diff --git a/regress/prompt-keys.sh b/regress/prompt-keys.sh
new file mode 100644
index 000000000..7fa7a673b
--- /dev/null
+++ b/regress/prompt-keys.sh
@@ -0,0 +1,300 @@
+#!/bin/sh
+
+PATH=/bin:/usr/bin
+TERM=screen
+LC_ALL=C.UTF-8
+LANG=C.UTF-8
+export TERM LC_ALL LANG
+
+[ -z "$TEST_TMUX" ] && TEST_TMUX=$(readlink -f ../tmux)
+OUT="$TEST_TMUX -Ltest -f/dev/null"		# outer (host for the client)
+IN="$TEST_TMUX -Ltest2 -f/dev/null"		# inner (under test)
+
+$OUT kill-server 2>/dev/null
+$IN kill-server 2>/dev/null
+trap "$OUT kill-server 2>/dev/null; $IN kill-server 2>/dev/null" EXIT
+
+fail() {
+	echo "[FAIL] $1"
+	exit 1
+}
+
+# Capture the outer pane: what the inner client rendered.  No -e, so we match
+# plain visible text, not styles or escape sequences.
+capture() {
+	$OUT capture-pane -p
+}
+
+# The "(search) ..." prompt row of a mode prompt.
+search_row() {
+	capture | grep '(search)' | head -1
+}
+
+# The inner status line is the last row of the outer capture (status is at the
+# bottom).  Used to assert a prompt is in the pane and not on the status line.
+status_line() {
+	capture | tail -1
+}
+
+# Inner mode must still be a tree mode (the prompt did not close or crash it).
+in_tree_mode() {
+	[ "$($IN display-message -p '#{pane_mode}')" = "tree-mode" ]
+}
+
+# Small settle for the key -> inner server -> inner client -> outer pane round
+# trip to redraw before we capture.  Matches the short waits other regress tests
+# use; we do not depend on exact timing beyond the redraw completing.
+settle() {
+	sleep 0.5
+}
+
+# Assert the mode search prompt currently shows exactly "(search) <want>".
+search_is() {
+	want=$1; msg=$2
+	search_row | grep -qF "(search) $want" || \
+		fail "$msg (wanted '(search) $want', got '$(search_row)')"
+}
+
+# --- Inner session under test. ---------------------------------------------
+#
+# Two windows so the tree has content; status on so we can distinguish the pane
+# from the status line; fixed size and manual sizing so the layout is stable.
+# A root-table key opens a status-line command prompt whose accept action writes
+# the final buffer into @r, so we can recover it exactly.
+$IN new -d -x80 -y24 "sh -c 'exec sleep 1000'" || exit 1
+$IN set -g status on || exit 1
+$IN set -g status-position bottom || exit 1
+$IN set -g status-keys emacs || exit 1
+$IN set -g window-size manual || exit 1
+$IN new-window -d "sh -c 'exec sleep 1000'" || exit 1
+$IN bind -n M-r command-prompt -p ">" "set -g @r '%%'" || exit 1
+
+# --- Outer session: attach the inner one inside its pane. -------------------
+$OUT new -d -x80 -y24 || exit 1
+$OUT set -g status off || exit 1
+$OUT set -g window-size manual || exit 1
+$OUT send-keys -l "$IN attach" || exit 1
+$OUT send-keys Enter || exit 1
+sleep 1
+
+# ===========================================================================
+# Mode prompt (choose-tree search): the thorough engine vehicle.
+# ===========================================================================
+
+$IN choose-tree || exit 1
+settle
+in_tree_mode || fail "choose-tree did not enter tree-mode"
+
+# --- 1. Search prompt is drawn in the pane, not on the status line. ---
+$IN send-keys C-s || exit 1
+settle
+search_row | grep -q '(search)' || fail "search prompt not drawn in the pane"
+status_line | grep -q '(search)' && \
+	fail "search prompt drawn on the status line, not in the pane"
+
+# --- 2. emacs editing: insert and delete at middle, start and end. ---
+# Cursor position is checked behaviourally: move, insert a marker, read the row.
