diff --git a/Runner/suites/System/Logging/DIAG_Functional_Validation/DIAG_Functional_Validation.yaml b/Runner/suites/System/Logging/DIAG_Functional_Validation/DIAG_Functional_Validation.yaml
new file mode 100755
index 000000000..e4a9a2c1c
--- /dev/null
+++ b/Runner/suites/System/Logging/DIAG_Functional_Validation/DIAG_Functional_Validation.yaml
@@ -0,0 +1,38 @@
+metadata:
+  name: diag-functional-validation
+  format: "Lava-Test Test Definition 1.0"
+  description: "Validate Qualcomm DIAG userspace infrastructure, normal and non-real-time diag_mdlog logging, output generation, and safe process cleanup."
+  os:
+    - linux
+  scope:
+    - functional
+
+params:
+  DIAG_DURATION_SECS: "10"
+  DIAG_NRT_DURATION_SECS: "5"
+  DIAG_STARTUP_TIMEOUT_SECS: "15"
+  DIAG_STOP_TIMEOUT_SECS: "10"
+  DIAG_FILE_SIZE: "20"
+  DIAG_FILE_COUNT: "2"
+  DIAG_TEST_NONREALTIME: "1"
+  DIAG_KEEP_ARTIFACTS: "1"
+  DIAG_PROBE_OPTIONAL_HELP: "0"
+  DIAG_ARTIFACT_DIR: "./diag_artifacts"
+
+  DIAG_MASK_FILE: ""
+  DIAG_MASK_LIST: ""
+  DIAG_PERIPHERAL_MASK: ""
+  DIAG_PROCESSOR_MASK: ""
+  DIAG_USERPD_MASK: ""
+  DIAG_QDSS_MASK: ""
+  DIAG_TX_MODE: ""
+  DIAG_BUFFER_PERIPHERAL_MASK: ""
+  DIAG_ETR_BUFFER_SIZE: ""
+  DIAG_QMDL2_V2: "0"
+
+run:
+  steps:
+    - REPO_PATH=$PWD
+    - cd Runner/suites/System/Logging/DIAG_Functional_Validation
+    - DIAG_DURATION_SECS="${DIAG_DURATION_SECS}" DIAG_NRT_DURATION_SECS="${DIAG_NRT_DURATION_SECS}" DIAG_STARTUP_TIMEOUT_SECS="${DIAG_STARTUP_TIMEOUT_SECS}" DIAG_STOP_TIMEOUT_SECS="${DIAG_STOP_TIMEOUT_SECS}" DIAG_FILE_SIZE="${DIAG_FILE_SIZE}" DIAG_FILE_COUNT="${DIAG_FILE_COUNT}" DIAG_TEST_NONREALTIME="${DIAG_TEST_NONREALTIME}" DIAG_KEEP_ARTIFACTS="${DIAG_KEEP_ARTIFACTS}" DIAG_PROBE_OPTIONAL_HELP="${DIAG_PROBE_OPTIONAL_HELP}" DIAG_ARTIFACT_DIR="${DIAG_ARTIFACT_DIR}" DIAG_MASK_FILE="${DIAG_MASK_FILE}" DIAG_MASK_LIST="${DIAG_MASK_LIST}" DIAG_PERIPHERAL_MASK="${DIAG_PERIPHERAL_MASK}" DIAG_PROCESSOR_MASK="${DIAG_PROCESSOR_MASK}" DIAG_USERPD_MASK="${DIAG_USERPD_MASK}" DIAG_QDSS_MASK="${DIAG_QDSS_MASK}" DIAG_TX_MODE="${DIAG_TX_MODE}" DIAG_BUFFER_PERIPHERAL_MASK="${DIAG_BUFFER_PERIPHERAL_MASK}" DIAG_ETR_BUFFER_SIZE="${DIAG_ETR_BUFFER_SIZE}" DIAG_QMDL2_V2="${DIAG_QMDL2_V2}" ./run.sh || true
+    - $REPO_PATH/Runner/utils/send-to-lava.sh DIAG_Functional_Validation.res || true
diff --git a/Runner/suites/System/Logging/DIAG_Functional_Validation/README.md b/Runner/suites/System/Logging/DIAG_Functional_Validation/README.md
new file mode 100644
index 000000000..320cadc64
--- /dev/null
+++ b/Runner/suites/System/Logging/DIAG_Functional_Validation/README.md
@@ -0,0 +1,384 @@
+# DIAG_Functional_Validation
+
+## Overview
+
+`DIAG_Functional_Validation` validates the Qualcomm DIAG userspace logging path on QLI Yocto, Debian, and Ubuntu targets.
+
+The testcase focuses on safe, non-destructive validation of:
+
+- DIAG userspace tool availability
+- `diag-router` process and Unix socket visibility
+- pre-existing `diag_mdlog` sessions
+- owned `diag_mdlog` startup and DIAG LSM initialization
+- socket connection and peripheral logging activation
+- bounded output-file configuration
+- output-directory and non-empty log-file generation
+- mask-aware PASS, FAIL, and SKIP handling
+- clean shutdown of processes started by the testcase
+- `diag_mdlog -b` non-real-time mode
+- runtime capability discovery for optional DIAG utilities
+
+The testcase never kills a DIAG process that it did not start.
+
+## Test Location
+
+```text
+Runner/suites/System/Logging/DIAG_Functional_Validation/
+```
+
+Shared helpers are located at:
+
+```text
+Runner/utils/diag/lib_diag.sh
+```
+
+## Files
+
+```text
+Runner/suites/System/Logging/DIAG_Functional_Validation/
+├── run.sh
+├── DIAG_Functional_Validation.yaml
+└── README.md
+
+Runner/utils/diag/
+└── lib_diag.sh
+```
+
+## Validation Flow
+
+### 1. Tool inventory
+
+The testcase checks for:
+
+- `diag_mdlog`
+- `diag-router`
+- `diag_klog`
+- `diag_socket_log`
+- `diag_uart_log`
+- `diag_callback_sample`
+- `diag_dci_sample`
+
+`diag_mdlog` is the required core utility. The remaining tools are treated as optional capabilities.
+
+The testcase always captures `diag_mdlog` help because its interface is required for core validation. Optional utility help probing is disabled by default to avoid accidentally starting an unknown overlay utility that does not implement conventional help handling. Set `DIAG_PROBE_OPTIONAL_HELP=1` to collect `--help` or `-h` output for optional tools. Optional missing utilities are reported as subtest SKIPs and do not skip the complete testcase.
+
+### 2. DIAG infrastructure
+
+The testcase checks:
+
+- whether `diag-router` is already running
+- whether a named DIAG Unix socket is visible in `/proc/net/unix`
+- whether `diag_mdlog` can connect to the active DIAG infrastructure
+
+A standalone `diag-router` process is not mandatory when `diag_mdlog` provides successful connection evidence.
+
+### 3. Existing-session protection
+
+Before starting logging, the testcase scans `/proc` for existing `diag_mdlog` instances.
+
+When an existing session is found:
+
+- it is not killed
+- a second conflicting session is not started
+- the existing process command line and UID are recorded
+- its `-o` output path is inspected when available
+- owned normal and non-real-time session checks are marked SKIP
+- the overall testcase can still PASS when the existing session is alive and functional evidence is available
+
+### 4. Owned normal logging session
+
+When no existing session is active, the testcase starts an owned session using bounded parameters:
+
+```sh
+diag_mdlog -o <test-output-dir> -s <size> -n <count>
+```
+
+It validates:
+
+- process remains active for the configured duration
+- `Diag_LSM_Init` success evidence
+- DIAG socket connection evidence
+- `logging switched` evidence
+- output-directory creation
+- non-empty data files when data is available
+- mask application behavior
+- clean TERM-based shutdown
+
+The testcase uses a dedicated artifact path and changes permissions only on that test-owned path. It does not run `chmod 777 /sdcard` or modify unrelated directories.
+
+### 5. Mask-aware data validation
+
+Without an explicit mask, `diag_mdlog` may report that default mask files are absent and continue with masks previously configured on the device.
+
+The testcase applies these rules:
+
+| Condition | Result |
+|---|---|
+| Explicit readable mask supplied and non-empty data is created | PASS |
+| Explicit mask supplied but cannot be read | FAIL |
+| Explicit mask supplied but no non-empty data is created | FAIL |
+| No explicit mask and prior masks produce data | PASS |
+| No explicit mask and no data is produced | SKIP for data-content check |
+
+Messages such as the following are not treated as fatal when no explicit mask was requested:
+
+```text
+No successful mask file reads.
+Running with masks that were set prior to diag_mdlog start-up.
+```
+
+### 6. Non-real-time mode
+
+When supported and enabled, the testcase starts a second owned session with:
+
+```sh
+diag_mdlog ... -b
+```
+
+This check runs only after the normal owned session has been stopped. It is skipped when another DIAG session is active or when the runtime help does not advertise `-b`.
+
+Non-real-time mode validates startup, DIAG initialization, connection evidence, output handling, and clean shutdown. Non-empty data is not mandatory because peripheral buffering and flush behavior can vary.
+
+## Safety Rules
+
+The testcase intentionally avoids destructive behavior:
+
+- does not kill pre-existing `diag_mdlog` processes
+- does not invoke `diag_mdlog -k`
+- does not restart `diag-router`
+- does not globally change `/sdcard` permissions
+- does not enable mask cleanup with `-c`
+- does not disable console logging with `-d`
+- does not request a wake lock with `-e`
+- cleans up only PIDs started by the testcase
+
+## Dependencies
+
+Required core command:
+
+```text
+diag_mdlog
+```
+
+Required base shell utilities:
+
+```text
+awk sed grep find wc tail tr chmod mkdir date head basename
+```
+
+Optional DIAG commands are reported individually.
