fix: address greptile review — trim persistence output, restore tests, move JSDoc

- stripPersistedAssistantText: add .trim() to prevent whitespace-only
  assistant messages after malformed-prefix cleanup (Greptile P2)
- Restore unit tests for byteSize and isThinkingPart removed during
  rewrite (Greptile P2)
- Move file-level JSDoc after import in text-complete.ts (Greptile P2)

Related to #97

Author: Zireael

packages/plugin/src/hooks/magic-context/tag-content-primitives.test.ts

@@ -1,6 +1,8 @@
 import { describe, expect, it } from "bun:test";
 
 import {
+    byteSize,
+    isThinkingPart,
     peelLeadingMcTagNotation,
     prependTag,
     stripPersistedAssistantText,
@@ -140,3 +142,53 @@ describe("peelLeadingMcTagNotation", () => {
         });
     });
 });
+
+describe("stripPersistedAssistantText edge cases", () => {
+    it("#given malformed prefix with trailing space #when strip runs #then trims result", () => {
+        expect(stripPersistedAssistantText(`${SECTION}15298">§15298§ `)).toBe("");
+    });
+
+    it("#given tag-only text with trailing space #when strip runs #then returns empty", () => {
+        expect(stripPersistedAssistantText(`${SECTION}42${SECTION} `)).toBe("");
+    });
+
+    it("#given whitespace-only after strip #when strip runs #then trims to empty", () => {
+        expect(stripPersistedAssistantText(`   `)).toBe("");
+    });
+});
+
+describe("byteSize", () => {
+    it("#given ascii string #when byteSize runs #then returns byte length", () => {
+        expect(byteSize("hello")).toBe(5);
+    });
+
+    it("#given empty string #when byteSize runs #then returns 0", () => {
+        expect(byteSize("")).toBe(0);
+    });
+
+    it("#given multibyte string #when byteSize runs #then returns encoded byte length", () => {
+        expect(byteSize("§42§")).toBe(6);
+    });
+});
+
+describe("isThinkingPart", () => {
+    it("#given thinking part #when isThinkingPart runs #then returns true", () => {
+        expect(isThinkingPart({ type: "thinking", thinking: "..." })).toBe(true);
+    });
+
+    it("#given reasoning part #when isThinkingPart runs #then returns true", () => {
+        expect(isThinkingPart({ type: "reasoning", reasoning: "..." })).toBe(true);
+    });
+
+    it("#given text part #when isThinkingPart runs #then returns false", () => {
+        expect(isThinkingPart({ type: "text", text: "hello" })).toBe(false);
+    });
+
+    it("#given null #when isThinkingPart runs #then returns false", () => {
+        expect(isThinkingPart(null)).toBe(false);
+    });
+
+    it("#given primitive #when isThinkingPart runs #then returns false", () => {
+        expect(isThinkingPart("string")).toBe(false);
+    });
+});

packages/plugin/src/hooks/magic-context/tag-content-primitives.ts

@@ -65,7 +65,7 @@ export function stripPersistedAssistantText(value: string): string {
     text = stripCompleteTagPairsGlobally(text);
     text = stripMalformedTagNotationGlobally(text);
     text = stripTagSectionCharacters(text);
-    return text;
+    return text.trim();
 }
 
 export function byteSize(value: string): number {

packages/plugin/src/hooks/magic-context/text-complete.ts

@@ -1,3 +1,5 @@
+import { stripPersistedAssistantText } from "./tag-content-primitives";
+
 /**
  * Persistence-boundary strip for assistant completions (`experimental.text.complete`).
  *
@@ -22,8 +24,6 @@
  * sentinels like `[dropped §N§]`.
  */
 
-import { stripPersistedAssistantText } from "./tag-content-primitives";
-
 export function createTextCompleteHandler() {
     return async (
         _input: { sessionID: string; messageID: string; partID: string },