diff --git a/ralph_loop.sh b/ralph_loop.sh
index a7c2f1e0..345436d8 100755
--- a/ralph_loop.sh
+++ b/ralph_loop.sh
@@ -482,25 +482,33 @@ setup_tmux_session() {
     local ralph_home="${RALPH_HOME:-$HOME/.ralph}"
     local project_dir="$(pwd)"
 
-    # Get the tmux base-index / pane-base-index to handle custom configurations
-    # (e.g. `set -g base-index 1`, `setw -g pane-base-index 1` — very common in
-    # dotfiles). Without this, pane targets like `.0` don't exist and the Ralph
-    # loop never starts, leaving empty panes. See: tmux pane-base-index.
-    local base_win base_pane
-    base_win=$(get_tmux_base_index)
-    base_pane=$(get_tmux_pane_base_index)
-    local pane0=$((base_pane + 0))   # Ralph loop (left)
-    local pane1=$((base_pane + 1))   # Claude output (right-top)
-    local pane2=$((base_pane + 2))   # Status monitor (right-bottom)
+    # base-index / pane-base-index are detected AFTER the server starts (below).
+    # Querying earlier fails on the very first `ralph --monitor` run when no tmux
+    # server exists yet: `tmux show-options` does NOT auto-start a server, so it
+    # errors out and detection silently defaults to 0. With a `base-index 1` /
+    # `pane-base-index 1` config that makes every `window.pane` target off-by-one
+    # (e.g. `1.0`, window `0`), the loop command is sent to a nonexistent pane,
+    # and tmux opens to empty idle panes. Starting the server first makes the
+    # detection reliable. See: tmux pane-base-index.
+    local base_win base_pane pane0 pane1 pane2
 
     log_status "INFO" "Setting up tmux session: $session_name"
 
     # Initialize live.log file
     echo "=== Ralph Live Output - Waiting for first loop... ===" > "$LIVE_LOG_FILE"
 
-    # Create new tmux session detached (left pane - Ralph loop)
+    # Create new tmux session detached (left pane - Ralph loop). This also starts
+    # the tmux server (sourcing the user's config), so the base-index /
+    # pane-base-index detection below is reliable even on the very first run.
     tmux new-session -d -s "$session_name" -c "$project_dir"
 
+    # Detect base-index / pane-base-index now that the server is running.
+    base_win=$(get_tmux_base_index)
+    base_pane=$(get_tmux_pane_base_index)
+    pane0=$((base_pane + 0))   # Ralph loop (left)
+    pane1=$((base_pane + 1))   # Claude output (right-top)
+    pane2=$((base_pane + 2))   # Status monitor (right-bottom)
+
     # Split window vertically (right side)
     tmux split-window -h -t "$session_name" -c "$project_dir"
 
diff --git a/tests/integration/test_monitor.bats b/tests/integration/test_monitor.bats
index 978b8d7c..c8ca5808 100644
--- a/tests/integration/test_monitor.bats
+++ b/tests/integration/test_monitor.bats
@@ -1,10 +1,11 @@
 #!/usr/bin/env bats
 # Integration tests for ralph_monitor.sh dashboard (Issue #15)
 #
-# Sourcing strategy: `head -n -1` loads all function definitions from
-# ralph_monitor.sh without triggering the unconditional `main` call on
-# the last line. This mirrors the inline/source pattern used in
-# test_tmux_integration.bats and test_loop_execution.bats.
+# Sourcing strategy: strip the final `main` line with `sed '$d'` (portable —
+# `head -n -1` is GNU-only and errors on BSD), then source from a TEMP FILE.
+# `source <(process-substitution)` does NOT define functions on macOS bash 3.2
+# (they silently stay undefined), so the pipe→file→source form is required for
+# portability. Mirrors the inline/source pattern in test_tmux_integration.bats.
 
 bats_require_minimum_version 1.5.0
 
@@ -18,13 +19,18 @@ setup() {
 
     MONITOR_SCRIPT="${BATS_TEST_DIRNAME}/../../ralph_monitor.sh"
 
-    # Load all monitor functions without calling main().
-    # head -n -1 strips the bare `main` call on the final line.
+    # Load all monitor functions without calling main(). `sed '$d'` strips the
+    # bare `main` call on the final line (portable — `head -n -1` is GNU-only).
     # The `trap cleanup ...` line is filtered out: sourcing it would REPLACE
     # bats' own EXIT trap, silently swallowing failing tests (the file then
     # reports "Executed N-1 instead of expected N" with no `not ok` line).
+    # Write to a temp file and source THAT: `source <(process-substitution)` does
+    # NOT define functions on macOS bash 3.2 (they silently stay undefined), so
+    # the pipe→file→source form is required for portability.
+    _monitor_funcs="$TEST_DIR/.monitor_funcs.sh"
+    sed '$d' "$MONITOR_SCRIPT" | grep -v '^trap cleanup ' > "$_monitor_funcs"
     # shellcheck disable=SC1090
-    source <(head -n -1 "$MONITOR_SCRIPT" | grep -v '^trap cleanup ')
+    source "$_monitor_funcs"
 
