diff --git a/.github/workflows/1mb-start-tests.yml b/.github/workflows/1mb-start-tests.yml
new file mode 100644
index 0000000..ae22c73
--- /dev/null
+++ b/.github/workflows/1mb-start-tests.yml
@@ -0,0 +1,49 @@
+name: 1MB start wrapper tests
+
+on:
+  push:
+    paths:
+      - "Resources/Server/1MB-start.sh"
+      - "Resources/Server/tests/1MB-start/**"
+      - ".github/workflows/1mb-start-tests.yml"
+  pull_request:
+    paths:
+      - "Resources/Server/1MB-start.sh"
+      - "Resources/Server/tests/1MB-start/**"
+      - ".github/workflows/1mb-start-tests.yml"
+  workflow_dispatch:
+
+permissions:
+  contents: read
+
+jobs:
+  test:
+    name: ${{ matrix.os }}
+    runs-on: ${{ matrix.os }}
+    timeout-minutes: 15
+    strategy:
+      fail-fast: false
+      matrix:
+        os:
+          - macos-latest
+          - ubuntu-latest
+
+    steps:
+      - name: Check out repository
+        uses: actions/checkout@v6
+
+      - name: Install ShellCheck on macOS
+        if: runner.os == 'macOS'
+        run: command -v shellcheck >/dev/null 2>&1 || brew install shellcheck
+
+      - name: Install ShellCheck on Ubuntu
+        if: runner.os == 'Linux'
+        run: |
+          if ! command -v shellcheck >/dev/null 2>&1; then
+            sudo apt-get update
+            sudo apt-get install --yes shellcheck
+          fi
+
+      - name: Run syntax, behavior, and lint tests
+        shell: bash
+        run: /bin/bash Resources/Server/tests/1MB-start/run-tests.sh all
diff --git a/Resources/Server/1MB-start.sh b/Resources/Server/1MB-start.sh
index 1e959da..55f25f4 100755
--- a/Resources/Server/1MB-start.sh
+++ b/Resources/Server/1MB-start.sh
@@ -1,7 +1,7 @@
 #!/usr/bin/env bash
 
 # @Filename: 1MB-start.sh
-# @Version: 2.17.9, build 082 for Minecraft 26.2 (Java 25, 64bit)
+# @Version: 2.18.3, build 086 for Minecraft 26.2 (Java 25, 64bit)
 # @Release: August 4th, 2026
 # @Description: Helps us start and fork a Minecraft 26.2 server session.
 # @Contact: I am @floris on Twitter, and mrfloris in MineCraft.
@@ -18,7 +18,8 @@
 ###
 
 _serverName="mcserver"
-# Keep the name short, simple, and lowercase (no numbers or weird characters).
+# Use 1-32 lowercase ASCII letters, numbers, hyphens or underscores. The first
+# character must be a letter or number.
 # The name makes it easier to recognize the session in 'tmux ls', you can
 # re-attach to the forked sessions with 'tmux attach -t (name)'.
 
@@ -30,6 +31,7 @@ _serverName="mcserver"
 ###
 
 _sibling="1MB-minecraft.sh"
+_startupCheckSeconds=2 # Check process liveness only; this is not Paper readiness.
 _debug=true # Set to false to minimize output.
 
 ### FUNCTIONS AND CODE
@@ -52,7 +54,7 @@ function _output {
     fi
 
     case "$_mode" in
-    oops|okay) _fd=2 ;;
+    oops) _fd=2 ;;
     esac
 
     if [ -z "${NO_COLOR+x}" ] && [ -t "$_fd" ]; then
@@ -68,7 +70,7 @@ function _output {
     ;;
     okay)
         _args="${*:2}"; _prefix="(Info)";
-        printf '\n%s%s%s %s%s\n' "$_yellow" "$_prefix" "$_cyan" "$_args" "$_reset" >&2; exit 1
+        printf '\n%s%s%s %s%s\n' "$_yellow" "$_prefix" "$_cyan" "$_args" "$_reset"; return 0
     ;;
     debug)
         _args="${*:2}"; _prefix="(Debug)";
@@ -131,46 +133,139 @@ function _showHelp {
         "  --attach [name]  Attach to the exact tmux session." \
         "  --help, -h       Show this help." \
         "" \
-        "The session name defaults to '$_serverName'."
+        "The session name defaults to '$_serverName'." \
+        "Names use 1-32 lowercase ASCII letters, numbers, hyphens or underscores." \
+        "The first character must be a letter or number."
 }
 
 function _setServerName {
-    local _requestedName="${1:-}"
-    local _input=""
+    local _requestedName="${1-}"
+    local LC_ALL=C
 
-    if [ -n "$_requestedName" ]; then
-        _input=$(printf '%s\n' "$_requestedName" | awk '{ print tolower($1) }')
-        _input=$(printf '%s\n' "$_input" | awk '{ print substr($0, 1, 16) }')
+    if [ "${#_requestedName}" -gt 32 ] || ! [[ "$_requestedName" =~ ^[a-z0-9][a-z0-9_-]*$ ]]; then
+        _output oops "Invalid session name. Use 1-32 lowercase ASCII letters, numbers, hyphens or underscores. The first character must be a letter or number."
+    fi
 
