try {
+        for (const width of [1440, 375]) {
+            const page = await browser.newPage({ viewport: { width, height: 900 } });
+            const errors = [];
+            page.on('pageerror', error => errors.push(error.message));
+            await page.goto(`http://127.0.0.1:${server.address().port}/`);
+            await page.evaluate(async () => {
+                window.queueBodies = []; window.generateBodies = [];
+                window.fetch = async (url, options = {}) => {
+                    const body = JSON.parse(options.body && typeof options.body === 'string' ? options.body : '{}');
+                    let data = {};
+                    if (url === '/von/api/images/upload') data = { image_attachment: { concept_id: '#V#fixture-image', filename: 'fixture.png' } };
+                    else if (url === '/von/api/chat_prompt_queue' && options.method === 'POST') {
+                        queueBodies.push(body);
+                        data = { success: true, item: { ...body, queue_id: `queue-${queueBodies.length}`, status: 'queued' } };
+                    } else if (url === '/von/generate') {
+                        generateBodies.push(body);
+                        return new Promise(resolve => { window.finishGenerate = () => resolve(new Response(JSON.stringify({ response: 'Received.', llm_debug: { model: 'fixture' } }))); });
+                    } else if (String(url).includes('render_markdown')) data = { html: body.text || '' };
+                    else if (String(url).includes('history/length')) data = { history_length: 0, authenticated: true };
+                    else data = { items: [], history: [] };
+                    return new Response(JSON.stringify(data), { headers: { 'Content-Type': 'application/json' } });
+                };
+                window.chat = await import('/static/js/chatTab.js');
+                chat.__testOnly_setActiveChatSession('fixture', 'Duplicate submission fixture');
+                const { initialiseConversationDraft } = await import('/static/js/components/conversationDraft.js');
+                const input = document.querySelector('#promptInput');
+                initialiseConversationDraft({ input, sendButton: document.querySelector('#sendButton'), onSubmit: () => { window.pending = chat.sendMessage(); } });
+                await chat.__testOnly_uploadFilesToVon([new File(['png'], 'fixture.png', { type: 'image/png' })]);
+            });
+            await page.locator('#promptInput').fill('Describe this image once');
+            await page.locator('#sendButton').dblclick();
+            await page.waitForFunction(() => generateBodies.length === 1);
+            if (width > 800) await page.locator('#promptInput').press('Enter');
+            else await page.locator('#sendButton').click();
+            assert.deepEqual(await page.evaluate(() => [queueBodies.length, generateBodies.length]), [1, 1]);
+            await page.screenshot({ path: path.join(output, `${width}-single-submission.png`) });
+            await page.locator('#promptInput').fill('A deliberate follow-up');
+            await page.locator('#sendButton').click();
+            await page.waitForFunction(() => queueBodies.length === 2);
+            assert.equal(await page.evaluate(() => queueBodies[1].prompt_raw), 'A deliberate follow-up');
+            await page.evaluate(() => finishGenerate());
+            assert.deepEqual(errors, []);
+            evidence.push({ width, generated: 1, admittedOriginal: 1, admittedFollowUp: 1, errors });
+            await page.close();
+        }
+        fs.writeFileSync(path.join(output, 'results.json'), JSON.stringify(evidence, null, 2));
+        console.log(JSON.stringify(evidence));
+    } finally { await browser.close(); server.close(); }
+})().catch(error => { console.error(error); server.close(); process.exitCode = 1; });
diff --git a/tests/frontend/chatAttachmentWorkflowInput.test.js b/tests/frontend/chatAttachmentWorkflowInput.test.js
index 4513bf30..91641f93 100644
--- a/tests/frontend/chatAttachmentWorkflowInput.test.js
+++ b/tests/frontend/chatAttachmentWorkflowInput.test.js
@@ -118,6 +118,82 @@ describe('chat attachment workflow input binding', () => {
         }
     );
 
+    test('concurrent sends while a conversation is being prepared admit only one prompt', async () => {
+        const { __testOnly_setActiveChatSession: select, sendMessage } = require(chatTabModulePath);
+        select(null);
+        let finishCreation;
+        const queueBodies = [];
+        const generateBodies = [];
+        global.fetch = jest.fn(async (url, options = {}) => {
+            if (url === '/von/api/session/create_chat_session') return new Promise(resolve => { finishCreation = resolve; });