     # Override clear_screen to suppress terminal-escape side-effects in tests.
     clear_screen() { :; }
@@ -226,12 +232,12 @@ EOF
         return 1
     }
 
-    # Verify ralph_monitor.sh registers an EXIT trap that calls cleanup
+    # Verify ralph_monitor.sh registers an EXIT trap that calls cleanup.
+    # Source from a temp file (not `source <(...)` — broken on macOS bash 3.2).
+    local _trap_src="$TEST_DIR/.mon_trap.sh"
+    sed '$d' "${BATS_TEST_DIRNAME}/../../ralph_monitor.sh" > "$_trap_src"
     local trap_output
-    trap_output=$(bash -c "
-        source <(head -n -1 '${BATS_TEST_DIRNAME}/../../ralph_monitor.sh')
-        trap -p EXIT
-    " 2>/dev/null)
+    trap_output=$(bash -c "source '$_trap_src'; trap -p EXIT" 2>/dev/null)
     echo "$trap_output" | grep -q "cleanup" || {
         echo "Expected EXIT trap to invoke cleanup; trap output: $trap_output"
         return 1
diff --git a/tests/integration/test_tmux_integration.bats b/tests/integration/test_tmux_integration.bats
index d5007216..a1b2fd54 100644
--- a/tests/integration/test_tmux_integration.bats
+++ b/tests/integration/test_tmux_integration.bats
@@ -61,22 +61,29 @@ setup_tmux_session() {
     local ralph_home="${RALPH_HOME:-$HOME/.ralph}"
     local project_dir="$(pwd)"
 
-    # Get the tmux base-index / pane-base-index to handle custom configurations
-    local base_win base_pane
-    base_win=$(get_tmux_base_index)
-    base_pane=$(get_tmux_pane_base_index)
-    local pane0=$((base_pane + 0))
-    local pane1=$((base_pane + 1))
-    local pane2=$((base_pane + 2))
+    # base-index / pane-base-index are detected AFTER the server starts (below).
+    # See ralph_loop.sh: querying earlier fails when no tmux server exists yet
+    # (first run) — `tmux show-options` does not auto-start a server, so detection
+    # silently defaults to 0. With a base-index 1 config that yields off-by-one
+    # pane targets and the loop never starts (tmux shows empty idle panes). Keep
+    # this inline mirror in sync with ralph_loop.sh.
+    local base_win base_pane pane0 pane1 pane2
 
     log_status "INFO" "Setting up tmux session: $session_name"
 
     # Initialize live.log file
     echo "=== Ralph Live Output - Waiting for first loop... ===" > "$LIVE_LOG_FILE"
 
-    # Create new tmux session detached (left pane - Ralph loop)
+    # Create new tmux session detached (left pane - Ralph loop). Starts the server.
     tmux new-session -d -s "$session_name" -c "$project_dir"
 
+    # Detect base-index / pane-base-index now that the server is running.
+    base_win=$(get_tmux_base_index)
+    base_pane=$(get_tmux_pane_base_index)
+    pane0=$((base_pane + 0))
+    pane1=$((base_pane + 1))
+    pane2=$((base_pane + 2))
+
     # Split window vertically (right side)
     tmux split-window -h -t "$session_name" -c "$project_dir"
 
@@ -348,6 +355,39 @@ assert_tmux_called_with() {
     assert_tmux_called_with "tmux show-options"
 }
 