+# This needs no cursor coordinates and fails if a movement/edit key is wrong.
+
+# Middle insert: "abcd", Left Left (cursor between b and c), insert X -> abXcd.
+$IN send-keys -l "abcd" || exit 1
+settle
+search_is "abcd" "literal input not shown in search prompt"
+$IN send-keys Left Left || exit 1
+$IN send-keys -l "X" || exit 1
+settle
+search_is "abXcd" "middle insert wrong (Left/insert)"
+
+# Middle delete: BSpace removes X (before cursor), DC removes c (at cursor).
+$IN send-keys BSpace || exit 1
+$IN send-keys DC || exit 1
+settle
+search_is "abd" "middle delete wrong (BSpace/Delete)"
+
+# Clear, then start/end insert with C-a and C-e.
+$IN send-keys C-u || exit 1
+$IN send-keys -l "mno" || exit 1
+$IN send-keys C-a || exit 1
+$IN send-keys -l "S" || exit 1
+$IN send-keys C-e || exit 1
+$IN send-keys -l "E" || exit 1
+settle
+search_is "SmnoE" "C-a/C-e start/end insert wrong"
+
+# Word kill: "hello world", C-w removes the last word leaving "hello " (with the
+# separating space).  capture-pane trims trailing spaces, so make the space
+# visible by inserting a marker after it: the buffer becomes "hello Z".
+$IN send-keys C-u || exit 1
+$IN send-keys -l "hello world" || exit 1
+$IN send-keys C-w || exit 1
+$IN send-keys -l "Z" || exit 1
+settle
+search_is "hello Z" "C-w did not kill a word"
+
+# C-a then C-k kills the whole line.
+$IN send-keys C-a || exit 1
+$IN send-keys C-k || exit 1
+settle
+search_row | grep -q '(search) [^ ]' && fail "C-a C-k did not clear the line"
+
+# --- 3. Editing kept the prompt open the whole time. ---
+in_tree_mode || fail "editing keys closed the mode"
+search_row | grep -q '(search)' || fail "editing keys closed the prompt"
+
+# --- 4. Unicode wide character: insert, render, delete as one unit. ---
+$IN send-keys C-u || exit 1
+$IN send-keys -l "a中b" || exit 1
+settle
+search_is "a中b" "wide character not shown"
+# Left moves over "b" (one column); BSpace deletes the wide "中" as a single
+# width-2 unit, leaving "ab".
+$IN send-keys Left || exit 1
+$IN send-keys BSpace || exit 1
+settle
+search_is "ab" "wide character not deleted as one unit"
+
+# --- 5. Control character: quote-next inserts it literally, shown as ^G. ---
+$IN send-keys C-u || exit 1
+$IN send-keys -l "a" || exit 1
+$IN send-keys C-v || exit 1		# quote next key
+$IN send-keys C-g || exit 1		# literal BEL -> displayed as ^G
+$IN send-keys -l "b" || exit 1
+settle
+search_is "a^Gb" "control character not shown as ^G"
+# Deleted as a single unit too.
+$IN send-keys Left || exit 1
+$IN send-keys BSpace || exit 1
+settle
+search_is "ab" "control character not deleted as one unit"
+
+# --- 6. Kill and yank: C-w fills the yank buffer, C-y pastes it at the cursor. ---
+# (prompt_key only fills the yank buffer from C-w; C-y then yanks that text, or
+# the top paste buffer if nothing has been killed.  Establish our own kill here
+# so the result is deterministic.)
+$IN send-keys C-u || exit 1
+$IN send-keys -l "one two" || exit 1
+$IN send-keys C-w || exit 1		# kill "two", buffer "one "
+$IN send-keys C-y || exit 1		# yank it back -> "one two"
+settle
+search_is "one two" "C-y did not yank the killed text"
+$IN send-keys C-y || exit 1		# yank again at cursor -> "one twotwo"
+settle
+search_is "one twotwo" "second C-y did not yank again"
+
+# --- 7. History: accept a string, reopen, Up recalls it. ---
+$IN send-keys C-u || exit 1
+$IN send-keys -l "alpha" || exit 1
+$IN send-keys Enter || exit 1
+settle
+$IN send-keys C-s || exit 1
+settle
+$IN send-keys Up || exit 1
+settle
+search_is "alpha" "history (Up) did not recall the previous entry"
+
+# --- 8. Escape closes the prompt but leaves the mode open. ---
+$IN send-keys Escape || exit 1
+settle
+search_row | grep -q '(search)' && fail "Escape left a dangling search prompt"
+in_tree_mode || fail "Escape closed the mode as well as the prompt"
+
+# Leave the mode.