+            if (url === '/von/api/chat_prompt_queue' && options.method === 'POST') {
+                const body = JSON.parse(options.body);
+                queueBodies.push(body);
+                return { ok: true, json: async () => ({ success: true, item: { ...body, queue_id: `queue-${queueBodies.length}`, status: 'queued' } }) };
+            }
+            if (url === '/von/generate') {
+                generateBodies.push(JSON.parse(options.body));
+                return { ok: true, json: async () => ({ response: 'Received.', llm_debug: { model: 'test-model' } }) };
+            }
+            if (String(url).startsWith('/von/history/length')) return { ok: true, json: async () => ({ history_length: 0, authenticated: true }) };
+            if (String(url).startsWith('/von/api/render_markdown')) return { ok: true, json: async () => ({ html: JSON.parse(options.body).text || '' }) };
+            return { ok: true, json: async () => ({ items: [], history: [] }) };
+        });
+        document.getElementById('promptInput').value = 'First message';
+        const first = sendMessage();
+        const repeated = sendMessage();
+        for (let i = 0; i < 50 && !finishCreation; i++) await new Promise(resolve => setTimeout(resolve, 5));
+        expect(finishCreation).toBeDefined();
+        expect(global.fetch.mock.calls.filter(([url]) => url === '/von/api/session/create_chat_session')).toHaveLength(1);
+        finishCreation({ ok: true, json: async () => ({ success: true, session_id: 'created-session', history: [] }) });
+        await Promise.all([first, repeated]);
+        expect(queueBodies).toHaveLength(1);
+        expect(generateBodies).toHaveLength(1);
+    });
+
+    test.each(['unchanged', 'edited', 'retyped'])('rapid repeat does not enqueue an in-flight attachment draft: %s', async mode => {
+        const { __testOnly_uploadFilesToVon, sendMessage } = require(chatTabModulePath);
+        let finish;
+        const queueBodies = [];
+        const generateBodies = [];
+        global.fetch = jest.fn(async (url, options = {}) => {
+            if (url === '/von/api/images/upload') return { ok: true, json: async () => ({ image_attachment: { concept_id: '#V#repeat-image', filename: 'repeat.png' } }) };
+            if (url === '/von/api/chat_prompt_queue' && options.method === 'POST') {
+                const body = JSON.parse(options.body);
+                queueBodies.push(body);
+                return { ok: true, json: async () => ({ success: true, item: { ...body, queue_id: `queue-${queueBodies.length}`, status: 'queued' } }) };
+            }
+            if (url === '/von/generate') {
+                generateBodies.push(JSON.parse(options.body));
+                return new Promise(resolve => { finish = resolve; });
+            }
+            if (String(url).startsWith('/von/history/length')) return { ok: true, json: async () => ({ history_length: 0, authenticated: true }) };
+            if (String(url).startsWith('/von/api/render_markdown')) return { ok: true, json: async () => ({ html: JSON.parse(options.body).text || '' }) };
+            return { ok: true, json: async () => ({ items: [] }) };
+        });
+        await __testOnly_uploadFilesToVon([new File(['png'], 'repeat.png', { type: 'image/png' })]);
+        const input = document.getElementById('promptInput');
+        input.value = 'Describe this image';
+        const pending = sendMessage();
+        await sendMessage();
+        for (let i = 0; i < 50 && !finish; i++) await new Promise(resolve => setTimeout(resolve, 5));
+        expect(finish).toBeDefined();
+        await sendMessage();
+        expect(generateBodies).toHaveLength(1);
+        expect(queueBodies).toHaveLength(1);
+        expect(input.value).toBe('Describe this image');
+        if (mode !== 'unchanged') {
+            input.value = 'A different follow-up';
+            input.dispatchEvent(new Event('input', { bubbles: true }));
+            if (mode === 'retyped') input.value = 'Describe this image';
+            await sendMessage();
+            expect(queueBodies).toHaveLength(2);
+            expect(queueBodies[1].prompt_raw).toBe(mode === 'retyped' ? 'Describe this image' : 'A different follow-up');
+        }
+        finish({ ok: true, json: async () => ({ response: 'Received.', llm_debug: { model: 'test-model' } }) });
+        await pending;
+    });
+
     test('successful text-only submission stays cleared after switching away and back', async () => {
         const { __testOnly_setActiveChatSession: select, sendMessage } = require(chatTabModulePath);
         global.fetch = jest.fn(async (url, options = {}) => ({ ok: true, json: async () => {