+# ==============================================================================
+# TEST 3a: setup_tmux_session detects base-index AFTER starting the server
+# Regression: with a base-index 1 / pane-base-index 1 config and no tmux server
+# running yet (the first `ralph --monitor`), detecting BEFORE new-session made
+# `tmux show-options` fail (it does not auto-start a server), silently defaulting
+# detection to 0. Every pane/window target was then off-by-one, so the `ralph
+# --live` loop command was sent to a nonexistent pane and tmux opened to empty
+# idle panes. The fix detects AFTER `tmux new-session` starts the server. This
+# test guards the call ORDER: the first `new-session` must precede the first
+# `show-options` in the tmux call log.
+# ==============================================================================
+@test "setup_tmux_session detects base-index only after new-session starts the server" {
+    export MOCK_TMUX_BASE_INDEX="1"
+    export MOCK_TMUX_PANE_BASE_INDEX="1"
+    run setup_tmux_session
+    [ "$status" -eq 0 ]
+
+    local new_session_line show_options_line
+    new_session_line=$(grep -nE '^tmux new-session -d' "$TMUX_CALL_LOG" | head -1 | cut -d: -f1)
+    show_options_line=$(grep -nE '^tmux show-options' "$TMUX_CALL_LOG" | head -1 | cut -d: -f1)
+
+    [ -n "$new_session_line" ]   || { echo "no new-session call logged:"; cat "$TMUX_CALL_LOG"; return 1; }
+    [ -n "$show_options_line" ] || { echo "no show-options call logged:"; cat "$TMUX_CALL_LOG"; return 1; }
+
+    # The ordering invariant: server starts first, THEN base-index is queried.
+    if [ "$new_session_line" -ge "$show_options_line" ]; then
+        echo "FAIL: new-session (line $new_session_line) must precede show-options (line $show_options_line)"
+        echo "--- tmux call log ---"
+        cat "$TMUX_CALL_LOG"
+        return 1
+    fi
+}
+
 # ==============================================================================
 # TEST 4: setup_tmux_session creates session with -d flag and ralph- prefix
 # ==============================================================================
diff --git a/tests/unit/test_log_rotation.bats b/tests/unit/test_log_rotation.bats
index 1a21ef47..6370e3f3 100644
--- a/tests/unit/test_log_rotation.bats
+++ b/tests/unit/test_log_rotation.bats
@@ -81,7 +81,10 @@ if [[ "\$1" == "-c%s" ]]; then
 fi
 if [[ "\$1" == "-f%z" ]]; then
   shift
-  exec "$real_stat" -c%s "\$@"
+  # Portable byte count — real stat's -c%s is GNU-only and fails on BSD/macOS,
+  # which silently defeated this fallback simulation there. wc -c works everywhere.
+  wc -c < "\$1"
+  exit 0
 fi
 exec "$real_stat" "\$@"
 STUBEOF
diff --git a/tests/unit/test_notifications.bats b/tests/unit/test_notifications.bats
index b8137b8b..ba316761 100644
--- a/tests/unit/test_notifications.bats
+++ b/tests/unit/test_notifications.bats
@@ -155,6 +155,10 @@ EOF
 # =============================================================================
 
 @test "send_notification uses notify-send on Linux when osascript unavailable" {
+    # osascript is always present on macOS (/usr/bin, and /bin symlinks to it),
+    # so the notify-send branch — which fires only when osascript is absent — is
+    # unreachable there and cannot be hidden via PATH. Exercise it on Linux only.
+    [[ "$(uname)" == "Darwin" ]] && skip "notify-send branch unreachable on macOS (osascript always present)"
     export ENABLE_NOTIFICATIONS=true
 
     # Create a private bin dir that has notify-send but NOT osascript
diff --git a/tests/unit/test_ralph_enable.bats b/tests/unit/test_ralph_enable.bats
index 8c7e0848..64c5fb78 100644
--- a/tests/unit/test_ralph_enable.bats
+++ b/tests/unit/test_ralph_enable.bats
@@ -294,8 +294,11 @@ EOF
         cd "'"$TEST_DIR"'"
         NON_INTERACTIVE=true
 
-        # Define phase_verification from ralph_enable.sh
-        source <(sed -n "/^phase_verification()/,/^}/p" "'"${BATS_TEST_DIRNAME}"'/../../ralph_enable.sh")
+        # Define phase_verification from ralph_enable.sh. Write to a temp file and
+        # source THAT — `source <(process-substitution)` does not define functions
+        # on macOS bash 3.2 (they silently stay undefined → "command not found").
+        sed -n "/^phase_verification()/,/^}/p" "'"${BATS_TEST_DIRNAME}"'/../../ralph_enable.sh" > .pv.sh
+        source .pv.sh
 
         phase_verification
     '
@@ -323,8 +326,11 @@ EOF
         cd "'"$TEST_DIR"'"
         NON_INTERACTIVE=true
 
-        # Define phase_verification from ralph_enable.sh
-        source <(sed -n "/^phase_verification()/,/^}/p" "'"${BATS_TEST_DIRNAME}"'/../../ralph_enable.sh")
+        # Define phase_verification from ralph_enable.sh. Write to a temp file and
+        # source THAT — `source <(process-substitution)` does not define functions
+        # on macOS bash 3.2 (they silently stay undefined → "command not found").
+        sed -n "/^phase_verification()/,/^}/p" "'"${BATS_TEST_DIRNAME}"'/../../ralph_enable.sh" > .pv.sh
+        source .pv.sh
 
         phase_verification
     '