From d38241026addc69e698e0e09dfe4c20913aa4ff0 Mon Sep 17 00:00:00 2001
From: jackmazac <jack.mazac@bcl.xyz>
Date: Thu, 30 Apr 2026 17:13:55 -0700
Subject: [PATCH] session: synthesize reasoning-start when stream omits it

wrapStream middleware enqueues reasoning-start before delta/end
when the provider skipped the opening chunk for that id.
---
 packages/opencode/src/session/llm.ts | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/packages/opencode/src/session/llm.ts b/packages/opencode/src/session/llm.ts
index b8b8911858fc..30df74567cda 100644
--- a/packages/opencode/src/session/llm.ts
+++ b/packages/opencode/src/session/llm.ts
@@ -397,6 +397,24 @@ const live: Layer.Layer<
                 }
                 return args.params
               },
+              async wrapStream({ doStream }) {
+                const result = await doStream()
+                const started = new Set<string>()
+                const fix = new TransformStream({
+                  transform(chunk, controller) {
+                    if (chunk.type === "reasoning-start") started.add(chunk.id)
+                    if (
+                      (chunk.type === "reasoning-delta" || chunk.type === "reasoning-end") &&
+                      !started.has(chunk.id)
+                    ) {
+                      started.add(chunk.id)
+                      controller.enqueue({ type: "reasoning-start", id: chunk.id })
+                    }
+                    controller.enqueue(chunk)
+                  },
+                })
+                return { ...result, stream: result.stream.pipeThrough(fix) }
+              },
             },
           ],
         }),