diff --git a/changelog.d/unreleased/1751.fixed.md b/changelog.d/unreleased/1751.fixed.md
new file mode 100644
index 0000000000..dc95d3c187
--- /dev/null
+++ b/changelog.d/unreleased/1751.fixed.md
@@ -0,0 +1,16 @@
+---
+category: fixed
+issues:
+  - 1751
+affected:
+  - install.sh
+  - tests/CodeIndex.Tests/InstallScriptTests.cs
+---
+
+## English
+
+- **The installer now verifies the installed binary before reporting success (#1751)** — `install.sh` runs `cdidx --version`, checks that the installed version matches the requested release, and reports likely architecture or native-runtime problems before printing the success path.
+
+## 日本語
+
+- **インストーラーが成功報告前にインストール済みバイナリを検証するようになりました (#1751)** — `install.sh` は `cdidx --version` を実行し、インストールされたバージョンが要求リリースと一致することを確認し、成功扱いにする前に architecture や native runtime の問題候補を表示します。
diff --git a/changelog.d/unreleased/1766.fixed.md b/changelog.d/unreleased/1766.fixed.md
new file mode 100644
index 0000000000..0e3f8b0851
--- /dev/null
+++ b/changelog.d/unreleased/1766.fixed.md
@@ -0,0 +1,16 @@
+---
+category: fixed
+issues:
+  - 1766
+affected:
+  - install.sh
+  - tests/CodeIndex.Tests/InstallScriptTests.cs
+---
+
+## English
+
+- **The installer now preflights temporary storage before `mktemp` use (#1766)** — `install.sh` checks that `TMPDIR` is a writable directory with at least 100 MiB free and warns when it appears to be mounted `noexec`.
+
+## 日本語
+
+- **インストーラーが `mktemp` 使用前に一時領域を事前検査するようになりました (#1766)** — `install.sh` は `TMPDIR` が書き込み可能なディレクトリで 100 MiB 以上の空き容量を持つことを確認し、`noexec` mount と思われる場合は警告します。
diff --git a/changelog.d/unreleased/2011.fixed.md b/changelog.d/unreleased/2011.fixed.md
new file mode 100644
index 0000000000..83b47bb2ee
--- /dev/null
+++ b/changelog.d/unreleased/2011.fixed.md
@@ -0,0 +1,16 @@
+---
+category: fixed
+issues:
+  - 2011
+affected:
+  - install.sh
+  - tests/CodeIndex.Tests/InstallScriptTests.cs
+---
+
+## English
+
+- **The installer can now update shell profiles for PATH setup on opt-in (#2011)** — users can rerun with `CDIDX_INSTALL_UPDATE_PATH=1` to append the installer PATH export to the detected shell profile and make the new path active for the installer process.
+
+## 日本語
+
+- **インストーラーが opt-in で shell profile の PATH 設定を更新できるようになりました (#2011)** — `CDIDX_INSTALL_UPDATE_PATH=1` を付けて再実行すると、検出した shell profile に installer の PATH export を追記し、インストーラー処理内でも新しい PATH を有効化します。
diff --git a/changelog.d/unreleased/2014.fixed.md b/changelog.d/unreleased/2014.fixed.md
new file mode 100644
index 0000000000..1c80373cce
--- /dev/null
+++ b/changelog.d/unreleased/2014.fixed.md
@@ -0,0 +1,16 @@
+---
+category: fixed
+issues:
+  - 2014
+affected:
+  - install.sh
+  - tests/CodeIndex.Tests/InstallScriptTests.cs
+---
+
+## English
+
+- **The installer now warns when an older `cdidx` shadows the new install on PATH (#2014)** — `check_path` resolves the active binary, lists every `cdidx` found on PATH with versions, and points users to put the install directory first.
+
+## 日本語
+
+- **古い `cdidx` が PATH 上で新しいインストールを shadow している場合に警告するようになりました (#2014)** — `check_path` は有効なバイナリを解決し、PATH 上の全 `cdidx` とバージョンを一覧表示して、インストール先ディレクトリを先頭に置くよう案内します。
diff --git a/install.sh b/install.sh
index 46bf87243d..4ae1cc9435 100755
--- a/install.sh
+++ b/install.sh
@@ -180,6 +180,54 @@ need_cmd() {
     fi
 }
 