-        if [[ "$_input" =~ ^[a-z]+$ ]]; then
-            _serverName="$_input"
-        else
-            _output oops "Provided input is invalid! Input is for a unique '_serverName'. Do not use numbers, spaces or weird chars. Keep it short, and a-z characters only."
+    _serverName="$_requestedName"
+}
+
+function _isPaneId {
+    local _paneId="${1:-}"
+    local _paneNumber=""
+
+    case "$_paneId" in
+    %*) _paneNumber="${_paneId#%}" ;;
+    *) return 1 ;;
+    esac
+
+    case "$_paneNumber" in
+    ""|*[!0-9]*) return 1 ;;
+    *) return 0 ;;
+    esac
+}
+
+function _verifyStartedPane {
+    local _paneId="${1:-}"
+    local _paneReport=""
+    local _paneDead=""
+    local _paneResult=""
+    local _paneStatus=""
+    local _paneSignal=""
+    local _exitDescription=""
+
+    _output debug "Checking whether '$_sibling' remains active for $_startupCheckSeconds seconds ..."
+
+    if ! sleep "$_startupCheckSeconds"; then
+        if ! tmux set-option -p -t "$_paneId" remain-on-exit off >/dev/null 2>&1; then
+            _output oops "The $_startupCheckSeconds-second startup check was interrupted, and tmux could not restore normal close-on-exit behavior. Inspect the '$_serverName' session before retrying."
         fi
+        _output oops "The $_startupCheckSeconds-second startup check was interrupted. The tmux session was not reported as started."
+    fi
+
+    if ! _paneReport=$(tmux display-message -p -t "$_paneId" '#{pane_dead}|#{pane_dead_status}|#{pane_dead_signal}' 2>/dev/null); then
+        tmux set-option -p -t "$_paneId" remain-on-exit off >/dev/null 2>&1 || true
+        _output oops "'$_sibling' ended or its tmux pane disappeared during the $_startupCheckSeconds-second startup check. Run './$_sibling' directly from '$_scriptDir' to inspect its full output."
     fi
+
+    _paneDead="${_paneReport%%|*}"
+    _paneResult="${_paneReport#*|}"
+    _paneStatus="${_paneResult%%|*}"
+    _paneSignal="${_paneResult#*|}"
+
+    case "$_paneDead" in
+    0)
+        if ! tmux set-option -p -t "$_paneId" remain-on-exit off >/dev/null 2>&1; then
+            _output oops "'$_sibling' remained active, but tmux could not restore normal close-on-exit behavior for pane '$_paneId'. Inspect the '$_serverName' session before retrying."
+        fi
+
+        if ! _paneDead=$(tmux display-message -p -t "$_paneId" '#{pane_dead}' 2>/dev/null); then
+            _output oops "'$_sibling' ended as the $_startupCheckSeconds-second startup check completed. The tmux session was not reported as started."
+        fi
+
+        if [ "$_paneDead" != 0 ]; then
+            tmux kill-pane -t "$_paneId" >/dev/null 2>&1 || true
+            _output oops "'$_sibling' ended as the $_startupCheckSeconds-second startup check completed. The tmux session was not reported as started."
+        fi
+        ;;
+    1)
+        if [ -n "$_paneStatus" ]; then
+            _exitDescription="exit status $_paneStatus"
+        fi
+        if [ -n "$_paneSignal" ]; then
+            if [ -n "$_exitDescription" ]; then
+                _exitDescription="$_exitDescription, signal $_paneSignal"
+            else
+                _exitDescription="signal $_paneSignal"
+            fi
+        fi
+        [ -z "$_exitDescription" ] && _exitDescription="unknown exit status"
+
+        tmux kill-pane -t "$_paneId" >/dev/null 2>&1 || true
+        _output oops "'$_sibling' exited during the $_startupCheckSeconds-second startup check ($_exitDescription). Run './$_sibling' directly from '$_scriptDir' to inspect its full output."
+        ;;
+    *)
+        tmux set-option -p -t "$_paneId" remain-on-exit off >/dev/null 2>&1 || true
+        _output oops "tmux returned an unexpected state for pane '$_paneId' during the startup check. The session was not reported as started."
+        ;;
+    esac
 }
 
 _action="start"
-_nameArgument="${1:-}"
+_nameArgument="$_serverName"
 
 case "${1:-}" in
 -h|--help)
+    [ "$#" -eq 1 ] || _output oops "Unexpected extra arguments. Run '$0 --help' for usage."
     _showHelp
     exit 0
     ;;
 --status)
+    [ "$#" -le 2 ] || _output oops "Unexpected extra arguments. Run '$0 --help' for usage."
     _action="status"
-    _nameArgument="${2:-}"
+    if [ "$#" -eq 2 ]; then
+        _nameArgument="$2"
+    fi
     ;;
 --attach)
+    [ "$#" -le 2 ] || _output oops "Unexpected extra arguments. Run '$0 --help' for usage."
     _action="attach"
-    _nameArgument="${2:-}"
+    if [ "$#" -eq 2 ]; then
+        _nameArgument="$2"
+    fi
     ;;
 --*)
     _output oops "Unknown option '$1'. Run '$0 --help' for usage."
     ;;
+*)
+    [ "$#" -le 1 ] || _output oops "Unexpected extra arguments. Run '$0 --help' for usage."
+    if [ "$#" -eq 1 ]; then
+        _nameArgument="$1"
+    fi
+    ;;
 esac
 
+_setServerName "$_nameArgument"
+
 [ "$EUID" -eq 0 ] && _output oops "*!* This script should not be run using sudo, or as the root user!"
 
 if [ "$_action" = start ]; then
@@ -182,8 +277,6 @@ if [ "$_action" = start ]; then
     fi
 fi
 
-_setServerName "$_nameArgument"
-
 if ! type "tmux" >/dev/null 2>&1; then
     _output oops "'tmux' is required but was not found. On macOS, install it with: brew install tmux"
 fi
@@ -214,9 +307,21 @@ _output debug "Using server directory: $_scriptDir"
 
 _output debug "Found 'tmux', attempting to start '$_sibling' in a detached tmux session ..."
 # Deliberately launch only ./1MB-minecraft.sh from the wrapper's own directory.
-if ! tmux new-session -d -s "$_serverName" -c "$_scriptDir" "exec \"./$_sibling\""; then
-    _output oops "Could not create the '$_serverName' tmux session and start '$_sibling'. Review the tmux error above and check with 'tmux ls'."
+_paneId=""
+if ! _paneId=$(tmux new-session -d -P -F '#{pane_id}' -s "$_serverName" -c "$_scriptDir" "exec \"./$_sibling\"" \; set-option -p -t "=$_serverName:" remain-on-exit on); then
+    if _isPaneId "$_paneId"; then
+        tmux kill-pane -t "$_paneId" >/dev/null 2>&1 || true
+    fi
+    _output oops "Could not create the '$_serverName' tmux session and prepare its startup check. Review the tmux error above and check with 'tmux ls'."
+fi
+
+if ! _isPaneId "$_paneId"; then
+    tmux kill-session -t "=$_serverName" >/dev/null 2>&1 || true
+    _output oops "tmux created the '$_serverName' session but did not return a valid pane identifier, so the new session was closed."
 fi
+
+_verifyStartedPane "$_paneId"
+
 [[ "$_debug" == true ]] && tmux ls; _output debug "To re-attach: tmux attach -t $_serverName"
 
 _output debug "tmux session started."
diff --git a/Resources/Server/1mb-start-todo.md b/Resources/Server/1mb-start-todo.md
index 298295b..54fe8ec 100644
--- a/Resources/Server/1mb-start-todo.md
+++ b/Resources/Server/1mb-start-todo.md
@@ -6,16 +6,16 @@ as deliberate follow-up changes.
 
 ## Known live baseline
 
-- Script version: `2.16.3`, build `072`
+- Script version: `2.17.9`, build `082`
 - Release date: August 4, 2026
 - Status: working, tested, and live in August 2026
-- Git baseline: `a2dc6cc8f5d14062b848c87389859e1eab1e4e48`
+- Git baseline: `c5f6c8c5c5ee4545ec4d0dcccaa46e8cc2fc52dc`
 - Baseline source:
-  `git show a2dc6cc8f5d14062b848c87389859e1eab1e4e48:Resources/Server/1MB-start.sh`
+  `git show c5f6c8c5c5ee4545ec4d0dcccaa46e8cc2fc52dc:Resources/Server/1MB-start.sh`
 
 The baseline records the proven production version; it is not a claim that the
-script was free of edge-case defects. New work begins with version `2.17.0`,
-build `073`.
+script is free of edge-case defects. Follow-up work continues with version
+`2.18.3`, build `086`.
 
 ## Completed in 2.17.0 build 073
 
@@ -111,6 +111,47 @@ scoped fix. The file's missing final newline was normalized mechanically.
 - [x] Kept sibling resolution and validation exclusive to normal startup, so
   existing sessions remain inspectable when the sibling file is unavailable.
 
