fix(issue-25): reuse a promoted plan only with --plan-file; drop the implicit newest-plan load

Without --plan, Phase 1 resolved a planner session automatically and globbed
<workspace_root>/.agents/reports/<planner>/plan-*.md for the newest file by
mtime, handing it to the Creator as "the plan already agreed on". Both keys are
wrong: the report directory belongs to a session, not to this task, so other
issues' plans pile up in it, and right after a clone or checkout mtime is
checkout order. 47 such plans are committed in this repository, so an ordinary
run could silently implement against an unrelated design.

Reuse is explicit now. --plan-file <path> is the only way to load an existing
plan; it is resolved against the control root, checked before a single job
exists, and refused if the file is missing, not a regular file, unreadable or
empty (an empty file would quietly turn into a "no plan" prompt). It cannot be
combined with --plan, and --review-only warns and ignores it because no
implementation job is delegated there. The implementation prompt itself is
unchanged, so the Creator's contract does not move.

Phase 1 now says which plan it loaded and where from, or that it loaded none.
The legacy shell loop (MAM_LOOP_PY=0) loses the same auto-load and rejects
--plan-file rather than duplicating the check on a path that is on its way out.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

.agents/skills/multi-agent-mux-loop/scripts/run_loop.sh

@@ -32,6 +32,7 @@ TARGET_AGENT=""
 TASK=""
 REVIEWER_LIST=""
 PLANNER_SESSION_OVERRIDE=""
+LOOP_PLAN_FILE=""
 LOOP_WORKTREE=""
 LOOP_BASE=""
 LOOP_REVIEW_ONLY=0
@@ -46,6 +47,7 @@ usage() {
   echo "  --plan                 Enable Planner agent intervention & design phase"
   echo "  --planner <name>       Planner session (requires --plan; default: auto-resolve)"
   echo "  --plan-talk N          Planner-Creator discussion limit turns (default: 1)"
+  echo "  --plan-file <path>     Reuse an existing plan file, relative to the control root (not with --plan)"
   echo "  --reviewer \"A,B\"       Targeted reviewer session name list (comma-separated)"
   echo "  --all-reviewer         Enforce PASS verdict from all active reviewer sessions"
   echo "  --max-loop N           Max execution-review corrective loop runs (default: 3)"
@@ -92,6 +94,7 @@ while [[ "$#" -gt 0 ]]; do
       exit 1
       ;;
     --planner) PLANNER_SESSION_OVERRIDE="$2"; shift 2 ;;
+    --plan-file) LOOP_PLAN_FILE="$2"; shift 2 ;;
     --task) TASK="$2"; shift 2 ;;
     --worktree) LOOP_WORKTREE="$2"; shift 2 ;;
     --base) LOOP_BASE="$2"; shift 2 ;;
@@ -121,11 +124,14 @@ fi
 
 # Issue #21 (D12): the legacy shell loop assumes a cwd-relative .mam/jobs and
 # diffs the checkout it runs in; the worktree/base options are Python-only.
+# Issue #25 (D9): --plan-file is too - its fail-closed check lives in the
+# runner and is not duplicated in a path that is on its way out.
 # Checked before the freeze and the loop lock (log_* are not defined yet).
 if [ "${MAM_LOOP_PY:-1}" = "0" ] && { [ -n "$LOOP_WORKTREE" ] || [ -n "$LOOP_BASE" ] \
      || [ "$LOOP_REVIEW_ONLY" = "1" ] || [ -n "${MAM_LOOP_WORKTREE:-}" ] \
-     || [ -n "$LOOP_REVIEW_ISOLATION" ] || [ -n "$LOOP_REMOTE_REVIEW" ]; }; then
-  echo "ERROR: --worktree/--base/--review-only/--review-isolation/--remote-review require the Python loop (MAM_LOOP_PY=1)" >&2
+     || [ -n "$LOOP_REVIEW_ISOLATION" ] || [ -n "$LOOP_REMOTE_REVIEW" ] \
+     || [ -n "$LOOP_PLAN_FILE" ]; }; then
+  echo "ERROR: --worktree/--base/--review-only/--review-isolation/--remote-review/--plan-file require the Python loop (MAM_LOOP_PY=1)" >&2
   exit 1
 fi
 
@@ -560,16 +566,11 @@ if [ "$PLAN_MODE" = true ]; then
   log_success "Interactive planning completed. Plan finalized."
 else
   log_info "=== Phase 1: Self-Planning Mode (Direct Execution) ==="
-  EXISTING_PLAN_FILE=""
-  if [ -n "$PLANNER_SESSION" ]; then
-    # Promoted plans are saved as plan-<job-id>.md by the Phase 3 promotion
-    # step below, not report-final.md; pick the most recently promoted one.
-    EXISTING_PLAN_FILE=$(ls -t ".agents/reports/$PLANNER_SESSION"/plan-*.md 2>/dev/null | head -n 1 || true)
-  fi
-  if [ -n "$EXISTING_PLAN_FILE" ] && [ -f "$EXISTING_PLAN_FILE" ]; then
-    log_info "Found existing promoted plan at '$EXISTING_PLAN_FILE'. Loading plan..."
-    CURRENT_PLAN=$(cat "$EXISTING_PLAN_FILE")
-  fi
+  # Issue #25 (D1/D9): no plan is loaded here. This used to take the newest
+  # promoted plan of the auto-resolved planner, keyed on mtime and on a session
+  # that says nothing about this task. Reuse is explicit and Python-only now
+  # (--plan-file), and this path rejects that option above.
+  log_info "No plan loaded; the Creator plans by itself."
 fi
 
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