+
+## Command-Line Options
+
+```text
+--duration <seconds>
+--nrt-duration <seconds>
+--file-size <value>
+--file-count <count>
+--mask-file <path>
+--mask-list <path>
+--peripheral-mask <mask>
+--no-nonrealtime
+--help
+```
+
+## Environment Variables
+
+### Core controls
+
+- `DIAG_DURATION_SECS`
+  - normal-session observation time
+  - default: `10`
+
+- `DIAG_NRT_DURATION_SECS`
+  - non-real-time-session observation time
+  - default: `5`
+
+- `DIAG_STARTUP_TIMEOUT_SECS`
+  - time allowed for initialization evidence
+  - default: `15`
+
+- `DIAG_STOP_TIMEOUT_SECS`
+  - TERM shutdown timeout before forced cleanup
+  - default: `5`
+
+- `DIAG_FILE_SIZE`
+  - value passed to `diag_mdlog -s`
+  - default: `20`
+  - the tested runtime help describes this as maximum file size in MB
+
+- `DIAG_FILE_COUNT`
+  - value passed to `diag_mdlog -n`
+  - default: `2`
+
+- `DIAG_TEST_NONREALTIME`
+  - `1` enables the `-b` validation
+  - default: `1`
+
+- `DIAG_ARTIFACT_DIR`
+  - root directory for help output, command logs, summaries, and DIAG data
+  - default: `./diag_artifacts`
+
+- `DIAG_KEEP_ARTIFACTS`
+  - `1` retains artifacts after execution
+  - default: `1`
+
+- `DIAG_PROBE_OPTIONAL_HELP`
+  - `1` probes `--help`/`-h` for optional DIAG utilities
+  - default: `0`
+  - keep disabled until the overlay tools are known to implement side-effect-free help handling
+
+### Mask controls
+
+Only one of these should be supplied:
+
+- `DIAG_MASK_FILE`
+  - passed using `diag_mdlog -f`
+
+- `DIAG_MASK_LIST`
+  - passed using `diag_mdlog -l`
+
+### Platform-specific optional controls
+
+These are used only when explicitly set and advertised by the runtime help:
+
+- `DIAG_PERIPHERAL_MASK` → `-p`
+- `DIAG_PROCESSOR_MASK` → `-j`
+- `DIAG_USERPD_MASK` → `-g`
+- `DIAG_QDSS_MASK` → `-q`
+- `DIAG_TX_MODE` → `-t`
+- `DIAG_BUFFER_PERIPHERAL_MASK` → `-x`
+- `DIAG_ETR_BUFFER_SIZE` → `-y`
+- `DIAG_QMDL2_V2=1` → `-u`
+
+## Examples
+
+Run with defaults:
+
+```sh
+cd Runner/suites/System/Logging/DIAG_Functional_Validation
+./run.sh
+```
+
+Run for 20 seconds and retain four bounded files:
+
+```sh
+./run.sh --duration 20 --file-size 50 --file-count 4
+```
+
+Run with an explicit mask:
+
+```sh
+./run.sh --mask-file /path/to/Diag.cfg
+```
+
+Run with a mask list:
+
+```sh
+./run.sh --mask-list /path/to/Diag_list.txt
+```
+
+Run with a platform peripheral mask:
+
+```sh
+./run.sh --peripheral-mask 0x1FFFFF
+```
+
+Disable non-real-time validation:
+
+```sh
+./run.sh --no-nonrealtime
+```
+
+Use environment variables:
+
+```sh
+DIAG_DURATION_SECS=15 \
+DIAG_FILE_SIZE=50 \
+DIAG_FILE_COUNT=5 \
+DIAG_TEST_NONREALTIME=1 \
+./run.sh
+```
+
+## Artifacts
+
+A run-specific directory is created under:
+
+```text
+./diag_artifacts/run_<pid>/
+```
+
+Typical contents include:
+
+```text
+results.tsv
+tool_help/
+normal_diag_mdlog.log
+normal_output/
+nonrealtime_diag_mdlog.log
+nonrealtime_output/
+```
+
+The full paths are printed to stdout for LAVA debugging.
+
+## Result Rules
+
+### PASS
+
+The testcase passes when:
+
+- `diag_mdlog` is installed
+- an existing or testcase-owned DIAG logging session is validated
+- no mandatory subtest fails
+- owned processes are cleaned up successfully
+
+### FAIL
+
+The testcase fails when:
+
+- installed `diag_mdlog` cannot initialize or remain active
+- a fatal socket or LSM startup error is detected
+- an explicit mask cannot be read
+- an explicit mask produces no non-empty data
+- a testcase-owned process cannot be stopped cleanly
+- an explicitly requested runtime option is unsupported
+
+### SKIP
+
+The testcase is skipped when:
+
+- `diag_mdlog` is not installed
+- DIAG functionality cannot be safely exercised
+- only optional capabilities are available
+
+Individual optional checks can be SKIP while the overall testcase remains PASS.
+
+## Result File
+
+```text
+DIAG_Functional_Validation.res
+```
+
+Possible values:
+
+```text
+DIAG_Functional_Validation PASS
+DIAG_Functional_Validation FAIL
+DIAG_Functional_Validation SKIP
+```
+
+The script exits `0` after writing the result file so LAVA can continue and report the `.res` result.
+
+## Current Coverage and Planned Extensions
+
+The first version functionally validates the core `diag_mdlog` path and inventories optional tools.
+
+The following optional utilities are capability-only until their exact runtime command-line behavior is confirmed on the target image:
+
+- `diag_klog`
+- `diag_socket_log`
+- `diag_uart_log`
+- `diag_callback_sample`
+- `diag_dci_sample`
+
+When `DIAG_PROBE_OPTIONAL_HELP=1`, their captured help output is retained in the artifact directory and can be used to add safe functional subtests without hardcoding incompatible command-line assumptions.
diff --git a/Runner/suites/System/Logging/DIAG_Functional_Validation/run.sh b/Runner/suites/System/Logging/DIAG_Functional_Validation/run.sh
new file mode 100755
index 000000000..c879ba644
--- /dev/null
+++ b/Runner/suites/System/Logging/DIAG_Functional_Validation/run.sh
@@ -0,0 +1,335 @@
+#!/bin/sh
+# Copyright (c) Qualcomm Technologies, Inc. and/or its subsidiaries.
+# SPDX-License-Identifier: BSD-3-Clause
+# DIAG userspace infrastructure and diag_mdlog functional validation.
+
+SCRIPT_DIR="$(
+    cd "$(dirname "$0")" || exit 1
+    pwd
+)"
+
+TESTNAME="DIAG_Functional_Validation"
+RES_FILE="./$TESTNAME.res"
+
+INIT_ENV=""
+SEARCH="$SCRIPT_DIR"
+
+while [ "$SEARCH" != "/" ]; do
+    if [ -f "$SEARCH/init_env" ]; then
+        INIT_ENV="$SEARCH/init_env"
+        break
+    fi
+    SEARCH=$(dirname "$SEARCH")
+done
+
+if [ -z "$INIT_ENV" ]; then
+    echo "[ERROR] Could not find init_env (starting at $SCRIPT_DIR)" >&2
+    echo "$TESTNAME FAIL" >"$RES_FILE" 2>/dev/null || true
+    exit 1
+fi
+
+REPO_ROOT="$(dirname "$INIT_ENV")"
+
+if [ -z "${INIT_ENV_LOADED:-}" ]; then
+    # shellcheck disable=SC1090
+    . "$INIT_ENV"
+    INIT_ENV_LOADED=1
+fi
+
+# shellcheck disable=SC1091
+. "$TOOLS/functestlib.sh"
+
+# --------- DIAG helper library ---------
+DIAG_LIB=""
+
+if [ -n "${TOOLS:-}" ] && [ -f "$TOOLS/lib_diag.sh" ]; then
+    DIAG_LIB="$TOOLS/lib_diag.sh"
+elif [ -n "${ROOT_DIR:-}" ] && [ -f "$ROOT_DIR/utils/lib_diag.sh" ]; then
+    DIAG_LIB="$ROOT_DIR/utils/lib_diag.sh"
+elif [ -n "${REPO_ROOT:-}" ] && [ -f "$REPO_ROOT/utils/lib_diag.sh" ]; then
+    DIAG_LIB="$REPO_ROOT/utils/lib_diag.sh"
+else
+    log_error "Missing DIAG helper library"
+    log_error "Checked ${TOOLS:-<TOOLS unset>}/lib_diag.sh"
+    log_error "Checked ${ROOT_DIR:-<ROOT_DIR unset>}/utils/lib_diag.sh"
+    log_error "Checked ${REPO_ROOT:-<REPO_ROOT unset>}/utils/lib_diag.sh"
+    echo "$TESTNAME FAIL" >"$RES_FILE"
+    exit 1
+fi
+
+# shellcheck source=../../../../utils/lib_diag.sh
+# shellcheck disable=SC1091
+. "$DIAG_LIB"
+
+test_path="$(find_test_case_by_name "$TESTNAME")"
+
+if [ -n "$test_path" ]; then
+    cd "$test_path" || exit 1
+else
+    cd "$SCRIPT_DIR" || exit 1
+fi
+
+RES_FILE="./$TESTNAME.res"
+rm -f "$RES_FILE"
+
+# --------- Configuration defaults ---------
+DIAG_DURATION_SECS="${DIAG_DURATION_SECS:-10}"
+DIAG_NRT_DURATION_SECS="${DIAG_NRT_DURATION_SECS:-5}"
+DIAG_STARTUP_TIMEOUT_SECS="${DIAG_STARTUP_TIMEOUT_SECS:-15}"
+DIAG_STOP_TIMEOUT_SECS="${DIAG_STOP_TIMEOUT_SECS:-5}"
+DIAG_FILE_SIZE="${DIAG_FILE_SIZE:-20}"
+DIAG_FILE_COUNT="${DIAG_FILE_COUNT:-2}"
+DIAG_TEST_NONREALTIME="${DIAG_TEST_NONREALTIME:-1}"
+DIAG_KEEP_ARTIFACTS="${DIAG_KEEP_ARTIFACTS:-1}"
+DIAG_PROBE_OPTIONAL_HELP="${DIAG_PROBE_OPTIONAL_HELP:-0}"
+DIAG_ARTIFACT_DIR="${DIAG_ARTIFACT_DIR:-./diag_artifacts}"
+DIAG_MASK_FILE="${DIAG_MASK_FILE:-}"
+DIAG_MASK_LIST="${DIAG_MASK_LIST:-}"
+DIAG_PERIPHERAL_MASK="${DIAG_PERIPHERAL_MASK:-}"
+DIAG_PROCESSOR_MASK="${DIAG_PROCESSOR_MASK:-}"
+DIAG_USERPD_MASK="${DIAG_USERPD_MASK:-}"
+DIAG_QDSS_MASK="${DIAG_QDSS_MASK:-}"
+DIAG_TX_MODE="${DIAG_TX_MODE:-}"
+DIAG_BUFFER_PERIPHERAL_MASK="${DIAG_BUFFER_PERIPHERAL_MASK:-}"
+DIAG_ETR_BUFFER_SIZE="${DIAG_ETR_BUFFER_SIZE:-}"
+DIAG_QMDL2_V2="${DIAG_QMDL2_V2:-0}"
+