+temp_root() {
+    printf '%s' "${TMPDIR:-/tmp}"
+}
+
+probe_temp_root() {
+    local root
+    root="$(temp_root)"
+
+    if [ ! -d "$root" ]; then
+        error "TMPDIR not usable: ${root} is not a directory. Set TMPDIR to a writable directory with at least 100 MiB free."
+    fi
+
+    local probe
+    if ! probe="$(mktemp "${root%/}/.cdidx-install-probe.XXXXXX")"; then
+        error "TMPDIR not writable: ${root}. Set TMPDIR to a writable directory and rerun the installer."
+    fi
+    rm -f "$probe"
+
+    local free_kb=""
+    if command -v df > /dev/null 2>&1; then
+        free_kb="$(df -Pk "$root" 2>/dev/null | awk 'NR==2 {print $4}' || true)"
+    fi
+
+    if [ -n "$free_kb" ] && [ "$free_kb" -lt 102400 ] 2>/dev/null; then
+        error "Insufficient temp space in ${root}: ${free_kb} KiB available; need at least 102400 KiB. Set TMPDIR to a larger writable directory."
+    fi
+
+    if command -v mount > /dev/null 2>&1 && mount 2>/dev/null | awk -v root="$root" '
+        index($0, " on " root " ") && index($0, "noexec") { found = 1 }
+        END { exit found ? 0 : 1 }
+    '; then
+        warn "TMPDIR appears to be on a noexec filesystem: ${root}. The installer will avoid executing staged files from TMPDIR."
+    fi
+}
+
+verify_temp_path_space() {
+    local path="$1"
+    local free_kb=""
+
+    if command -v df > /dev/null 2>&1; then
+        free_kb="$(df -Pk "$path" 2>/dev/null | awk 'NR==2 {print $4}' || true)"
+    fi
+
+    if [ -n "$free_kb" ] && [ "$free_kb" -lt 102400 ] 2>/dev/null; then
+        error "Insufficient temp space for ${path}: ${free_kb} KiB available; need at least 102400 KiB."
+    fi
+}
+
 acquire_install_lock() {
     mkdir -p "$INSTALL_DIR"
 
@@ -228,6 +276,39 @@ semver_ge() {
         }'
 }
 
+verify_cdidx_binary() {
+    local binary_path="$1"
+    local expected_version="${VERSION#v}"
+    local version_output=""
+    local actual_version=""
+
+    if [ ! -x "$binary_path" ]; then
+        report_error "Installed binary is not executable: ${binary_path}."
+        return 1
+    fi
+
+    if ! version_output="$("$binary_path" --version 2>&1)"; then
+        report_error "Installed binary failed to run: ${binary_path} --version."
+        report_error "Output: ${version_output}"
+        report_error "Likely causes include a wrong-architecture release asset or missing native runtime dependency next to the binary."
+        return 1
+    fi
+
+    actual_version="$(semver_core "$version_output")"
+    if [ -z "$actual_version" ]; then
+        report_error "Installed binary returned an unparsable version from ${binary_path}: ${version_output}"
+        return 1
+    fi
+
+    if [ -n "$expected_version" ] && [ "$actual_version" != "$expected_version" ]; then
+        report_error "Installed binary version mismatch at ${binary_path}: expected ${expected_version}, got ${actual_version}."
+        report_error "Check for a stale release archive, wrong architecture, or PATH shadowing by an older cdidx."
+        return 1
+    fi
+
+    return 0
+}
+
 extract_release_tag_name() {
     local api_response="$1"
     local version=""
@@ -403,10 +484,12 @@ curl_http_get() {
     local http_code
     local curl_stderr
 
