diff --git a/agent-health-check.prose.md b/agent-health-check.prose.md
index e7a438d..ea36f55 100644
--- a/agent-health-check.prose.md
+++ b/agent-health-check.prose.md
@@ -38,7 +38,15 @@ Runs every 4 hours (2, 6, 10, 14, 18, 22 UTC at :35) via cron (`35 2,6,10,14,18,
 - ct_liveness: map of CT → active status
 - config_integrity: map of config file → valid/invalid
 
-## Execution
+(## Execution
+)
+**Execution model**: This contract is executed by a host-scheduled cron job (see
+`scripts/contract-run.sh`). The cron job runs the monitoring script directly on the
+target host and appends the result to `/var/log/contract-runs/<contract>.log`. An
+agent-session acknowledgement (a `done:` line in the ops status log) is NOT
+execution — it only proves the agent read the result and reported it. The actual
+monitoring work happens in the host cron job.
+
 
 ### check-health
 
diff --git a/disk-gc-threat-response.prose.md b/disk-gc-threat-response.prose.md
index a18a081..49023e6 100644
--- a/disk-gc-threat-response.prose.md
+++ b/disk-gc-threat-response.prose.md
@@ -159,7 +159,15 @@ from the `report_only_guests` YAML block above.
 - `timeout`: 300 seconds per CT (GC may take time on large docker hosts)
 - `retry`: 2 attempts for SSH failures before marking a CT unreachable
 
-## Execution
+(## Execution
+)
+**Execution model**: This contract is executed by a host-scheduled cron job (see
+`scripts/contract-run.sh`). The cron job runs the monitoring script directly on the
+target host and appends the result to `/var/log/contract-runs/<contract>.log`. An
+agent-session acknowledgement (a `done:` line in the ops status log) is NOT
+execution — it only proves the agent read the result and reported it. The actual
+monitoring work happens in the host cron job.
+
 
 ### Host filesystems: report-only, NEVER auto-delete
 
diff --git a/infrastructure-monitoring.prose.md b/infrastructure-monitoring.prose.md
index 52b1ac6..bb5db97 100644
--- a/infrastructure-monitoring.prose.md
+++ b/infrastructure-monitoring.prose.md
@@ -101,7 +101,15 @@ GPU .8 (RTX 3090)    GPU .110 (RTX 5070)   GPU .15 (Strix Halo)
 - LiteLLM metrics (requests, tokens, latency, errors) visible alongside GPU metrics
 - Stack persists across reboots (systemd for exporters, Docker restart policy)
 
-## Execution
+(## Execution
+)
+**Execution model**: This contract is executed by a host-scheduled cron job (see
+`scripts/contract-run.sh`). The cron job runs the monitoring script directly on the
+target host and appends the result to `/var/log/contract-runs/<contract>.log`. An
+agent-session acknowledgement (a `done:` line in the ops status log) is NOT
+execution — it only proves the agent read the result and reported it. The actual
+monitoring work happens in the host cron job.
+
 
 ### Liveness rule (scoped)
 
diff --git a/litellm-health.prose.md b/litellm-health.prose.md
index 0c95c1b..af7c5aa 100644
--- a/litellm-health.prose.md
+++ b/litellm-health.prose.md
@@ -110,7 +110,15 @@ contracts — read them there. Do not re-add retired names (`gemma-4-12b`, `gpu-
 | harness-grafana | grafana/grafana | :3000→:3001 | /api/health |
 | harness-prometheus | prom/prometheus | :9090 | /-/healthy |
 
-## Execution
+(## Execution
+)
+**Execution model**: This contract is executed by a host-scheduled cron job (see
+`scripts/contract-run.sh`). The cron job runs the monitoring script directly on the
+target host and appends the result to `/var/log/contract-runs/<contract>.log`. An
+agent-session acknowledgement (a `done:` line in the ops status log) is NOT
+execution — it only proves the agent read the result and reported it. The actual
+monitoring work happens in the host cron job.
+
 
 1. **Read parameters** — Use provided values or defaults
 
diff --git a/pm2-self-heal.prose.md b/pm2-self-heal.prose.md
index 01a7d00..c386a44 100644
--- a/pm2-self-heal.prose.md
+++ b/pm2-self-heal.prose.md
@@ -50,7 +50,15 @@ description: >
   This was the root cause of the 18-restart accumulation. Threshold raised
   and PM2 counter reset on 2026-06-28.
 
