diff --git a/config/reliability-gates.jsonc b/config/reliability-gates.jsonc
index 2b1ab1071c7..bd1b3c20ad6 100644
--- a/config/reliability-gates.jsonc
+++ b/config/reliability-gates.jsonc
@@ -600,6 +600,76 @@
       ],
       "demotionRule": "Keep experimental until CI soak; investigate failures without relaxing fidelity, liveness or resource-count assertions."
     },
+    {
+      "id": "terminal-performance.vertical-control-scan",
+      "title": "Main terminal preview scanning skips ordinary output between controls",
+      "maturity": "experimental",
+      "protection": "partial",
+      "owner": "terminal-runtime",
+      "layer": "main-runtime-unit",
+      "surfaces": ["terminal output ingestion", "terminal preview and read tails"],
+      "platforms": ["macos", "linux", "windows"],
+      "providers": ["local", "daemon", "ssh", "remote-runtime"],
+      "coveredPlatforms": ["macos"],
+      "coveredProviders": ["local"],
+      "motivatingLinks": [
+        "https://github.com/stablyai/orca/blob/main/.agents/skills/perf/SKILL.md"
+      ],
+      "flakeHistory": {
+        "status": "not-started",
+        "evidence": "Initial local validation; no CI soak history."
+      },
+      "promotionCriteria": [
+        "Complete CI soak with zero unexplained flakes and preserve the observable oracle."
+      ],
+      "demotionRule": "Keep experimental until CI soak; investigate failures without relaxing fidelity or resource-count assertions.",
+      "coverageNotes": "Pure shared-host string semantics and main runtime tests cover the production scanner on macOS. Folder/git workspaces, local/daemon/SSH/remote-runtime authority, wire content and mobile/relay behavior are unchanged. No live native remote session was launched.",
+      "invariant": "Main terminal preview/read tails choose the same append/redraw path while ordinary text is skipped without a JavaScript code-unit walk. Complete string-control payloads are not interpreted as vertical controls; incomplete controls stop at the same point.",
+      "oracle": "Plain, colored and vertical-CSI output uses fewer than 16 code-unit inspections with the same recognition result. Canonical and noncanonical CSI, embedded CSI in OSC/DCS/SOS/PM/APC, ESC inside CSI parameter bytes, back-to-back controls and incomplete sequences preserve decisions. Production normalization and tail append retain exact cursor-up redraw rows.",
+      "commands": [
+        "ORCA_BACKGROUND_LAUNCH=1 pnpm test src/main/runtime/terminal-vertical-control-scan.test.ts"
+      ],
+      "testFiles": ["src/main/runtime/terminal-vertical-control-scan.test.ts"],
+      "assertionRefs": [
+        {
+          "file": "src/main/runtime/terminal-vertical-control-scan.test.ts",
+          "assertions": [
+            "bounds code-unit inspections on %s output",
+            "preserves numeric CSI A recognition for %j",
+            "skips embedded CSI and stops at an incomplete %s",
+            "resumes scanning after a parsed control for %j",
+            "preserves tail rows when ordinary output is followed by a cursor-up redraw"
+          ]
+        }
+      ],
+      "evidenceRuns": [
+        {
+          "date": "2026-09-07",
+          "runner": "local",
+          "platform": "macos",
+          "command": "ORCA_BACKGROUND_LAUNCH=1 pnpm test src/main/runtime/terminal-vertical-control-scan.test.ts",
+          "result": "passed",
+          "durationSeconds": 0.325,
+          "summary": "29 scanner work-budget, control recognition, scan-resumption and complete-tail integration tests passed."
+        }
+      ],
+      "runtimeBudget": {
+        "p95Seconds": 15,
+        "scope": "Focused scanner and tail-contract suite; local runtime budget, not an established p95."
+      },
+      "redGreenEvidence": {
+        "status": "complete",
+        "evidence": "Baseline inspections 90,112/90,119/98,307 become 0/5/2. Frozen differential matched 204,925 predicate cases and 3,000 complete tail transitions. Broader integrated validation passed 1,308 tests with one existing skip across six files. Independent original-base normalizer with only this scanner change passed 1,298 tests with one existing skip across five files (20.55 seconds), using a temporary Vite source override; this confirms independence from the pending-storage PR."
+      },
+      "performanceBudget": {
+        "required": true,
+        "evidence": "Actual normalize, append-tail, transcript and preview pipeline: 4 MiB/64 KiB-chunk CPU medians plain 43.418 to 37.932 ms, colored 49.321 to 42.570, wide 41.022 to 32.883, dense newlines 37.112 to 31.601, no-newline 32.009 to 25.100. 10,000 sequential single-character writes into a growing partial line 190.374 to 126.820 ms. Equal-bundle rotated controls show no material tiny-echo/redraw regression. Forward native ESC search skips only ground text; no new retained state, scheduling, timer or provider calls."
+      },
+      "knownGaps": [
+        "No live end-to-end input latency, many-pane frame measurement or launched Electron/SSH/WSL/Linux/Windows journey.",
+        "Existing preview fidelity and incomplete-control handling remain unchanged; broader runtime suite has one existing skipped case."
