feat(flush): add auto mode with self-injected /clear for unattended runs

Long autonomous sessions bloat or hit auto-compaction because /clear is a prompt keystroke no tool call can execute. Auto mode closes that gap: after the write-verified checkpoint, the agent derives its own tmux pane, arms self-inject.sh through tmux run-shell -b, and ends the turn so /clear and a resume line land at an idle prompt. The server-owned arm is load-bearing: a detached child of a tool call dies at the turn boundary. The pane must be derived before arming because ancestry detection can't work under the tmux server.

self-inject.sh joins the synced scripts with a six-test bats suite, tmux stubbed at the boundary. work-the-backlog now auto-flushes between tasks when context grows heavy, and its speedrun preset gained the per-item disposition rule: feature-level work gets a spec, unguessable decisions get a VERIFY, well-defined tasks get implemented. The mechanism was proven live in another project's session and its design note is preserved under docs/design/.

1 files changed, 68 insertions, 0 deletions

diff --git a/.ai/scripts/self-inject.sh b/.ai/scripts/self-inject.sh
new file mode 100755
index 0000000..e7340c1
--- /dev/null
+++ b/.ai/scripts/self-inject.sh
@@ -0,0 +1,68 @@
+#!/bin/sh
+# self-inject.sh — type text into the tmux pane running this agent session.
+#
+# The building block for AUTO-FLUSH: an agent checkpoints its session-context,
+# then has tmux type "/clear" and a resume prompt at its own idle prompt, so a
+# session flushes with no human at the keyboard.
+#
+# Usage:
+#   self-inject.sh -t %PANE <delay> <text> [<delay2> <text2> ...]
+#   self-inject.sh <delay> <text> [...]          # derive pane from ancestry
+#   self-inject.sh [-t %PANE]                    # no pairs: report the pane
+#
+# Each pair: sleep <delay> seconds, then type <text> literally and press Enter.
+#
+# TWO HARD-WON GOTCHAS (2026-07-02, archsetup session):
+# 1. A detached child (setsid/nohup/&) of an agent tool call DIES when the
+#    tool call ends — the harness cleans up the process group. The arm step
+#    must run under the tmux SERVER instead:
+#      tmux run-shell -b "self-inject.sh -t %1 25 '/clear' 15 'go — resume...'"
+# 2. Under tmux run-shell the process is a child of the tmux server, so
+#    ancestry-based pane detection CANNOT work there. Derive the pane FIRST,
+#    synchronously from the agent's own shell (no -t), then pass it
+#    explicitly with -t when arming.
+#
+# Collision hazard: if the user happens to be typing when the send fires, the
+# injected text merges into their input line (a real /clear became "/clearto"
+# mid-word). Auto-flush is for sessions running unattended; warn the user to
+# keep hands off for the armed window if they're present.
+
+PANE=""
+if [ "$1" = "-t" ]; then
+    PANE=$2; shift 2
+fi
+
+ppid_of() {
+    # /proc/<pid>/stat: pid (comm) state ppid ... — comm may contain spaces,
+    # so take the 2nd field after the LAST ')'.
+    stat=$(cat "/proc/$1/stat" 2>/dev/null) || return 1
+    # shellcheck disable=SC2086  # word-splitting the stat tail is the point
+    set -- ${stat##*) }
+    echo "$2"
+}
+
+find_pane() {
+    anc=" "
+    pid=$$
+    while [ -n "$pid" ] && [ "$pid" -gt 1 ] 2>/dev/null; do
+        anc="$anc$pid "
+        pid=$(ppid_of "$pid") || break
+    done
+    tmux list-panes -a -F "#{pane_pid} #{pane_id}" 2>/dev/null | \
+    while read -r ppid pane; do
+        case "$anc" in *" $ppid "*) echo "$pane"; break;; esac
+    done
+}
+
+[ -n "$PANE" ] || PANE=$(find_pane)
+[ -n "$PANE" ] || { echo "self-inject: no owning pane found (pass -t %PANE)" >&2; exit 1; }
+
+# With no delay/text pairs, just report the pane (the derive-first step).
+[ $# -ge 2 ] || { echo "$PANE"; exit 0; }
+
+while [ $# -ge 2 ]; do
+    sleep "$1"
+    tmux send-keys -t "$PANE" -l "$2"
+    tmux send-keys -t "$PANE" Enter
+    shift 2
+done