fix(opencode): classify ZlibError from Bun fetch as retryable instead of unknown (#19104)

Co-authored-by: Aiden Cline <[email protected]>

4 files changed, 66 insertions, 2 deletions

diff --git a/packages/opencode/src/session/message-v2.ts b/packages/opencode/src/session/message-v2.ts
index d90910650..86e431565 100644
--- a/packages/opencode/src/session/message-v2.ts
+++ b/packages/opencode/src/session/message-v2.ts
@@ -15,6 +15,13 @@ import type { SystemError } from "bun"
 import type { Provider } from "@/provider/provider"
 import { ModelID, ProviderID } from "@/provider/schema"
 
+/** Error shape thrown by Bun's fetch() when gzip/br decompression fails mid-stream */
+interface FetchDecompressionError extends Error {
+  code: "ZlibError"
+  errno: number
+  path: string
+}
+
 export namespace MessageV2 {
   export function isMedia(mime: string) {
     return mime.startsWith("image/") || mime === "application/pdf"
@@ -906,7 +913,10 @@ export namespace MessageV2 {
     return result
   }
 
-  export function fromError(e: unknown, ctx: { providerID: ProviderID }): NonNullable<Assistant["error"]> {
+  export function fromError(
+    e: unknown,
+    ctx: { providerID: ProviderID; aborted?: boolean },
+  ): NonNullable<Assistant["error"]> {
     switch (true) {
       case e instanceof DOMException && e.name === "AbortError":
         return new MessageV2.AbortedError(
@@ -938,6 +948,21 @@ export namespace MessageV2 {
           },
           { cause: e },
         ).toObject()
+      case e instanceof Error && (e as FetchDecompressionError).code === "ZlibError":
+        if (ctx.aborted) {
+          return new MessageV2.AbortedError({ message: e.message }, { cause: e }).toObject()
+        }
+        return new MessageV2.APIError(
+          {
+            message: "Response decompression failed",
+            isRetryable: true,
+            metadata: {
+              code: (e as FetchDecompressionError).code,
+              message: e.message,
+            },
+          },
+          { cause: e },
+        ).toObject()
       case APICallError.isInstance(e):
         const parsed = ProviderError.parseAPICallError({
           providerID: ctx.providerID,
diff --git a/packages/opencode/src/session/processor.ts b/packages/opencode/src/session/processor.ts
index ccb09e71a..84ea76656 100644
--- a/packages/opencode/src/session/processor.ts
+++ b/packages/opencode/src/session/processor.ts
@@ -356,7 +356,7 @@ export namespace SessionProcessor {
               error: e,
               stack: JSON.stringify(e.stack),
             })
-            const error = MessageV2.fromError(e, { providerID: input.model.providerID })
+            const error = MessageV2.fromError(e, { providerID: input.model.providerID, aborted: input.abort.aborted })
             if (MessageV2.ContextOverflowError.isInstance(error)) {
               needsCompaction = true
               Bus.publish(Session.Event.Error, {
diff --git a/packages/opencode/test/session/message-v2.test.ts b/packages/opencode/test/session/message-v2.test.ts
index 0d5b89730..7d416597a 100644
--- a/packages/opencode/test/session/message-v2.test.ts
+++ b/packages/opencode/test/session/message-v2.test.ts
@@ -927,4 +927,31 @@ describe("session.message-v2.fromError", () => {
       },
     })
   })
+
+  test("classifies ZlibError from fetch as retryable APIError", () => {
+    const zlibError = new Error(
+      'ZlibError fetching "https://opencode.cloudflare.dev/anthropic/messages". For more information, pass `verbose: true` in the second argument to fetch()',
+    )
+    ;(zlibError as any).code = "ZlibError"
+    ;(zlibError as any).errno = 0
+    ;(zlibError as any).path = ""
+
+    const result = MessageV2.fromError(zlibError, { providerID })
+
+    expect(MessageV2.APIError.isInstance(result)).toBe(true)
+    expect((result as MessageV2.APIError).data.isRetryable).toBe(true)
+    expect((result as MessageV2.APIError).data.message).toInclude("decompression")
+  })
+
+  test("classifies ZlibError as AbortedError when abort context is provided", () => {
+    const zlibError = new Error(
+      'ZlibError fetching "https://opencode.cloudflare.dev/anthropic/messages". For more information, pass `verbose: true` in the second argument to fetch()',
+    )
+    ;(zlibError as any).code = "ZlibError"
+    ;(zlibError as any).errno = 0
+
+    const result = MessageV2.fromError(zlibError, { providerID, aborted: true })
+
+    expect(result.name).toBe("MessageAbortedError")
+  })
 })
diff --git a/packages/opencode/test/session/retry.test.ts b/packages/opencode/test/session/retry.test.ts
index 621ad99e9..a61c44262 100644
--- a/packages/opencode/test/session/retry.test.ts
+++ b/packages/opencode/test/session/retry.test.ts
@@ -125,6 +125,18 @@ describe("session.retry.retryable", () => {
 
     expect(SessionRetry.retryable(error)).toBeUndefined()
   })
+
+  test("retries ZlibError decompression failures", () => {
+    const error = new MessageV2.APIError({
+      message: "Response decompression failed",
+      isRetryable: true,
+      metadata: { code: "ZlibError" },
+    }).toObject() as MessageV2.APIError
+
+    const retryable = SessionRetry.retryable(error)
+    expect(retryable).toBeDefined()
+    expect(retryable).toBe("Response decompression failed")
+  })
 })
 
 describe("session.message-v2.fromError", () => {