fix(dispatcher): a session error reports the provider's text from error.data.message

src/dispatcher/EventDispatcher.ts

@@ -290,7 +290,14 @@ export class EventDispatcher {
         this.semantic.publish({
           type: 'api_error',
           turnId: this.turns.getActiveTurnId(),
-          message: getString(payload, ['message', 'error.message']) ?? 'OpenCode session error',
+          // `error.data.message` first (Agent Code #1018): OpenCode 1.18
+          // publishes session.error as { sessionID, error: { name, data: {
+          // message, statusCode, ... } } }, the same shape as the assistant
+          // row's error in its database. The old lookup found nothing there,
+          // so every failure, a usage limit included, read "OpenCode session
+          // error". The Terminal runtime's LiveStateProjector already reads it
+          // this way.
+          message: getString(payload, ['message', 'error.data.message', 'error.message', 'error.name']) ?? 'OpenCode session error',
           error: payload,
           source: 'opencode-sse',
           ts: Date.now(),

src/dispatcher/sessionError.test.ts

@@ -0,0 +1,25 @@
+import { readFileSync } from 'node:fs'
+import { expect, it } from 'vitest'
+
+import { CommittedChannel } from '../channels/CommittedChannel.js'
+import { ScreenChannel } from '../channels/ScreenChannel.js'
+import { SemanticChannel } from '../channels/SemanticChannel.js'
+import { EventDispatcher } from './EventDispatcher.js'
+
+// Agent Code #1018: an orchestration child's usage-limit failure reached the
+// parent as "OpenCode session error". The error is the REAL one from an
+// OpenCode 1.18.31 database row (testing/fixtures/session-error), and
+// session.error carries it as `error` beside the sessionID.
+const recorded = JSON.parse(readFileSync(new URL('../../testing/fixtures/session-error/usage-limit-1.18.31.json', import.meta.url), 'utf8')) as {
+  sessionID: string
+  error: { name: string; data: { message: string } }
+}
+
+it('reports the provider\'s own text for a session error, not the generic fallback', () => {
+  const semantic = new SemanticChannel()
+  const errors: Array<{ message: string }> = []
+  semantic.on('api_error', event => errors.push(event as { message: string }))
+  const dispatcher = new EventDispatcher({ semantic, screen: new ScreenChannel(), committed: new CommittedChannel(), sessionID: recorded.sessionID })
+  dispatcher.dispatch({ type: 'session.error', properties: { sessionID: recorded.sessionID, error: recorded.error } })
+  expect(errors).toEqual([expect.objectContaining({ message: 'Usage limit reached for 5 hour. Your limit will reset at 2026-09-19 14:14:24' })])
+})

testing/fixtures/session-error/usage-limit-1.18.31.json

@@ -0,0 +1,13 @@
+{
+  "provenance": "Agent Code testing/fixtures/orchestration-api-error/opencode-structured-usage-limit-terminal.json (OpenCode 1.18.31 database, 2026-09-19): the assistant row error of a zai usage-limit failure. session.error publishes {sessionID, error: assistantMessage.error}, so this is the payload's error field verbatim (response headers dropped).",
+  "sessionID": "ses_f47fca718ffePibDCd10YM7Jc8",
+  "error": {
+    "name": "APIError",
+    "data": {
+      "message": "Usage limit reached for 5 hour. Your limit will reset at 2026-09-19 14:14:24",
+      "statusCode": 429,
+      "isRetryable": true,
+      "responseBody": "{\"error\":{\"code\":\"1308\",\"message\":\"Usage limit reached for 5 hour. Your limit will reset at 2026-09-19 14:14:24\"}}"
+    }
+  }
+}