+    probe_temp_root
     if ! curl_stderr="$(mktemp)"; then
         report_error "Failed to create temporary curl stderr capture while fetching ${source_label} at $url."
         return 1
     fi
+    verify_temp_path_space "$curl_stderr"
 
     if http_code="$(run_curl_with_optional_loopback_bypass "$url" -sSL -o "$output_path" -w '%{http_code}' "$url" 2>"$curl_stderr")"; then
         rm -f "$curl_stderr"
@@ -457,9 +540,11 @@ fetch_latest_release_version() {
     api_url="$(latest_release_api_url)"
     api_label="$(latest_release_api_diagnostic_label)"
     local response_file
+    probe_temp_root
     if ! response_file="$(mktemp)"; then
         error "Failed to create temporary file for latest-release lookup."
     fi
+    verify_temp_path_space "$response_file"
 
     local http_code
     if ! http_code="$(curl_http_get "$api_url" "$response_file" "$api_label")"; then
@@ -884,6 +969,7 @@ download_and_install() {
     need_cmd curl
     need_cmd tar
     need_cmd mktemp
+    need_cmd awk
 
     local archive_name="CodeIndex-${RID}.tar.gz"
     local base_url
@@ -892,9 +978,11 @@ download_and_install() {
     local checksums_url="${base_url}/sha256sums.txt"
 
     local tmpdir
+    probe_temp_root
     if ! tmpdir="$(mktemp -d)"; then
         error "Failed to create temporary working directory for install."
     fi
+    verify_temp_path_space "$tmpdir"
     TMPDIR_CLEANUP="$tmpdir"
 
     info "Downloading ${archive_name}..."
@@ -1016,6 +1104,9 @@ download_and_install() {
     done
     write_integrity_version_json "${stage_dir}/version.json"
     chmod +x "${stage_dir}/${BINARY_NAME}"
+    if ! verify_cdidx_binary "${stage_dir}/${BINARY_NAME}"; then
+        return 1
+    fi
 
     local backup_dir
     if ! backup_dir="$(mktemp -d "${INSTALL_DIR}/.cdidx-backup.XXXXXX")"; then
@@ -1029,6 +1120,10 @@ download_and_install() {
     if ! promote_staged_install "$stage_dir" "$backup_dir" "$INSTALL_DIR" "$required_files" "$staged_assets"; then
         return 1
     fi
+    chmod +x "${INSTALL_DIR}/${BINARY_NAME}"
+    if ! verify_cdidx_binary "${INSTALL_DIR}/${BINARY_NAME}"; then
+        return 1
+    fi
 
     rm -rf "$stage_dir"
     STAGE_DIR_CLEANUP=""
@@ -1040,11 +1135,74 @@ download_and_install() {
 
 # --- PATH guidance / PATHガイダンス ---
 
+active_cdidx_path() {
+    command -v "$BINARY_NAME" 2>/dev/null || true
+}
+
+list_path_cdidx_binaries() {
+    local old_ifs="$IFS"
+    local dir
+    IFS=:
+    for dir in ${PATH:-}; do
+        [ -n "$dir" ] || dir="."
+        if [ -x "${dir}/${BINARY_NAME}" ]; then
+            printf '%s\n' "${dir}/${BINARY_NAME}"
+        fi
+    done
+    IFS="$old_ifs"
+}
+
+print_path_cdidx_versions() {
+    local binary
+    list_path_cdidx_binaries | while IFS= read -r binary; do
+        [ -n "$binary" ] || continue
+        printf '    %s -> %s\n' "$binary" "$("$binary" --version 2>/dev/null || printf '%s' "unavailable")"
+    done
+}
+
+candidate_shell_profile() {
+    local shell_name
+    shell_name="$(basename "${SHELL:-/bin/bash}")"
+    case "$shell_name" in
+        zsh)  printf '%s' "${HOME}/.zshrc" ;;
+        bash)
+            if [ -f "${HOME}/.bash_profile" ]; then
+                printf '%s' "${HOME}/.bash_profile"
+            else
+                printf '%s' "${HOME}/.bashrc"
+            fi
+            ;;
+        *)    printf '%s' "${HOME}/.profile" ;;
+    esac
+}
+
+append_path_to_shell_profile() {
+    local profile_path
+    profile_path="$(candidate_shell_profile)"
+    mkdir -p "$(dirname "$profile_path")"
+
+    if [ -f "$profile_path" ] && grep -F "export PATH=\"${INSTALL_DIR}:\$PATH\"" "$profile_path" >/dev/null 2>&1; then
+        info "PATH export already present in ${profile_path}"
+        return 0
+    fi
+
+    {
+        printf '\n# Added by cdidx installer\n'
+        printf 'export PATH="%s:$PATH"\n' "$INSTALL_DIR"
+    } >> "$profile_path"
+
+    info "Added ${INSTALL_DIR} to PATH in ${profile_path}"
+}
+
 check_path() {
     if [ "${SELF_TEST_LOCAL_MIRROR:-0}" = "1" ]; then
         return 0
     fi
 
