diff --git a/packages/web/server/lib/markdown-image-grants/DOCUMENTATION.md b/packages/web/server/lib/markdown-image-grants/DOCUMENTATION.md
index 1b2a390d..845d2fce 100644
--- a/packages/web/server/lib/markdown-image-grants/DOCUMENTATION.md
+++ b/packages/web/server/lib/markdown-image-grants/DOCUMENTATION.md
@@ -34,3 +34,7 @@ server implementation. VS Code does not call this route for workspace images;
 those use its local filesystem bridge. If called, the grant route returns an
 explicit unsupported response because OpenCode temporary images are not
 supported there.
+
+Requests to OpenCode carry the directory in a percent-encoded
+`x-opencode-directory` header, matching the SDK wire format; OpenCode rejects
+raw non-ASCII header values.
diff --git a/packages/web/server/lib/markdown-image-grants/routes.js b/packages/web/server/lib/markdown-image-grants/routes.js
index 25b36c7d..a30c83ce 100644
--- a/packages/web/server/lib/markdown-image-grants/routes.js
+++ b/packages/web/server/lib/markdown-image-grants/routes.js
@@ -200,7 +200,9 @@ const fetchMessage = async ({ sessionId, messageId, directory, buildOpenCodeUrl,
   const response = await fetch(url, {
     headers: {
       accept: 'application/json',
-      'x-opencode-directory': directory,
+      // Percent-encoded to match the SDK wire format; raw non-ASCII values
+      // are rejected by OpenCode.
+      'x-opencode-directory': encodeURIComponent(directory),
       ...getOpenCodeAuthHeaders(),
     },
     signal: AbortSignal.timeout(10_000),
diff --git a/packages/web/server/lib/markdown-image-grants/routes.test.js b/packages/web/server/lib/markdown-image-grants/routes.test.js
index d44661b2..8916fbdc 100644
--- a/packages/web/server/lib/markdown-image-grants/routes.test.js
+++ b/packages/web/server/lib/markdown-image-grants/routes.test.js
@@ -74,6 +74,20 @@ const prepare = (app, directory, sources) => request(app)
   .expect(200);
 
 describe('session image assets', () => {
+  it('percent-encodes the directory header on the message fetch', async () => {
+    const fixture = await createFixture();
+    await prepare(fixture.app, fixture.directory, ['image.png']);
+
+    expect(fixture.fetchMock).toHaveBeenCalledWith(
+      expect.any(URL),
+      expect.objectContaining({
+        headers: expect.objectContaining({
+          'x-opencode-directory': encodeURIComponent(fixture.directory),
+        }),
+      }),
+    );
+  });
+
   it('prepares workspace and OpenCode temporary images with one message fetch', async () => {
     const fixture = await createFixture({ sources: ['workspace.png'] });
     await fs.writeFile(path.join(fixture.directory, 'workspace.png'), PNG);
diff --git a/packages/web/server/lib/openchamber-sessions/routes.js b/packages/web/server/lib/openchamber-sessions/routes.js
index 7c69df0a..6c58b333 100644
--- a/packages/web/server/lib/openchamber-sessions/routes.js
+++ b/packages/web/server/lib/openchamber-sessions/routes.js
@@ -83,7 +83,10 @@ const resolveVariant = (providers, providerID, modelID, variant) => {
 const parseConfigModel = (value) => splitModel(value);
 
 const buildDirectoryHeaders = (directory) => ({
-  ...(directory ? { 'x-opencode-directory': directory } : {}),
+  // OpenCode rejects non-ASCII header values; the official SDK sends this
+  // header percent-encoded, so match that wire format (non-ASCII checkout
+  // paths such as "Masaüstü" otherwise fail every dispatched prompt).
+  ...(directory ? { 'x-opencode-directory': encodeURIComponent(directory) } : {}),
 });
 
 const fetchJson = async (url, authHeaders, fallback, directory) => {
diff --git a/packages/web/server/lib/openchamber-sessions/routes.test.js b/packages/web/server/lib/openchamber-sessions/routes.test.js
index 3f6fbe5b..c95fd6e2 100644
--- a/packages/web/server/lib/openchamber-sessions/routes.test.js
+++ b/packages/web/server/lib/openchamber-sessions/routes.test.js
@@ -161,6 +161,29 @@ describe('openchamber session routes', () => {
     }
   });
 
+  it('percent-encodes the directory header for non-ASCII checkout paths', async () => {
+    const originalFetch = globalThis.fetch;
+    globalThis.fetch = vi.fn(async () => ({ ok: true, json: async () => ({ id: 'ses_123' }) }));
+    try {
+      const { app } = createApp();
+      await request(app)
+        .post('/api/openchamber/sessions')
+        .send({ directory: '/home/user/Masaüstü/projeler', title: 'Side task' })
+        .expect(200);
+
+      expect(globalThis.fetch).toHaveBeenCalledWith(
+        expect.any(String),
+        expect.objectContaining({
+          headers: expect.objectContaining({
+            'x-opencode-directory': encodeURIComponent('/home/user/Masaüstü/projeler'),
+          }),
+        }),
+      );
+    } finally {
+      globalThis.fetch = originalFetch;
+    }
+  });
+
   it('parses JSON body without global middleware', async () => {
     const originalFetch = globalThis.fetch;
     globalThis.fetch = vi.fn(async () => ({ ok: true, json: async () => ({ id: 'ses_123' }) }));