+$IN send-keys q || exit 1
+settle
+
+# ===========================================================================
+# Status-line prompt (command-prompt): the same engine on the status line.
+# Keys go through the inner client's terminal (outer send-keys); the accepted
+# buffer is recovered exactly via %% -> @r.
+# ===========================================================================
+
+# --- 10. Prompt is drawn on the status line (the last row). ---
+$IN set -g @r "" || exit 1
+$OUT send-keys M-r || exit 1
+settle
+status_line | grep -q '>' || fail "status-line prompt not drawn on the status line"
+
+# --- 11. emacs cursor-marker edit, accept recovers the exact buffer. ---
+$OUT send-keys -l "abc" || exit 1
+$OUT send-keys Home || exit 1
+$OUT send-keys -l "X" || exit 1
+settle
+status_line | grep -qF "> Xabc" || \
+	fail "status-line edit wrong (got '$(status_line)')"
+$OUT send-keys Enter || exit 1
+settle
+[ "$($IN show -gv @r)" = "Xabc" ] || \
+	fail "status-line accept recovered '$($IN show -gv @r)', wanted 'Xabc'"
+
+# --- 12. Unicode on the status line: insert, move, delete wide char. ---
+$IN set -g @r "" || exit 1
+$OUT send-keys M-r || exit 1
+settle
+$OUT send-keys -l "a㋡b" || exit 1
+settle
+status_line | grep -qF "a㋡b" || \
+	fail "status-line wide character not shown (got '$(status_line)')"
+# Home, insert Z (start); End, BSpace (delete b); BSpace (delete wide char).
+$OUT send-keys Home || exit 1
+$OUT send-keys -l "Z" || exit 1
+$OUT send-keys End || exit 1
+$OUT send-keys BSpace || exit 1
+$OUT send-keys BSpace || exit 1
+settle
+$OUT send-keys Enter || exit 1
+settle
+[ "$($IN show -gv @r)" = "Za" ] || \
+	fail "status-line wide edit recovered '$($IN show -gv @r)', wanted 'Za'"
+
+# --- 13. Overflow: more text than fits stays within the line and is kept. ---
+big="0123456789012345678901234567890123456789012345678901234567890123456789ABCDEFGHIJ"
+$IN set -g @r "" || exit 1
+$OUT send-keys M-r || exit 1
+settle
+$OUT send-keys -l "$big" || exit 1
+settle
+# The drawn status line must not exceed the client width (80): no wrap, no crash.
+width=$(status_line | awk '{print length($0)}')
+[ "$width" -le 80 ] || fail "overflowing prompt drew $width columns, wider than 80"
+$OUT send-keys Enter || exit 1
+settle
+# The whole buffer was kept despite only part being visible.
+[ "$($IN show -gv @r)" = "$big" ] || fail "overflowing prompt lost buffer content"
+
+# --- 14. Escape closes the status-line prompt cleanly. ---
+$IN set -g @r "SENTINEL" || exit 1
+$OUT send-keys M-r || exit 1
+settle
+$OUT send-keys -l "discard" || exit 1
+$OUT send-keys Escape || exit 1
+settle
+status_line | grep -q '> discard' && fail "Escape left a dangling status-line prompt"
+[ "$($IN show -gv @r)" = "SENTINEL" ] || fail "Escape ran the prompt's accept action"
+
+# ===========================================================================
+# Two clients attached to the same window: a mode prompt must render on both.