+      ]
+    },
     {
       "id": "terminal-performance.padded-fullscreen-redraw",
       "title": "Fullscreen redraw padding does not stall terminal delivery",
diff --git a/src/main/runtime/terminal-ansi-normalization.ts b/src/main/runtime/terminal-ansi-normalization.ts
index 4fbdf8aa932..df76da3c35e 100644
--- a/src/main/runtime/terminal-ansi-normalization.ts
+++ b/src/main/runtime/terminal-ansi-normalization.ts
@@ -60,14 +60,9 @@ export function hasCanonicalNumericCsiParams(params: string): boolean {
   return /^[0-9;]*$/.test(params)
 }
 
-const ESCAPE_CHAR_CODE = 0x1b
-
 export function containsTerminalVerticalLineControl(value: string): boolean {
-  for (let index = 0; index < value.length; index += 1) {
-    // Why charCodeAt: `value[index]` mints a one-char string per position on every chunk.
-    if (value.charCodeAt(index) !== ESCAPE_CHAR_CODE) {
-      continue
-    }
+  // Only ESC can introduce a vertical control; ordinary output needs no code-unit walk.
+  for (let index = value.indexOf('\x1b'); index !== -1; index = value.indexOf('\x1b', index + 1)) {
     const parsed = parseAnsiControlSequence(value, index)
     if (!parsed) {
       return false
diff --git a/src/main/runtime/terminal-vertical-control-scan.test.ts b/src/main/runtime/terminal-vertical-control-scan.test.ts
new file mode 100644
index 00000000000..b672e28c921
--- /dev/null
+++ b/src/main/runtime/terminal-vertical-control-scan.test.ts
@@ -0,0 +1,85 @@
+import { describe, expect, it, vi } from 'vitest'
+import {
+  containsTerminalVerticalLineControl,
+  normalizeTerminalChunk
+} from './terminal-ansi-normalization'
+import { appendNormalizedToTailBuffer } from './terminal-tail-buffer'
+
+describe('terminal vertical-control scanning', () => {
+  it.each([
+    ['plain', 'log output '.repeat(8192), false],
+    ['nonvertical CSI', `\x1b[31m${'log output '.repeat(8192)}\x1b[0m`, false],
+    ['vertical CSI', `${'漢字😀 output '.repeat(8192)}\x1b[2A`, true]
+  ] as const)('bounds code-unit inspections on %s output', (_name, input, expected) => {
+    const charCodeAt = vi.spyOn(String.prototype, 'charCodeAt')
+    let actual: boolean
+    let inspections: number
+    try {
+      actual = containsTerminalVerticalLineControl(input)
+      inspections = charCodeAt.mock.calls.length
+    } finally {
+      charCodeAt.mockRestore()
+    }
+
+    expect(actual).toBe(expected)
+    expect(inspections).toBeLessThan(16)
+  })
+
+  it.each([
+    ['\x1b[A', true],
+    ['\x1b[0A', true],
+    ['\x1b[;A', true],
+    ['\x1b[12;34A', true],
+    ['\x1b[?1A', false],
+    ['\x1b[1:2A', false],
+    ['\x1b[1 A', false],
+    ['\x1b[1\nA', false],
+    ['\x1b[1B', false],
+    ['\x9b1A', false],
+    ['\x1b', false],
+    ['\x1b[123', false]
+  ] as const)('preserves numeric CSI A recognition for %j', (input, expected) => {
+    expect(containsTerminalVerticalLineControl(input)).toBe(expected)
+  })
+
+  it.each([
+    ['OSC BEL', '\x1b]2;title', '\x07'],
+    ['OSC ST', '\x1b]2;title', '\x1b\\'],
+    ['DCS', '\x1bPpayload', '\x1b\\'],
+    ['SOS', '\x1bXpayload', '\x1b\\'],
+    ['PM', '\x1b^payload', '\x1b\\'],
+    ['APC', '\x1b_payload', '\x1b\\']
+  ])('skips embedded CSI and stops at an incomplete %s', (_name, prefix, terminator) => {
+    const incomplete = `${prefix}\x1b[2A`
+    expect(containsTerminalVerticalLineControl(incomplete)).toBe(false)
+    expect(containsTerminalVerticalLineControl(`${incomplete}${terminator}ordinary`)).toBe(false)
+    expect(containsTerminalVerticalLineControl(`${incomplete}${terminator}\x1b[3A`)).toBe(true)
+  })
+
+  it.each([
+    // An ESC inside CSI parameter bytes is consumed by that control, not treated as a new introducer.
+    ['\x1b[\x1b[A', false],
+    ['\x1b[\x1b[2A\x1b[1A', true],
+    ['\x1b[31m\x1b[1A', true],
+    ['\x1b]0;t\x07\x1b[1A', true],
+    ['\x1b[1A\x1b', true],
+    ['ordinary\x1b', false],
+    ['ordinary\x1b[0m more\x1b[1;A', true]
+  ] as const)('resumes scanning after a parsed control for %j', (input, expected) => {
+    expect(containsTerminalVerticalLineControl(input)).toBe(expected)
+  })
+
+  it('preserves tail rows when ordinary output is followed by a cursor-up redraw', () => {
+    const first = appendNormalizedToTailBuffer([], '', 'first\nold\n')
+    const normalized = normalizeTerminalChunk('\x1b[1A\x1b[2K\x1b[32mnew\x1b[0m\n')
+    const next = appendNormalizedToTailBuffer(
+      first.lines,
+      first.partialLine,
+      normalized.text,
+      first.redrawCursor
+    )
+
+    expect(next.lines).toEqual(['first', 'new'])
+    expect(next.partialLine).toBe('')
+  })
+})