-## Execution
+(## Execution
+)
+**Execution model**: This contract is executed by a host-scheduled cron job (see
+`scripts/contract-run.sh`). The cron job runs the monitoring script directly on the
+target host and appends the result to `/var/log/contract-runs/<contract>.log`. An
+agent-session acknowledgement (a `done:` line in the ops status log) is NOT
+execution — it only proves the agent read the result and reported it. The actual
+monitoring work happens in the host cron job.
+
 
 1. **Check PM2 status** — Run `pm2 status --no-color` and parse the table (5th data column = PID, 8th = restarts, 9th = status)
 2. **Check abiba-telegram** (safe to auto-restart):
diff --git a/scripts/contract-run.sh b/scripts/contract-run.sh
index f58461b..0203f52 100755
--- a/scripts/contract-run.sh
+++ b/scripts/contract-run.sh
@@ -12,7 +12,7 @@
 #   zulip-health              -> scripts/zulip-monitor.sh
 #   agent-health-check        -> scripts/agent-health-check.py
 #   litellm-health            -> scripts/litellm-health-check.py
-#   disk-gc-threat-response   -> (Python script, needs investigation)
+#   disk-gc-threat-response   -> scripts/disk-gc-scan.py
 #   pm2-self-heal             -> scripts/pm2-self-heal.sh
 #
 # Exit codes:
diff --git a/scripts/proxmox-monitor.sh b/scripts/proxmox-monitor.sh
index 68b9010..ff18a7c 100755
--- a/scripts/proxmox-monitor.sh
+++ b/scripts/proxmox-monitor.sh
@@ -79,8 +79,11 @@ if [ "$PBS_GC_OUTPUT" = "000" ]; then
     echo "  🔴 PBS GC: probe-failed: storepve:192.168.68.6 (expected JSON, got 000)"
     FAILED+=("pbs-gc")
 else
-    # Parse the JSON to get storepve-datastore's state
-    # last-run-endtime: epoch timestamp of last completion (0 when not run or in progress)
+    # Parse the JSON to get storepve-datastore's state with four distinct outcomes:
+    # 1. probe-failed: non-zero ssh status / empty / unparseable JSON
+    # 2. running: collection in progress (last-run-endtime absent or 0, but upid present)
+    # 3. stale: no completed run within 48h
+    # 4. healthy: completed within 48h
     PBS_GC_RESULT=$(echo "$PBS_GC_OUTPUT" | python3 -c "
 import sys, json
 try:
@@ -88,41 +91,64 @@ try:
     for store in data:
         if store['store'] == 'storepve-datastore':
             endtime = store.get('last-run-endtime')
+            upid = store.get('upid')
             pending = store.get('pending-bytes', 0)
+
+            # State 2: Running (collection in progress) — last-run-endtime absent while run is in progress
+            if (endtime is None or endtime == 0) and upid is not None:
+                print(f'running|{pending}')
+                break
+
+            # State 3: No completed run (never-run or stale)
             if endtime is None or endtime == 0:
-                print('never-run')
-            else:
-                print(f'{endtime}|{pending}')
+                print(f'no-completed-run|{pending}')
+                break
+
+            # States 3 & 4: Completed (has endtime)
+            print(f'completed|{endtime}|{pending}')
             break
     else:
-        print('absent')
+        print(f'absent|0')
 except json.JSONDecodeError:
-    print('unparseable')
+    print(f'unparseable|0')
 " 2>/dev/null)
     
