diff --git a/src/content/da-api.js b/src/content/da-api.js
index 22d843df5..ae640dc61 100644
--- a/src/content/da-api.js
+++ b/src/content/da-api.js
@@ -140,7 +140,10 @@ export class DaClient {
   }
 
   /**
-   * Uploads a file via PUT.
+   * Uploads a file via multipart POST — the documented DA API contract.
+   * Raw body uploads are only supported by DA for text/html; all other types
+   * (including application/json) are silently ignored and must use form-data.
+   * See: https://docs.da.live/developers/api/source
    * @param {string} org
    * @param {string} site
    * @param {string} daPath
@@ -148,18 +151,20 @@ export class DaClient {
    * @param {string} contentType
    * @returns {Promise<object>} API response body
    */
-  async putSource(org, site, daPath, buffer, contentType) {
+  async postSource(org, site, daPath, buffer, contentType) {
     const url = `${DA_ADMIN}/source/${org}/${site}${daPath}`;
+    const formData = new FormData();
+    formData.append('data', new Blob([buffer], { type: contentType }));
     const res = await this.fetch(url, {
-      method: 'PUT',
-      headers: { ...this.authHeader, 'Content-Type': contentType },
-      body: buffer,
+      method: 'POST',
+      headers: { ...this.authHeader },
+      body: formData,
     });
     if (res.status === 401) {
       throw new Error('Unauthorized: invalid or missing token');
     }
     if (!res.ok) {
-      throw new Error(`PUT failed for ${daPath}: ${res.status} ${res.statusText}`);
+      throw new Error(`POST failed for ${daPath}: ${res.status} ${res.statusText}`);
     }
     return res.json();
   }
diff --git a/src/content/push.cmd.js b/src/content/push.cmd.js
index 9473e4b18..4222f311a 100644
--- a/src/content/push.cmd.js
+++ b/src/content/push.cmd.js
@@ -123,7 +123,7 @@ export default class PushCommand {
         const ext = daPath.split('.').pop();
         try {
           const buffer = await fse.readFile(localPath);
-          await client.putSource(org, site, daPath, buffer, getContentType(ext));
+          await client.postSource(org, site, daPath, buffer, getContentType(ext));
           log.info(`  ✓ ${daPath}`);
           return { ok: true };
         } catch (err) {
diff --git a/test/content/content-test-utils.js b/test/content/content-test-utils.js
index 5e9dac119..b284a29e0 100644
--- a/test/content/content-test-utils.js
+++ b/test/content/content-test-utils.js
@@ -78,10 +78,10 @@ export async function stageAllAndCommit(contentDir, message) {
  * @param {Array}   opts.files           files returned by listAll
  * @param {string}  opts.sourceContent   content returned by getSource (null = 404)
  * @param {number}  opts.remoteLastModified lastModified returned by getRemoteLastModified
- * @param {boolean} opts.putFails        if true, putSource throws
+ * @param {boolean} opts.uploadFails        if true, postSource throws
  * @param {boolean} opts.deleteFails     if true, deleteSource throws
  * @param {Function} opts.onGetSource   called with (owner, repo, daPath) when getSource is called
- * @param {Function} opts.onPut         called with (daPath) when putSource is called
+ * @param {Function} opts.onUpload         called with (daPath, buffer, contentType)
  * @param {Function} opts.onDelete      called with (daPath) when deleteSource is called
  */
 export function createDaClientClass(opts = {}) {
@@ -125,12 +125,13 @@ export function createDaClientClass(opts = {}) {
     return opts.remoteLastModified !== undefined ? opts.remoteLastModified : null;
   };
 
