feat: land the revision-preflight guard, fixed and wired into contract execution

A contract verdict is only meaningful if it came from the merged copy. The
fleet has been bitten three times on 2026-09-25 (a clone parked on a merged
feature branch while executing from another clone; a script copied into the
runner clone by hand; a stale local origin/master making an ancestry check
report unlanded work). The control for this existed as an untracked draft and
protected nobody, because it was entirely fail-open.

Defect in the draft, preserved verbatim as tests/fixtures/revision-preflight.prefix.sh:

  git -C "$CLONE" show "origin/master:$(basename "$SCRIPT")"

basename drops the scripts/ prefix, so for any script under scripts/ it queried
the repo root, failed, took the "warn but don't block" branch and exited 0 -
passing a script that exists in no revision at all. Reproduced:
  pre-fix + scripts/demo.sh under scripts/  -> 'could not resolve', EXIT=0
  pre-fix + a script in no revision          -> EXIT=0

Fixed guard (scripts/revision-preflight.sh):
* resolves the repo-relative path inside the clone, so scripts/ paths resolve;
* FAILS CLOSED - a path absent from the ref, an unresolvable ref, or a failed
  fetch is a failure, never a warning;
* fetches the remote by default, because a stale local ref would otherwise
  pass a stale script as current; --no-fetch states the assumption instead of
  hiding it.

Wiring (scripts/contract-run.sh): before executing, the wrapper runs the guard
against the clone it lives in. Default CONTRACT_REVISION_PREFLIGHT=enforce
withholds the verdict, alerts and exits 2 on mismatch; =warn logs and
continues; =off skips. Verified live: match -> contract proceeds and PASSes;
mismatch -> 'VERDICT WITHHELD', exit 2; =warn -> continues.

Pinning (docs/contract-execution-pinning.md): every contract pins the clone
contract-run.sh lives in - the deployed runner being /opt/contract-runner on
CT 100. Documented that daily-health-digest has no contract file at all, which
is why its execution copy was silently operator-chosen.

Tests: tests/test_revision_preflight.sh, 15 assertions over a throwaway clone
with a real bare remote. It runs the pre-fix draft against the same cases and
shows it passing a ghost script, so the tests provably bite.

shellcheck: scripts/revision-preflight.sh and the new test are clean. The three
findings remaining in contract-run.sh (SC2086 x2, SC2034) are pre-existing and
byte-identical on master.

scripts/contract-run.sh

@@ -18,6 +18,14 @@
 #   litellm-health            -> scripts/litellm-health-check.py
 #   disk-gc-threat-response   -> scripts/disk-gc-scan.py
 #   pm2-self-heal             -> scripts/pm2-self-heal.sh
+#   search-stack-visibility   -> scripts/search-stack-check.py
+#
+# Execution copy: every contract pins the clone this script lives in (see
+# docs/contract-execution-pinning.md). Before a contract runs, this wrapper
+# proves the script it is about to execute byte-matches origin/master:
+#   CONTRACT_REVISION_PREFLIGHT=enforce (default) refuse to report on mismatch
+#   CONTRACT_REVISION_PREFLIGHT=warn            log the mismatch and continue
+#   CONTRACT_REVISION_PREFLIGHT=off             skip the check entirely
 #
 # Exit codes:
 #   0 = contract passed
@@ -111,6 +119,35 @@ echo "Started: $(date -u '+%Y-%m-%d %H:%M:%S UTC')" | tee -a "$LOG_FILE"
 echo "Script: $SCRIPT_PATH" | tee -a "$LOG_FILE"
 echo "" | tee -a "$LOG_FILE"
 