+    local installed_bin="${INSTALL_DIR}/${BINARY_NAME}"
+    local active_bin
+    active_bin="$(active_cdidx_path)"
+
     case ":${PATH}:" in
         *":${INSTALL_DIR}:"*) ;;
         *)
@@ -1073,6 +1231,36 @@ check_path() {
             echo ""
             ;;
     esac
+
+    if [ "${CDIDX_INSTALL_UPDATE_PATH:-0}" = "1" ]; then
+        append_path_to_shell_profile
+        case ":${PATH}:" in
+            *":${INSTALL_DIR}:"*) ;;
+            *) PATH="${INSTALL_DIR}:${PATH}"; export PATH ;;
+        esac
+    else
+        echo "  To let the installer update your shell profile, rerun with CDIDX_INSTALL_UPDATE_PATH=1."
+        echo ""
+    fi
+
+    active_bin="$(active_cdidx_path)"
+    if [ -n "$active_bin" ] && [ "$active_bin" != "$installed_bin" ]; then
+        warn "The active cdidx on PATH is ${active_bin}, not the newly installed ${installed_bin}."
+        warn "An earlier PATH entry is shadowing the new install."
+        echo ""
+        echo "  cdidx binaries found on PATH:"
+        print_path_cdidx_versions
+        echo ""
+        echo "  Put ${INSTALL_DIR} before the earlier directory in PATH, or rerun with CDIDX_INSTALL_UPDATE_PATH=1."
+        echo ""
+        return 0
+    fi
+
+    if [ -n "$active_bin" ]; then
+        if ! "$active_bin" --version >/dev/null 2>&1; then
+            warn "The active cdidx at ${active_bin} failed to run --version. Check architecture and native runtime assets."
+        fi
+    fi
 }
 