+## Completed in 2.18.0 build 083
+
+- [x] Added a two-second liveness check for the exact tmux pane created for
+  `1MB-minecraft.sh`; attach guidance and success output now wait for it.
+- [x] Temporarily retain only that new pane during the check, allowing immediate
+  clean exits, nonzero statuses, and terminating signals to be reported.
+- [x] Restore `remain-on-exit=off` after a successful check so the tmux session
+  still closes normally whenever `1MB-minecraft.sh` later exits.
+- [x] Keep the check explicitly bounded to process liveness; it does not claim
+  that Paper completed startup.
+
+## Completed in 2.18.1 build 084
+
+- [x] Successful `_output okay` messages now write to stdout, return status
+  `0`, and allow the caller to continue instead of terminating the wrapper.
+- [x] The fatal `_output oops` path remains unchanged: it writes to stderr and
+  exits with status `1`.
+
+## Completed in 2.18.2 build 085
+
+- [x] Validate the complete requested session name without lowercasing,
+  splitting or truncating it. Names use 1-32 lowercase ASCII letters, numbers,
+  hyphens or underscores and must begin with a letter or number.
+- [x] Validate the configured default name through the same path and reject
+  empty, uppercase, overlong or otherwise invalid names with a clear error.
+- [x] Reject unexpected extra arguments for startup, `--help`, `--status` and
+  `--attach` instead of silently ignoring them.
+
+## Completed in 2.18.3 build 086
+
+- [x] Added a committed Bash 3.2-compatible test runner with syntax, behavioral
+  and ShellCheck modes under `Resources/Server/tests/1MB-start/`.
+- [x] Added scenario-driven fake `tmux` and instant fake `sleep` executables.
+  Disposable fixtures exercise startup success and failure without contacting
+  a real tmux server or launching Paper.
+- [x] Covered exact atomic launch arguments, duplicate sessions, pane and child
+  exit states, probe-boundary races, status and attach behavior, sibling and
+  dependency failures, session names, argument arity, and output semantics.
+- [x] Added a path-filtered GitHub Actions workflow that runs the complete suite
+  with ShellCheck on current macOS and Ubuntu hosted runners.
+
 ## Critical
 
 - [x] Stop immediately when tmux session creation fails; never send startup
@@ -128,9 +169,9 @@ scoped fix. The file's missing final newline was normalized mechanically.
 - [x] Replace the two-stage `tmux new` plus `tmux send-keys` launch with one
   checked, atomic `tmux new-session -d` command that starts the sibling
   directly. Completed in `2.17.2`, build `075`.
-- [ ] Detect and report when the child exits immediately after tmux successfully
-  creates the session. The tmux command confirms session creation, not that
-  Paper completed startup.
+- [x] Detect and report when the child exits immediately after tmux successfully
+  creates the session. Completed in `2.18.0`, build `083`, with a two-second
+  exact-pane liveness check that does not claim Paper completed startup.
 - [x] Fix `_debug=false`: disabled debug messages now return success, so an
   otherwise successful wrapper exits successfully. Completed in `2.17.5`,
   build `078`.
@@ -142,9 +183,10 @@ scoped fix. The file's missing final newline was normalized mechanically.
 
 ## Medium priority
 
-- [ ] Stop splitting and truncating the requested session name before
+- [x] Stop splitting and truncating the requested session name before
   validation. Validate the complete input and length, reject invalid or
-  overlong names, and reject unexpected extra arguments.
+  overlong names, and reject unexpected extra arguments. Completed in
+  `2.18.2`, build `085`.
 - [x] Close the tmux session when `1MB-minecraft.sh` exits. Approved and
   completed in `2.17.2`, build `075`; the launcher is now the pane's direct
   process.
@@ -163,8 +205,8 @@ scoped fix. The file's missing final newline was normalized mechanically.
   build `077`.
 - [x] Make output-function variables local and remove the undefined `B` and `X`
   colour variables. Completed in `2.17.4`, build `077`.
-- [ ] Correct the `okay` branch so a successful status message does not exit
-  with status `1`.
+- [x] Correct the `okay` branch so a successful status message does not exit
+  with status `1`. Completed in `2.18.1`, build `084`.
 - [x] Emit ANSI colours only to an interactive terminal and honor `NO_COLOR`
   so launchd/systemd logs remain clean. Completed in `2.17.4`, build `077`.
 - [x] Verify that the sibling is a regular readable and executable file, and
@@ -188,9 +230,10 @@ scoped fix. The file's missing final newline was normalized mechanically.
   `set -o pipefail` can then be evaluated safely.
 - [x] Add small `--help`, `--status`, and `--attach` commands. Completed in
   `2.17.9`, build `082`; `--version` was intentionally not added.
-- [ ] Add repeatable checks with `bash -n`, ShellCheck, and disposable fake or
+- [x] Add repeatable checks with `bash -n`, ShellCheck, and disposable fake or
   isolated tmux sessions for success, duplicate-name, missing-sibling, and
-  missing-dependency paths.
+  missing-dependency paths. Completed in `2.18.3`, build `086`, with committed
+  local tests and path-filtered macOS/Ubuntu CI.
 - [ ] Consider an optional `umask 027` only after auditing backup, web, and
   group-access requirements. Do not change inherited Paper file permissions
   as part of an unrelated launcher update.
@@ -213,7 +256,8 @@ scoped fix. The file's missing final newline was normalized mechanically.
 