+print_usage() {
+    cat <<EOF_USAGE
+Usage: $0 [options]
+
+Options:
+  --duration <seconds> Normal diag_mdlog observation time. Default: 10
+  --nrt-duration <seconds> Non-real-time observation time. Default: 5
+  --file-size <value> Value passed to diag_mdlog -s. Default: 20
+  --file-count <count> Value passed to diag_mdlog -n. Default: 2
+  --mask-file <path> Mask file passed through diag_mdlog -f
+  --mask-list <path> Mask-list file passed through diag_mdlog -l
+  --peripheral-mask <mask> Peripheral mask passed through diag_mdlog -p
+  --no-nonrealtime Do not validate diag_mdlog -b
+  --help Show this help text
+
+Environment-only platform options:
+  DIAG_PROCESSOR_MASK
+  DIAG_USERPD_MASK
+  DIAG_QDSS_MASK
+  DIAG_TX_MODE
+  DIAG_BUFFER_PERIPHERAL_MASK
+  DIAG_ETR_BUFFER_SIZE
+  DIAG_QMDL2_V2=0|1
+  DIAG_ARTIFACT_DIR
+  DIAG_KEEP_ARTIFACTS=0|1
+  DIAG_PROBE_OPTIONAL_HELP=0|1
+EOF_USAGE
+}
+
+require_option_value() {
+    if [ "$#" -lt 2 ] || [ -z "${2:-}" ]; then
+        log_error "Missing value for ${1:-option}"
+        print_usage
+        echo "$TESTNAME FAIL" >"$RES_FILE"
+        exit 1
+    fi
+}
+
+# --------- Argument parsing ---------
+while [ "$#" -gt 0 ]; do
+    case "$1" in
+        --duration)
+            require_option_value "$@"
+            shift
+            DIAG_DURATION_SECS="$1"
+            ;;
+        --nrt-duration)
+            require_option_value "$@"
+            shift
+            DIAG_NRT_DURATION_SECS="$1"
+            ;;
+        --file-size)
+            require_option_value "$@"
+            shift
+            DIAG_FILE_SIZE="$1"
+            ;;
+        --file-count)
+            require_option_value "$@"
+            shift
+            DIAG_FILE_COUNT="$1"
+            ;;
+        --mask-file)
+            require_option_value "$@"
+            shift
+            DIAG_MASK_FILE="$1"
+            ;;
+        --mask-list)
+            require_option_value "$@"
+            shift
+            DIAG_MASK_LIST="$1"
+            ;;
+        --peripheral-mask)
+            require_option_value "$@"
+            shift
+            DIAG_PERIPHERAL_MASK="$1"
+            ;;
+        --no-nonrealtime)
+            DIAG_TEST_NONREALTIME=0
+            ;;
+        --help)
+            print_usage
+            exit 0
+            ;;
+        *)
+            log_error "Unknown argument: $1"
+            print_usage
+            echo "$TESTNAME FAIL" >"$RES_FILE"
+            exit 1
+            ;;
+    esac
+
+    shift
+done
+
+# --------- Artifact setup ---------
+mkdir -p "$DIAG_ARTIFACT_DIR" || {
+    log_fail "$TESTNAME FAIL: unable to create artifact directory $DIAG_ARTIFACT_DIR"
+    echo "$TESTNAME FAIL" >"$RES_FILE"
+    exit 0
+}
+
+DIAG_ARTIFACT_DIR="$(
+    cd "$DIAG_ARTIFACT_DIR" || exit 1
+    pwd
+)"
+
+DIAG_RUN_DIR="$DIAG_ARTIFACT_DIR/run_$$"
+
+mkdir -p "$DIAG_RUN_DIR" || {
+    log_fail "$TESTNAME FAIL: unable to create run directory $DIAG_RUN_DIR"
+    echo "$TESTNAME FAIL" >"$RES_FILE"
+    exit 0
+}
+
+chmod 0777 "$DIAG_ARTIFACT_DIR" "$DIAG_RUN_DIR" 2>/dev/null || true
+
+DIAG_RESULT_TABLE="$DIAG_RUN_DIR/results.tsv"
+: >"$DIAG_RESULT_TABLE"
+
+trap 'diag_cleanup_owned_processes' EXIT
+trap 'diag_cleanup_owned_processes; exit 130' HUP INT TERM
+
+log_info "--------------------------------------------------------------------------"
+log_info "------------------- Starting $TESTNAME Testcase --------------------------"
+log_info "Using DIAG helper library: $DIAG_LIB"
+log_info "Artifacts: $DIAG_RUN_DIR"
+log_info "Configuration: duration=${DIAG_DURATION_SECS}s nrt_duration=${DIAG_NRT_DURATION_SECS}s file_size=$DIAG_FILE_SIZE file_count=$DIAG_FILE_COUNT nonrealtime=$DIAG_TEST_NONREALTIME optional_help=$DIAG_PROBE_OPTIONAL_HELP"
+
+if command -v detect_platform >/dev/null 2>&1; then
+    detect_platform
+fi
+
+log_info "Platform Details: machine='${PLATFORM_MACHINE:-unknown}' target='${PLATFORM_TARGET:-unknown}' kernel='$(uname -r 2>/dev/null || echo unknown)' arch='$(uname -m 2>/dev/null || echo unknown)'"
+
+# --------- Dependency validation ---------
+if ! CHECK_DEPS_NO_EXIT=1 check_dependencies \
+    awk \
+    sed \
+    grep \
+    find \
+    wc \
+    tail \
+    tr \
+    chmod \
+    mkdir \
+    date \
+    head \
+    basename \
+    cat \
+    rm \
+    sleep \
+    uname \
+    dirname; then
+
+    log_skip "$TESTNAME SKIP: missing base runtime dependencies"
+    echo "$TESTNAME SKIP" >"$RES_FILE"
+    exit 0
+fi
+
+# --------- DIAG capability inventory ---------
+if ! diag_inventory_tools; then
+    diag_print_summary
+    log_skip "$TESTNAME SKIP: diag_mdlog is not available"
+    echo "$TESTNAME SKIP" >"$RES_FILE"
+    exit 0
+fi
+
+# --------- Router and socket validation ---------
+diag_validate_router_socket
+
+# --------- Requested configuration validation ---------
+if ! diag_validate_requested_configuration; then
+    diag_print_summary
+    log_fail "$TESTNAME FAIL: invalid DIAG configuration"
+    echo "$TESTNAME FAIL" >"$RES_FILE"
+    exit 0
+fi
+
+# --------- DIAG session validation ---------
+DIAG_CORE_STATUS="SKIP"
+DIAG_OWNED_NORMAL_VALIDATED=0
+
+if diag_validate_existing_mdlog_session; then
+    DIAG_CORE_STATUS="PASS"
+else
+    if diag_validate_normal_session; then
+        if diag_has_validated_session; then
+            DIAG_CORE_STATUS="PASS"
+            DIAG_OWNED_NORMAL_VALIDATED=1
+        fi
+    else
+        if diag_has_session_conflict; then
+            log_warn "An external diag_mdlog session became active while starting the owned session"
+
+            if diag_validate_existing_mdlog_session; then
+                DIAG_CORE_STATUS="PASS"
+            fi
+        fi
+    fi
+
+    if [ "$DIAG_OWNED_NORMAL_VALIDATED" -eq 1 ]; then
+        diag_validate_nonrealtime_session || true
+    elif ! diag_has_session_conflict; then
+        diag_record_result \
+            "Non-real-time session" \
+            "SKIP" \
+            "normal owned session was not validated"
+    fi
+fi
+
+# --------- Final result ---------
+DIAG_OVERALL_RESULT="$(
+    diag_compute_overall_result "$DIAG_CORE_STATUS"
+)"
+
+diag_print_summary
+log_info "DIAG artifacts retained at: $DIAG_RUN_DIR"
+
+case "$DIAG_OVERALL_RESULT" in
+    PASS)
+        log_pass "$TESTNAME PASS"
+        echo "$TESTNAME PASS" >"$RES_FILE"
+        ;;
+    FAIL)
+        log_fail "$TESTNAME FAIL"
+        echo "$TESTNAME FAIL" >"$RES_FILE"
+        ;;
+    *)
+        log_skip "$TESTNAME SKIP"
+        echo "$TESTNAME SKIP" >"$RES_FILE"
+        ;;
+esac
+
+if [ "$DIAG_KEEP_ARTIFACTS" = "0" ]; then
+    log_info "Removing DIAG artifacts because DIAG_KEEP_ARTIFACTS=0"
+    rm -rf "$DIAG_RUN_DIR"
+fi
+
+exit 0
diff --git a/Runner/utils/lib_diag.sh b/Runner/utils/lib_diag.sh
new file mode 100755
index 000000000..0349f7268
--- /dev/null
+++ b/Runner/utils/lib_diag.sh
@@ -0,0 +1,1641 @@
+#!/bin/sh
+# Copyright (c) Qualcomm Technologies, Inc. and/or its subsidiaries.
+# SPDX-License-Identifier: BSD-3-Clause
+# Shared helpers for DIAG userspace functional validation.
+
+# Expected globals provided by the caller:
+# DIAG_RESULT_TABLE
+# DIAG_RUN_DIR
+# DIAG_MDLOG_HELP_FILE
+# DIAG_DURATION_SECS
+# DIAG_NRT_DURATION_SECS
+# DIAG_STARTUP_TIMEOUT_SECS
+# DIAG_STOP_TIMEOUT_SECS
+# DIAG_FILE_SIZE
+# DIAG_FILE_COUNT
+# DIAG_MASK_FILE
+# DIAG_MASK_LIST
+# DIAG_PERIPHERAL_MASK
+# DIAG_PROCESSOR_MASK
+# DIAG_USERPD_MASK
+# DIAG_QDSS_MASK
+# DIAG_TX_MODE
+# DIAG_BUFFER_PERIPHERAL_MASK
+# DIAG_ETR_BUFFER_SIZE
+# DIAG_QMDL2_V2
+
+DIAG_OWNED_PIDS=""
+DIAG_MDLOG_PATH=""
+DIAG_EXPLICIT_MASK=0
+DIAG_SESSION_VALIDATED=0
+DIAG_SESSION_CONFLICT=0
+DIAG_LAST_PID=""
+DIAG_LAST_LOG=""
+DIAG_LAST_OUTPUT_ROOT=""
+DIAG_LAST_OUTPUT_DIR=""
+DIAG_ROUTER_PID=""
+DIAG_ROUTER_LOG=""
+DIAG_ROUTER_OWNED=0
+
+diag_has_validated_session() {
+    [ "${DIAG_SESSION_VALIDATED:-0}" -eq 1 ]
+}
+
+diag_has_session_conflict() {
+    [ "${DIAG_SESSION_CONFLICT:-0}" -eq 1 ]
+}
+
+# Convert arbitrary command output to one safe summary-table field.