 report_local_mirror_start_failure() {
diff --git a/tests/CodeIndex.Tests/InstallScriptTests.cs b/tests/CodeIndex.Tests/InstallScriptTests.cs
index 37e84fcfea..ef31afc434 100644
--- a/tests/CodeIndex.Tests/InstallScriptTests.cs
+++ b/tests/CodeIndex.Tests/InstallScriptTests.cs
@@ -1383,7 +1383,7 @@ public void DownloadAndInstall_BackupDirMktempFailure_PreservesExistingHealthyIn
             mkdir -p "{{payloadDir}}"
             cat > "{{Path.Combine(payloadDir, "cdidx")}}" <<'EOF'
             #!/usr/bin/env bash
-            echo "NEW_BINARY"
+            echo "cdidx v1.2.3"
             EOF
             chmod +x "{{Path.Combine(payloadDir, "cdidx")}}"
             printf '{"version":"1.2.3"}' > "{{Path.Combine(payloadDir, "version.json")}}"
@@ -1482,7 +1482,7 @@ public void DownloadAndInstall_MissingAsset_DoesNotOverwriteExistingHealthyInsta
             mkdir -p "{{payloadDir}}"
             cat > "{{Path.Combine(payloadDir, "cdidx")}}" <<'EOF'
             #!/usr/bin/env bash
-            echo "BROKEN_NEW_BINARY"
+            echo "cdidx v1.2.3"
             EOF
             chmod +x "{{Path.Combine(payloadDir, "cdidx")}}"
             printf '{"version":"1.2.3"}' > "{{Path.Combine(payloadDir, "version.json")}}"
@@ -1586,7 +1586,7 @@ public void DownloadAndInstall_MoveFailure_RollsBackExistingHealthyInstall()
             mkdir -p "{{payloadDir}}"
             cat > "{{Path.Combine(payloadDir, "cdidx")}}" <<'EOF'
             #!/usr/bin/env bash
-            echo "NEW_BINARY"
+            echo "cdidx v1.2.3"
             EOF
             chmod +x "{{Path.Combine(payloadDir, "cdidx")}}"
             printf '{"version":"1.2.3"}' > "{{Path.Combine(payloadDir, "version.json")}}"
@@ -1718,7 +1718,7 @@ public void DownloadAndInstall_BackupMoveFailure_PreservesExistingHealthyInstall
             mkdir -p "{{payloadDir}}"
             cat > "{{Path.Combine(payloadDir, "cdidx")}}" <<'EOF'
             #!/usr/bin/env bash
-            echo "NEW_BINARY"
+            echo "cdidx v1.2.3"
             EOF
             chmod +x "{{Path.Combine(payloadDir, "cdidx")}}"
             printf '{"version":"1.2.3"}' > "{{Path.Combine(payloadDir, "version.json")}}"
@@ -1854,7 +1854,7 @@ public void DownloadAndInstall_RollbackFailure_PreservesRecoveryArtifacts()
             mkdir -p "{{payloadDir}}"
             cat > "{{Path.Combine(payloadDir, "cdidx")}}" <<'EOF'
             #!/usr/bin/env bash
-            echo "NEW_BINARY"
+            echo "cdidx v1.2.3"
             EOF
             chmod +x "{{Path.Combine(payloadDir, "cdidx")}}"
             printf '{"version":"1.2.3"}' > "{{Path.Combine(payloadDir, "version.json")}}"
@@ -3226,6 +3226,125 @@ shift 2
         Assert.Contains("https://mirror.example/releases/Widthdom/CodeIndex/releases/download/v1.2.3/sha256sums.txt", stdout);
     }
 