+# ── Revision preflight ───────────────────────────────────────────────────────
+# A verdict is only meaningful if it came from the merged copy. Refuse to report
+# one from a mismatched or unverifiable copy; that is a probe failure (exit 2),
+# not a contract verdict, because the result would be untrustworthy.
+# See docs/contract-execution-pinning.md.
+REVISION_PREFLIGHT_MODE="${CONTRACT_REVISION_PREFLIGHT:-enforce}"
+REPO_ROOT="$(cd "${SCRIPTS_DIR}/.." && pwd)"
+if [ "$REVISION_PREFLIGHT_MODE" != "off" ] && [ -x "${SCRIPTS_DIR}/revision-preflight.sh" ]; then
+    if "${SCRIPTS_DIR}/revision-preflight.sh" "$SCRIPT_PATH" "$REPO_ROOT" 2>&1 | tee -a "$LOG_FILE"; then
+        :
+    elif [ "$REVISION_PREFLIGHT_MODE" = "warn" ]; then
+        echo "⚠️  revision preflight failed — continuing because CONTRACT_REVISION_PREFLIGHT=warn" | tee -a "$LOG_FILE"
+    else
+        echo "🚫 VERDICT WITHHELD: executing copy does not match the merged revision" | tee -a "$LOG_FILE"
+        ALERT_MSG="🔴 Contract $CONTRACT_NAME: revision mismatch — verdict withheld. Log: $LOG_FILE"
+        ZULIP_API_URL="${ZULIP_API_URL:-https://chat.sysloggh.net/api/v1}"
+        ZULIP_API_KEY="${ZULIP_API_KEY:-}"
+        ZULIP_USER="${ZULIP_USER:-abiba-bot@chat.sysloggh.net}"
+        if [ -n "$ZULIP_API_KEY" ] && command -v curl &> /dev/null; then
+            curl -sf -X POST "${ZULIP_API_URL}/messages" \
+                -u "${ZULIP_USER}:${ZULIP_API_KEY}" \
+                -d "type=private" \
+                -d "to=9" \
+                -d "content=${ALERT_MSG}" > /dev/null 2>&1 || true
+        fi
+        exit 2
+    fi
+fi
+
 # Use timeout to prevent hangs (10 minutes default)
 TIMEOUT=600
 timeout "$TIMEOUT" $INTERPRETER "$SCRIPT_PATH" 2>&1 | tee -a "$LOG_FILE"

