fix: extract lib/formula-session.sh to eliminate duplicate code blocks

Shared helpers for formula-driven cron agents: lock, memory guard,
formula loading, context building, session startup, crash recovery.

- planner-run.sh uses shared helpers instead of inline code
- gardener-agent.sh delegates crash recovery to formula_phase_callback
- agent-smoke.sh updated for renamed planner script + new lib file

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

lib/formula-session.sh

@@ -0,0 +1,125 @@
+#!/usr/bin/env bash
+# formula-session.sh — Shared helpers for formula-driven cron agents
+#
+# Provides reusable functions for the common cron-wrapper + tmux-session
+# pattern used by planner-run.sh and gardener-agent.sh.
+#
+# Functions:
+#   acquire_cron_lock   LOCK_FILE          — PID lock with stale cleanup
+#   check_memory        [MIN_MB]           — skip if available RAM too low
+#   load_formula        FORMULA_FILE       — sets FORMULA_CONTENT
+#   build_context_block FILE [FILE ...]    — sets CONTEXT_BLOCK
+#   start_formula_session SESSION WORKDIR PHASE_FILE — create tmux + claude
+#   formula_phase_callback PHASE           — standard crash-recovery callback
+#
+# Requires: lib/agent-session.sh sourced first (for create_agent_session,
+# agent_kill_session, agent_inject_into_session).
+# Globals used by formula_phase_callback: SESSION_NAME, PHASE_FILE,
+# PROJECT_REPO_ROOT, PROMPT (set by the calling script).
+
+# ── Cron guards ──────────────────────────────────────────────────────────
+
+# acquire_cron_lock LOCK_FILE
+# Acquires a PID lock. Exits 0 if another instance is running.
+# Sets an EXIT trap to clean up the lock file.
+acquire_cron_lock() {
+  _CRON_LOCK_FILE="$1"
+  if [ -f "$_CRON_LOCK_FILE" ]; then
+    local lock_pid
+    lock_pid=$(cat "$_CRON_LOCK_FILE" 2>/dev/null || true)
+    if [ -n "$lock_pid" ] && kill -0 "$lock_pid" 2>/dev/null; then
+      log "run: already running (PID $lock_pid)"
+      exit 0
+    fi
+    rm -f "$_CRON_LOCK_FILE"
+  fi
+  echo $$ > "$_CRON_LOCK_FILE"
+  trap 'rm -f "$_CRON_LOCK_FILE"' EXIT
+}
+
+# check_memory [MIN_MB]
+# Exits 0 (skip) if available memory is below MIN_MB (default 2000).
+check_memory() {
+  local min_mb="${1:-2000}"
+  local avail_mb
+  avail_mb=$(free -m | awk '/Mem:/{print $7}')
+  if [ "${avail_mb:-0}" -lt "$min_mb" ]; then
+    log "run: skipping — only ${avail_mb}MB available (need ${min_mb})"
+    exit 0
+  fi
+}
+
+# ── Formula loading ──────────────────────────────────────────────────────
+
+# load_formula FORMULA_FILE
+# Reads formula TOML into FORMULA_CONTENT. Exits 1 if missing.
+load_formula() {
+  local formula_file="$1"
+  if [ ! -f "$formula_file" ]; then
+    log "ERROR: formula not found: $formula_file"
+    exit 1
+  fi
+  # shellcheck disable=SC2034  # consumed by the calling script
+  FORMULA_CONTENT=$(cat "$formula_file")
+}
+
+# build_context_block FILE [FILE ...]
+# Reads each file from $PROJECT_REPO_ROOT and builds CONTEXT_BLOCK.
+build_context_block() {
+  CONTEXT_BLOCK=""
+  local ctx ctx_path
+  for ctx in "$@"; do
+    ctx_path="${PROJECT_REPO_ROOT}/${ctx}"
+    if [ -f "$ctx_path" ]; then
+      CONTEXT_BLOCK="${CONTEXT_BLOCK}
+### ${ctx}
+$(cat "$ctx_path")
+"
+    fi
+  done
+}
+
+# ── Session management ───────────────────────────────────────────────────
+
+# start_formula_session SESSION WORKDIR PHASE_FILE
+# Kills stale session, resets phase file, creates new tmux + claude session.
+# Returns 0 on success, 1 on failure.
+start_formula_session() {
+  local session="$1" workdir="$2" phase_file="$3"
+  agent_kill_session "$session"
+  rm -f "$phase_file"
+  log "Creating tmux session: ${session}"
+  if ! create_agent_session "$session" "$workdir" "$phase_file"; then
+    log "ERROR: failed to create tmux session ${session}"
+    return 1
+  fi
+}
+
+# formula_phase_callback PHASE
+# Standard crash-recovery phase callback for formula sessions.
+# Requires globals: SESSION_NAME, PHASE_FILE, PROJECT_REPO_ROOT, PROMPT.
+# Uses _FORMULA_CRASH_COUNT (auto-initialized) for single-retry limit.
+# shellcheck disable=SC2154  # SESSION_NAME, PHASE_FILE, PROJECT_REPO_ROOT, PROMPT set by caller
+formula_phase_callback() {
+  local phase="$1"
+  log "phase: ${phase}"
+  case "$phase" in
+    PHASE:crashed)
+      if [ "${_FORMULA_CRASH_COUNT:-0}" -gt 0 ]; then
+        log "ERROR: session crashed again after recovery — giving up"
+        return 0
+      fi
+      _FORMULA_CRASH_COUNT=$(( ${_FORMULA_CRASH_COUNT:-0} + 1 ))
+      log "WARNING: tmux session died unexpectedly — attempting recovery"
+      if create_agent_session "${_MONITOR_SESSION:-$SESSION_NAME}" "$PROJECT_REPO_ROOT" "$PHASE_FILE" 2>/dev/null; then
+        agent_inject_into_session "${_MONITOR_SESSION:-$SESSION_NAME}" "$PROMPT"
+        log "Recovery session started"
+      else
+        log "ERROR: could not restart session after crash"
+      fi
+      ;;
+    PHASE:done|PHASE:failed|PHASE:needs_human|PHASE:merged)
+      agent_kill_session "${_MONITOR_SESSION:-$SESSION_NAME}"
+      ;;
+  esac
+}