+    [Fact]
+    public void ProbeTempRoot_UnwritableTmpdir_PrintsSpecificError()
+    {
+        if (OperatingSystem.IsWindows())
+            return;
+
+        var tmpdir = Path.Combine(_tempRoot, "not_a_dir");
+        File.WriteAllText(tmpdir, "not a directory");
+
+        var (exitCode, _, stderr) = RunInstallerSnippet(
+            """
+            probe_temp_root
+            """,
+            new Dictionary<string, string?>
+            {
+                ["TMPDIR"] = tmpdir,
+            },
+            enforceStrictMode: false);
+
+        Assert.Equal(1, exitCode);
+        Assert.Contains("TMPDIR not usable", stderr);
+    }
+
+    [Fact]
+    public void VerifyCdidxBinary_VersionMismatch_FailsBeforeSuccess()
+    {
+        if (OperatingSystem.IsWindows())
+            return;
+
+        var binDir = Path.Combine(_tempRoot, "verify_mismatch");
+        Directory.CreateDirectory(binDir);
+        var binaryPath = Path.Combine(binDir, "cdidx");
+        File.WriteAllText(binaryPath, "#!/usr/bin/env bash\necho 'cdidx v9.9.9'\n");
+        File.SetUnixFileMode(binaryPath, UnixFileMode.UserRead | UnixFileMode.UserWrite | UnixFileMode.UserExecute);
+
+        var (exitCode, stdout, stderr) = RunInstallerSnippet(
+            $$"""
+            VERSION="v1.2.3"
+            verify_cdidx_binary "{{binaryPath}}"
+            echo "UNREACHABLE"
+            """,
+            enforceStrictMode: false);
+
+        Assert.Equal(1, exitCode);
+        Assert.DoesNotContain("UNREACHABLE", stdout);
+        Assert.Contains("Installed binary version mismatch", stderr);
+        Assert.Contains("expected 1.2.3, got 9.9.9", stderr);
+    }
+
+    [Fact]
+    public void CheckPath_WhenOlderCdidxPrecedesInstallDir_WarnsAboutShadowing()
+    {
+        if (OperatingSystem.IsWindows())
+            return;
+
+        var oldDir = Path.Combine(_tempRoot, "old_path_bin");
+        var installDir = Path.Combine(_tempRoot, "new_path_bin");
+        Directory.CreateDirectory(oldDir);
+        Directory.CreateDirectory(installDir);
+        var oldBinary = Path.Combine(oldDir, "cdidx");
+        var newBinary = Path.Combine(installDir, "cdidx");
+        File.WriteAllText(oldBinary, "#!/usr/bin/env bash\necho 'cdidx v1.0.0'\n");
+        File.WriteAllText(newBinary, "#!/usr/bin/env bash\necho 'cdidx v1.2.3'\n");
+        File.SetUnixFileMode(oldBinary, UnixFileMode.UserRead | UnixFileMode.UserWrite | UnixFileMode.UserExecute);
+        File.SetUnixFileMode(newBinary, UnixFileMode.UserRead | UnixFileMode.UserWrite | UnixFileMode.UserExecute);
+
+        var (exitCode, stdout, stderr) = RunInstallerSnippet(
+            """
+            check_path
+            """,
+            new Dictionary<string, string?>
+            {
+                ["CDIDX_INSTALL_DIR"] = installDir,
+                ["PATH"] = oldDir + Path.PathSeparator + installDir,
+            });
+
+        Assert.Equal(0, exitCode);
+        Assert.Contains("cdidx binaries found on PATH", stdout);
+        Assert.Contains(oldBinary, stdout);
+        Assert.Contains(newBinary, stdout);
+        Assert.Contains("shadowing the new install", stderr);
+    }
+
+    [Fact]
+    public void CheckPath_UpdatePathOptIn_AppendsProfileExportAndUpdatesCurrentPath()
+    {
+        if (OperatingSystem.IsWindows())
+            return;
+
+        var homeDir = Path.Combine(_tempRoot, "path_profile_home");
+        var installDir = Path.Combine(_tempRoot, "profile_install_bin");
+        Directory.CreateDirectory(homeDir);
+        Directory.CreateDirectory(installDir);
+        var newBinary = Path.Combine(installDir, "cdidx");
+        File.WriteAllText(newBinary, "#!/usr/bin/env bash\necho 'cdidx v1.2.3'\n");
+        File.SetUnixFileMode(newBinary, UnixFileMode.UserRead | UnixFileMode.UserWrite | UnixFileMode.UserExecute);
+
+        var (exitCode, stdout, stderr) = RunInstallerSnippet(
+            $$"""
+            export HOME="{{homeDir}}"
+            export SHELL="/bin/bash"
+            check_path
+            echo "ACTIVE:$(command -v cdidx)"
+            cat "{{Path.Combine(homeDir, ".bashrc")}}"
+            """,
+            new Dictionary<string, string?>
+            {
+                ["CDIDX_INSTALL_DIR"] = installDir,
+                ["CDIDX_INSTALL_UPDATE_PATH"] = "1",
+                ["PATH"] = "/usr/bin:/bin",
+            });
+
+        Assert.Equal(0, exitCode);
+        Assert.Contains($"Added {installDir} to PATH", stdout);
+        Assert.Contains($"ACTIVE:{newBinary}", stdout);
+        Assert.Contains($"export PATH=\"{installDir}:$PATH\"", stdout);
+        Assert.Contains($"{installDir} is not in your PATH", stderr);
+    }
+
     [Fact]
     public void ReinstallReal_WithoutVersionArgument_FailsWithUsageError()
     {