 ## Compatibility decisions before the next larger revision
 
-1. Confirm whether session names remain letters-only or expand to a documented
-   safe character set.
+1. [x] Session names use a documented safe set: 1-32 lowercase ASCII letters,
+   numbers, hyphens or underscores, beginning with a letter or number.
+   Completed in `2.18.2`, build `085`.
 2. Confirm which quality-of-life commands, if any, belong in this intentionally
    small wrapper.
diff --git a/Resources/Server/tests/1MB-start/README.md b/Resources/Server/tests/1MB-start/README.md
new file mode 100644
index 0000000..7ff28a6
--- /dev/null
+++ b/Resources/Server/tests/1MB-start/README.md
@@ -0,0 +1,52 @@
+# `1MB-start.sh` tests
+
+This suite tests `../../1MB-start.sh` without starting Paper or contacting a
+real tmux server. Every behavioral test runs against disposable copies under a
+temporary directory and prepends the committed fake `tmux` and `sleep`
+executables to `PATH`. The runner refuses to continue unless those exact fakes
+resolve first and also assigns a disposable `TMUX_TMPDIR` as a second isolation
+layer.
+
+Run the complete suite from the repository root:
+
+```bash
+Resources/Server/tests/1MB-start/run-tests.sh
+```
+
+The default `all` mode runs:
+
+- `bash -n` with macOS's Bash 3.2 and any supported modern Bash found locally;
+- fake-tmux behavioral tests with every discovered Bash interpreter;
+- ShellCheck over the production wrapper, runner, and fake executables.
+
+ShellCheck is the only additional dependency for `all` and `lint` mode:
+
+```bash
+# macOS
+brew install shellcheck
+
+# Ubuntu
+sudo apt install shellcheck
+```
+
+Individual modes are available when needed:
+
+```bash
+# Bash syntax and fake-tmux behavior only
+Resources/Server/tests/1MB-start/run-tests.sh test
+
+# ShellCheck only
+Resources/Server/tests/1MB-start/run-tests.sh lint
+```
+
+The behavior suite covers healthy startup, exact tmux targets, duplicate
+sessions, child exit statuses and signals, probe-boundary failures,
+`remain-on-exit` restoration, missing or invalid siblings, missing tmux,
+status and attach behavior, session-name validation, argument validation, and
+output return/stream behavior. The fake `sleep` makes the two-second liveness
+probe complete immediately.
+
+Tests must not be run with `sudo`: the production wrapper deliberately refuses
+to run as root. When a test fails, its disposable state and tmux call log are
+retained and their location is printed. Successful runs remove their temporary
+state.
diff --git a/Resources/Server/tests/1MB-start/fake-bin/sleep b/Resources/Server/tests/1MB-start/fake-bin/sleep
new file mode 100755
index 0000000..1dc7ee8
--- /dev/null
+++ b/Resources/Server/tests/1MB-start/fake-bin/sleep
@@ -0,0 +1,18 @@
+#!/usr/bin/env bash
+
+# Instant sleep replacement for deterministic startup-probe tests.
+
+_stateDir="${FAKE_TMUX_STATE_DIR:-}"
+_scenario="${FAKE_TMUX_SCENARIO:-healthy}"
+
+if [ -z "$_stateDir" ] || [ ! -d "$_stateDir" ]; then
+    printf '%s\n' "fake sleep: FAKE_TMUX_STATE_DIR is missing or invalid" >&2
+    exit 90
+fi
+
+printf '%s\n' "$*" >>"$_stateDir/sleep.log"
+
+case "$_scenario" in
+sleep-failure|sleep-failure-restore-failure) exit 1 ;;
+*) exit 0 ;;
+esac
diff --git a/Resources/Server/tests/1MB-start/fake-bin/tmux b/Resources/Server/tests/1MB-start/fake-bin/tmux
new file mode 100755
index 0000000..59fa74f
--- /dev/null
+++ b/Resources/Server/tests/1MB-start/fake-bin/tmux
@@ -0,0 +1,117 @@
+#!/usr/bin/env bash
+
+# Scenario-driven tmux replacement used only by the 1MB-start.sh test suite.
+# It must never write diagnostics to stdout for new-session because stdout is
+# the pane-ID channel consumed by the wrapper.
+
+_stateDir="${FAKE_TMUX_STATE_DIR:-}"
+_scenario="${FAKE_TMUX_SCENARIO:-healthy}"
+
+if [ -z "$_stateDir" ] || [ ! -d "$_stateDir" ]; then
+    printf '%s\n' "fake tmux: FAKE_TMUX_STATE_DIR is missing or invalid" >&2
+    exit 90
+fi
+
+_logFile="$_stateDir/tmux.log"
+_command="${1:-}"
+
+printf '%s' "$_command" >>"$_logFile"
+shift || true
+for _argument in "$@"; do
+    printf '\t%s' "$_argument" >>"$_logFile"
+done
+printf '\n' >>"$_logFile"
+
+case "$_command" in
+new-session)
+    case "$_scenario" in
+    duplicate)
+        printf '%s\n' "duplicate session: mcserver" >&2
+        exit 1
+        ;;
+    new-failure-with-pane)
+        printf '%s\n' '%42'
+        exit 1
+        ;;
+    new-failure)
+        exit 1
+        ;;
+    empty-pane)
+        exit 0
+        ;;
+    malformed-pane)
+        printf '%s\n' 'not-a-pane'
+        exit 0
+        ;;
+    *)
+        printf '%s\n' '%42'
+        exit 0
+        ;;
+    esac
+    ;;
+has-session)
+    case "$_scenario" in
+    status-running|attach-running) exit 0 ;;
+    *) exit 1 ;;
+    esac
+    ;;
+attach-session)
+    case "$_scenario" in
+    attach-running) exit 23 ;;
+    *) exit 1 ;;
+    esac
+    ;;
+display-message)
+    _format=""
+    for _argument in "$@"; do
+        _format="$_argument"
+    done
+
+    case "$_format" in
+    '#{pane_dead}|#{pane_dead_status}|#{pane_dead_signal}')
+        case "$_scenario" in
+        first-display-missing) exit 1 ;;
+        child-exit-zero) printf '%s\n' '1|0|' ;;
+        child-exit-seven) printf '%s\n' '1|7|' ;;
+        child-signal-fifteen) printf '%s\n' '1||15' ;;
+        child-unknown-exit) printf '%s\n' '1||' ;;
+        unexpected-pane-state) printf '%s\n' 'unexpected||' ;;
+        *) printf '%s\n' '0||' ;;
+        esac
+        ;;
+    '#{pane_dead}')
+        case "$_scenario" in
+        boundary-disappeared) exit 1 ;;
+        boundary-dead) printf '%s\n' '1' ;;
+        *) printf '%s\n' '0' ;;
+        esac
+        ;;
+    *)
+        printf '%s\n' "fake tmux: unexpected display format: $_format" >&2
+        exit 91
+        ;;
+    esac
+    ;;
+set-option)
+    case "$_scenario" in
+    restore-failure|sleep-failure-restore-failure) exit 1 ;;
+    *) exit 0 ;;
+    esac
+    ;;
+kill-pane|kill-session)
+    exit 0
+    ;;
+ls)
+    case "$_scenario" in
+    list-failure) exit 1 ;;
+    *)
