core: track retry attempts with detailed error context on assistant entries

users can now see when transient failures occur during assistant responses,
such as rate limits or provider overloads, giving visibility into what
issues were encountered and automatically resolved before the final response

packages/opencode/test/session/session-entry-stepper.test.ts

@@ -27,6 +27,24 @@ function assistant() {
     type: "assistant",
     time: { created: time(0) },
     content: [],
+    retries: [],
+  })
+}
+
+function retryError(message: string) {
+  return new SessionEvent.RetryError({
+    message,
+    isRetryable: true,
+  })
+}
+
+function retry(attempt: number, message: string, created: number) {
+  return new SessionEntry.AssistantRetry({
+    attempt,
+    error: retryError(message),
+    time: {
+      created: time(created),
+    },
   })
 }
 
@@ -78,6 +96,12 @@ function tool(state: SessionEntryStepper.MemoryState, callID: string) {
   return tools(state).find((x) => x.callID === callID)
 }
 
+function retriesOf(state: SessionEntryStepper.MemoryState) {
+  const entry = last(state)
+  if (!entry) return []
+  return entry.retries ?? []
+}
+
 function adapterStore() {
   return {
     committed: [] as SessionEntry.Entry[],
@@ -168,6 +192,33 @@ describe("session-entry-stepper", () => {
       ])
       expect(store.committed[0].time.completed).toEqual(time(7))
     })
+
+    test("aggregates retry events onto the current assistant", () => {
+      const store = adapterStore()
+      store.committed.push(assistant())
+
+      SessionEntryStepper.stepWith(
+        adapterFor(store),
+        SessionEvent.Retried.create({
+          attempt: 1,
+          error: retryError("rate limited"),
+          timestamp: time(1),
+        }),
+      )
+      SessionEntryStepper.stepWith(
+        adapterFor(store),
+        SessionEvent.Retried.create({
+          attempt: 2,
+          error: retryError("provider overloaded"),
+          timestamp: time(2),
+        }),
+      )
+
+      expect(store.committed[0]?.type).toBe("assistant")
+      if (store.committed[0]?.type !== "assistant") return
+
+      expect(store.committed[0].retries).toEqual([retry(1, "rate limited", 1), retry(2, "provider overloaded", 2)])
+    })
   })
 
   describe("memory", () => {
@@ -231,6 +282,21 @@ describe("session-entry-stepper", () => {
 
       expect(reasons(state)).toEqual([{ type: "reasoning", text: "final" }])
     })
+
+    test("stepWith through memory records retries", () => {
+      const state = active()
+
+      SessionEntryStepper.stepWith(
+        SessionEntryStepper.memory(state),
+        SessionEvent.Retried.create({
+          attempt: 1,
+          error: retryError("rate limited"),
+          timestamp: time(1),
+        }),
+      )
+
+      expect(retriesOf(state)).toEqual([retry(1, "rate limited", 1)])
+    })
   })
 
   describe("step", () => {
@@ -481,6 +547,27 @@ describe("session-entry-stepper", () => {
       })
     })
 
+    test("records retries on the pending assistant", () => {
+      const next = run(
+        [
+          SessionEvent.Retried.create({
+            attempt: 1,
+            error: retryError("rate limited"),
+            timestamp: time(1),
+          }),
+          SessionEvent.Retried.create({
+            attempt: 2,
+            error: retryError("provider overloaded"),
+            timestamp: time(2),
+          }),
+        ],
+        active(),
+      )
+
+      expect(retriesOf(next)).toEqual([retry(1, "rate limited", 1), retry(2, "provider overloaded", 2)])
+    })
+  })
+
     describe("known reducer gaps", () => {
       test("prompt appends immutably when no assistant is pending", () => {
         FastCheck.assert(