diff --git a/src/cli/config-manager/opencode-binary.test.ts b/src/cli/config-manager/opencode-binary.test.ts
new file mode 100644
index 000000000..b298c1027
--- /dev/null
+++ b/src/cli/config-manager/opencode-binary.test.ts
@@ -0,0 +1,85 @@
+/// <reference types="bun-types" />
+
+import { afterEach, beforeEach, describe, expect, it, spyOn } from "bun:test"
+
+import * as configContext from "./config-context"
+import * as spawnHelpers from "../../shared/spawn-with-windows-hide"
+
+type OpenCodeBinaryModule = typeof import("./opencode-binary")
+
+type CreateProcOptions = {
+  exitCode?: number | null
+  output?: { stdout?: string; stderr?: string }
+}
+
+function createProc(options: CreateProcOptions = {}): ReturnType<typeof spawnHelpers.spawnWithWindowsHide> {
+  const exitCode = options.exitCode ?? 0
+  return {
+    exited: Promise.resolve(exitCode),
+    exitCode,
+    stdout: options.output?.stdout !== undefined ? new Blob([options.output.stdout]).stream() : undefined,
+    stderr: options.output?.stderr !== undefined ? new Blob([options.output.stderr]).stream() : undefined,
+    kill: () => {},
+  } satisfies ReturnType<typeof spawnHelpers.spawnWithWindowsHide>
+}
+
+describe("getOpenCodeVersion (installer)", () => {
+  let spawnSpy: ReturnType<typeof spyOn>
+  let initConfigContextSpy: ReturnType<typeof spyOn>
+  let getOpenCodeVersion: OpenCodeBinaryModule["getOpenCodeVersion"]
+
+  beforeEach(async () => {
+    spawnSpy = spyOn(spawnHelpers, "spawnWithWindowsHide")
+    initConfigContextSpy = spyOn(configContext, "initConfigContext").mockImplementation(() => {})
+    const mod = await import(`./opencode-binary?test=${Date.now()}-${Math.random()}`)
+    getOpenCodeVersion = mod.getOpenCodeVersion
+  })
+
+  afterEach(() => {
+    spawnSpy.mockRestore()
+    initConfigContextSpy.mockRestore()
+  })
+
+  describe("#given clean opencode --version stdout #when getOpenCodeVersion #then returns the semver string", () => {
+    it("plain semver", async () => {
+      spawnSpy.mockReturnValue(createProc({ output: { stdout: "1.14.33\n" } }))
+
+      const result = await getOpenCodeVersion()
+
+      expect(result).toBe("1.14.33")
+    })
+  })
+
+  describe("#given Electron-polluted opencode --version stdout #when getOpenCodeVersion #then returns extracted semver, not the timestamp-prefixed line", () => {
+    it("regression for #3765 installer caller", async () => {
+      const polluted = "00:24:25.202 > app starting { version: '1.14.33', packaged: true }"
+      spawnSpy.mockReturnValue(createProc({ output: { stdout: polluted } }))
+
+      const result = await getOpenCodeVersion()
+
+      expect(result).toBe("1.14.33")
+    })
+  })
+
+  describe("#given non-semver-shaped stdout #when getOpenCodeVersion #then falls back to trimmed output", () => {
+    it("preserves legacy behavior for unrecognized formats", async () => {
+      spawnSpy.mockReturnValue(createProc({ output: { stdout: "  custom-build\n" } }))
+
+      const result = await getOpenCodeVersion()
+
+      expect(result).toBe("custom-build")
+    })
+  })
+
+  describe("#given no opencode binary on PATH #when getOpenCodeVersion #then returns null", () => {
+    it("all candidate spawns throw", async () => {
+      spawnSpy.mockImplementation(() => {
+        throw new Error("ENOENT")
+      })
+
+      const result = await getOpenCodeVersion()
+
+      expect(result).toBe(null)
+    })
+  })
+})
diff --git a/src/cli/config-manager/opencode-binary.ts b/src/cli/config-manager/opencode-binary.ts
index 6fb140403..d5256a0b0 100644
--- a/src/cli/config-manager/opencode-binary.ts
+++ b/src/cli/config-manager/opencode-binary.ts
@@ -1,3 +1,4 @@
+import { extractSemverFromOutput } from "../../shared/extract-semver"
 import type { OpenCodeBinaryType } from "../../shared/opencode-config-dir-types"
 import { spawnWithWindowsHide } from "../../shared/spawn-with-windows-hide"
 import { initConfigContext } from "./config-context"
@@ -19,7 +20,7 @@ async function findOpenCodeBinaryWithVersion(): Promise<OpenCodeBinaryResult | n
       const output = await new Response(proc.stdout).text()
       await proc.exited
       if (proc.exitCode === 0) {
-        const version = output.trim()
+        const version = extractSemverFromOutput(output) ?? output.trim()
         initConfigContext(binary, version)
         return { binary, version }
       }
diff --git a/src/cli/doctor/checks/system-binary.test.ts b/src/cli/doctor/checks/system-binary.test.ts
index 701f54d93..55742230b 100644
--- a/src/cli/doctor/checks/system-binary.test.ts
+++ b/src/cli/doctor/checks/system-binary.test.ts
@@ -1,7 +1,7 @@
 /// <reference types="bun-types" />
 