+# ===========================================================================
+
+$OUT new-window || exit 1
+$OUT set -g status off || exit 1
+$OUT send-keys -l "$IN attach" || exit 1
+$OUT send-keys Enter || exit 1
+sleep 1
+
+$IN choose-tree || exit 1
+settle
+$IN send-keys C-s || exit 1
+settle
+$IN send-keys -l "dual" || exit 1
+settle
+for w in $($OUT list-windows -F '#{window_index}'); do
+	$OUT capture-pane -t ":$w" -p | grep -qF "(search) dual" || \
+		fail "mode prompt not shown on client in outer window $w"
+done
+$IN send-keys Escape || exit 1
+settle
+
+# --- Inner tmux is still alive and responsive. ---
+$IN display-message -p '#{version}' >/dev/null 2>&1 || fail "inner tmux died"
+
+exit 0
diff --git a/regress/prompt-mechanics.sh b/regress/prompt-mechanics.sh
new file mode 100644
index 000000000..6f3e5294e
--- /dev/null
+++ b/regress/prompt-mechanics.sh
@@ -0,0 +1,336 @@
+#!/bin/sh
+
+# Exercise the prompt mechanics shared by all three host paths of the prompt
+# engine in prompt.c:
+#
+#   status.c     status_prompt_set     - the status-line command prompt.
+#   window.c     window_pane_set_prompt - a prompt drawn over a pane (-P).
+#   mode-tree.c  mode_tree_set_prompt   - search/filter prompts in tree modes.
+#
+# prompt-keys.sh covers the editing keys; this test covers that each path OPENS
+# and DRAWS in the right place and that the prompt flags select the right engine
+# behaviour: -1 (single), -N (numeric), -i (incremental), -k (key), -e
+# (backspace exit), -I (prefill), multi prompts, type-scoped history and command
+# completion.
+
+PATH=/bin:/usr/bin
+TERM=screen
+LC_ALL=C.UTF-8
+LANG=C.UTF-8
+export TERM LC_ALL LANG
+
+[ -z "$TEST_TMUX" ] && TEST_TMUX=$(readlink -f ../tmux)
+OUT="$TEST_TMUX -Ltest -f/dev/null"		# outer (host for the client)
+IN="$TEST_TMUX -Ltest2 -f/dev/null"		# inner (under test)
+
+$OUT kill-server 2>/dev/null
+$IN kill-server 2>/dev/null
+trap "$OUT kill-server 2>/dev/null; $IN kill-server 2>/dev/null" EXIT
+
+fail() {
+	echo "[FAIL] $1"
+	exit 1
+}
+
+# Capture the outer pane: what the inner client rendered.  Pane-area prompts
+# (over a pane or in a tree mode) and the status-line prompt all end up here.
+capture() {
+	$OUT capture-pane -p
+}
+
+# The inner status line is the last row of the outer capture.
+status_line() {
+	capture | tail -1
+}
+
+# The recovered buffer.  Every prompt below accepts into the @r option so the
+# exact final string can be checked; reset it to a sentinel first so we can tell
+# "accept ran" from "prompt cancelled".
+got() {
+	$IN show -gv @r
+}
+reset() {
+	$IN set -g @r "SENTINEL" || exit 1
+}
+
+# Settle for the key -> inner server -> inner client -> outer pane redraw round
+# trip, as in prompt-keys.sh.
+settle() {
+	sleep 0.5
+}
+
+# --- Inner session under test. ---------------------------------------------
+#
+# The window is created at -y23 so that, with a one-row bottom status, the pane
+# area (23) exactly fills the 24-row client: a pane prompt drawn on the pane's
+# bottom row lands on visible row 23, just above the status line on row 24.  A
+# second, distinctively named window gives the tree something to filter.
+$IN new -d -x80 -y23 -n YAK "sh -c 'exec sleep 1000'" || exit 1
+$IN set -g status on || exit 1
+$IN set -g status-position bottom || exit 1
+$IN set -g status-keys emacs || exit 1
+$IN set -g window-size manual || exit 1
+$IN new-window -d -n ZEBRA "sh -c 'exec sleep 1000'" || exit 1
+
+# One root-table key per path/flag.  The accept template records the final
+# buffer in @r (or both buffers, for the multi-prompt case).
