diff --git a/src/renderer/src/lib/pane-manager/terminal-cjk-output-repaint-decision.test.ts b/src/renderer/src/lib/pane-manager/terminal-cjk-output-repaint-decision.test.ts
new file mode 100644
index 00000000000..91a57385a87
--- /dev/null
+++ b/src/renderer/src/lib/pane-manager/terminal-cjk-output-repaint-decision.test.ts
@@ -0,0 +1,194 @@
+import { describe, expect, it } from 'vitest'
+
+import {
+  terminalOutputContainsEastAsianRendererRisk,
+  windowsEastAsianOutputPrefersRenderRefresh
+} from './terminal-complex-script'
+
+/**
+ * #12164 comment 1 / #5921: agent output containing double-width glyphs renders
+ * duplicated character-by-character, while ASCII in the same line stays clean.
+ * No IME, no composition, no keystroke — the user never types the CJK; Codex (and
+ * Antigravity CLI) emit it. The reporter characterised the dynamic as incremental
+ * repaint: a block flashes duplicated, then normalises once the next repaint moves on.
+ *
+ * `be3f30e2f8d` ("Fix Windows CJK terminal repaint and ConPTY wrap markers", PR #6890)
+ * is the named owner. Its whole delta on this path is a second, independent disjunct:
+ * before it, a wide-glyph chunk elected a repaint only when the user had recently
+ * typed; after it, native ConPTY agent output elects one with no keystroke at all.
+ *
+ * Recorded output, transcribed verbatim from the issue threads (SHA-256 of the exact
+ * UTF-8 literal above each pair). `.tmp/` is gitignored, so these are inlined rather
+ * than loaded; they are the *actual*, matched here against the production detector.
+ *
+ * Split from `terminal-complex-script.test.ts` (406 lines against an 800-line cap) for
+ * cohesion, not to stay under `max-lines`.
+ */
+
+// #5921, StillHanWind, 2026-06-20, Orca v1.4.83, Windows/PowerShell, Codex CLI.
+// clean b6b001338d44efe028ef8253fdeec4da0e87fce52cfbc224ebd07cceed9b4ffb
+// actual d5c3ec6a9f54e48674d4c45defc7a327db2cf65f07e6b3be877e6f61b12aa014
+const CHINESE_CLEAN = '如果还在主 checkout，请创建前端/设计专用 worktree：'
+const CHINESE_CORRUPTED =
+  '如如果果还还在在主主 checkout，，请请创创建建前前端端/设设计计专专用用 worktree：：'
+
+// #5921 reopen request, pobbye-star, 2026-07-25, Windows 11 build 26100 — i.e. after
+// #6890 shipped. Same shape in Korean.
+// clean 017d41fc33b39d24d73d0178eb93277cfa3528fe810ee23df5a3793a92d41cb4
+// actual 06fba393f10c436c0e84f658e85453732c982efc0e894c161b4a4cbe56f34984
+const KOREAN_HEADING_CLEAN = '### 1. 매뉴얼 분석 결과 [확정]'
+const KOREAN_HEADING_CORRUPTED = '### 1. 매매뉴뉴얼얼 분분석석 결결과과 [확확정정]'
+
+// clean 04c3a0660e8921ce4202af3803eecbc9093a8e78863cd19fb960c3ea28af707f
+// actual 580a5fc229ea2d5b9879ee03430a53691c17948d679b5aa8cce67696279191cd
+const KOREAN_BODY_CLEAN =
+  '제시해 주신 매뉴얼은 예스스트레이더의 자바스크립트(JavaScript) 기반 시스템 트레이딩/자동매매'
+const KOREAN_BODY_CORRUPTED =
+  '제제시시해해 주주신신 매매뉴뉴얼얼은은 예예스스스스트트레레이이더더의의 자자바바스크크립립트트(JavaScript) 기기반반 시시스템템 트트레레이이딩딩/자자동동매매매매'
+
+const RECORDED_OUTPUT = [
+  { issue: '#5921 zh-CN', clean: CHINESE_CLEAN, corrupted: CHINESE_CORRUPTED },
+  { issue: '#5921 ko heading', clean: KOREAN_HEADING_CLEAN, corrupted: KOREAN_HEADING_CORRUPTED },
+  { issue: '#5921 ko body', clean: KOREAN_BODY_CLEAN, corrupted: KOREAN_BODY_CORRUPTED }
+]
+
+const MAX_INTERACTIVE_REDRAW_CHARS = 128 * 1024
+
+/** Agent streaming its own output: native ConPTY, user has not touched the keyboard. */
+const UNTYPED_AGENT_OUTPUT = {
+  isWindowsClient: true,
+  isNativeWindowsConpty: true,
+  hadRecentInput: false,
+  maxInteractiveRedrawChars: MAX_INTERACTIVE_REDRAW_CHARS
+}
+
+const TYPED_INPUT_ECHO = { ...UNTYPED_AGENT_OUTPUT, hadRecentInput: true }
+
+/**
+ * The predicate as it stood immediately before #6890, transcribed from
+ * `git show be3f30e2f8d^:src/renderer/src/components/terminal-pane/pty-connection.ts`
+ * lines 3091-3094. This is the mutation arm — reverting #6890 on this path is exactly
+ * dropping the `isNativeWindowsConpty` disjunct.
+ */
+function pre6890PrefersRenderRefresh(data: string, state: typeof UNTYPED_AGENT_OUTPUT): boolean {
+  return (
+    state.isWindowsClient &&
+    state.hadRecentInput &&
+    data.length <= state.maxInteractiveRedrawChars &&
+    terminalOutputContainsEastAsianRendererRisk(data)
+  )
+}
+
+/**
+ * Split a line into the maximal runs the PTY repaints as units, classified by the
+ * production detector itself rather than by a width table of our own.
