feat(implement-issue): make child agent dispatch agent-agnostic

- Add formal arg syntax: --agent, --base, --force
- Add process-tree detection scripts (Linux / macOS) to auto-detect parent agent
- Add dispatch table supporting pi, opencode, goose, codex, claude + unknown fallback
- Write child prompt to temp file instead of inline escaping
- Name tmux windows for discoverability
- Add new pre-flight checks: tmux session, agent detection, binary on PATH

common/engineering/implement-issue/detect-agent-linux.sh

@@ -0,0 +1,44 @@
+#!/usr/bin/env bash
+# Walk the process tree upward from $PPID to find a known agent binary.
+# Outputs the agent name on stdout if found, exits 0.
+# Outputs nothing and exits 1 if no known agent is found.
+
+set -euo pipefail
+
+# Dispatch table: binary names we recognize.
+KNOWN_AGENTS="pi opencode goose codex claude"
+
+pid=$PPID
+
+while [ "$pid" -gt 1 ]; do
+    # Read command name and parent PID from /proc.
+    comm=$(cat /proc/$pid/comm 2>/dev/null) || { pid=1; continue; }
+    ppid=$(awk '{print $4}' /proc/$pid/stat 2>/dev/null) || ppid=1
+
+    # Direct match against known binaries.
+    for agent in $KNOWN_AGENTS; do
+        if [ "$comm" = "$agent" ]; then
+            echo "$agent"
+            exit 0
+        fi
+    done
+
+    # If the process is node or bun, inspect cmdline for agent script paths.
+    case "$comm" in
+        node|bun)
+            cmdline=$(tr '\0' ' ' < /proc/$pid/cmdline 2>/dev/null) || cmdline=""
+            for agent in $KNOWN_AGENTS; do
+                case "$cmdline" in
+                    *"$agent"*)
+                        echo "$agent"
+                        exit 0
+                        ;;
+                esac
+            done
+            ;;
+    esac
+
+    pid=$ppid
+done
+
+exit 1