+$IN bind -n M-s command-prompt    -p '(stat)'         "set -g @r '%%'"      || exit 1
+$IN bind -n M-p command-prompt -P -p '(pane)'         "set -g @r '%%'"      || exit 1
+$IN bind -n M-o command-prompt -P -1 -p '(one)'       "set -g @r '%%'"      || exit 1
+$IN bind -n M-n command-prompt -P -N -I 5 -p '(num)'  "set -g @r '%%'"      || exit 1
+$IN bind -n M-i command-prompt -P -i -p '(inc)'       "set -g @r '%%'"      || exit 1
+$IN bind -n M-k command-prompt -P -k -p '(key)'       "set -g @r '%%'"      || exit 1
+$IN bind -n M-e command-prompt -P -e -p '(bs)'        "set -g @r '%%'"      || exit 1
+$IN bind -n M-j command-prompt -P -I hello -p '(pre)' "set -g @r '%%'"      || exit 1
+$IN bind -n M-m command-prompt    -p 'first,second'   "set -g @r '%1/%2'"   || exit 1
+$IN bind -n M-c command-prompt    -p '(cmd)'          "set -g @r '%%'"      || exit 1
+$IN bind -n M-h command-prompt -T search -p '(srch)'  "set -g @r '%%'"      || exit 1
+
+# --- Outer session: attach the inner one inside its pane. -------------------
+$OUT new -d -x80 -y24 || exit 1
+$OUT set -g status off || exit 1
+$OUT set -g window-size manual || exit 1
+$OUT send-keys -l "$IN attach" || exit 1
+$OUT send-keys Enter || exit 1
+sleep 1
+
+# ===========================================================================
+# 1. Each path opens and draws in the right place.
+# ===========================================================================
+
+# --- 1a. status.c: drawn on the status line (the last row). ---
+reset
+$OUT send-keys M-s || exit 1
+settle
+status_line | grep -qF '(stat)' || \
+	fail "status-line prompt not on the status line (got '$(status_line)')"
+$OUT send-keys -l "go" || exit 1
+$OUT send-keys Enter || exit 1
+settle
+[ "$(got)" = "go" ] || fail "status-line accept recovered '$(got)', wanted 'go'"
+
+# --- 1b. window.c: drawn over the pane, not on the status line. ---
+reset
+$OUT send-keys M-p || exit 1
+settle
+capture | grep -qF '(pane)' || fail "pane prompt not drawn in the pane"
+status_line | grep -qF '(pane)' && \
+	fail "pane prompt drawn on the status line, not over the pane"
+$OUT send-keys -l "deep" || exit 1
+$OUT send-keys Enter || exit 1
+settle
+[ "$(got)" = "deep" ] || fail "pane prompt accept recovered '$(got)', wanted 'deep'"
+
+# --- 1c. mode-tree.c: search prompt drawn in the pane. ---
+$IN choose-tree || exit 1
+settle
+[ "$($IN display-message -p '#{pane_mode}')" = "tree-mode" ] || \
+	fail "choose-tree did not enter tree-mode"
+$IN send-keys C-s || exit 1
+settle
+capture | grep -qF '(search)' || fail "mode-tree search prompt not drawn in the pane"
+status_line | grep -qF '(search)' && \
+	fail "mode-tree search prompt drawn on the status line"
+$IN send-keys Escape || exit 1
+settle
+
+# --- 1d. mode-tree.c: filter prompt opens, applies, prefills, and clears. ---
+$IN send-keys f || exit 1
+settle
+capture | grep -qF '(filter)' || fail "mode-tree filter prompt not drawn"
+$IN send-keys -l "ZEBRA" || exit 1
+$IN send-keys Enter || exit 1
+settle
+capture | grep -q 'filter: active' || fail "accepting the filter did not apply it"
+# Reopening the filter prompt prefills it with the current filter.
+$IN send-keys f || exit 1
+settle
+capture | grep -qF '(filter) ZEBRA' || \
+	fail "filter prompt not prefilled with the current filter"
+$IN send-keys Escape || exit 1
+settle
+# 'c' clears the filter.