 import { describe, expect, it } from "bun:test"
-import { extractSemverFromOutput } from "./system-binary"
+import { extractSemverFromOutput } from "../../../shared/extract-semver"
 
 describe("extractSemverFromOutput", () => {
   describe("#given clean version output #when extractSemverFromOutput #then returns the semver token", () => {
diff --git a/src/cli/doctor/checks/system-binary.ts b/src/cli/doctor/checks/system-binary.ts
index 4a76648fd..9a92f7232 100644
--- a/src/cli/doctor/checks/system-binary.ts
+++ b/src/cli/doctor/checks/system-binary.ts
@@ -1,10 +1,13 @@
 import { existsSync } from "node:fs"
 import { homedir } from "node:os"
 import { join } from "node:path"
+import { extractSemverFromOutput } from "../../../shared/extract-semver"
 import { spawnWithTimeout } from "../spawn-with-timeout"
 
 import { OPENCODE_BINARIES } from "../constants"
 
+export { extractSemverFromOutput }
+
 const WINDOWS_EXECUTABLE_EXTS = [".exe", ".cmd", ".bat", ".ps1"]
 
 export interface OpenCodeBinaryInfo {
@@ -105,17 +108,6 @@ export async function findOpenCodeBinary(): Promise<OpenCodeBinaryInfo | null> {
   return findDesktopBinary()
 }
 
-export function extractSemverFromOutput(output: string): string | null {
-  const trimmed = output.trim()
-  if (!trimmed) return null
-  // Match a semver-shaped token, allowing optional `v` prefix and `-prerelease+build` suffix.
-  // The negative lookbehind `(?<![\d:])` prevents matching the milliseconds segment of timestamps
-  // like `00:24:25.202` that the Electron-based OpenCode binary leaks into stdout.
-  const semverPattern = /(?<![\d:])v?(\d+\.\d+\.\d+(?:[-+][\w.]+)*)/
-  const match = trimmed.match(semverPattern)
-  return match?.[1] ?? null
-}
-
 export async function getOpenCodeVersion(
   binaryPath: string,
   platform: NodeJS.Platform = process.platform
diff --git a/src/shared/extract-semver.ts b/src/shared/extract-semver.ts
new file mode 100644
index 000000000..37e55d052
--- /dev/null
+++ b/src/shared/extract-semver.ts
@@ -0,0 +1,9 @@
+export function extractSemverFromOutput(output: string): string | null {
+  const trimmed = output.trim()
+  if (!trimmed) return null
+  // The negative lookbehind `(?<![\d:])` prevents matching the milliseconds segment of timestamps
+  // like `00:24:25.202` that the Electron-based OpenCode binary leaks into stdout.
+  const semverPattern = /(?<![\d:])v?(\d+\.\d+\.\d+(?:[-+][\w.]+)*)/
+  const match = trimmed.match(semverPattern)
+  return match?.[1] ?? null
+}