fix(ai-chat): strip unclosed <summary> tag leaking into compaction summary (#9750)

* fix(ai-chat): strip unclosed <summary> tag leaking into compaction summary

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

* fix(ai-chat): strip analysis before matching summary to avoid scratchpad leak

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

frontend/src/lib/components/copilot/chat/compactionPrompt.test.ts

@@ -34,6 +34,37 @@ chronological thinking the model should not keep
 		expect(formatCompactSummary(raw)).toBe('a\n\nb')
 	})
 
+	it('keeps the summary content when <summary> has no closing tag', () => {
+		const raw = '<summary>\n1. Primary Request and Intent: build the thing\n2. Pending Tasks: none'
+		const formatted = formatCompactSummary(raw)
+		expect(formatted).not.toContain('<summary>')
+		expect(formatted).toContain('Primary Request and Intent: build the thing')
+		expect(formatted).toContain('Pending Tasks: none')
+	})
+
+	it('drops the analysis scratchpad even when <summary> is left unclosed', () => {
+		const raw =
+			'<analysis>\nchronological thinking the model should not keep\n</analysis>\n<summary>\nthe real summary'
+		const formatted = formatCompactSummary(raw)
+		expect(formatted).not.toContain('chronological thinking')
+		expect(formatted).not.toContain('<analysis>')
+		expect(formatted).not.toContain('<summary>')
+		expect(formatted).toBe('the real summary')
+	})
+
+	it('strips an orphaned closing summary tag', () => {
+		expect(formatCompactSummary('plain summary</summary>')).toBe('plain summary')
+	})
+
+	it('does not leak analysis scratchpad that mentions a literal <summary> tag', () => {
+		const raw = `<analysis>scratchpad mentions <summary> before output</analysis>
+<summary>real summary</summary>`
+		const formatted = formatCompactSummary(raw)
+		expect(formatted).toBe('real summary')
+		expect(formatted).not.toContain('scratchpad')
+		expect(formatted).not.toContain('before output')
+	})
+
 	it('strips every analysis block, not just the first, when the summary is untagged', () => {
 		const raw = '<analysis>first</analysis>\nkept one\n<analysis>second</analysis>\nkept two'
 		const formatted = formatCompactSummary(raw)

frontend/src/lib/components/copilot/chat/compactionPrompt.ts

@@ -100,13 +100,27 @@ export function getCompactionSummaryPrompt(): string {
  * well-formed-but-untagged summary is still usable.
  */
 export function formatCompactSummary(raw: string): string {
+	// Strip the analysis scratchpad first: it precedes the summary and may itself
+	// mention <summary>/<analysis> tokens that would otherwise be mistaken for the
+	// real summary boundary.
 	let formatted = raw.replace(/<analysis>[\s\S]*?<\/analysis>/gi, '')
 
 	const summaryMatch = formatted.match(/<summary>([\s\S]*?)<\/summary>/i)
 	if (summaryMatch) {
 		formatted = (summaryMatch[1] ?? '').trim()
+	} else {
+		// A truncated response or a weaker model sometimes opens <summary> without
+		// closing it. The text after the opener is still the summary, so keep it
+		// rather than leak the bare tag.
+		const openIdx = formatted.search(/<summary>/i)
+		if (openIdx !== -1) {
+			formatted = formatted.slice(openIdx)
+		}
 	}
 
+	// An orphaned opener or closer left by either branch must never reach the user.
+	formatted = formatted.replace(/<\/?(?:analysis|summary)>/gi, '')
+
 	// Collapse the blank-line runs left behind by stripping the analysis block.
 	return formatted.replace(/\n{3,}/g, '\n\n').trim()
 }