+        printf '%s\n' 'fake-session: 1 windows (created for tests)'
+        exit 0
+        ;;
+    esac
+    ;;
+*)
+    printf '%s\n' "fake tmux: unexpected command: $_command" >&2
+    exit 92
+    ;;
+esac
diff --git a/Resources/Server/tests/1MB-start/run-tests.sh b/Resources/Server/tests/1MB-start/run-tests.sh
new file mode 100755
index 0000000..49e1d7b
--- /dev/null
+++ b/Resources/Server/tests/1MB-start/run-tests.sh
@@ -0,0 +1,743 @@
+#!/usr/bin/env bash
+
+# Repeatable, non-production tests for Resources/Server/1MB-start.sh.
+# Compatible with the Bash 3.2 shipped by macOS.
+
+_suiteDir=$(cd -P -- "$(dirname -- "${BASH_SOURCE[0]}")" >/dev/null 2>&1 && pwd -P) || exit 1
+_serverDir=$(cd -P -- "$_suiteDir/../.." >/dev/null 2>&1 && pwd -P) || exit 1
+_target="$_serverDir/1MB-start.sh"
+_runner="$_suiteDir/run-tests.sh"
+_fakeTmux="$_suiteDir/fake-bin/tmux"
+_fakeSleep="$_suiteDir/fake-bin/sleep"
+_originalPath="$PATH"
+_mode="${1:-all}"
+
+_passed=0
+_failed=0
+_skipped=0
+_caseNumber=0
+_caseFailed=0
+_caseLabel=""
+_tempRoot=""
+_bashUnderTest=""
+_caseDir=""
+_caseServerDir=""
+_caseStateDir=""
+_caseWrapper=""
+_stdoutFile=""
+_stderrFile=""
+_runStatus=0
+
+function _usage {
+    printf '%s\n' \
+        "Usage: ${0##*/} [all|test|lint]" \
+        "" \
+        "  all   Run syntax, fake-tmux behavior, and ShellCheck (default)." \
+        "  test  Run syntax and fake-tmux behavior without ShellCheck." \
+        "  lint  Run ShellCheck only."
+}
+
+if [ "$#" -gt 1 ]; then
+    _usage >&2
+    exit 2
+fi
+
+case "$_mode" in
+all|test|lint)
+    ;;
+-h|--help)
+    _usage
+    exit 0
+    ;;
+*)
+    _usage >&2
+    exit 2
+    ;;
+esac
+
+function _pass {
+    _passed=$((_passed + 1))
+    printf 'PASS: %s\n' "$1"
+}
+
+function _fail {
+    _failed=$((_failed + 1))
+    printf 'FAIL: %s\n' "$1" >&2
+}
+
+function _skip {
+    _skipped=$((_skipped + 1))
+    printf 'SKIP: %s\n' "$1"
+}
+
+function _beginCase {
+    _caseLabel="$1"
+    _caseFailed=0
+}
+
+function _problem {
+    _caseFailed=1
+    printf '  %s\n' "$1" >&2
+    if [ -n "$_caseDir" ]; then
+        printf '  fixture: %s\n' "$_caseDir" >&2
+    fi
+}
+
+function _showFile {
+    local _label="$1"
+    local _file="$2"
+
+    if [ -s "$_file" ]; then
+        printf '  %s:\n' "$_label" >&2
+        sed 's/^/    /' "$_file" >&2
+    fi
+}
+
+function _finishCase {
+    if [ "$_caseFailed" -eq 0 ]; then
+        _pass "$_caseLabel"
+        return 0
+    fi
+
+    _showFile "stdout" "$_stdoutFile"
+    _showFile "stderr" "$_stderrFile"
+    if [ -n "$_caseStateDir" ]; then
+        _showFile "fake tmux calls" "$_caseStateDir/tmux.log"
+        _showFile "fake sleep calls" "$_caseStateDir/sleep.log"
+    fi
+    _fail "$_caseLabel"
+    return 1
+}
+
+function _cleanup {
+    if [ -z "$_tempRoot" ] || [ ! -d "$_tempRoot" ]; then
+        return
+    fi
+
+    if [ "$_failed" -eq 0 ]; then
+        rm -rf -- "$_tempRoot"
+    else
+        printf 'Failed-test artifacts retained at: %s\n' "$_tempRoot" >&2
+    fi
+}
+
+trap _cleanup EXIT
+trap 'exit 129' HUP
+trap 'exit 130' INT
+trap 'exit 143' TERM
+
+function _addBash {
+    local _candidate="$1"
+    local _candidateDir=""
+    local _candidatePath=""
+    local _known=""
+
+    [ -x "$_candidate" ] || return 0
+    _candidateDir=$(cd -P -- "$(dirname -- "$_candidate")" >/dev/null 2>&1 && pwd -P) || return 0
+    _candidatePath="$_candidateDir/$(basename -- "$_candidate")"
+
+    for _known in "${_bashPaths[@]}"; do
+        [ "$_known" = "$_candidatePath" ] && return 0
+    done
+    _bashPaths[${#_bashPaths[@]}]="$_candidatePath"
+}
+
+function _discoverBashes {
+    local _pathBash=""
+
+    _bashPaths=()
+    _addBash /bin/bash
+    _pathBash=$(command -v bash 2>/dev/null || true)
+    [ -n "$_pathBash" ] && _addBash "$_pathBash"
+    _addBash /opt/homebrew/bin/bash
+    _addBash /usr/local/bin/bash
+}
+
+function _newFixture {
+    local _siblingMode="${1:-executable}"
+
+    _caseNumber=$((_caseNumber + 1))
+    _caseDir="$_tempRoot/case-$_caseNumber"
+    _caseServerDir="$_caseDir/server directory with spaces"
+    _caseStateDir="$_caseDir/state"
+    _caseWrapper="$_caseServerDir/1MB-start.sh"
+    _stdoutFile="$_caseDir/stdout"
+    _stderrFile="$_caseDir/stderr"
+
+    mkdir -p "$_caseServerDir" "$_caseStateDir/tmux-socket"
+    cp "$_target" "$_caseWrapper"
+    chmod 0755 "$_caseWrapper"
+
+    case "$_siblingMode" in
+    executable)
+        printf '%s\n' '#!/usr/bin/env bash' 'exit 0' >"$_caseServerDir/1MB-minecraft.sh"
+        chmod 0755 "$_caseServerDir/1MB-minecraft.sh"
+        ;;
+    nonexecutable)
+        printf '%s\n' '#!/usr/bin/env bash' 'exit 0' >"$_caseServerDir/1MB-minecraft.sh"
+        chmod 0644 "$_caseServerDir/1MB-minecraft.sh"
+        ;;
+    unreadable)
+        printf '%s\n' '#!/usr/bin/env bash' 'exit 0' >"$_caseServerDir/1MB-minecraft.sh"
+        chmod 0111 "$_caseServerDir/1MB-minecraft.sh"
+        ;;
+    directory)
+        mkdir "$_caseServerDir/1MB-minecraft.sh"
+        ;;
+    symlink)
+        ln -s "1MB-start.sh" "$_caseServerDir/1MB-minecraft.sh"
+        ;;
+    missing)
+        ;;
+    *)
+        printf '%s\n' "Unknown sibling fixture mode: $_siblingMode" >&2
+        exit 2
+        ;;
+    esac
+}
+
+function _runWrapper {
+    local _scenario="$1"
+    shift
+
+    : >"$_stdoutFile"
+    : >"$_stderrFile"
+    FAKE_TMUX_SCENARIO="$_scenario" \
+        FAKE_TMUX_STATE_DIR="$_caseStateDir" \
+        NO_COLOR=1 \
+        PATH="$_suiteDir/fake-bin:$_originalPath" \
+        TMUX='' \
+        TMUX_TMPDIR="$_caseStateDir/tmux-socket" \
+        "$_bashUnderTest" "$_caseWrapper" "$@" >"$_stdoutFile" 2>"$_stderrFile"
+    _runStatus=$?
+}
+
+function _expectStatus {
+    local _expected="$1"
+    if [ "$_runStatus" -ne "$_expected" ]; then
+        _problem "expected exit $_expected, got $_runStatus"
+    fi
+}
+
+function _expectEmpty {
+    local _file="$1"
+    local _description="$2"
+    [ ! -s "$_file" ] || _problem "expected empty $_description"
+}
+
+function _expectContains {
+    local _file="$1"
