fix(llm): isolate retry policy histories

examples/headless-agent/tests/fixtures/retry-snapshot-backend.mjs

@@ -0,0 +1,53 @@
+/** Deterministic provider adapter for the headless retry-policy snapshot. */
+
+import {
+  LlmAdapter,
+  LlmError,
+  resolveRetryPolicy,
+} from '@deepseek-ai/dsh-llm'
+
+class RetrySnapshotAdapter extends LlmAdapter {
+  requests = 0
+  firstMessages
+  policy = resolveRetryPolicy({
+    mode: 'normal',
+    maxRetries: 1,
+    retryableCodes: ['RATE_LIMIT'],
+    backoff: { initialDelayMs: 1, maxDelayMs: 1, jitterRatio: 0 },
+  }, 'retry-snapshot-backend.retryPolicy')
+
+  providerRetryPolicy() {
+    return this.policy
+  }
+
+  async * stream(options) {
+    const messages = JSON.stringify(options.messages)
+    this.requests++
+    if (this.requests === 1) {
+      this.firstMessages = messages
+      throw new LlmError('snapshot transient failure', 'RATE_LIMIT', { status: 429 })
+    }
+    if (this.requests === 2 && messages !== this.firstMessages) {
+      throw new Error('retry snapshot changed the model-visible messages')
+    }
+    const text = 'RETRY_OK'
+    yield { type: 'block-start', index: 0, blockType: 'text' }
+    yield { type: 'text-delta', index: 0, text }
+    yield { type: 'block-end', index: 0, block: { type: 'text', text } }
+    yield { type: 'usage', usage: { inputTokens: 4, outputTokens: 2 } }
+    yield { type: 'finish', reason: { kind: 'stop' } }
+  }
+}
+
+/** Cordis plugin name. */
+export const name = 'retry-snapshot-backend'
+/** Required LLM registry service. */
+export const inject = ['llm']
+
+/**
+ * Register the deterministic provider adapter.
+ * @param {import('cordis').Context} ctx - plugin context carrying the LLM service.
+ */
+export function apply(ctx) {
+  ctx.llm.registerAdapter(['deepseek'], new RetrySnapshotAdapter())
+}