scripts/revision-preflight.sh

@@ -0,0 +1,128 @@
+#!/usr/bin/env bash
+# revision-preflight.sh — prove the copy a contract is about to execute is the
+# copy that is merged.
+#
+# Usage:
+#   revision-preflight.sh [options] <script-path> <clone-path>
+#
+# Options:
+#   --ref <ref>   Ref to compare against (default: origin/master)
+#   --no-fetch    Do not refresh the ref first (see FRESHNESS below)
+#   --quiet       Print nothing on success
+#   -h, --help    Show this help
+#
+# Exit codes:
+#   0  the executing script byte-matches <ref>:<repo-relative-path>
+#   1  MISMATCH, or the revision could not be resolved (see FAIL CLOSED)
+#
+# FRESHNESS
+#   A guard is only as good as the ref it compares against. On 2026-09-25 a
+#   stale local origin/master made an ancestry check on this fleet report
+#   "unlanded work" for a branch that had in fact merged, and it would equally
+#   have passed a stale script as current. So by default this guard FETCHES the
+#   remote before comparing. With --no-fetch it compares against whatever the
+#   local ref points at and says so out loud; it never silently assumes
+#   freshness.
+#
+# FAIL CLOSED
+#   An unresolvable path or ref is a FAILURE, never a warning. "Cannot verify"
+#   is precisely the state a stale or hand-edited copy produces, so treating it
+#   as success would defeat the guard. The original draft of this script did
+#   exactly that: it resolved the master revision with
+#   `git show origin/master:$(basename "$SCRIPT")`, which drops the scripts/
+#   prefix, queries the repo root, fails, and exited 0 — passing a script that
+#   exists in no revision at all.
+#
+# WHICH CLONE
+#   Pass the clone the contract is actually executing from. See
+#   docs/contract-execution-pinning.md for which clone each contract pins.
+
+set -euo pipefail
+
+REF="origin/master"
+FETCH=1
+QUIET=0
+
+usage() {
+    sed -n '2,45p' "$0" | sed 's/^# \{0,1\}//'
+}
+
+while [[ $# -gt 0 ]]; do
+    case "$1" in
+        --ref)
+            [[ $# -ge 2 ]] || { echo "revision-preflight: --ref needs a value" >&2; exit 1; }
+            REF="$2"; shift 2 ;;
+        --no-fetch) FETCH=0; shift ;;
+        --quiet) QUIET=1; shift ;;
+        -h|--help) usage; exit 0 ;;
+        --) shift; break ;;
+        -*) echo "revision-preflight: unknown option: $1" >&2; exit 1 ;;
+        *) break ;;
+    esac
+done
+
+if [[ $# -lt 2 ]]; then
+    usage >&2
+    exit 1
+fi
+
+SCRIPT="$1"
+CLONE="$2"
+
+say() { [[ $QUIET -eq 1 ]] || echo "$@" >&2; }
+fail() { echo "❌ revision-preflight: $*" >&2; exit 1; }
+
+# ── 1. inputs must exist ──────────────────────────────────────────────────────
+[[ -f "$SCRIPT" ]] || fail "executing script not found: $SCRIPT"
+[[ -d "$CLONE" ]] || fail "clone path is not a directory: $CLONE"
+git -C "$CLONE" rev-parse --git-dir >/dev/null 2>&1 \
+    || fail "not a git clone: $CLONE"
+
+# ── 2. resolve the repo-relative path (the original defect) ───────────────────
+CLONE_ABS=$(cd "$CLONE" && pwd)
+SCRIPT_ABS=$(cd "$(dirname "$SCRIPT")" && pwd)/$(basename "$SCRIPT")
+case "$SCRIPT_ABS" in
+    "$CLONE_ABS"/*) REL="${SCRIPT_ABS#"$CLONE_ABS"/}" ;;
+    *) fail "script is outside the clone: $SCRIPT_ABS is not under $CLONE_ABS" ;;
+esac
+
+# ── 3. refresh the ref so staleness cannot mask a stale script ────────────────
+if [[ $FETCH -eq 1 ]]; then
+    REMOTE="${REF%%/*}"
+    [[ "$REMOTE" == "$REF" ]] && REMOTE="origin"
+    if ! git -C "$CLONE" fetch --quiet "$REMOTE" 2>/dev/null; then
+        fail "cannot fetch '$REMOTE' in $CLONE — refusing to verify against a possibly stale '$REF'. Re-run with network access, or pass --no-fetch to compare against the local ref deliberately."
+    fi
+else
+    say "⚠️  revision-preflight: --no-fetch — comparing against the LOCAL '$REF'; freshness is assumed, not verified"
+fi
+
+# ── 4. resolve the merged revision; unresolvable is a failure ────────────────
+git -C "$CLONE" rev-parse --verify --quiet "$REF" >/dev/null \
+    || fail "ref '$REF' does not resolve in $CLONE"
+REF_COMMIT=$(git -C "$CLONE" rev-parse --short "$REF")
+
+TMPFILE=$(mktemp)
+trap 'rm -f "$TMPFILE"' EXIT
+
+if ! git -C "$CLONE" show "$REF:$REL" > "$TMPFILE" 2>/dev/null; then
+    fail "'$REL' does not exist in $REF ($REF_COMMIT) — cannot verify $SCRIPT. A path that is absent from $REF can never be a merged copy."
+fi
+
+# ── 5. compare ───────────────────────────────────────────────────────────────
+EXEC_SHA=$(sha256sum "$SCRIPT" | cut -d' ' -f1)
+MERGED_SHA=$(sha256sum "$TMPFILE" | cut -d' ' -f1)
+
+if [[ "$EXEC_SHA" != "$MERGED_SHA" ]]; then
+    {
+        echo "❌ revision-preflight: MISMATCH — refusing to report from this copy"
+        echo "   script:   $SCRIPT_ABS"
+        echo "   clone:    $CLONE_ABS"
+        echo "   executed: $EXEC_SHA"
+        echo "   merged:   $MERGED_SHA  ($REF:$REL @ $REF_COMMIT)"
+    } >&2
+    exit 1
+fi
+
+say "✅ revision-preflight: $REL matches $REF @ $REF_COMMIT ($EXEC_SHA)"
+exit 0