+    local _text="$2"
+    local _description="$3"
+    grep -Fq "$_text" "$_file" || _problem "missing $_description: $_text"
+}
+
+function _expectNotContains {
+    local _file="$1"
+    local _text="$2"
+    local _description="$3"
+    if grep -Fq "$_text" "$_file"; then
+        _problem "unexpected $_description: $_text"
+    fi
+}
+
+function _expectNoTmuxCall {
+    if [ -s "$_caseStateDir/tmux.log" ]; then
+        _problem "tmux was called unexpectedly"
+    fi
+}
+
+function _expectLogLine {
+    local _line="$1"
+    if ! grep -Fqx "$_line" "$_caseStateDir/tmux.log" 2>/dev/null; then
+        _problem "missing exact tmux call: $_line"
+    fi
+}
+
+function _expectNoLogCommand {
+    local _command="$1"
+    if grep -q "^${_command}" "$_caseStateDir/tmux.log" 2>/dev/null; then
+        _problem "unexpected tmux command: $_command"
+    fi
+}
+
+function _setExpectedLaunch {
+    local _name="$1"
+    printf -v _expectedLaunch 'new-session\t-d\t-P\t-F\t#{pane_id}\t-s\t%s\t-c\t%s\texec "./1MB-minecraft.sh"\t;\tset-option\t-p\t-t\t=%s:\tremain-on-exit\ton' \
+        "$_name" "$_caseServerDir" "$_name"
+}
+
+function _expectFilesEqual {
+    local _expected="$1"
+    local _actual="$2"
+    local _description="$3"
+    if ! cmp -s "$_expected" "$_actual"; then
+        _problem "$_description differs"
+        diff -u "$_expected" "$_actual" >&2 || true
+    fi
+}
+
+function _testHealthyStart {
+    local _expectedLog=""
+    local _escape=""
+
+    _beginCase "healthy startup uses exact atomic tmux calls"
+    _newFixture executable
+    _runWrapper healthy mcserver-2
+    _expectStatus 0
+    _expectEmpty "$_stderrFile" "stderr"
+    _expectContains "$_stdoutFile" "To re-attach: tmux attach -t mcserver-2" "attach guidance"
+    _expectContains "$_stdoutFile" "tmux session started." "success message"
+    _escape=$(printf '\033')
+    _expectNotContains "$_stdoutFile" "$_escape" "ANSI escape"
+    _setExpectedLaunch mcserver-2
+    _expectedLog="$_caseDir/expected-tmux.log"
+    printf '%s\n' \
+        "$_expectedLaunch" \
+        $'display-message\t-p\t-t\t%42\t#{pane_dead}|#{pane_dead_status}|#{pane_dead_signal}' \
+        $'set-option\t-p\t-t\t%42\tremain-on-exit\toff' \
+        $'display-message\t-p\t-t\t%42\t#{pane_dead}' \
+        'ls' >"$_expectedLog"
+    _expectFilesEqual "$_expectedLog" "$_caseStateDir/tmux.log" "tmux call order"
+    printf '%s\n' '2' >"$_caseDir/expected-sleep.log"
+    _expectFilesEqual "$_caseDir/expected-sleep.log" "$_caseStateDir/sleep.log" "sleep call"
+    _finishCase
+}
+
+function _testConfiguredDefaultName {
+    _beginCase "omitted name validates and preserves the configured default"
+
+    _newFixture executable
+    _runWrapper healthy
+    _expectStatus 0
+    _setExpectedLaunch mcserver
+    _expectLogLine "$_expectedLaunch"
+    _expectContains "$_stdoutFile" "tmux attach -t mcserver" "default attach guidance"
+
+    _newFixture executable
+    _runWrapper status-running --status
+    _expectStatus 0
+    _expectLogLine $'has-session\t-t\t=mcserver'
+    _expectContains "$_stdoutFile" "tmux session 'mcserver' is running" "default status"
+    _finishCase
+}
+
+function _testListFailureIsNonfatal {
+    _beginCase "tmux list failure does not redefine startup success"
+    _newFixture executable
+    _runWrapper list-failure mcserver
+    _expectStatus 0
+    _expectContains "$_stdoutFile" "tmux session started." "success message"
+    _expectLogLine 'ls'
+    _finishCase
+}
+
+function _testDuplicateSession {
+    _beginCase "duplicate session fails without mutating an existing session"
+    _newFixture executable
+    _runWrapper duplicate mcserver
+    _expectStatus 1
+    _expectContains "$_stderrFile" "duplicate session" "tmux duplicate error"
+    _expectContains "$_stderrFile" "Could not create" "wrapper failure"
+    _expectNotContains "$_stdoutFile" "tmux session started." "success message"
+    _expectNoLogCommand kill-pane
+    _expectNoLogCommand kill-session
+    _expectNoLogCommand send-keys
+    _finishCase
+}
+
+function _testNewFailureWithPane {
+    _beginCase "partial new-session failure cleans only the returned pane"
+    _newFixture executable
+    _runWrapper new-failure-with-pane mcserver
+    _expectStatus 1
+    _expectLogLine $'kill-pane\t-t\t%42'
+    _expectNoLogCommand kill-session
+    _finishCase
+}
+
+function _testInvalidPane {
+    local _scenario="$1"
+    local _label="$2"
+
+    _beginCase "$_label"
+    _newFixture executable
+    _runWrapper "$_scenario" mcserver
+    _expectStatus 1
+    _expectContains "$_stderrFile" "did not return a valid pane identifier" "invalid-pane error"
+    _expectLogLine $'kill-session\t-t\t=mcserver'
+    _expectNotContains "$_stdoutFile" "tmux session started." "success message"
+    _finishCase
+}
+
+function _testChildExit {
+    local _scenario="$1"
+    local _expectedText="$2"
+    local _label="$3"
+
+    _beginCase "$_label"
+    _newFixture executable
+    _runWrapper "$_scenario" mcserver
+    _expectStatus 1
+    _expectContains "$_stderrFile" "$_expectedText" "exit description"
+    _expectLogLine $'kill-pane\t-t\t%42'
+    _expectNoLogCommand ls
+    _expectNotContains "$_stdoutFile" "tmux session started." "success message"
+    _finishCase
+}
+
+function _testFirstDisplayMissing {
+    _beginCase "disappearing pane fails and restores close-on-exit best-effort"
+    _newFixture executable
+    _runWrapper first-display-missing mcserver
+    _expectStatus 1
+    _expectContains "$_stderrFile" "pane disappeared" "missing-pane error"
+    _expectLogLine $'set-option\t-p\t-t\t%42\tremain-on-exit\toff'
+    _expectNoLogCommand ls
+    _finishCase
+}
+
+function _testUnexpectedPaneState {
+    _beginCase "unexpected pane state fails closed"
+    _newFixture executable
+    _runWrapper unexpected-pane-state mcserver
+    _expectStatus 1
+    _expectContains "$_stderrFile" "unexpected state" "unexpected-state error"
+    _expectLogLine $'set-option\t-p\t-t\t%42\tremain-on-exit\toff'
+    _expectNoLogCommand ls
+    _finishCase
+}
+
