fix(tools/tmux): unique per-invocation paste buffer; track auto-submit-drafts.sh

Upstream the 2026-07-09 live hot-fix from web1: send-message.sh used a fixed
tmux buffer name (__mosaic_send) shared by all concurrent senders on one
server — load-buffer overwrote load-buffer and paste-buffer -d deleted
underneath peers, cross-delivering or dropping messages. Bit the fleet during
the simultaneous restart (standing briefs swapped between sessions). Buffer
name is now unique per invocation (PID + nanoseconds).

Also brings auto-submit-drafts.sh (coordinator draft-flush watchdog, until now
only a loose file in the deployed ~/.config/mosaic/tools/tmux/) under source
control, and extends test-send-message-socket.sh with a concurrency lock:
5 parallel sends to distinct panes, asserting no drop and no cross-delivery.
The lock fails 3/3 runs against the pre-fix script and passes post-fix.

Without this, the next framework redeploy would regress the live fix.

packages/mosaic/framework/tools/tmux/auto-submit-drafts.sh

@@ -0,0 +1,80 @@
+#!/usr/bin/env bash
+# auto-submit-drafts.sh — watchdog for Claude Code panes that receive channel
+# messages but leave them as unsubmitted prompt drafts. Intended for Mos only.
+set -uo pipefail
+
+TARGET="${1:-mos-claude}"
+INTERVAL="${INTERVAL:-2}"
+STABLE_SECONDS="${STABLE_SECONDS:-4}"
+LOG_PREFIX="[auto-submit-drafts:$TARGET]"
+
+last_prompt=""
+first_seen=0
+
+prompt_text() {
+  tmux capture-pane -t "$TARGET" -p 2>/dev/null | python3 -c '
+import sys, re
+lines = sys.stdin.read().splitlines()
+idx = None
+for i in range(len(lines)-1, -1, -1):
+    if "❯" in lines[i]:
+        idx = i
+        break
+if idx is None:
+    raise SystemExit
+parts = []
+after = lines[idx].split("❯", 1)[1]
+parts.append(after)
+for line in lines[idx+1:]:
+    # Stop at Claude Code separator/border lines.
+    if "─" in line or "╰" in line or "╭" in line:
+        break
+    s = line.replace("\u00a0", " ")
+    s = re.sub(r"[\x00-\x1f\x7f]", "", s).strip()
+    if s:
+        parts.append(s)
+text = " ".join(parts).replace("\u00a0", " ")
+text = re.sub(r"[\x00-\x1f\x7f]", "", text).strip()
+print(text)
+'
+}
+
+while true; do
+  if ! tmux has-session -t "$TARGET" 2>/dev/null; then
+    echo "$LOG_PREFIX target missing; waiting" >&2
+    sleep "$INTERVAL"
+    last_prompt=""
+    first_seen=0
+    continue
+  fi
+
+  current="$(prompt_text || true)"
+  now="$(date +%s)"
+
+  if [[ -z "$current" ]]; then
+    last_prompt=""
+    first_seen=0
+    sleep "$INTERVAL"
+    continue
+  fi
+
+  if [[ "$current" != "$last_prompt" ]]; then
+    last_prompt="$current"
+    first_seen="$now"
+    sleep "$INTERVAL"
+    continue
+  fi
+
+  age=$(( now - first_seen ))
+  if (( age >= STABLE_SECONDS )); then
+    echo "$LOG_PREFIX submitting stable draft after ${age}s: ${current:0:120}" >&2
+    tmux send-keys -t "$TARGET" C-j
+    sleep 0.8
+    tmux send-keys -t "$TARGET" C-m
+    sleep 2
+    last_prompt=""
+    first_seen=0
+  else
+    sleep "$INTERVAL"
+  fi
+done