+diag_sanitize_text() {
+    printf '%s' "${1:-}" \
+        | tr '\n\r\t|' ' ' \
+        | sed 's/[[:space:]][[:space:]]*/ /g; s/^ //; s/ $//'
+}
+
+diag_record_result() {
+    diag_rr_check="$(diag_sanitize_text "${1:-unknown}")"
+    diag_rr_result="${2:-SKIP}"
+    diag_rr_details="$(diag_sanitize_text "${3:-}")"
+
+    case "$diag_rr_result" in
+        PASS|FAIL|SKIP) ;;
+        *) diag_rr_result="FAIL" ;;
+    esac
+
+    printf '%s|%s|%s\n' \
+        "$diag_rr_check" \
+        "$diag_rr_result" \
+        "$diag_rr_details" >>"$DIAG_RESULT_TABLE"
+
+    case "$diag_rr_result" in
+        PASS)
+            log_pass "$diag_rr_check: $diag_rr_details"
+            ;;
+        FAIL)
+            log_fail "$diag_rr_check: $diag_rr_details"
+            ;;
+        SKIP)
+            log_skip "$diag_rr_check: $diag_rr_details"
+            ;;
+    esac
+}
+
+diag_result_count() {
+    diag_rc_wanted="${1:-}"
+
+    awk -F '|' -v wanted="$diag_rc_wanted" '
+        $2 == wanted {
+            count++
+        }
+        END {
+            print count + 0
+        }
+    ' "$DIAG_RESULT_TABLE" 2>/dev/null
+}
+
+diag_print_summary() {
+    diag_ps_passed="$(diag_result_count PASS)"
+    diag_ps_failed="$(diag_result_count FAIL)"
+    diag_ps_skipped="$(diag_result_count SKIP)"
+
+    log_info "DIAG Validation Summary"
+    printf '%s\n' "--------------------------------------------------------------------------------"
+    printf '%-34s %-7s %s\n' "Check" "Result" "Details"
+    printf '%s\n' "--------------------------------------------------------------------------------"
+
+    while IFS='|' read -r diag_ps_check diag_ps_result diag_ps_details; do
+        [ -n "$diag_ps_check" ] || continue
+
+        printf '%-34s %-7s %s\n' \
+            "$diag_ps_check" \
+            "$diag_ps_result" \
+            "$diag_ps_details"
+    done <"$DIAG_RESULT_TABLE"
+
+    printf '%s\n' "--------------------------------------------------------------------------------"
+    printf 'Passed: %s Failed: %s Skipped: %s\n' \
+        "$diag_ps_passed" \
+        "$diag_ps_failed" \
+        "$diag_ps_skipped"
+}
+
+diag_compute_overall_result() {
+    diag_cor_core_status="${1:-SKIP}"
+    diag_cor_failed="$(diag_result_count FAIL)"
+
+    if [ "$diag_cor_failed" -gt 0 ]; then
+        printf '%s\n' "FAIL"
+    elif [ "$diag_cor_core_status" = "PASS" ]; then
+        printf '%s\n' "PASS"
+    else
+        printf '%s\n' "SKIP"
+    fi
+}
+
+diag_is_positive_integer() {
+    case "${1:-}" in
+        ''|*[!0-9]*)
+            return 1
+            ;;
+        0)
+            return 1
+            ;;
+        *)
+            return 0
+            ;;
+    esac
+}
+
+diag_is_boolean() {
+    case "${1:-}" in
+        0|1)
+            return 0
+            ;;
+        *)
+            return 1
+            ;;
+    esac
+}
+
+diag_shell_quote_arg() {
+    diag_sqa_arg="${1:-}"
+
+    case "$diag_sqa_arg" in
+        "")
+            printf "''"
+            ;;
+        *[!A-Za-z0-9_./:=,+%@#-]*)
+            printf "'%s'" "$(printf '%s' "$diag_sqa_arg" | sed "s/'/'\\\\''/g")"
+            ;;
+        *)
+            printf '%s' "$diag_sqa_arg"
+            ;;
+    esac
+}
+
+diag_log_command() {
+    diag_lc_message=""
+
+    for diag_lc_arg in "$@"; do
+        diag_lc_quoted="$(diag_shell_quote_arg "$diag_lc_arg")"
+
+        if [ -n "$diag_lc_message" ]; then
+            diag_lc_message="$diag_lc_message $diag_lc_quoted"
+        else
+            diag_lc_message="$diag_lc_quoted"
+        fi
+    done
+
+    log_info "RUN: $diag_lc_message"
+}
+
+# Execute a command with a portable watchdog. Returns 124 on timeout.
+diag_run_with_timeout() {
+    diag_rwt_timeout="${1:-5}"
+    shift
+
+    if ! diag_is_positive_integer "$diag_rwt_timeout"; then
+        diag_rwt_timeout=5
+    fi
+
+    diag_rwt_tag="$(date +%s 2>/dev/null || echo 0)"
+    diag_rwt_marker="${TMPDIR:-/tmp}/diag_timeout.$$.$diag_rwt_tag"
+    rm -f "$diag_rwt_marker" 2>/dev/null || true
+
+    "$@" &
+    diag_rwt_pid=$!
+
+    (
+        sleep "$diag_rwt_timeout" 2>/dev/null || true
+
+        if kill -0 "$diag_rwt_pid" 2>/dev/null; then
+            echo 1 >"$diag_rwt_marker" 2>/dev/null || true
+            kill -TERM "$diag_rwt_pid" 2>/dev/null || true
+            sleep 1 2>/dev/null || true
+
+            if kill -0 "$diag_rwt_pid" 2>/dev/null; then
+                kill -KILL "$diag_rwt_pid" 2>/dev/null || true
+            fi
+        fi
+    ) &
+    diag_rwt_watchdog=$!
+
+    wait "$diag_rwt_pid"
+    diag_rwt_rc=$?
+
+    kill "$diag_rwt_watchdog" 2>/dev/null || true
+    wait "$diag_rwt_watchdog" 2>/dev/null || true
+
+    if [ -f "$diag_rwt_marker" ]; then
+        rm -f "$diag_rwt_marker" 2>/dev/null || true
+        return 124
+    fi
+
+    rm -f "$diag_rwt_marker" 2>/dev/null || true
+    return "$diag_rwt_rc"
+}
+
+diag_capture_help() {
+    diag_ch_tool="${1:-}"
+    diag_ch_file="${2:-}"
+
+    [ -n "$diag_ch_tool" ] || return 1
+    [ -n "$diag_ch_file" ] || return 1
+
+    : >"$diag_ch_file"
+
+    diag_run_with_timeout 5 "$diag_ch_tool" --help \
+        >"$diag_ch_file" 2>&1 || true
+
+    if [ ! -s "$diag_ch_file" ]; then
+        diag_run_with_timeout 5 "$diag_ch_tool" -h \
+            >"$diag_ch_file" 2>&1 || true
+    fi
+
+    [ -s "$diag_ch_file" ]
+}
+
+diag_help_supports_option() {
+    diag_hso_file="${1:-}"
+    diag_hso_option="${2:-}"
+
+    [ -s "$diag_hso_file" ] || return 1
+    [ -n "$diag_hso_option" ] || return 1
+
+    grep -Eq -- \
+        "(^|[[:space:],])${diag_hso_option}([[:space:],]|$)" \
+        "$diag_hso_file"
+}
+
+diag_find_pids_by_name() {
+    diag_fpn_name="${1:-}"
+ 
+    [ -n "$diag_fpn_name" ] || return 0
+ 
+    for diag_fpn_proc in /proc/[0-9]*; do
+        [ -d "$diag_fpn_proc" ] || continue
+ 
+        diag_fpn_pid="${diag_fpn_proc#/proc/}"
+        diag_fpn_comm="$(cat "$diag_fpn_proc/comm" 2>/dev/null || true)"
+ 
+        if [ "$diag_fpn_comm" = "$diag_fpn_name" ]; then
+            printf '%s\n' "$diag_fpn_pid"
+            continue
+        fi
+ 
+        diag_fpn_first="$(
+            tr '\000' '\n' <"$diag_fpn_proc/cmdline" 2>/dev/null \
+                | head -n 1
+        )"
+ 
+        [ -n "$diag_fpn_first" ] || continue
+ 
+        # Do not use basename here. Process arguments may begin with '-',
+        # which some basename implementations interpret as an option.
+        diag_fpn_base="${diag_fpn_first##*/}"
+ 
+        if [ "$diag_fpn_base" = "$diag_fpn_name" ]; then
+            printf '%s\n' "$diag_fpn_pid"
+        fi
+    done
+}
+
+diag_pid_alive() {
+    diag_pa_pid="${1:-}"
+
+    [ -n "$diag_pa_pid" ] || return 1
+    [ -r "/proc/$diag_pa_pid/status" ] || return 1
+
+    diag_pa_state="$(
+        awk '/^State:/ { print $2; exit }' \
+            "/proc/$diag_pa_pid/status" 2>/dev/null || true
+    )"
+
+    [ "$diag_pa_state" = "Z" ] && return 1
+
+    kill -0 "$diag_pa_pid" 2>/dev/null
+}
+
+diag_process_description() {
+    diag_pd_pid="${1:-}"
+
+    diag_pd_uid="$(
+        awk '/^Uid:/ { print $2; exit }' \
+            "/proc/$diag_pd_pid/status" 2>/dev/null || true
+    )"
+
+    diag_pd_cmd="$(
+        tr '\000' ' ' \
+            <"/proc/$diag_pd_pid/cmdline" 2>/dev/null || true
+    )"
+
+    printf 'pid=%s uid=%s cmd=%s\n' \
+        "${diag_pd_pid:-unknown}" \
+        "${diag_pd_uid:-unknown}" \
+        "${diag_pd_cmd:-unknown}"
+}
+
+diag_get_process_option() {
+    diag_gpo_pid="${1:-}"
+    diag_gpo_option="${2:-}"
+    diag_gpo_expect_value=0
+
+    tr '\000' '\n' <"/proc/$diag_gpo_pid/cmdline" 2>/dev/null \
+        | while IFS= read -r diag_gpo_arg; do
+            if [ "$diag_gpo_expect_value" -eq 1 ]; then
+                printf '%s\n' "$diag_gpo_arg"
+                break
+            fi
+
+            if [ "$diag_gpo_arg" = "$diag_gpo_option" ]; then
+                diag_gpo_expect_value=1
+            fi
+        done
+}
+
+diag_register_owned_pid() {
+    diag_rop_pid="${1:-}"
+
+    [ -n "$diag_rop_pid" ] || return 0
+
+    case " $DIAG_OWNED_PIDS " in
+        *" $diag_rop_pid "*)
+            ;;
+        *)
+            DIAG_OWNED_PIDS="$DIAG_OWNED_PIDS $diag_rop_pid"
+            ;;
+    esac
+}
+
+diag_unregister_owned_pid() {
+    diag_uop_target="${1:-}"
+    diag_uop_remaining=""
+
+    [ -n "$diag_uop_target" ] || return 0
+
+    for diag_uop_pid in $DIAG_OWNED_PIDS; do
+        [ "$diag_uop_pid" = "$diag_uop_target" ] && continue
+        diag_uop_remaining="$diag_uop_remaining $diag_uop_pid"
+    done
+
+    DIAG_OWNED_PIDS="$diag_uop_remaining"
+}
+
+diag_wait_for_pid_exit() {
+    diag_wpe_pid="${1:-}"
+    diag_wpe_timeout="${2:-5}"
+    diag_wpe_waited=0
+
+    while diag_pid_alive "$diag_wpe_pid"; do
+        if [ "$diag_wpe_waited" -ge "$diag_wpe_timeout" ]; then
+            return 1
+        fi
+
+        sleep 1
+        diag_wpe_waited=$((diag_wpe_waited + 1))
+    done
+
+    wait "$diag_wpe_pid" >/dev/null 2>&1 || true
+    return 0
+}
+
+diag_stop_pid() {
+    diag_sp_pid="${1:-}"
+    diag_sp_timeout="${2:-10}"
+ 
+    if ! diag_is_positive_integer "$diag_sp_timeout"; then
+        diag_sp_timeout=10
+    fi
+ 
+    if ! diag_pid_alive "$diag_sp_pid"; then
+        wait "$diag_sp_pid" >/dev/null 2>&1 || true
+        diag_unregister_owned_pid "$diag_sp_pid"
+        return 0
+    fi
+ 
+    # Prefer SIGINT because diag_mdlog normally performs its orderly
+    # deinitialization through the interactive Ctrl+C shutdown path.