-  DaClientMock.prototype.putSource = async function putSource(org, site, daPath) {
-    if (opts.putFails) {
-      throw new Error(`PUT failed for ${daPath}`);
+  // eslint-disable-next-line max-len
+  DaClientMock.prototype.postSource = async function postSource(org, site, daPath, buffer, contentType) {
+    if (opts.uploadFails) {
+      throw new Error(`POST failed for ${daPath}`);
     }
-    if (opts.onPut) {
-      opts.onPut(daPath);
+    if (opts.onUpload) {
+      opts.onUpload(daPath, buffer, contentType);
     }
     return {};
   };
diff --git a/test/content/da-api.test.js b/test/content/da-api.test.js
index 33a902a14..ae85f36af 100644
--- a/test/content/da-api.test.js
+++ b/test/content/da-api.test.js
@@ -270,22 +270,60 @@ describe('DaClient', () => {
     });
   });
 
-  describe('putSource', () => {
+  describe('postSource', () => {
     it('returns parsed JSON on success', async () => {
       const responseBody = { status: 'ok' };
       client.fetch = async () => mockResponse(200, responseBody);
-      const result = await client.putSource('org', 'repo', '/file.html', Buffer.from('<html>'), 'text/html');
+      const result = await client.postSource('org', 'repo', '/file.html', Buffer.from('<html>'), 'text/html');
       assert.deepStrictEqual(result, responseBody);
     });
 
-    it('sends PUT request', async () => {
+    it('sends POST request', async () => {
       let method;
       client.fetch = async (url, opts) => {
         method = opts.method;
         return mockResponse(200, {});
       };
-      await client.putSource('org', 'repo', '/file.html', Buffer.from(''), 'text/html');
-      assert.strictEqual(method, 'PUT');
+      await client.postSource('org', 'repo', '/file.html', Buffer.from(''), 'text/html');
+      assert.strictEqual(method, 'POST');
+    });
+
+    it('sends multipart form-data body with file content in data field', async () => {
+      const content = '<html><body>hello</body></html>';
+      let body;
+      client.fetch = async (url, opts) => {
+        body = opts.body;
+        return mockResponse(200, {});
+      };
+      await client.postSource('org', 'repo', '/file.html', Buffer.from(content), 'text/html');
+      assert.ok(body instanceof FormData, 'body should be FormData');
+      const dataField = body.get('data');
+      assert.ok(dataField != null, 'FormData should have a data field');
+      assert.strictEqual(await dataField.text(), content);
+    });
+
+    it('sets correct content type on the data Blob for each file type', async () => {
+      for (const [ext, expectedType] of [['html', 'text/html'], ['json', 'application/json']]) {
+        let body;
+        client.fetch = async (url, opts) => {
+          body = opts.body;
+          return mockResponse(200, {});
+        };
+        // eslint-disable-next-line no-await-in-loop
+        await client.postSource('org', 'repo', `/file.${ext}`, Buffer.from('content'), expectedType);
+        const dataField = body.get('data');
+        assert.strictEqual(dataField.type, expectedType, `Blob type should be ${expectedType} for .${ext}`);
+      }
+    });
+
+    it('does not set Content-Type header directly (lets fetch set multipart boundary)', async () => {
+      let reqHeaders;
+      client.fetch = async (url, opts) => {
+        reqHeaders = opts.headers;
+        return mockResponse(200, {});
+      };
+      await client.postSource('org', 'repo', '/file.json', Buffer.from('{}'), 'application/json');
+      assert.ok(!('Content-Type' in reqHeaders), 'Content-Type must not be set manually on multipart requests');
     });
 
     it('calls correct source URL', async () => {
@@ -294,14 +332,14 @@ describe('DaClient', () => {
         calledUrl = url;
         return mockResponse(200, {});
       };
-      await client.putSource('org', 'repo', '/page.html', Buffer.from(''), 'text/html');
+      await client.postSource('org', 'repo', '/page.html', Buffer.from(''), 'text/html');
       assert.strictEqual(calledUrl, 'https://admin.da.live/source/org/repo/page.html');
     });
 