-    if [ -z "$PBS_GC_RESULT" ] || [ "$PBS_GC_RESULT" = "unparseable" ]; then
+    # Parse the state|endtime|pending format
+    PBS_GC_STATE=$(echo "$PBS_GC_RESULT" | cut -d'|' -f1)
+    
+    if [ "$PBS_GC_STATE" = "unparseable" ]; then
+        # State 1: probe-failed (unparseable JSON)
         echo "  🔴 PBS GC: probe-failed: storepve:192.168.68.6 (unparseable JSON)"
         FAILED+=("pbs-gc")
-    elif [ "$PBS_GC_RESULT" = "absent" ]; then
-        echo "  🔴 PBS GC: never-run (storepve-datastore not found in GC list)"
+    elif [ "$PBS_GC_STATE" = "absent" ]; then
+        # State 1: probe-failed (store not found)
+        echo "  🔴 PBS GC: probe-failed: storepve:192.168.68.6 (storepve-datastore not found)"
         FAILED+=("pbs-gc")
-    elif [ "$PBS_GC_RESULT" = "never-run" ]; then
-        echo "  🔴 PBS GC: never-run (storepve-datastore has no last-run-endtime)"
+    elif [ "$PBS_GC_STATE" = "running" ]; then
+        # State 2: collection in progress — do NOT fail
+        PENDING_BYTES=$(echo "$PBS_GC_RESULT" | cut -d'|' -f2)
+        echo "  ⏳ PBS GC: running (started: in-progress, pending-bytes: ${PENDING_BYTES} B)"
+    elif [ "$PBS_GC_STATE" = "no-completed-run" ]; then
+        # State 3: no completed run within 48h
+        PENDING_BYTES=$(echo "$PBS_GC_RESULT" | cut -d'|' -f2)
+        echo "  🔴 PBS GC: no completed run within 48h (pending-bytes: ${PENDING_BYTES} B)"
         FAILED+=("pbs-gc")
     else
-        # Parse the endtime|pending format
-        LAST_RUN_ENDTIME=$(echo "$PBS_GC_RESULT" | cut -d'|' -f1)
-        PENDING_BYTES=$(echo "$PBS_GC_RESULT" | cut -d'|' -f2)
+        # States 3 & 4: completed (has endtime)
+        LAST_RUN_ENDTIME=$(echo "$PBS_GC_RESULT" | cut -d'|' -f2)
+        PENDING_BYTES=$(echo "$PBS_GC_RESULT" | cut -d'|' -f3)
         
         # Convert epoch to age in hours
         NOW_EPOCH=$(date -u +%s)
         AGE_HOURS=$(( (NOW_EPOCH - LAST_RUN_ENDTIME) / 3600 ))
         