+    kill -INT "$diag_sp_pid" 2>/dev/null || true
+ 
+    if diag_wait_for_pid_exit "$diag_sp_pid" "$diag_sp_timeout"; then
+        diag_unregister_owned_pid "$diag_sp_pid"
+        return 0
+    fi
+ 
+    log_warn "PID $diag_sp_pid did not stop after INT; trying TERM"
+    kill -TERM "$diag_sp_pid" 2>/dev/null || true
+ 
+    if diag_wait_for_pid_exit "$diag_sp_pid" "$diag_sp_timeout"; then
+        diag_unregister_owned_pid "$diag_sp_pid"
+        return 2
+    fi
+ 
+    log_warn "PID $diag_sp_pid did not stop after TERM; using KILL"
+    kill -KILL "$diag_sp_pid" 2>/dev/null || true
+ 
+    if diag_wait_for_pid_exit "$diag_sp_pid" 2; then
+        diag_unregister_owned_pid "$diag_sp_pid"
+        return 3
+    fi
+ 
+    return 1
+}
+
+diag_stop_router_pid() {
+    diag_srp_pid="${1:-}"
+    diag_srp_timeout="${2:-5}"
+
+    if ! diag_is_positive_integer "$diag_srp_timeout"; then
+        diag_srp_timeout=5
+    fi
+
+    if ! diag_pid_alive "$diag_srp_pid"; then
+        wait "$diag_srp_pid" >/dev/null 2>&1 || true
+        diag_unregister_owned_pid "$diag_srp_pid"
+        return 0
+    fi
+
+    kill -TERM "$diag_srp_pid" 2>/dev/null || true
+
+    if diag_wait_for_pid_exit "$diag_srp_pid" "$diag_srp_timeout"; then
+        diag_unregister_owned_pid "$diag_srp_pid"
+        return 0
+    fi
+
+    log_warn "diag-router PID $diag_srp_pid did not stop after TERM; using KILL"
+    kill -KILL "$diag_srp_pid" 2>/dev/null || true
+
+    if diag_wait_for_pid_exit "$diag_srp_pid" 2; then
+        diag_unregister_owned_pid "$diag_srp_pid"
+        return 2
+    fi
+
+    return 1
+}
+
+diag_cleanup_owned_processes() {
+    for diag_cop_pid in $DIAG_OWNED_PIDS; do
+        diag_pid_alive "$diag_cop_pid" || continue
+ 
+        if [ -n "${DIAG_ROUTER_PID:-}" ] && \
+           [ "$diag_cop_pid" = "$DIAG_ROUTER_PID" ]; then
+ 
+            log_info "Stopping owned diag-router PID $diag_cop_pid during cleanup"
+ 
+            diag_stop_router_pid \
+                "$diag_cop_pid" \
+                "${DIAG_STOP_TIMEOUT_SECS:-5}" || true
+        else
+            log_info "Stopping owned DIAG process PID $diag_cop_pid during cleanup"
+ 
+            diag_stop_pid \
+                "$diag_cop_pid" \
+                "${DIAG_STOP_TIMEOUT_SECS:-10}" || true
+        fi
+    done
+}
+
+diag_wait_for_log_pattern() {
+    diag_wlp_file="${1:-}"
+    diag_wlp_pattern="${2:-}"
+    diag_wlp_timeout="${3:-10}"
+    diag_wlp_elapsed=0
+
+    while [ "$diag_wlp_elapsed" -lt "$diag_wlp_timeout" ]; do
+        if [ -f "$diag_wlp_file" ] && \
+           grep -Eq "$diag_wlp_pattern" "$diag_wlp_file" 2>/dev/null; then
+            return 0
+        fi
+
+        sleep 1
+        diag_wlp_elapsed=$((diag_wlp_elapsed + 1))
+    done
+
+    return 1
+}
+
+diag_wait_pid_duration() {
+    diag_wpd_pid="${1:-}"
+    diag_wpd_duration="${2:-1}"
+    diag_wpd_elapsed=0
+
+    while [ "$diag_wpd_elapsed" -lt "$diag_wpd_duration" ]; do
+        diag_pid_alive "$diag_wpd_pid" || return 1
+        sleep 1
+        diag_wpd_elapsed=$((diag_wpd_elapsed + 1))
+    done
+
+    diag_pid_alive "$diag_wpd_pid"
+}
+
+diag_log_tail() {
+    diag_lt_prefix="${1:-diag}"
+    diag_lt_file="${2:-}"
+    diag_lt_lines="${3:-60}"
+
+    [ -f "$diag_lt_file" ] || return 0
+
+    log_info "[DEBUG] Tail of $diag_lt_file:"
+
+    tail -n "$diag_lt_lines" "$diag_lt_file" 2>/dev/null \
+        | while IFS= read -r diag_lt_line; do
+            [ -n "$diag_lt_line" ] && \
+                log_info "[$diag_lt_prefix] $diag_lt_line"
+        done
+}
+
+diag_nonempty_file_count() {
+    diag_nfc_root="${1:-}"
+
+    if [ ! -d "$diag_nfc_root" ]; then
+        printf '%s\n' 0
+        return 0
+    fi
+
+    find "$diag_nfc_root" -type f -size +0c 2>/dev/null \
+        | wc -l \
+        | awk '{ print $1 + 0 }'
+}
+
+diag_first_child_directory() {
+    diag_fcd_root="${1:-}"
+
+    [ -d "$diag_fcd_root" ] || return 1
+
+    for diag_fcd_entry in "$diag_fcd_root"/*; do
+        [ -d "$diag_fcd_entry" ] || continue
+        printf '%s\n' "$diag_fcd_entry"
+        return 0
+    done
+
+    return 1
+}
+
+diag_extract_output_dir_from_log() {
+    diag_eod_file="${1:-}"
+
+    [ -f "$diag_eod_file" ] || return 1
+
+    sed -n \
+        's/.*Output dirs \([^[:space:]]*\)[[:space:]].*/\1/p' \
+        "$diag_eod_file" \
+        | tail -n 1
+}
+
+diag_inventory_tools() {
+    diag_it_help_dir="$DIAG_RUN_DIR/tool_help"
+    mkdir -p "$diag_it_help_dir" || return 1
+
+    DIAG_MDLOG_PATH="$(command -v diag_mdlog 2>/dev/null || true)"
+
+    if [ -z "$DIAG_MDLOG_PATH" ]; then
+        diag_record_result \
+            "diag_mdlog binary" \
+            "SKIP" \
+            "diag_mdlog is not installed"
+    else
+        DIAG_MDLOG_HELP_FILE="$diag_it_help_dir/diag_mdlog_help.txt"
+
+        if diag_capture_help "$DIAG_MDLOG_PATH" "$DIAG_MDLOG_HELP_FILE"; then
+            diag_record_result \
+                "diag_mdlog binary" \
+                "PASS" \
+                "path=$DIAG_MDLOG_PATH help=$DIAG_MDLOG_HELP_FILE"
+        else
+            diag_record_result \
+                "diag_mdlog binary" \
+                "PASS" \
+                "path=$DIAG_MDLOG_PATH; help output unavailable"
+        fi
+    fi
+
+    for diag_it_tool in \
+        diag-router \
+        diag_klog \
+        diag_socket_log \
+        diag_uart_log \
+        diag_callback_sample \
+        diag_dci_sample; do
+
+        diag_it_path="$(command -v "$diag_it_tool" 2>/dev/null || true)"
+        diag_it_help_file="$diag_it_help_dir/${diag_it_tool}_help.txt"
+
+        if [ -z "$diag_it_path" ]; then
+            diag_record_result \
+                "$diag_it_tool capability" \
+                "SKIP" \
+                "binary not installed"
+            continue
+        fi
+
+        if [ "${DIAG_PROBE_OPTIONAL_HELP:-0}" = "1" ]; then
+            if diag_capture_help "$diag_it_path" "$diag_it_help_file"; then
+                diag_record_result \
+                    "$diag_it_tool capability" \
+                    "PASS" \
+                    "path=$diag_it_path help=$diag_it_help_file"
+            else
+                diag_record_result \
+                    "$diag_it_tool capability" \
+                    "PASS" \
+                    "path=$diag_it_path; help output unavailable"
+            fi
+        else
+            diag_record_result \
+                "$diag_it_tool capability" \
+                "PASS" \
+                "path=$diag_it_path; optional help probe disabled"
+        fi
+    done
+
+    [ -n "$DIAG_MDLOG_PATH" ]
+}
+
+diag_validate_router_socket() {
+    diag_vrs_router_path="$(command -v diag-router 2>/dev/null || true)"
+    diag_vrs_router_log="$DIAG_RUN_DIR/diag_router.log"
+    diag_vrs_router_pid="$(diag_find_active_router_pid || true)"
+    diag_vrs_router_ready=0
+ 
+    if [ -n "$diag_vrs_router_pid" ]; then
+        DIAG_ROUTER_PID="$diag_vrs_router_pid"
+        DIAG_ROUTER_LOG=""
+        DIAG_ROUTER_OWNED=0
+        diag_vrs_router_ready=1
+ 
+        diag_vrs_description="$(
+            diag_process_description "$diag_vrs_router_pid"
+        )"
+ 
+        diag_record_result \
+            "diag-router process" \
+            "PASS" \
+            "existing router: $diag_vrs_description"
+    else
+        if [ -z "$diag_vrs_router_path" ]; then
+            diag_record_result \
+                "diag-router process" \
+                "FAIL" \
+                "diag-router binary is not installed"
+ 
+            diag_record_result \
+                "DIAG transport readiness" \
+                "FAIL" \
+                "router is unavailable"
+ 
+            return 1
+        fi
+ 
+        log_info "No existing diag-router process found"
+ 
+        if diag_start_router_process \
+            "initial DIAG validation" \
+            "$diag_vrs_router_log"; then
+ 
+            diag_vrs_router_ready=1
+ 
+            diag_vrs_description="$(
+                diag_process_description "$DIAG_ROUTER_PID"
+            )"
+ 
+            diag_record_result \
+                "diag-router process" \
+                "PASS" \
+                "started owned router: $diag_vrs_description log=$DIAG_ROUTER_LOG"
+        else
+            diag_record_result \
+                "diag-router process" \
+                "FAIL" \
+                "diag-router exited during startup; log=$diag_vrs_router_log"
+ 
+            diag_log_tail \
+                "diag-router" \
+                "$diag_vrs_router_log" \
+                80
+ 
+            diag_record_result \
+                "DIAG transport readiness" \