     it('throws Unauthorized on 401', async () => {
       client.fetch = async () => mockResponse(401, 'Unauthorized', false);
       await assert.rejects(
-        () => client.putSource('org', 'repo', '/file.html', Buffer.from(''), 'text/html'),
+        () => client.postSource('org', 'repo', '/file.html', Buffer.from(''), 'text/html'),
         /Unauthorized/,
       );
     });
@@ -309,8 +347,8 @@ describe('DaClient', () => {
     it('throws on non-ok status', async () => {
       client.fetch = async () => mockResponse(500, 'Error', false);
       await assert.rejects(
-        () => client.putSource('org', 'repo', '/file.html', Buffer.from(''), 'text/html'),
-        /PUT failed/,
+        () => client.postSource('org', 'repo', '/file.html', Buffer.from(''), 'text/html'),
+        /POST failed/,
       );
     });
   });
diff --git a/test/content/push.cmd.test.js b/test/content/push.cmd.test.js
index 08fb6a6a2..af547114e 100644
--- a/test/content/push.cmd.test.js
+++ b/test/content/push.cmd.test.js
@@ -116,7 +116,7 @@ describe('PushCommand', () => {
 
       let putCalled = false;
       const DaClientClass = createDaClientClass({
-        onPut: () => {
+        onUpload: () => {
           putCalled = true;
         },
       });
@@ -167,7 +167,7 @@ describe('PushCommand', () => {
       let putCalled = false;
       const DaClientClass = createDaClientClass({
         remoteLastModified: Date.now() + 60_000,
-        onPut: () => { putCalled = true; },
+        onUpload: () => { putCalled = true; },
       });
       const log = makeLogger();
       const mod = await esmock('../../src/content/push.cmd.js', {
@@ -190,7 +190,7 @@ describe('PushCommand', () => {
       await stageAllAndCommit(contentDir, 'edit index');
 
       const pushed = [];
-      const DaClientClass = createDaClientClass({ onPut: (p) => pushed.push(p) });
+      const DaClientClass = createDaClientClass({ onUpload: (p) => pushed.push(p) });
       const log = makeLogger();
       const mod = await esmock('../../src/content/push.cmd.js', {
         '../../src/content/da-auth.js': { getValidToken: async () => 'token' },
@@ -206,6 +206,48 @@ describe('PushCommand', () => {
       assert.ok(pushed.includes('/index.html'));
     });
 
+    it('pushes modified JSON file with correct content and content-type', async () => {
+      const contentDir = await setupContentDir(testRoot);
+
+      // Add a JSON file in the baseline (the synced point)
+      await fse.writeFile(path.join(contentDir, 'metadata.json'), '{"title":"original"}');
+      await stageAllAndCommit(contentDir, 'add json');
+
+      // Write synced ref to this new HEAD so the json file is the baseline
+      const baseOid = await git.resolveRef({ fs, dir: contentDir, ref: 'HEAD' });
+      await git.writeRef({
+        fs, dir: contentDir, ref: DA_SYNCED_REF, value: baseOid, force: true,
+      });
+
+      // Now modify the JSON — this is the scenario Claude edits then user commits/pushes
+      const updatedContent = '{"title":"updated"}';
+      await fse.writeFile(path.join(contentDir, 'metadata.json'), updatedContent);
+      await stageAllAndCommit(contentDir, 'edit json');
+
+      const puts = {};
+      const DaClientClass = createDaClientClass({
+        onUpload: (daPath, buffer, contentType) => {
+          puts[daPath] = { body: buffer.toString('utf-8'), contentType };
+        },
+      });
+
+      // Use real getContentType so we can verify application/json is sent
+      const { getContentType: realGetContentType } = await import('../../src/content/da-api.js');
+      const mod = await esmock('../../src/content/push.cmd.js', {
+        '../../src/content/da-auth.js': { getValidToken: async () => 'token' },
+        '../../src/content/da-api.js': {
+          DaClient: DaClientClass,
+          getContentType: realGetContentType,
+        },
+      });
+      const Cmd = mod.default;
+      await new Cmd(makeLogger()).withDirectory(testRoot).run();
+
+      assert.ok('/metadata.json' in puts, 'JSON file should be pushed');
+      assert.strictEqual(puts['/metadata.json'].body, updatedContent, 'pushed content should match modified file');
+      assert.strictEqual(puts['/metadata.json'].contentType, 'application/json', 'content-type should be application/json');
+    });
+
     it('deletes removed files from da.live', async () => {
       const contentDir = await setupContentDir(testRoot);
       await fse.remove(path.join(contentDir, 'index.html'));
@@ -235,7 +277,7 @@ describe('PushCommand', () => {
       await stageAllAndCommit(contentDir, 'edit pages');
 