+$IN send-keys c || exit 1
+settle
+capture | grep -q 'filter: active' && fail "'c' did not clear the filter"
+$IN send-keys q || exit 1
+settle
+
+# ===========================================================================
+# 2. Flags select the right engine behaviour.
+# ===========================================================================
+
+# --- 2a. -1 (PROMPT_SINGLE): one keystroke closes and accepts that char. ---
+reset
+$OUT send-keys M-o || exit 1
+settle
+capture | grep -qF '(one)' || fail "single prompt did not open"
+$OUT send-keys -l "q" || exit 1
+settle
+[ "$(got)" = "q" ] || fail "single prompt recovered '$(got)', wanted 'q'"
+capture | grep -qF '(one)' && fail "single prompt stayed open after one key"
+
+# --- 2b. -N (PROMPT_NUMERIC): prefilled, digits append, non-digit closes. ---
+reset
+$OUT send-keys M-n || exit 1
+settle
+capture | grep -qF '(num) 5' || fail "numeric prompt not prefilled with 5"
+$OUT send-keys -l "7" || exit 1		# 57
+$OUT send-keys Enter || exit 1		# Enter is a non-digit: close
+settle
+[ "$(got)" = "57" ] || fail "numeric accept recovered '$(got)', wanted '57'"
+# A non-digit key closes the prompt with the existing buffer, dropping the key.
+reset
+$OUT send-keys M-n || exit 1
+settle
+$OUT send-keys -l "x" || exit 1
+settle
+[ "$(got)" = "5" ] || fail "numeric non-digit close recovered '$(got)', wanted '5'"
+capture | grep -qF '(num)' && fail "numeric prompt stayed open after a non-digit"
+
+# --- 2c. -i (PROMPT_INCREMENTAL): callback fires on every edit, stays open. ---
+# The incremental code path prefixes the buffer with '=' (or +/-), so the '='
+# proves the value came through the incremental callback, not a plain accept.
+reset
+$OUT send-keys M-i || exit 1
+settle
+[ "$(got)" = "=" ] || fail "incremental prompt did not fire on open (got '$(got)')"
+$OUT send-keys -l "a" || exit 1
+settle
+[ "$(got)" = "=a" ] || fail "incremental did not fire after 'a' (got '$(got)')"
+$OUT send-keys -l "b" || exit 1
+settle
+[ "$(got)" = "=ab" ] || fail "incremental did not fire after 'b' (got '$(got)')"
+capture | grep -qF '(inc)' || fail "incremental prompt closed during editing"
+$OUT send-keys Escape || exit 1
+settle
+capture | grep -qF '(inc)' && fail "Escape did not close the incremental prompt"
+
+# --- 2d. -k (PROMPT_KEY): the next key closes and delivers its name. ---
+reset
+$OUT send-keys M-k || exit 1
+settle
+capture | grep -qF '(key)' || fail "key prompt did not open"
+$OUT send-keys -l "z" || exit 1
+settle
+[ "$(got)" = "z" ] || fail "key prompt recovered '$(got)', wanted 'z'"
+capture | grep -qF '(key)' && fail "key prompt stayed open after a key"
+
+# --- 2e. -e (PROMPT_BSPACE_EXIT): backspace on empty cancels (no accept). ---
+reset
+$OUT send-keys M-e || exit 1
+settle
+$OUT send-keys BSpace || exit 1
+settle
+[ "$(got)" = "SENTINEL" ] || fail "backspace-exit ran the accept action (got '$(got)')"
+capture | grep -qF '(bs)' && fail "backspace on empty did not close the prompt"
+
+# --- 2f. -I (prefill): prompt opens with the given buffer. ---
+reset
+$OUT send-keys M-j || exit 1
+settle
+capture | grep -qF '(pre) hello' || fail "prefill not shown (got '$(capture | grep -F '(pre)')')"
+$OUT send-keys Enter || exit 1
+settle
+[ "$(got)" = "hello" ] || fail "prefill accept recovered '$(got)', wanted 'hello'"
+
+# --- 2g. Multi prompt: accept advances to the next, both are delivered. ---
+reset
+$OUT send-keys M-m || exit 1
+settle
+capture | grep -qF 'first' || fail "first of multi prompt not shown"
+$OUT send-keys -l "X" || exit 1
+$OUT send-keys Enter || exit 1
+settle
+capture | grep -qF 'second' || fail "multi prompt did not advance to the second"
+$OUT send-keys -l "Y" || exit 1
+$OUT send-keys Enter || exit 1
+settle
+[ "$(got)" = "X/Y" ] || fail "multi prompt recovered '$(got)', wanted 'X/Y'"
+
+# ===========================================================================
+# 3. Type-scoped history and command completion.