+                "FAIL" \
+                "router startup failed"
+ 
+            return 1
+        fi
+    fi
+ 
+    diag_vrs_socket=""
+    diag_vrs_socket_waited=0
+ 
+    while [ "$diag_vrs_socket_waited" -lt 5 ]; do
+        if [ -r /proc/net/unix ]; then
+            diag_vrs_socket="$(
+                grep -i 'diag' /proc/net/unix 2>/dev/null \
+                    | head -n 1
+            )"
+        fi
+ 
+        [ -n "$diag_vrs_socket" ] && break
+ 
+        if ! diag_pid_alive "$DIAG_ROUTER_PID"; then
+            diag_vrs_router_ready=0
+            break
+        fi
+ 
+        sleep 1
+        diag_vrs_socket_waited=$((diag_vrs_socket_waited + 1))
+    done
+ 
+    if [ "$diag_vrs_router_ready" -ne 1 ]; then
+        diag_record_result \
+            "DIAG transport readiness" \
+            "FAIL" \
+            "diag-router terminated while transport readiness was being checked"
+ 
+        diag_log_tail \
+            "diag-router" \
+            "$DIAG_ROUTER_LOG" \
+            80
+ 
+        return 1
+    fi
+ 
+    if [ -n "$diag_vrs_socket" ]; then
+        diag_record_result \
+            "DIAG transport readiness" \
+            "PASS" \
+            "named DIAG Unix socket found: $diag_vrs_socket"
+    elif [ "$DIAG_ROUTER_OWNED" -eq 1 ]; then
+        diag_record_result \
+            "DIAG transport readiness" \
+            "PASS" \
+            "owned diag-router is active; this implementation does not expose a named socket in /proc/net/unix"
+    else
+        diag_record_result \
+            "DIAG transport readiness" \
+            "PASS" \
+            "existing diag-router is active; this implementation does not expose a named socket in /proc/net/unix"
+    fi
+ 
+    return 0
+}
+
+diag_validate_requested_configuration() {
+    DIAG_EXPLICIT_MASK=0
+    diag_vrc_error=0
+ 
+    if ! diag_is_positive_integer "$DIAG_DURATION_SECS"; then
+        diag_record_result \
+            "DIAG configuration" \
+            "FAIL" \
+            "DIAG_DURATION_SECS must be a positive integer"
+        diag_vrc_error=1
+    fi
+ 
+    if ! diag_is_positive_integer "$DIAG_NRT_DURATION_SECS"; then
+        diag_record_result \
+            "DIAG configuration" \
+            "FAIL" \
+            "DIAG_NRT_DURATION_SECS must be a positive integer"
+        diag_vrc_error=1
+    fi
+ 
+    if ! diag_is_positive_integer "$DIAG_STARTUP_TIMEOUT_SECS"; then
+        diag_record_result \
+            "DIAG configuration" \
+            "FAIL" \
+            "DIAG_STARTUP_TIMEOUT_SECS must be a positive integer"
+        diag_vrc_error=1
+    fi
+ 
+    if ! diag_is_positive_integer "$DIAG_STOP_TIMEOUT_SECS"; then
+        diag_record_result \
+            "DIAG configuration" \
+            "FAIL" \
+            "DIAG_STOP_TIMEOUT_SECS must be a positive integer"
+        diag_vrc_error=1
+    fi
+ 
+    if ! diag_is_positive_integer "$DIAG_FILE_SIZE"; then
+        diag_record_result \
+            "DIAG configuration" \
+            "FAIL" \
+            "DIAG_FILE_SIZE must be a positive integer"
+        diag_vrc_error=1
+    fi
+ 
+    if ! diag_is_positive_integer "$DIAG_FILE_COUNT"; then
+        diag_record_result \
+            "DIAG configuration" \
+            "FAIL" \
+            "DIAG_FILE_COUNT must be a positive integer"
+        diag_vrc_error=1
+    fi
+ 
+    if ! diag_is_boolean "$DIAG_TEST_NONREALTIME"; then
+        diag_record_result \
+            "DIAG configuration" \
+            "FAIL" \
+            "DIAG_TEST_NONREALTIME must be 0 or 1"
+        diag_vrc_error=1
+    fi
+ 
+    if ! diag_is_boolean "$DIAG_KEEP_ARTIFACTS"; then
+        diag_record_result \
+            "DIAG configuration" \
+            "FAIL" \
+            "DIAG_KEEP_ARTIFACTS must be 0 or 1"
+        diag_vrc_error=1
+    fi
+ 
+    if ! diag_is_boolean "$DIAG_PROBE_OPTIONAL_HELP"; then
+        diag_record_result \
+            "DIAG configuration" \
+            "FAIL" \
+            "DIAG_PROBE_OPTIONAL_HELP must be 0 or 1"
+        diag_vrc_error=1
+    fi
+ 
+    if ! diag_is_boolean "$DIAG_QMDL2_V2"; then
+        diag_record_result \
+            "DIAG configuration" \
+            "FAIL" \
+            "DIAG_QMDL2_V2 must be 0 or 1"
+        diag_vrc_error=1
+    fi
+ 
+    if [ -n "$DIAG_MASK_FILE" ] && [ -n "$DIAG_MASK_LIST" ]; then
+        diag_record_result \
+            "Mask configuration" \
+            "FAIL" \
+            "set only one of DIAG_MASK_FILE or DIAG_MASK_LIST"
+        diag_vrc_error=1
+    elif [ -n "$DIAG_MASK_FILE" ]; then
+        DIAG_EXPLICIT_MASK=1
+ 
+        if [ ! -r "$DIAG_MASK_FILE" ]; then
+            diag_record_result \
+                "Mask configuration" \
+                "FAIL" \
+                "mask file is not readable: $DIAG_MASK_FILE"
+            diag_vrc_error=1
+        elif ! diag_help_supports_option \
+            "$DIAG_MDLOG_HELP_FILE" \
+            "-f"; then
+ 
+            diag_record_result \
+                "Mask configuration" \
+                "FAIL" \
+                "diag_mdlog does not advertise -f support"
+            diag_vrc_error=1
+        else
+            diag_record_result \
+                "Mask configuration" \
+                "PASS" \
+                "using explicit mask file $DIAG_MASK_FILE"
+        fi
+    elif [ -n "$DIAG_MASK_LIST" ]; then
+        DIAG_EXPLICIT_MASK=1
+ 
+        if [ ! -r "$DIAG_MASK_LIST" ]; then
+            diag_record_result \
+                "Mask configuration" \
+                "FAIL" \
+                "mask list is not readable: $DIAG_MASK_LIST"
+            diag_vrc_error=1
+        elif ! diag_help_supports_option \
+            "$DIAG_MDLOG_HELP_FILE" \
+            "-l"; then
+ 
+            diag_record_result \
+                "Mask configuration" \
+                "FAIL" \
+                "diag_mdlog does not advertise -l support"
+            diag_vrc_error=1
+        else
+            diag_record_result \
+                "Mask configuration" \
+                "PASS" \
+                "using explicit mask list $DIAG_MASK_LIST"
+        fi
+    else
+        diag_record_result \
+            "Mask configuration" \
+            "PASS" \
+            "default or previously configured device masks selected"
+    fi
+ 
+    diag_vrc_requested=""
+ 
+    for diag_vrc_pair in \
+        "-p|$DIAG_PERIPHERAL_MASK" \
+        "-j|$DIAG_PROCESSOR_MASK" \
+        "-g|$DIAG_USERPD_MASK" \
+        "-q|$DIAG_QDSS_MASK" \
+        "-t|$DIAG_TX_MODE" \
+        "-x|$DIAG_BUFFER_PERIPHERAL_MASK" \
+        "-y|$DIAG_ETR_BUFFER_SIZE"; do
+ 
+        diag_vrc_option="${diag_vrc_pair%%|*}"
+        diag_vrc_value="${diag_vrc_pair#*|}"
+ 
+        [ -n "$diag_vrc_value" ] || continue
+ 
+        if ! diag_help_supports_option \
+            "$DIAG_MDLOG_HELP_FILE" \
+            "$diag_vrc_option"; then
+ 
+            diag_record_result \
+                "Requested mdlog options" \
+                "FAIL" \
+                "$diag_vrc_option was requested but is not advertised by diag_mdlog"
+            diag_vrc_error=1
+        else
+            diag_vrc_requested="$diag_vrc_requested $diag_vrc_option=$diag_vrc_value"
+        fi
+    done
+ 
+    if [ "$DIAG_QMDL2_V2" = "1" ]; then
+        if ! diag_help_supports_option \
+            "$DIAG_MDLOG_HELP_FILE" \
+            "-u"; then
+ 
+            diag_record_result \
+                "Requested mdlog options" \
+                "FAIL" \
+                "-u was requested but is not advertised by diag_mdlog"
+            diag_vrc_error=1
+        else
+            diag_vrc_requested="$diag_vrc_requested -u"
+        fi
+    fi
+ 
+    if [ -n "$diag_vrc_requested" ]; then
+        diag_record_result \
+            "Requested mdlog options" \
+            "PASS" \
+            "$diag_vrc_requested"
+    elif [ "$diag_vrc_error" -eq 0 ]; then
+        diag_record_result \
+            "Requested mdlog options" \
+            "PASS" \
+            "default diag_mdlog option set selected"
+    fi
+ 
+    [ "$diag_vrc_error" -eq 0 ]
+}
+
+diag_start_router_process() {
+    diag_srp_context="${1:-DIAG}"
+    diag_srp_log="${2:-$DIAG_RUN_DIR/diag_router.log}"
+    diag_srp_path="$(command -v diag-router 2>/dev/null || true)"
+
+    DIAG_ROUTER_PID=""
+    DIAG_ROUTER_LOG="$diag_srp_log"
+    DIAG_ROUTER_OWNED=0
+
+    [ -n "$diag_srp_path" ] || return 1
+
+    : >"$diag_srp_log" || return 1
+
+    log_info "Starting owned diag-router for $diag_srp_context"
+    diag_log_command "$diag_srp_path"
+
+    "$diag_srp_path" >"$diag_srp_log" 2>&1 &
+    diag_srp_pid=$!
