diff --git a/packages/web/server/lib/opencode/project-directory-runtime.js b/packages/web/server/lib/opencode/project-directory-runtime.js
index b6c90347..2e289752 100644
--- a/packages/web/server/lib/opencode/project-directory-runtime.js
+++ b/packages/web/server/lib/opencode/project-directory-runtime.js
@@ -64,14 +64,18 @@ export const createProjectDirectoryRuntime = (dependencies) => {
     const queryDirectory = Array.isArray(req.query?.directory)
       ? req.query.directory[0]
       : req.query?.directory;
-    const requested = headerDirectory || queryDirectory || null;
+    const requested = [headerDirectory, queryDirectory].filter(Boolean);
 
-    if (requested) {
-      const validated = await validateDirectoryPath(requested);
-      if (!validated.ok) {
-        return { directory: null, error: validated.error };
+    if (requested.length > 0) {
+      let lastError = null;
+      for (const candidate of requested) {
+        const validated = await validateDirectoryPath(candidate);
+        if (validated.ok) {
+          return { directory: validated.directory, error: null };
+        }
+        lastError = validated.error;
       }
-      return { directory: validated.directory, error: null };
+      return { directory: null, error: lastError };
     }
 
     const readSettings = typeof getReadSettingsFromDiskMigrated === 'function'
@@ -119,18 +123,21 @@ export const createProjectDirectoryRuntime = (dependencies) => {
     const queryDirectory = Array.isArray(req.query?.directory)
       ? req.query.directory[0]
       : req.query?.directory;
-    const requested = headerDirectory || queryDirectory || null;
+    const requested = [headerDirectory, queryDirectory].filter(Boolean);
 
-    if (!requested) {
+    if (requested.length === 0) {
       return { directory: null, error: null };
     }
 
-    const validated = await validateDirectoryPath(requested);
-    if (!validated.ok) {
-      return { directory: null, error: validated.error };
+    let lastError = null;
+    for (const candidate of requested) {
+      const validated = await validateDirectoryPath(candidate);
+      if (validated.ok) {
+        return { directory: validated.directory, error: null };
+      }
+      lastError = validated.error;
     }
-
-    return { directory: validated.directory, error: null };
+    return { directory: null, error: lastError };
   };
 
   return {
diff --git a/packages/web/server/lib/opencode/project-directory-runtime.test.js b/packages/web/server/lib/opencode/project-directory-runtime.test.js
index 94b57b1a..2a12a79a 100644
--- a/packages/web/server/lib/opencode/project-directory-runtime.test.js
+++ b/packages/web/server/lib/opencode/project-directory-runtime.test.js
@@ -180,6 +180,28 @@ describe('project directory runtime', () => {
       expect(result).toEqual({ directory: rawPath, error: null });
     });
 
+    it('falls back to query directory when an unmarked encoded header is invalid', async () => {
+      const validPath = '/home/user/workspace/project';
+      const runtime = createTestRuntime({
+        fsPromises: {
+          stat: async (p) => {
+            if (p === validPath) return { isDirectory: () => true };
+            throw { code: 'ENOENT' };
+          },
+          realpath: async (p) => p,
+        },
+      });
+
+      const req = {
+        get: (header) => header === 'x-opencode-directory' ? encodeURIComponent(validPath) : null,
+        query: { directory: validPath },
+      };
+
+      const result = await runtime.resolveProjectDirectory(req);
+
+      expect(result).toEqual({ directory: validPath, error: null });
+    });
+
     it('resolves symlinks in query directory parameter', async () => {
       const runtime = createTestRuntime({
         fsPromises: {
diff --git a/packages/web/server/lib/opencode/proxy.js b/packages/web/server/lib/opencode/proxy.js
index 73897026..bb5e87aa 100644
--- a/packages/web/server/lib/opencode/proxy.js
+++ b/packages/web/server/lib/opencode/proxy.js
@@ -31,6 +31,25 @@ export const createDirectoryQueryCanonicalizer = ({ realpath, ...cacheOptions }
   };
 };
 
