fix(stream): close thinking block before text or tool output

If upstream omits reasoning-end and starts emitting text-delta or
tool-call events, the thinking block remained open causing
thinking_start -> thinking_delta -> text_start -> ... -> thinking_end
ordering. Now endThinking() is called at the start of text-delta and
tool-call handlers so thinking_end always precedes text_start or
toolcall_start.

Adds 2 regression tests for the missing reasoning-end edge case.

src/core.ts

@@ -223,6 +223,7 @@ export function createStreamCommandCode(deps: CoreDependencies) {
 
         switch (event.type) {
           case "text-delta": {
+            endThinking()
             if (!textBlock) {
               textBlock = { type: "text", text: "" }
               output.content.push(textBlock)
@@ -286,6 +287,7 @@ export function createStreamCommandCode(deps: CoreDependencies) {
 
           case "tool-call": {
             endTextBlock()
+            endThinking()
             const toolCall: ToolCallContent = {
               type: "toolCall",
               id: stringValue(event.toolCallId) ?? "",