+
+    diag_register_owned_pid "$diag_srp_pid"
+
+    diag_srp_waited=0
+
+    while [ "$diag_srp_waited" -lt 5 ]; do
+        if diag_pid_alive "$diag_srp_pid"; then
+            DIAG_ROUTER_PID="$diag_srp_pid"
+            DIAG_ROUTER_LOG="$diag_srp_log"
+            DIAG_ROUTER_OWNED=1
+            return 0
+        fi
+
+        sleep 1
+        diag_srp_waited=$((diag_srp_waited + 1))
+    done
+
+    wait "$diag_srp_pid" >/dev/null 2>&1 || true
+    diag_unregister_owned_pid "$diag_srp_pid"
+
+    return 1
+}
+
+diag_find_active_router_pid() {
+    diag_farp_pids="$(diag_find_pids_by_name diag-router)"
+
+    for diag_farp_pid in $diag_farp_pids; do
+        if diag_pid_alive "$diag_farp_pid"; then
+            printf '%s\n' "$diag_farp_pid"
+            return 0
+        fi
+    done
+
+    return 1
+}
+
+diag_ensure_router_for_session() {
+    diag_erfs_label="${1:-DIAG}"
+    diag_erfs_active_pid="$(diag_find_active_router_pid || true)"
+
+    if [ -n "$diag_erfs_active_pid" ]; then
+        DIAG_ROUTER_PID="$diag_erfs_active_pid"
+        return 0
+    fi
+
+    if [ -n "${DIAG_ROUTER_PID:-}" ]; then
+        diag_record_result \
+            "$diag_erfs_label router continuity" \
+            "FAIL" \
+            "diag-router PID $DIAG_ROUTER_PID terminated unexpectedly after the previous DIAG session"
+    else
+        diag_record_result \
+            "$diag_erfs_label router continuity" \
+            "FAIL" \
+            "no active diag-router process was found"
+    fi
+
+    diag_erfs_log="$DIAG_RUN_DIR/diag_router_recovery.log"
+
+    if diag_start_router_process \
+        "$diag_erfs_label recovery" \
+        "$diag_erfs_log"; then
+
+        diag_record_result \
+            "$diag_erfs_label router recovery" \
+            "PASS" \
+            "restarted owned diag-router pid=$DIAG_ROUTER_PID log=$diag_erfs_log"
+
+        sleep 2
+        return 0
+    fi
+
+    diag_record_result \
+        "$diag_erfs_label router recovery" \
+        "FAIL" \
+        "unable to restart diag-router; log=$diag_erfs_log"
+
+    diag_log_tail \
+        "diag-router-recovery" \
+        "$diag_erfs_log" \
+        80
+
+    return 1
+}
+
+diag_start_mdlog_session() {
+    diag_sms_mode="${1:-normal}"
+    diag_sms_output_root="${2:-}"
+    diag_sms_log_file="${3:-}"
+
+    DIAG_LAST_PID=""
+    DIAG_LAST_LOG="$diag_sms_log_file"
+    DIAG_LAST_OUTPUT_ROOT="$diag_sms_output_root"
+    DIAG_LAST_OUTPUT_DIR=""
+
+    mkdir -p "$diag_sms_output_root" || return 1
+    chmod 0777 "$diag_sms_output_root" 2>/dev/null || return 1
+    : >"$diag_sms_log_file" || return 1
+
+    set -- "$DIAG_MDLOG_PATH" \
+        -o "$diag_sms_output_root" \
+        -s "$DIAG_FILE_SIZE" \
+        -n "$DIAG_FILE_COUNT"
+
+    if [ -n "$DIAG_MASK_FILE" ]; then
+        set -- "$@" -f "$DIAG_MASK_FILE"
+    elif [ -n "$DIAG_MASK_LIST" ]; then
+        set -- "$@" -l "$DIAG_MASK_LIST"
+    fi
+
+    if [ -n "$DIAG_PERIPHERAL_MASK" ]; then
+        set -- "$@" -p "$DIAG_PERIPHERAL_MASK"
+    fi
+
+    if [ -n "$DIAG_PROCESSOR_MASK" ]; then
+        set -- "$@" -j "$DIAG_PROCESSOR_MASK"
+    fi
+
+    if [ -n "$DIAG_USERPD_MASK" ]; then
+        set -- "$@" -g "$DIAG_USERPD_MASK"
+    fi
+
+    if [ -n "$DIAG_QDSS_MASK" ]; then
+        set -- "$@" -q "$DIAG_QDSS_MASK"
+    fi
+
+    if [ -n "$DIAG_TX_MODE" ]; then
+        set -- "$@" -t "$DIAG_TX_MODE"
+    fi
+
+    if [ -n "$DIAG_BUFFER_PERIPHERAL_MASK" ]; then
+        set -- "$@" -x "$DIAG_BUFFER_PERIPHERAL_MASK"
+    fi
+
+    if [ -n "$DIAG_ETR_BUFFER_SIZE" ]; then
+        set -- "$@" -y "$DIAG_ETR_BUFFER_SIZE"
+    fi
+
+    if [ "$DIAG_QMDL2_V2" = "1" ]; then
+        set -- "$@" -u
+    fi
+
+    if [ "$diag_sms_mode" = "nonrealtime" ]; then
+        set -- "$@" -b
+    fi
+
+    log_info "Starting owned diag_mdlog session: mode=$diag_sms_mode output=$diag_sms_output_root size=$DIAG_FILE_SIZE count=$DIAG_FILE_COUNT"
+    diag_log_command "$@"
+
+    "$@" >"$diag_sms_log_file" 2>&1 &
+    DIAG_LAST_PID=$!
+
+    diag_register_owned_pid "$DIAG_LAST_PID"
+
+    return 0
+}
+
+diag_validate_started_session() {
+    diag_vss_label="${1:-Normal}"
+    diag_vss_duration="${2:-5}"
+    diag_vss_require_data="${3:-1}"
+    diag_vss_pid="$DIAG_LAST_PID"
+    diag_vss_log="$DIAG_LAST_LOG"
+    diag_vss_output_root="$DIAG_LAST_OUTPUT_ROOT"
+    diag_vss_prefix="$(printf '%s' "$diag_vss_label" | tr ' ' '-')"
+ 
+    sleep 1
+ 
+    if ! diag_pid_alive "$diag_vss_pid"; then
+        if grep -qiE \
+            'Session for peripheral mask .* is active with PID' \
+            "$diag_vss_log" 2>/dev/null; then
+ 
+            diag_vss_conflict="$(
+                grep -iE \
+                    'Session for peripheral mask .* is active with PID' \
+                    "$diag_vss_log" 2>/dev/null \
+                    | tail -n 1
+            )"
+ 
+            diag_record_result \
+                "$diag_vss_label logging startup" \
+                "SKIP" \
+                "session conflict: $diag_vss_conflict"
+ 
+            DIAG_SESSION_CONFLICT=1
+ 
+            diag_log_tail \
+                "$diag_vss_prefix" \
+                "$diag_vss_log" \
+                60
+ 
+            return 2
+        fi
+ 
+        diag_record_result \
+            "$diag_vss_label logging startup" \
+            "FAIL" \
+            "diag_mdlog exited during startup; log=$diag_vss_log"
+ 
+        diag_log_tail \
+            "$diag_vss_prefix" \
+            "$diag_vss_log" \
+            80
+ 
+        return 1
+    fi
+ 
+    if grep -qiE \
+        'Diag_LSM_Init.*(fail|error)|failed to connect to socket|unable to connect to socket|segmentation fault|fatal error' \
+        "$diag_vss_log" 2>/dev/null; then
+ 
+        diag_record_result \
+            "$diag_vss_label logging startup" \
+            "FAIL" \
+            "fatal DIAG startup error detected; log=$diag_vss_log"
+ 
+        diag_log_tail \
+            "$diag_vss_prefix" \
+            "$diag_vss_log" \
+            80
+ 
+        diag_stop_pid \
+            "$diag_vss_pid" \
+            "$DIAG_STOP_TIMEOUT_SECS" || true
+ 
+        return 1
+    fi
+ 
+    if ! diag_wait_pid_duration \
+        "$diag_vss_pid" \
+        "$diag_vss_duration"; then
+ 
+        diag_record_result \
+            "$diag_vss_label logging startup" \
+            "FAIL" \
+            "PID $diag_vss_pid exited before ${diag_vss_duration}s"
+ 
+        diag_log_tail \
+            "$diag_vss_prefix" \
+            "$diag_vss_log" \
+            80
+ 
+        diag_stop_pid \
+            "$diag_vss_pid" \
+            "$DIAG_STOP_TIMEOUT_SECS" || true
+ 
+        return 1
+    fi
+ 
+    DIAG_SESSION_VALIDATED=1
+ 
+    # Stop the process before evaluating its complete log. diag_mdlog may
+    # buffer stdout while running and flush initialization messages at exit.
+    diag_stop_pid \
+        "$diag_vss_pid" \
+        "$DIAG_STOP_TIMEOUT_SECS"
+ 
+    diag_vss_stop_rc=$?
+ 
+    case "$diag_vss_stop_rc" in
+        0)
+            diag_record_result \
+                "$diag_vss_label clean shutdown" \
+                "PASS" \
+                "owned PID $diag_vss_pid stopped through the orderly INT path"
+            ;;
+        2)
+            diag_record_result \
+                "$diag_vss_label clean shutdown" \
+                "PASS" \
+                "owned PID $diag_vss_pid stopped after TERM fallback"
+            ;;
+        3)
+            diag_record_result \
+                "$diag_vss_label clean shutdown" \
+                "FAIL" \
+                "owned PID $diag_vss_pid required KILL"
+            ;;
+        *)
+            diag_record_result \
+                "$diag_vss_label clean shutdown" \
+                "FAIL" \
+                "unable to stop owned PID $diag_vss_pid"
+            ;;
+    esac
+ 
+    # Allow redirected output to be fully flushed.