       const pushed = [];
-      const DaClientClass = createDaClientClass({ onPut: (p) => pushed.push(p) });
+      const DaClientClass = createDaClientClass({ onUpload: (p) => pushed.push(p) });
       const log = makeLogger();
       const mod = await esmock('../../src/content/push.cmd.js', {
         '../../src/content/da-auth.js': { getValidToken: async () => 'token' },
@@ -260,7 +302,7 @@ describe('PushCommand', () => {
       await stageAllAndCommit(contentDir, 'edit blog and add blog2');
 
       const pushed = [];
-      const DaClientClass = createDaClientClass({ onPut: (p) => pushed.push(p) });
+      const DaClientClass = createDaClientClass({ onUpload: (p) => pushed.push(p) });
       const log = makeLogger();
       const mod = await esmock('../../src/content/push.cmd.js', {
         '../../src/content/da-auth.js': { getValidToken: async () => 'token' },
@@ -284,7 +326,7 @@ describe('PushCommand', () => {
       await stageAllAndCommit(contentDir, 'edit pages');
 
       const pushed = [];
-      const DaClientClass = createDaClientClass({ onPut: (p) => pushed.push(p) });
+      const DaClientClass = createDaClientClass({ onUpload: (p) => pushed.push(p) });
       const log = makeLogger();
       const mod = await esmock('../../src/content/push.cmd.js', {
         '../../src/content/da-auth.js': { getValidToken: async () => 'token' },
@@ -334,6 +376,36 @@ describe('PushCommand', () => {
       assert.strictEqual(syncedOid, headOid);
     });
 
+    it('does not advance synced ref when an upload fails on the server', async () => {
+      const contentDir = await setupContentDir(testRoot);
+      await fse.writeFile(path.join(contentDir, 'index.html'), 'changed');
+      await stageAllAndCommit(contentDir, 'edit index');
+
+      const DaClientClass = createDaClientClass({ uploadFails: true });
+      const log = makeLogger();
+      const mod = await esmock('../../src/content/push.cmd.js', {
+        '../../src/content/da-auth.js': { getValidToken: async () => 'token' },
+        '../../src/content/da-api.js': {
+          DaClient: DaClientClass,
+          getContentType: () => 'text/html',
+        },
+      });
+      const Cmd = mod.default;
+      const cmd = new Cmd(log).withDirectory(testRoot);
+      await cmd.run();
+
+      const headOid = await git.resolveRef({ fs, dir: contentDir, ref: 'HEAD' });
+      let syncedOid;
+      try {
+        syncedOid = await git.resolveRef({ fs, dir: contentDir, ref: DA_SYNCED_REF });
+      } catch {
+        syncedOid = null;
+      }
+      assert.notStrictEqual(syncedOid, headOid);
+      assert.ok(log.logs.some((l) => l.msg.includes('Sync ref not updated')));
+      assert.ok(log.logs.some((l) => l.msg.includes('error') || l.msg.includes('✗')));
+    });
+
     it('does not advance synced ref when a delete fails on the server', async () => {
       const contentDir = await setupContentDir(testRoot);
       await fse.remove(path.join(contentDir, 'index.html'));