+# ===========================================================================
+
+# --- 3a. Command history is recalled with Up; search history is separate. ---
+reset
+$OUT send-keys M-c || exit 1
+settle
+$OUT send-keys -l "alpha" || exit 1
+$OUT send-keys Enter || exit 1
+settle
+[ "$(got)" = "alpha" ] || fail "command prompt accept recovered '$(got)'"
+# Reopen the command prompt: Up recalls the command-type entry.
+$OUT send-keys M-c || exit 1
+settle
+$OUT send-keys Up || exit 1
+settle
+capture | grep -qF '(cmd) alpha' || fail "Up did not recall command history"
+$OUT send-keys Escape || exit 1
+settle
+# A search-type prompt must NOT recall the command-type entry (separate rings).
+$OUT send-keys M-h || exit 1
+settle
+$OUT send-keys Up || exit 1
+settle
+capture | grep -qF 'alpha' && fail "search prompt recalled command-type history"
+$OUT send-keys Escape || exit 1
+settle
+
+# --- 3b. Tab completion works in a command prompt (command type only). ---
+$OUT send-keys M-c || exit 1
+settle
+$OUT send-keys -l "new-w" || exit 1
+$OUT send-keys Tab || exit 1
+settle
+status_line | grep -qF 'new-window' || \
+	fail "Tab did not complete new-w to new-window (got '$(status_line)')"
+$OUT send-keys Escape || exit 1
+settle
+# A search-type prompt does not complete commands: Tab is literal / inert.
+$OUT send-keys M-h || exit 1
+settle
+$OUT send-keys -l "new-w" || exit 1
+$OUT send-keys Tab || exit 1
+settle
+status_line | grep -qF 'new-window' && fail "search prompt completed a command"
+$OUT send-keys Escape || exit 1
+settle
+
+# ===========================================================================
+# 4. Robustness: re-entrancy guard and Escape, then liveness.
+# ===========================================================================
+
+# --- 4a. A second prompt while one is open is refused (status path). ---
+client=$($IN list-clients -F '#{client_name}' | head -1)
+reset
+$OUT send-keys M-s || exit 1
+settle
+$OUT send-keys -l "AAA" || exit 1
+settle
+$IN command-prompt -t"$client" -p '(re)' "set -g @r 'REENTERED'" 2>/dev/null
+settle
+capture | grep -qF '(re)' && fail "a second status prompt opened over the first"
+status_line | grep -qF '(stat) AAA' || fail "first status prompt was disturbed"
+$OUT send-keys Escape || exit 1
+settle
+[ "$(got)" = "SENTINEL" ] || fail "Escape ran the status prompt accept action"
+
+# --- 4b. A second pane prompt while one is open is refused (pane path). ---
+reset
+$OUT send-keys M-p || exit 1
+settle
+$OUT send-keys -l "BBB" || exit 1
+settle
+$IN command-prompt -P -t"$client" -p '(re)' "set -g @r 'REENTERED'" 2>/dev/null
+settle
+capture | grep -qF '(re)' && fail "a second pane prompt opened over the first"
+capture | grep -qF '(pane) BBB' || fail "first pane prompt was disturbed"
+$OUT send-keys Escape || exit 1
+settle
+[ "$(got)" = "SENTINEL" ] || fail "Escape ran the pane prompt accept action"
+
+# --- 4c. Inner tmux survived every path and flag. ---
+$IN display-message -p '#{version}' >/dev/null 2>&1 || fail "inner tmux died"
+
+exit 0