+    sleep 1
+ 
+    if grep -qiE \
+        'Diag_LSM_Init.*(fail|error)|failed to connect to socket|unable to connect to socket|segmentation fault|fatal error' \
+        "$diag_vss_log" 2>/dev/null; then
+ 
+        diag_record_result \
+            "$diag_vss_label logging startup" \
+            "FAIL" \
+            "fatal DIAG error detected in the final process log"
+ 
+        diag_log_tail \
+            "$diag_vss_prefix" \
+            "$diag_vss_log" \
+            80
+ 
+        return 1
+    fi
+ 
+    DIAG_LAST_OUTPUT_DIR="$(
+        diag_extract_output_dir_from_log "$diag_vss_log" || true
+    )"
+ 
+    if [ -n "$DIAG_LAST_OUTPUT_DIR" ] && \
+       [ -d "$DIAG_LAST_OUTPUT_DIR" ]; then
+ 
+        diag_record_result \
+            "$diag_vss_label output directory" \
+            "PASS" \
+            "$DIAG_LAST_OUTPUT_DIR"
+    else
+        DIAG_LAST_OUTPUT_DIR="$(
+            diag_first_child_directory "$diag_vss_output_root" || true
+        )"
+ 
+        if [ -n "$DIAG_LAST_OUTPUT_DIR" ] && \
+           [ -d "$DIAG_LAST_OUTPUT_DIR" ]; then
+ 
+            diag_record_result \
+                "$diag_vss_label output directory" \
+                "PASS" \
+                "$DIAG_LAST_OUTPUT_DIR"
+        elif find "$diag_vss_output_root" -type f 2>/dev/null \
+            | grep -q .; then
+ 
+            diag_record_result \
+                "$diag_vss_label output directory" \
+                "PASS" \
+                "diag_mdlog wrote directly under $diag_vss_output_root"
+        elif [ -d "$diag_vss_output_root" ]; then
+            diag_record_result \
+                "$diag_vss_label output directory" \
+                "SKIP" \
+                "output root exists, but no DIAG output was detected"
+        else
+            diag_record_result \
+                "$diag_vss_label output directory" \
+                "FAIL" \
+                "output directory was not created"
+        fi
+    fi
+ 
+    diag_vss_nonempty="$(
+        diag_nonempty_file_count "$diag_vss_output_root"
+    )"
+ 
+    if [ "$diag_vss_nonempty" -gt 0 ]; then
+        diag_record_result \
+            "$diag_vss_label log data" \
+            "PASS" \
+            "$diag_vss_nonempty non-empty file(s) created"
+    elif [ "$DIAG_EXPLICIT_MASK" -eq 1 ] && \
+         [ "$diag_vss_require_data" -eq 1 ]; then
+ 
+        diag_record_result \
+            "$diag_vss_label log data" \
+            "FAIL" \
+            "explicit mask was supplied but no non-empty log file was created"
+    else
+        diag_record_result \
+            "$diag_vss_label log data" \
+            "SKIP" \
+            "no non-empty DIAG log file was observed"
+    fi
+ 
+    # LSM initialization evidence.
+    if grep -qiE \
+        'Diag_LSM_Init succeeded|Diag_LSM_Init: done' \
+        "$diag_vss_log" 2>/dev/null; then
+ 
+        diag_record_result \
+            "$diag_vss_label LSM initialization" \
+            "PASS" \
+            "DIAG LSM initialization confirmed in process log"
+    elif [ "$diag_vss_nonempty" -gt 0 ]; then
+        diag_record_result \
+            "$diag_vss_label LSM initialization" \
+            "PASS" \
+            "validated indirectly by a stable session and non-empty DIAG output"
+    else
+        diag_record_result \
+            "$diag_vss_label LSM initialization" \
+            "SKIP" \
+            "LSM initialization could not be confirmed"
+    fi
+ 
+    # Socket or DIAG transport connection evidence.
+    if grep -qiE \
+        'successfully connected to socket' \
+        "$diag_vss_log" 2>/dev/null; then
+ 
+        diag_record_result \
+            "$diag_vss_label socket connection" \
+            "PASS" \
+            "diag_mdlog connected to the DIAG socket"
+    elif [ -r /proc/net/unix ] && \
+         grep -qi 'diag' /proc/net/unix 2>/dev/null; then
+ 
+        diag_record_result \
+            "$diag_vss_label socket connection" \
+            "PASS" \
+            "named DIAG Unix socket is visible"
+    elif [ "$diag_vss_nonempty" -gt 0 ]; then
+        diag_record_result \
+            "$diag_vss_label socket connection" \
+            "PASS" \
+            "DIAG transport validated indirectly by non-empty logging output"
+    else
+        diag_record_result \
+            "$diag_vss_label socket connection" \
+            "SKIP" \
+            "DIAG transport connection could not be confirmed"
+    fi
+ 
+    # Logging-switch evidence.
+    if grep -qiE \
+        'logging switched' \
+        "$diag_vss_log" 2>/dev/null; then
+ 
+        diag_record_result \
+            "$diag_vss_label logging switch" \
+            "PASS" \
+            "peripheral logging switch confirmed in process log"
+    elif [ "$diag_vss_nonempty" -gt 0 ]; then
+        diag_record_result \
+            "$diag_vss_label logging switch" \
+            "PASS" \
+            "validated indirectly because DIAG data was captured"
+    else
+        diag_record_result \
+            "$diag_vss_label logging switch" \
+            "SKIP" \
+            "logging-switch operation could not be confirmed"
+    fi
+ 
+    diag_record_result \
+        "$diag_vss_label logging startup" \
+        "PASS" \
+        "PID $diag_vss_pid remained active for ${diag_vss_duration}s"
+ 
+    # Mask validation.
+    if [ "$DIAG_EXPLICIT_MASK" -eq 1 ] && \
+       grep -qiE \
+           "can't open mask file|Error reading mask file|No mask files have been successfully read" \
+           "$diag_vss_log" 2>/dev/null; then
+ 
+        diag_record_result \
+            "$diag_vss_label mask application" \
+            "FAIL" \
+            "explicit mask could not be read; see $diag_vss_log"
+    elif [ "$DIAG_EXPLICIT_MASK" -eq 1 ]; then
+        diag_record_result \
+            "$diag_vss_label mask application" \
+            "PASS" \
+            "explicit mask was accepted without a mask-read error"
+    elif [ "$diag_vss_nonempty" -gt 0 ]; then
+        diag_record_result \
+            "$diag_vss_label mask application" \
+            "PASS" \
+            "default or previously configured masks produced non-empty DIAG data"
+    else
+        diag_record_result \
+            "$diag_vss_label mask application" \
+            "SKIP" \
+            "no explicit mask supplied and no DIAG data was observed"
+    fi
+ 
+    return 0
+}
+
+diag_validate_existing_mdlog_session() {
+    diag_vems_pids="$(diag_find_pids_by_name diag_mdlog)"
+
+    [ -n "$diag_vems_pids" ] || return 1
+
+    diag_vems_details=""
+    diag_vems_first_pid=""
+
+    for diag_vems_pid in $diag_vems_pids; do
+        diag_pid_alive "$diag_vems_pid" || continue
+
+        if [ -z "$diag_vems_first_pid" ]; then
+            diag_vems_first_pid="$diag_vems_pid"
+        fi
+
+        diag_vems_desc="$(diag_process_description "$diag_vems_pid")"
+
+        if [ -n "$diag_vems_details" ]; then
+            diag_vems_details="$diag_vems_details; $diag_vems_desc"
+        else
+            diag_vems_details="$diag_vems_desc"
+        fi
+    done
+
+    [ -n "$diag_vems_first_pid" ] || return 1
+
+    diag_record_result \
+        "Existing mdlog session" \
+        "PASS" \
+        "$diag_vems_details"
+
+    diag_record_result \
+        "Owned normal session" \
+        "SKIP" \
+        "not started because an existing diag_mdlog session is active"
+
+    diag_record_result \
+        "Non-real-time session" \
+        "SKIP" \
+        "not started because an existing diag_mdlog session is active"
+
+    diag_vems_output="$(
+        diag_get_process_option "$diag_vems_first_pid" -o \
+            | head -n 1
+    )"
+
+    if [ -n "$diag_vems_output" ] && \
+       [ -d "$diag_vems_output" ]; then
+
+        diag_vems_count="$(
+            diag_nonempty_file_count "$diag_vems_output"
+        )"
+
+        if [ "$diag_vems_count" -gt 0 ]; then
+            diag_record_result \
+                "Existing session output" \
+                "PASS" \
+                "$diag_vems_count non-empty file(s) under $diag_vems_output"
+        else
+            diag_record_result \
+                "Existing session output" \
+                "SKIP" \
+                "output path exists but no non-empty file was observed: $diag_vems_output"
+        fi
+    else
+        diag_record_result \
+            "Existing session output" \
+            "SKIP" \
+            "existing process output path could not be determined"
+    fi
+
+    DIAG_SESSION_VALIDATED=1
+    return 0
+}
+
+diag_validate_normal_session() {
+    diag_vns_output="$DIAG_RUN_DIR/normal_output"
+    diag_vns_log="$DIAG_RUN_DIR/normal_diag_mdlog.log"
+
+    if ! diag_start_mdlog_session \
+        normal \
+        "$diag_vns_output" \
+        "$diag_vns_log"; then
+
+        diag_record_result \
+            "Normal logging startup" \
+            "FAIL" \
+            "unable to prepare or start diag_mdlog"
+        return 1
+    fi
+
+    diag_validate_started_session \
+        "Normal" \
+        "$DIAG_DURATION_SECS" \
+        1
+}
+
+diag_validate_nonrealtime_session() {
+    if [ "${DIAG_TEST_NONREALTIME:-1}" != "1" ]; then
+        diag_record_result \
+            "Non-real-time session" \
+            "SKIP" \
+            "disabled by DIAG_TEST_NONREALTIME"
+
+        return 0
+    fi
+
+    if ! diag_help_supports_option \
+        "$DIAG_MDLOG_HELP_FILE" \
+        "-b"; then
+
+        diag_record_result \
+            "Non-real-time session" \
+            "SKIP" \
+            "diag_mdlog does not advertise -b support"
+
+        return 0
+    fi
+
+    diag_vnrs_existing="$(diag_find_pids_by_name diag_mdlog)"
+
+    if [ -n "$diag_vnrs_existing" ]; then
+        diag_record_result \
+            "Non-real-time session" \
+            "SKIP" \
+            "another diag_mdlog session is active: $diag_vnrs_existing"
+
+        return 0
+    fi
+
+    if ! diag_ensure_router_for_session "Non-real-time"; then
+        diag_record_result \
+            "Non-real-time logging startup" \
+            "FAIL" \
+            "diag-router is unavailable and recovery failed"
+
+        return 1
+    fi
+
+    diag_vnrs_output="$DIAG_RUN_DIR/nonrealtime_output"
+    diag_vnrs_log="$DIAG_RUN_DIR/nonrealtime_diag_mdlog.log"
+
+    if ! diag_start_mdlog_session \
+        nonrealtime \
+        "$diag_vnrs_output" \
+        "$diag_vnrs_log"; then
+
+        diag_record_result \
+            "Non-real-time logging startup" \
+            "FAIL" \
+            "unable to prepare or start diag_mdlog -b"
+
+        return 1
+    fi
+
+    diag_validate_started_session \
+        "Non-real-time" \
+        "$DIAG_NRT_DURATION_SECS" \
+        0
+}