fix: identify OpenCode Go requests by session

packages/web/server/lib/small-model/DOCUMENTATION.md

@@ -91,6 +91,10 @@ other runtime API.
   a blocker instead of a raw 500 message.
 - `call.js` — wire formats and per-provider auth, replicating OpenCode's
   plugin auth loaders:
+  - OpenCode-hosted providers receive `x-opencode-session`. Session-backed
+    features reuse the real OpenCode session id, walkthrough retries reuse the
+    walkthrough cache key, and standalone one-shot actions receive a fresh
+    opaque id for that generation.
   - **GitHub Copilot**: fetches the requested model's authenticated `/models`
     metadata from `https://api.githubcopilot.com` (or
     `copilot-api.<enterprise>`) and honors its advertised endpoint, preferring

packages/web/server/lib/small-model/call.js

@@ -1,6 +1,7 @@
 import fs from 'fs';
 import os from 'os';
 import path from 'path';
+import { randomUUID } from 'node:crypto';
 import { readAuthFile, writeAuthFile } from '../opencode/auth.js';
 import { readConfig, readConfigLayers, isPlainObject } from '../opencode/shared.js';
 import { getCatalogProvider } from './catalog.js';
@@ -645,7 +646,7 @@ export async function resolveProviderLogin({ auth, workingDirectory, providerID
     || null;
 }
 
-export async function callSmallModel({ auth, catalog, workingDirectory, providerID, modelID, prompt, system, maxOutputTokens, responseSchema, timeoutMs, signal }) {
+export async function callSmallModel({ auth, catalog, workingDirectory, sessionID, providerID, modelID, prompt, system, maxOutputTokens, responseSchema, timeoutMs, signal }) {
   const tokens = Number(maxOutputTokens) > 0 ? Number(maxOutputTokens) : DEFAULT_MAX_OUTPUT_TOKENS;
   const providerConfig = readProviderConfig(workingDirectory, providerID);
   const runtimeProvider = await getRuntimeProvider(providerID);
@@ -795,7 +796,12 @@ export async function callSmallModel({ auth, catalog, workingDirectory, provider
     baseURL,
     // Configured headers last: a gateway that authenticates on its own header
     // must be able to override the bearer default rather than sit beside it.
-    headers: mergeHeadersCaseInsensitive({ Authorization: `Bearer ${apiKey}` }, providerConfig?.headers),
+    headers: mergeHeadersCaseInsensitive(
+      mergeHeadersCaseInsensitive({ Authorization: `Bearer ${apiKey}` }, providerConfig?.headers),
+      providerID.startsWith('opencode')
+        ? { 'x-opencode-session': typeof sessionID === 'string' && sessionID.trim() ? sessionID.trim() : randomUUID() }
+        : null,
+    ),
     modelID,
     prompt,
     system,

packages/web/server/lib/small-model/call.test.js

@@ -483,6 +483,29 @@ describe('callSmallModel — custom provider config', () => {
   });
 
   describe('catalog-based base URL (no config override)', () => {
+    it('identifies OpenCode Go requests with the owning conversation', async () => {
+      readConfig.mockReturnValue({});
+      fetchMock.mockResolvedValue(ok('ok'));
+
+      await callSmallModel({
+        auth: { 'opencode-go': { type: 'api', key: 'go-key' } },
+        catalog: {
+          'opencode-go': {
+            id: 'opencode-go',
+            api: 'https://opencode.ai/zen/go/v1',
+            models: { utility: { id: 'utility' } },
+          },
+        },
+        workingDirectory: '/proj',
+        sessionID: 'ses_conversation',
+        providerID: 'opencode-go',
+        modelID: 'utility',
+        prompt: 'hi',
+      });
+
+      expect(lastCall(fetchMock).init.headers['x-opencode-session']).toBe('ses_conversation');
+    });
+
     it('uses the catalog api field when no config baseURL is set', async () => {
       readConfig.mockReturnValue({});
       fetchMock.mockResolvedValue(ok('ok'));

packages/web/server/lib/small-model/index.js

@@ -102,7 +102,7 @@ const readConfiguredSmallModel = (workingDirectory) => {
  * Generates text with the user's small model, resolved and authenticated
  * entirely server-side from the OpenCode config and auth store.
  */
-export async function generateSmallModelText({ prompt, system, maxOutputTokens, model, directory, preferredProviderID, preferredModelID, restrictToPreferredProvider = false, responseSchema, timeoutMs, signal, onOverflow = 'truncate' }) {
+export async function generateSmallModelText({ prompt, system, maxOutputTokens, model, directory, sessionID, preferredProviderID, preferredModelID, restrictToPreferredProvider = false, responseSchema, timeoutMs, signal, onOverflow = 'truncate' }) {
   if (typeof prompt !== 'string' || !prompt.trim()) {
     throw Object.assign(new Error('prompt is required'), { statusCode: 400 });
   }
@@ -169,6 +169,7 @@ export async function generateSmallModelText({ prompt, system, maxOutputTokens,
     auth,
     catalog,
     workingDirectory: directory,
+    sessionID,
     providerID: resolved.providerID,
     modelID: resolved.modelID,
     prompt: clamped.prompt,

packages/web/server/lib/small-model/routes.js

@@ -21,13 +21,14 @@ export function registerSmallModelRoutes(app, { getSmallModelService }) {
   app.post('/api/small-model/generate', async (req, res) => {
     try {
       const { generateSmallModelText } = await getSmallModelService();
-      const { prompt, system, maxOutputTokens, model, directory, preferredProviderID, preferredModelID, restrictToPreferredProvider } = req.body || {};
+      const { prompt, system, maxOutputTokens, model, directory, sessionID, preferredProviderID, preferredModelID, restrictToPreferredProvider } = req.body || {};
       const result = await generateSmallModelText({
         prompt,
         system,
         maxOutputTokens,
         model,
         directory,
+        sessionID,
         preferredProviderID,
         preferredModelID,
         restrictToPreferredProvider: restrictToPreferredProvider === true,