core: split message part updates into delta events for smoother streaming

Streaming text and reasoning content now uses incremental delta events instead of sending full message parts on each update. This reduces bandwidth and improves real-time response smoothness in the TUI.

packages/opencode/src/session/processor.ts

@@ -63,17 +63,19 @@ export namespace SessionProcessor {
                   if (value.id in reasoningMap) {
                     continue
                   }
-                  reasoningMap[value.id] = {
+                  const reasoningPart = {
                     id: Identifier.ascending("part"),
                     messageID: input.assistantMessage.id,
                     sessionID: input.assistantMessage.sessionID,
-                    type: "reasoning",
+                    type: "reasoning" as const,
                     text: "",
                     time: {
                       start: Date.now(),
                     },
                     metadata: value.providerMetadata,
                   }
+                  reasoningMap[value.id] = reasoningPart
+                  await Session.updatePart(reasoningPart)
                   break
 
                 case "reasoning-delta":
@@ -81,7 +83,13 @@ export namespace SessionProcessor {
                     const part = reasoningMap[value.id]
                     part.text += value.text
                     if (value.providerMetadata) part.metadata = value.providerMetadata
-                    if (part.text) await Session.updatePart({ part, delta: value.text })
+                    await Session.updatePartDelta({
+                      sessionID: part.sessionID,
+                      messageID: part.messageID,
+                      partID: part.id,
+                      field: "text",
+                      delta: value.text,
+                    })
                   }
                   break
 
@@ -288,17 +296,20 @@ export namespace SessionProcessor {
                     },
                     metadata: value.providerMetadata,
                   }
+                  await Session.updatePart(currentText)
                   break
 
                 case "text-delta":
                   if (currentText) {
                     currentText.text += value.text
                     if (value.providerMetadata) currentText.metadata = value.providerMetadata
-                    if (currentText.text)
-                      await Session.updatePart({
-                        part: currentText,
-                        delta: value.text,
-                      })
+                    await Session.updatePartDelta({
+                      sessionID: currentText.sessionID,
+                      messageID: currentText.messageID,
+                      partID: currentText.id,
+                      field: "text",
+                      delta: value.text,
+                    })
                   }
                   break