+function _testRestoreFailure {
+    _beginCase "failure to restore close-on-exit prevents success"
+    _newFixture executable
+    _runWrapper restore-failure mcserver
+    _expectStatus 1
+    _expectContains "$_stderrFile" "could not restore normal close-on-exit behavior" "restore error"
+    _expectNoLogCommand ls
+    _finishCase
+}
+
+function _testBoundaryResult {
+    local _scenario="$1"
+    local _label="$2"
+
+    _beginCase "$_label"
+    _newFixture executable
+    _runWrapper "$_scenario" mcserver
+    _expectStatus 1
+    _expectContains "$_stderrFile" "ended as the 2-second startup check completed" "boundary error"
+    _expectNoLogCommand ls
+    if [ "$_scenario" = boundary-dead ]; then
+        _expectLogLine $'kill-pane\t-t\t%42'
+    else
+        _expectNoLogCommand kill-pane
+    fi
+    _finishCase
+}
+
+function _testSleepFailure {
+    local _scenario="$1"
+    local _expectedText="$2"
+    local _label="$3"
+
+    _beginCase "$_label"
+    _newFixture executable
+    _runWrapper "$_scenario" mcserver
+    _expectStatus 1
+    _expectContains "$_stderrFile" "$_expectedText" "sleep interruption error"
+    _expectLogLine $'set-option\t-p\t-t\t%42\tremain-on-exit\toff'
+    _expectNoLogCommand display-message
+    _expectNoLogCommand ls
+    printf '%s\n' '2' >"$_caseDir/expected-sleep.log"
+    _expectFilesEqual "$_caseDir/expected-sleep.log" "$_caseStateDir/sleep.log" "sleep call"
+    _finishCase
+}
+
+function _testStatusCommands {
+    _beginCase "status uses an exact session target and meaningful statuses"
+
+    _newFixture executable
+    _runWrapper status-running --status mcserver-2
+    _expectStatus 0
+    _expectContains "$_stdoutFile" "'mcserver-2' is running" "running status"
+    _expectLogLine $'has-session\t-t\t=mcserver-2'
+
+    _newFixture executable
+    _runWrapper status-missing --status mcserver-2
+    _expectStatus 1
+    _expectContains "$_stdoutFile" "'mcserver-2' is not running" "missing status"
+    _expectLogLine $'has-session\t-t\t=mcserver-2'
+    _finishCase
+}
+
+function _testAttachCommands {
+    _beginCase "attach uses exec, an exact target, and preserves tmux status"
+
+    _newFixture executable
+    _runWrapper attach-running --attach mcserver_3
+    _expectStatus 23
+    _expectLogLine $'has-session\t-t\t=mcserver_3'
+    _expectLogLine $'attach-session\t-t\t=mcserver_3'
+
+    _newFixture executable
+    _runWrapper attach-missing --attach mcserver_3
+    _expectStatus 1
+    _expectContains "$_stderrFile" "No tmux session named 'mcserver_3'" "missing attach error"
+    _expectLogLine $'has-session\t-t\t=mcserver_3'
+    _expectNoLogCommand attach-session
+    _finishCase
+}
+
+function _testSiblingValidation {
+    local _mode=""
+
+    _beginCase "invalid sibling file types and permissions fail before tmux"
+    for _mode in missing nonexecutable unreadable directory symlink; do
+        _newFixture "$_mode"
+        _runWrapper healthy mcserver
+        _expectStatus 1
+        _expectContains "$_stderrFile" "must be a regular, non-symlink, readable and executable file" "sibling validation"
+        _expectNoTmuxCall
+    done
+    _finishCase
+}
+
+function _testMissingTmux {
+    local _emptyPath=""
+
+    _beginCase "missing tmux fails clearly without falling back"
+    _newFixture executable
+    _emptyPath="$_caseDir/empty-path"
+    mkdir -p "$_emptyPath"
+    : >"$_stdoutFile"
+    : >"$_stderrFile"
+    NO_COLOR=1 \
+        PATH="$_emptyPath" \
+        TMUX='' \
+        TMUX_TMPDIR="$_caseStateDir/tmux-socket" \
+        "$_bashUnderTest" "$_caseWrapper" --status mcserver >"$_stdoutFile" 2>"$_stderrFile"
+    _runStatus=$?
+    _expectStatus 1
+    _expectContains "$_stderrFile" "'tmux' is required but was not found" "missing-tmux error"
+    _expectNoTmuxCall
+    _finishCase
+}
+
+function _testNames {
+    local _name=""
+    local _validNames=(a 0 mcserver1 mcserver-2 mcserver_3 1mb abcdefghijklmnopq a1234567890123456789012345678901)
+    local _invalidNames=("" MCServer -server _server " mcserver" "mcserver " "mc server" $'mc\tserver' $'mc\nserver' mcserver:1 mcserver.1 'mcserver*' 'mcserver?' mc/server '=mcserver' "\$1" @mcserver +mcserver a12345678901234567890123456789012 'mcsérver')
+
+    _beginCase "complete session names are preserved or rejected without tmux"
+    for _name in "${_validNames[@]}"; do
+        _newFixture executable
+        _runWrapper status-running --status "$_name"
+        _expectStatus 0
+        _expectContains "$_stdoutFile" "tmux session '$_name' is running" "preserved session name"
+        _expectLogLine "has-session"$'\t'"-t"$'\t'"=$_name"
+    done
+
+    for _name in "${_invalidNames[@]}"; do
+        _newFixture executable
+        _runWrapper status-running --status "$_name"
+        _expectStatus 1
+        _expectContains "$_stderrFile" "Invalid session name." "invalid-name error"
+        _expectNoTmuxCall
+    done
+    _finishCase
+}
+
+function _testArgumentsAndHelp {
+    _beginCase "help works and surplus or unknown arguments fail before tmux"
+
+    _newFixture executable
+    _runWrapper healthy --help
+    _expectStatus 0
+    _expectContains "$_stdoutFile" "Names use 1-32 lowercase ASCII letters" "name help"
+    _expectNoTmuxCall
+
+    _newFixture executable
+    _runWrapper healthy --help extra
+    _expectStatus 1
+    _expectContains "$_stderrFile" "Unexpected extra arguments." "help arity error"
+    _expectNoTmuxCall
+
+    _newFixture executable
+    _runWrapper healthy --status mcserver extra
+    _expectStatus 1
+    _expectContains "$_stderrFile" "Unexpected extra arguments." "status arity error"
+    _expectNoTmuxCall
+
+    _newFixture executable
+    _runWrapper healthy --attach mcserver extra
+    _expectStatus 1
+    _expectContains "$_stderrFile" "Unexpected extra arguments." "attach arity error"
+    _expectNoTmuxCall
+
+    _newFixture executable
+    _runWrapper healthy mcserver extra
+    _expectStatus 1
+    _expectContains "$_stderrFile" "Unexpected extra arguments." "startup arity error"
+    _expectNoTmuxCall
+
