test(terminal): pin the carried renderer risk scan tail

The foreground renderer-risk scan splices the carried tail onto the
incoming chunk before classifying it, and nothing covered that ordering:
a pre-gate moved back above the concatenation would silently drop the
refresh for a background SGR split across ConPTY chunks.

Also pins the escape-free ASCII path and the shared global SGR pattern's
statelessness across calls, since the background hit returns mid-loop.

src/renderer/src/components/terminal-pane/pty-connection/foreground-renderer-risk-scan-tail.test.ts

@@ -0,0 +1,64 @@
+import { describe, expect, it } from 'vitest'
+import { bindFreshSpawnFollowReset } from './fresh-spawn-follow-reset'
+import type { ConnectPanePtySession } from './connect-pane-pty-session'
+
+/**
+ * The foreground renderer-risk scan classifies the carried tail SPLICED onto the
+ * incoming chunk, not the raw chunk. ConPTY splits a background SGR mid-sequence
+ * routinely, and the continuation carries no escape of its own — so any cheap
+ * pre-gate that inspects `data` instead of `scanData` silently drops the refresh
+ * for exactly the redraws this path exists to catch.
+ */
+function buildSession(): ConnectPanePtySession {
+  // oxlint-disable-next-line typescript/consistent-type-assertions -- SAFETY: the bag names every field the renderer-risk scan reads; the cast only supplies the rest of the session shape, which this suite never reaches.
+  const session = {
+    pane: { id: 'pane-1', terminal: {} },
+    foregroundRefreshRiskScanTail: ''
+  } as unknown as ConnectPanePtySession
+  bindFreshSpawnFollowReset(session)
+  return session
+}
+
+describe('foregroundRendererRiskOutputPrefersRenderRefresh', () => {
+  it('refreshes a background SGR split across chunks', () => {
+    const session = buildSession()
+
+    expect(session.foregroundRendererRiskOutputPrefersRenderRefresh('\x1b[4')).toBe(false)
+    expect(session.foregroundRefreshRiskScanTail).toBe('\x1b[4')
+
+    expect(session.foregroundRendererRiskOutputPrefersRenderRefresh('1m x')).toBe(true)
+    expect(session.foregroundRefreshRiskScanTail).toBe('')
+  })
+
+  it('carries a bare escape split before the CSI introducer', () => {
+    const session = buildSession()
+
+    expect(session.foregroundRendererRiskOutputPrefersRenderRefresh('\x1b')).toBe(false)
+    expect(session.foregroundRefreshRiskScanTail).toBe('\x1b')
+
+    expect(session.foregroundRendererRiskOutputPrefersRenderRefresh('[104m x')).toBe(true)
+  })
+
+  it('does not refresh the continuation chunk on its own', () => {
+    // The discriminator for the splice: '1m x' is escape-free ASCII.
+    expect(buildSession().foregroundRendererRiskOutputPrefersRenderRefresh('1m x')).toBe(false)
+  })
+
+  it('does not carry a completed sequence into the next chunk', () => {
+    const session = buildSession()
+
+    expect(session.foregroundRendererRiskOutputPrefersRenderRefresh('\x1b[32mplain green')).toBe(
+      false
+    )
+    expect(session.foregroundRefreshRiskScanTail).toBe('')
+  })
+
+  it('keeps an empty chunk from dropping the pending tail', () => {
+    const session = buildSession()
+
+    session.foregroundRendererRiskOutputPrefersRenderRefresh('\x1b[4')
+    expect(session.foregroundRendererRiskOutputPrefersRenderRefresh('')).toBe(false)
+    expect(session.foregroundRefreshRiskScanTail).toBe('\x1b[4')
+    expect(session.foregroundRendererRiskOutputPrefersRenderRefresh('8;5;33m x')).toBe(true)
+  })
+})

src/renderer/src/lib/pane-manager/terminal-complex-script.test.ts

@@ -76,6 +76,17 @@ describe('terminalOutputPrefersRenderRefresh', () => {
       false
     )
   })
+
+  it('skips the SGR scan for escape-free ASCII output', () => {
+    expect(terminalOutputPrefersRenderRefresh('plain ascii progress 42%')).toBe(false)
+  })
+
+  it('keeps the shared SGR scan stateless across calls', () => {
+    // Why: the module-level pattern is global and the background hit returns
+    // mid-loop, so a dropped lastIndex reset would resume past the next match.
+    expect(terminalOutputPrefersRenderRefresh('\x1b[41m selected \x1b[0m')).toBe(true)
+    expect(terminalOutputPrefersRenderRefresh('\x1b[44m x\x1b[0m')).toBe(true)
+  })
 })
 
 describe('terminalOutputContainsEastAsianRendererRisk', () => {