         if [ $AGE_HOURS -gt 48 ]; then
-            echo "  🔴 PBS GC: stale (last run ${AGE_HOURS}h ago, pending-bytes: ${PENDING_BYTES} B)"
+            # State 3: stale (no completed run within 48h)
+            echo "  🔴 PBS GC: stale — last completed run was ${AGE_HOURS}h ago (pending-bytes: ${PENDING_BYTES} B)"
             FAILED+=("pbs-gc")
         else
-            echo "  ✅ PBS GC: healthy (last run ${AGE_HOURS}h ago, pending-bytes: ${PENDING_BYTES} B)"
+            # State 4: healthy (completed within 48h)
+            echo "  ✅ PBS GC: healthy — last completed run ${AGE_HOURS}h ago (pending-bytes: ${PENDING_BYTES} B)"
         fi
     fi
 fi
diff --git a/tests/test_pbs_gc_states.sh b/tests/test_pbs_gc_states.sh
new file mode 100755
index 0000000..f116471
--- /dev/null
+++ b/tests/test_pbs_gc_states.sh
@@ -0,0 +1,81 @@
+#!/bin/bash
+# test_pbs_gc_states.sh — Tests for PBS GC four-state logic
+
+set -uo pipefail
+
+TEST_DIR="$(cd "$(dirname "$0")" && pwd)"
+SCRIPTS_DIR="$(dirname "$TEST_DIR")/scripts"
+PROXMOX_MONITOR="${1:-${SCRIPTS_DIR}/proxmox-monitor.sh}"
+
+PASS=0
+FAIL=0
+
+run_test() {
+    local name="$1"
+    local json="$2"
+    local pattern="$3"
+    local behavior="$4"
+    
+    local wrapper monitor
+    wrapper=$(mktemp /tmp/pbs-test-wrapper.XXXXXX)
+    monitor=$(mktemp /tmp/pbs-test-monitor.XXXXXX)
+    
+    printf '%s\n' "$json" > "$wrapper"
+    cp "$PROXMOX_MONITOR" "$monitor"
+    
+    # Replace the SSH call with cat "$wrapper"
+    python3 /tmp/replace_ssh.py "$wrapper" "$monitor"
+    
+    local output exit_code
+    output=$(bash "$monitor" 2>&1)
+    exit_code=$?
+    
+    local ok=true
+    if [ "$behavior" = "fail" ]; then
+        if ! echo "$output" | grep -q "🔴 PBS GC"; then ok=false; fi
+        if [ $exit_code -eq 0 ]; then ok=false; fi
+    else
+        if ! echo "$output" | grep -q "$pattern"; then ok=false; fi
+        if echo "$output" | grep -q "🔴 PBS GC"; then ok=false; fi
+    fi
+    
+    if $ok; then
+        echo "  ✅ $name"
+        PASS=$((PASS + 1))
+    else
+        echo "  🔴 $name FAILED (exit=$exit_code)"
+        echo "$output" | grep "PBS GC" | sed 's/^/     /'
+        FAIL=$((FAIL + 1))
+    fi
+    
+    rm -f "$wrapper" "$monitor"
+}
+
+echo "=== PBS GC Four-State Tests ==="
+echo "Script: $PROXMOX_MONITOR"
+echo ""
+
+echo "1. probe-failed (unparseable JSON)"
+run_test "unparseable-json" "NOT JSON {{{" "probe-failed" "fail"
+
+echo "2. probe-failed (store not found)"
+run_test "store-missing" '[{"store": "other", "last-run-endtime": 1000}]' "probe-failed" "fail"
+
+echo "3. probe-failed (empty body)"
+run_test "empty-body" "" "probe-failed" "fail"
+
+echo "4. running (in progress - upid set, no last-run-endtime)"
+run_test "running" '[{"store": "storepve-datastore", "upid": "UPID:123:1:456:gc:root@pam", "pending-bytes": 100}]' "⏳ PBS GC: running" "pass"
+
+echo "5. stale (last run >48h)"
+STALE=$(date -u -d "50 hours ago" +%s)
+run_test "stale" "[{\"store\": \"storepve-datastore\", \"last-run-endtime\": $STALE, \"pending-bytes\": 200}]" "stale" "fail"
+
+echo "6. healthy (completed <48h)"
+HEALTHY=$(date -u -d "1 hour ago" +%s)
+run_test "healthy" "[{\"store\": \"storepve-datastore\", \"last-run-endtime\": $HEALTHY, \"pending-bytes\": 0}]" "✅ PBS GC: healthy" "pass"
+
+echo ""
+echo "=== Results: $PASS passed, $FAIL failed ==="
+[ $FAIL -eq 0 ] && echo "✅ All passed" || echo "🔴 Some failed"
+[ $FAIL -eq 0 ] && exit 0 || exit 1
diff --git a/zulip-health.prose.md b/zulip-health.prose.md
index c28fbfb..0e0202d 100644
--- a/zulip-health.prose.md
+++ b/zulip-health.prose.md
@@ -125,7 +125,15 @@ grep -c "async def edit_message" ~/.hermes/plugins/*/zulip*/adapter.py
 - **On `zulip-status` command**: Run on-demand and report to user
 - **On critical alert**: Escalate to relay message immediately, don't wait for schedule
 
-## Execution
+(## Execution
+)
+**Execution model**: This contract is executed by a host-scheduled cron job (see
+`scripts/contract-run.sh`). The cron job runs the monitoring script directly on the
+target host and appends the result to `/var/log/contract-runs/<contract>.log`. An
+agent-session acknowledgement (a `done:` line in the ops status log) is NOT
+execution — it only proves the agent read the result and reported it. The actual
+monitoring work happens in the host cron job.
+
 
 ### Liveness rule (scoped)