+export const normalizeForwardedDirectoryHeaders = (headers) => {
+  const rawDirectory = headers?.['x-opencode-directory'];
+  if (typeof rawDirectory !== 'string') {
+    return headers;
+  }
+
+  if (headers['x-opencode-directory-encoding'] !== 'uri') {
+    return headers;
+  }
+
+  try {
+    headers['x-opencode-directory'] = decodeURIComponent(rawDirectory);
+  } catch {
+    // Leave malformed values untouched; upstream will reject invalid paths.
+  }
+  delete headers['x-opencode-directory-encoding'];
+  return headers;
+};
+
 export const waitForSseDrain = (res, signal) => new Promise((resolve) => {
   if (signal?.aborted || res.writableEnded || res.destroyed) {
     resolve();
@@ -295,7 +314,9 @@ export const registerOpenCodeProxy = (app, deps) => {
         ? req.originalUrl
         : (typeof req.url === 'string' ? req.url : '');
       const upstreamPath = requestUrl.startsWith('/api') ? requestUrl.slice(4) || '/' : requestUrl;
-      const headers = collectForwardProxyHeaders(req.headers, getOpenCodeAuthHeaders());
+      const headers = normalizeForwardedDirectoryHeaders(
+        collectForwardProxyHeaders(req.headers, getOpenCodeAuthHeaders())
+      );
       headers.accept ??= 'text/event-stream';
       headers['cache-control'] ??= 'no-cache';
 
@@ -414,7 +435,7 @@ export const registerOpenCodeProxy = (app, deps) => {
   const fetchSessionListPayload = async (upstreamPath, { req = null, timeoutMs = null } = {}) => {
     const headers = req
       ? {
-          ...collectForwardProxyHeaders(req.headers, getOpenCodeAuthHeaders()),
+          ...normalizeForwardedDirectoryHeaders(collectForwardProxyHeaders(req.headers, getOpenCodeAuthHeaders())),
           accept: 'application/json',
           'accept-encoding': 'identity',
         }
@@ -654,6 +675,18 @@ export const registerOpenCodeProxy = (app, deps) => {
           proxyReq.setHeader('Authorization', authHeaders.Authorization);
         }
 
+        if (req.headers?.['x-opencode-directory-encoding'] === 'uri') {
+          const rawDirectory = req.headers['x-opencode-directory'];
+          if (typeof rawDirectory === 'string') {
+            try {
+              proxyReq.setHeader('x-opencode-directory', decodeURIComponent(rawDirectory));
+            } catch {
+              proxyReq.setHeader('x-opencode-directory', rawDirectory);
+            }
+          }
+          proxyReq.removeHeader?.('x-opencode-directory-encoding');
+        }
+
         // Defensive: request identity encoding from upstream OpenCode.
         // This avoids compressed-body/header mismatches in multi-proxy setups.
         proxyReq.setHeader('accept-encoding', 'identity');
diff --git a/packages/web/server/lib/opencode/proxy.test.js b/packages/web/server/lib/opencode/proxy.test.js
index 5829b1e5..91326d71 100644
--- a/packages/web/server/lib/opencode/proxy.test.js
+++ b/packages/web/server/lib/opencode/proxy.test.js
@@ -1,6 +1,6 @@
 import { describe, expect, it } from 'vitest';
 
-import { createDirectoryQueryCanonicalizer } from './proxy.js';
+import { createDirectoryQueryCanonicalizer, normalizeForwardedDirectoryHeaders } from './proxy.js';
 
 describe('createDirectoryQueryCanonicalizer', () => {
   it('canonicalizes directory query params and preserves other params', async () => {
@@ -70,3 +70,26 @@ describe('createDirectoryQueryCanonicalizer', () => {
     await expect(canonicalize('/session?foo=1')).resolves.toBe('/session?foo=1');
   });
 });
+
+describe('normalizeForwardedDirectoryHeaders', () => {
+  it('decodes marked directory headers before forwarding to OpenCode', () => {
+    const headers = normalizeForwardedDirectoryHeaders({
+      'x-opencode-directory': encodeURIComponent('/Users/example/project'),
+      'x-opencode-directory-encoding': 'uri',
+    });
+
+    expect(headers).toEqual({
+      'x-opencode-directory': '/Users/example/project',
+    });
+  });
+
+  it('preserves unmarked percent sequences from direct clients', () => {
+    const headers = normalizeForwardedDirectoryHeaders({
+      'x-opencode-directory': '/Users/example/project%20literal',
+    });
+
+    expect(headers).toEqual({
+      'x-opencode-directory': '/Users/example/project%20literal',
+    });
+  });
+});