+ */
+function segmentByRendererRiskClass(line: string): { risky: boolean; text: string }[] {
+  const runs: { risky: boolean; text: string }[] = []
+  for (const character of line) {
+    const risky = terminalOutputContainsEastAsianRendererRisk(character)
+    const open = runs.at(-1)
+    if (open && open.risky === risky) {
+      open.text += character
+    } else {
+      runs.push({ risky, text: character })
+    }
+  }
+  return runs
+}
+
+describe('recorded CJK agent output vs the repaint detector', () => {
+  it('corrupts a run if and only if the detector flags it, across all recorded output', () => {
+    const verdicts: { corrupted: boolean; risky: boolean }[] = []
+    for (const { issue, clean, corrupted } of RECORDED_OUTPUT) {
+      const cleanRuns = segmentByRendererRiskClass(clean)
+      const corruptedRuns = segmentByRendererRiskClass(corrupted)
+      // Corruption never moves a run across the class boundary, so the two segmentations align.
+      expect(
+        corruptedRuns.map((run) => run.risky),
+        issue
+      ).toEqual(cleanRuns.map((run) => run.risky))
+      cleanRuns.forEach((run, index) => {
+        verdicts.push({ corrupted: run.text !== corruptedRuns[index]?.text, risky: run.risky })
+      })
+    }
+
+    // Assert the precondition before the correspondence: both classes are actually present,
+    // so neither half of the biconditional is vacuously satisfied.
+    expect(verdicts.filter((verdict) => verdict.risky)).toHaveLength(17)
+    expect(verdicts.filter((verdict) => !verdict.risky)).toHaveLength(16)
+
+    expect(verdicts.filter((verdict) => verdict.corrupted)).toHaveLength(17)
+    for (const verdict of verdicts) {
+      expect(verdict.corrupted).toBe(verdict.risky)
+    }
+  })
+
+  it('leaves the ASCII in the same line byte-identical', () => {
+    // The reporter's own negative: "English text such as `checkout` is not duplicated."
+    // It is co-located with the corrupted CJK, not a separate run.
+    const narrowRuns = RECORDED_OUTPUT.flatMap(({ clean, corrupted }) => {
+      const corruptedRuns = segmentByRendererRiskClass(corrupted)
+      return segmentByRendererRiskClass(clean)
+        .map((run, index) => ({ ...run, after: corruptedRuns[index]?.text }))
+        .filter((run) => !run.risky)
+    })
+
+    expect(narrowRuns.map((run) => run.text)).toContain(' checkout')
+    expect(narrowRuns.map((run) => run.text)).toContain('(JavaScript) ')
+    for (const run of narrowRuns) {
+      expect(run.after).toBe(run.text)
+      expect(windowsEastAsianOutputPrefersRenderRefresh(run.text, UNTYPED_AGENT_OUTPUT)).toBe(false)
+    }
+  })
+
+  it('does not double every character in a corrupted run', () => {
+    // The doubling tracks the repaint region, not the character: `자바스크립트` loses one
+    // `스` and `시스템` loses another. A test asserting uniform doubling would assert
+    // something this evidence contradicts.
+    const nonUniform = RECORDED_OUTPUT.flatMap(({ clean, corrupted }) => {
+      const corruptedRuns = segmentByRendererRiskClass(corrupted)
+      return segmentByRendererRiskClass(clean)
+        .map((run, index) => ({ run, after: corruptedRuns[index]?.text ?? '' }))
+        .filter(({ run, after }) => run.risky && after.length !== run.text.length * 2)
+    })
+
+    expect(nonUniform.map(({ run }) => run.text)).toEqual(['자바스크립트', '시스템'])
+    expect(nonUniform.map(({ after }) => after)).toEqual(['자자바바스크크립립트트', '시시스템템'])
+  })
+})
+
+describe('#6890 as the discriminating mutation', () => {
+  const riskyRuns = (): { risky: boolean; text: string }[] =>
+    RECORDED_OUTPUT.flatMap(({ clean }) =>
+      segmentByRendererRiskClass(clean).filter((run) => run.risky)
+    )
+
+  it('elects a repaint for every corrupted run when the agent types nothing', () => {
+    const refreshed = riskyRuns().filter((run) =>
+      windowsEastAsianOutputPrefersRenderRefresh(run.text, UNTYPED_AGENT_OUTPUT)
+    )
+    expect(refreshed).toHaveLength(17)
+  })
+
+  it('elects none of them once #6890 is reverted', () => {
+    const refreshed = riskyRuns().filter((run) =>
+      pre6890PrefersRenderRefresh(run.text, UNTYPED_AGENT_OUTPUT)
+    )
+    // 17 -> 0. Untyped wide-glyph output was never repainted before #6890, which is the
+    // condition #12164 comment 1 reports and the only condition the two arms disagree on.
+    expect(refreshed).toHaveLength(0)
+  })
+
+  it('agrees with the reverted predicate whenever the user has recently typed', () => {
+    for (const run of riskyRuns()) {
+      expect(windowsEastAsianOutputPrefersRenderRefresh(run.text, TYPED_INPUT_ECHO)).toBe(
+        pre6890PrefersRenderRefresh(run.text, TYPED_INPUT_ECHO)
+      )
+    }
+    const refreshed = riskyRuns().filter((run) =>
+      pre6890PrefersRenderRefresh(run.text, TYPED_INPUT_ECHO)
+    )
+    expect(refreshed).toHaveLength(17)
+  })
+})