+    _newFixture executable
+    _runWrapper healthy --unknown
+    _expectStatus 1
+    _expectContains "$_stderrFile" "Unknown option '--unknown'" "unknown-option error"
+    _expectNoTmuxCall
+    _finishCase
+}
+
+function _testOutputHelper {
+    local _fragment=""
+    local _escape=""
+
+    _beginCase "output helper preserves success, failure, debug, and no-color behavior"
+    _newFixture executable
+    _fragment="$_caseDir/output-function.sh"
+    sed -n '/^function _output {$/,/^}$/p' "$_target" >"$_fragment"
+
+    : >"$_stdoutFile"
+    : >"$_stderrFile"
+    # The nested Bash, not this runner, deliberately expands these variables.
+    # shellcheck disable=SC2016
+    "$_bashUnderTest" -c '_debug=true; unset NO_COLOR; source "$1"; _output okay "successful message"; result=$?; printf "continued:%s\n" "$result"; exit "$result"' _ "$_fragment" >"$_stdoutFile" 2>"$_stderrFile"
+    _runStatus=$?
+    _expectStatus 0
+    _expectContains "$_stdoutFile" "successful message" "okay output"
+    _expectContains "$_stdoutFile" "continued:0" "caller continuation"
+    _expectEmpty "$_stderrFile" "okay stderr"
+    _escape=$(printf '\033')
+    _expectNotContains "$_stdoutFile" "$_escape" "non-TTY ANSI escape"
+
+    : >"$_stdoutFile"
+    : >"$_stderrFile"
+    # shellcheck disable=SC2016
+    "$_bashUnderTest" -c '_debug=true; source "$1"; _output oops "fatal message"; printf "unreachable\n"' _ "$_fragment" >"$_stdoutFile" 2>"$_stderrFile"
+    _runStatus=$?
+    _expectStatus 1
+    _expectEmpty "$_stdoutFile" "oops stdout"
+    _expectContains "$_stderrFile" "fatal message" "oops output"
+    _expectNotContains "$_stderrFile" "unreachable" "post-oops output"
+
+    : >"$_stdoutFile"
+    : >"$_stderrFile"
+    # shellcheck disable=SC2016
+    "$_bashUnderTest" -c '_debug=false; source "$1"; _output debug "hidden"; result=$?; exit "$result"' _ "$_fragment" >"$_stdoutFile" 2>"$_stderrFile"
+    _runStatus=$?
+    _expectStatus 0
+    _expectEmpty "$_stdoutFile" "disabled debug stdout"
+    _expectEmpty "$_stderrFile" "disabled debug stderr"
+    _finishCase
+}
+
+function _runBehaviorForBash {
+    local _version=""
+
+    _bashUnderTest="$1"
+    _version=$("$_bashUnderTest" --version | sed -n '1p')
+    printf '\nBehavior tests with %s\n' "$_version"
+
+    _testHealthyStart
+    _testConfiguredDefaultName
+    _testListFailureIsNonfatal
+    _testDuplicateSession
+    _testNewFailureWithPane
+    _testInvalidPane empty-pane "empty pane identifier closes only the new session"
+    _testInvalidPane malformed-pane "malformed pane identifier closes only the new session"
+    _testChildExit child-exit-zero "exit status 0" "immediate clean child exit is reported"
+    _testChildExit child-exit-seven "exit status 7" "immediate nonzero child exit is reported"
+    _testChildExit child-signal-fifteen "signal 15" "immediate signal termination is reported"
+    _testChildExit child-unknown-exit "unknown exit status" "missing child exit metadata is reported"
+    _testFirstDisplayMissing
+    _testUnexpectedPaneState
+    _testRestoreFailure
+    _testBoundaryResult boundary-dead "death at the probe boundary fails safely"
+    _testBoundaryResult boundary-disappeared "disappearance at the probe boundary fails safely"
+    _testSleepFailure sleep-failure "startup check was interrupted" "interrupted probe restores close-on-exit"
+    _testSleepFailure sleep-failure-restore-failure "could not restore normal close-on-exit behavior" "interrupted probe reports restore failure"
+    _testStatusCommands
+    _testAttachCommands
+    _testSiblingValidation
+    _testMissingTmux
+    _testNames
+    _testArgumentsAndHelp
+    _testOutputHelper
+}
+
+function _runSyntaxChecks {
+    local _bashPath=""
+    local _file=""
+    local _version=""
+    local _syntaxFailed=0
+    local _files=("$_target" "$_runner" "$_fakeTmux" "$_fakeSleep")
+
+    for _bashPath in "${_bashPaths[@]}"; do
+        _version=$("$_bashPath" --version | sed -n '1p')
+        _syntaxFailed=0
+        for _file in "${_files[@]}"; do
+            if ! "$_bashPath" -n "$_file"; then
+                _syntaxFailed=1
+            fi
+        done
+        if [ "$_syntaxFailed" -eq 0 ]; then
+            _pass "syntax with $_version"
+        else
+            _fail "syntax with $_version"
+        fi
+    done
+}
+
+function _runShellCheck {
+    if ! command -v shellcheck >/dev/null 2>&1; then
+        _fail "ShellCheck is required for '$_mode' (macOS: brew install shellcheck; Ubuntu: apt install shellcheck)"
+        return
+    fi
+
+    if shellcheck --shell=bash "$_target" "$_runner" "$_fakeTmux" "$_fakeSleep"; then
+        _pass "ShellCheck"
+    else
+        _fail "ShellCheck"
+    fi
+}
+
+if [ ! -f "$_target" ] || [ ! -f "$_runner" ] || \
+    [ ! -f "$_fakeTmux" ] || [ ! -x "$_fakeTmux" ] || \
+    [ ! -f "$_fakeSleep" ] || [ ! -x "$_fakeSleep" ]; then
+    printf '%s\n' "Test suite files are incomplete." >&2
+    exit 2
+fi
+
+if [ "$(PATH="$_suiteDir/fake-bin:$_originalPath" command -v tmux 2>/dev/null)" != "$_fakeTmux" ] || \
+    [ "$(PATH="$_suiteDir/fake-bin:$_originalPath" command -v sleep 2>/dev/null)" != "$_fakeSleep" ]; then
+    printf '%s\n' "The test fakes do not take precedence in PATH; refusing to run." >&2
+    exit 2
+fi
+
+_discoverBashes
+if [ "${#_bashPaths[@]}" -eq 0 ]; then
+    printf '%s\n' "No Bash interpreter was found." >&2
+    exit 2
+fi
+
+if [ "$_mode" != lint ]; then
+    if [ "$EUID" -eq 0 ]; then
+        printf '%s\n' "Behavior tests must not run as root because the wrapper intentionally rejects root." >&2
+        exit 2
+    fi
+
+    _tempRoot=$(mktemp -d "${TMPDIR:-/tmp}/1mb-start-tests.XXXXXX") || exit 2
+    _tempRoot=$(cd -P -- "$_tempRoot" >/dev/null 2>&1 && pwd -P) || exit 2
+    _runSyntaxChecks
+    for _bashUnderTest in "${_bashPaths[@]}"; do
+        _runBehaviorForBash "$_bashUnderTest"
+    done
+fi
+
+if [ "$_mode" != test ]; then
+    _runShellCheck
+fi
+
+printf '\nSummary: %s passed, %s failed, %s skipped\n' "$_passed" "$_failed" "$_skipped"
+[ "$_failed" -eq 0 ]