diff --git a/engine/hooks/hooks.toml b/engine/hooks/hooks.toml
index 7c8f4268..82d9d6be 100644
--- a/engine/hooks/hooks.toml
+++ b/engine/hooks/hooks.toml
@@ -212,6 +212,11 @@ summary = "Stops drift after the user narrowed the task twice."
 enabled_by = "CATSTACK_REFLECT_ENFORCEMENT"
 rule_modes = { "scope-lock.prompt-instruction" = "warn", "scope-lock.reflection-acknowledged" = "warn" }
 
+[hooks.spreadsheet-completeness-guard]
+mode = "stop"
+why_mode = "attention"
+summary = "Blocks spreadsheet completion claims without source-backed entity coverage."
+
 [hooks.scratchpad-collision]
 mode = "stop"
 why_mode = "outward"
diff --git a/engine/hooks/spreadsheet-completeness-guard/README.md b/engine/hooks/spreadsheet-completeness-guard/README.md
new file mode 100644
index 00000000..b8cd9959
--- /dev/null
+++ b/engine/hooks/spreadsheet-completeness-guard/README.md
@@ -0,0 +1,8 @@
+# spreadsheet-completeness-guard
+
+Stop hook for spreadsheet completion claims. A completion claim must carry a
+source-backed `SPREADSHEET_COVERAGE: PASS` receipt from the expected-entity
+validator. Missing observations must be explicitly classified; estimates and
+zeros are not substitutes for absent competitor data.
+
+Tests: `python3 -m unittest discover -s engine/hooks/spreadsheet-completeness-guard/tests -v`
diff --git a/engine/hooks/spreadsheet-completeness-guard/claude.hook.json b/engine/hooks/spreadsheet-completeness-guard/claude.hook.json
new file mode 100644
index 00000000..3562a0c9
--- /dev/null
+++ b/engine/hooks/spreadsheet-completeness-guard/claude.hook.json
@@ -0,0 +1,5 @@
+{
+  "hooks": {
+    "Stop": [{"matcher": "*", "hooks": [{"type": "command", "command": "python3 $HOME/.claude/hooks/spreadsheet-completeness-guard/claude_stop_check.py", "timeout": 10}]}]
+  }
+}
diff --git a/engine/hooks/spreadsheet-completeness-guard/claude_stop_check.py b/engine/hooks/spreadsheet-completeness-guard/claude_stop_check.py
new file mode 100644
index 00000000..4a4d8806
--- /dev/null
+++ b/engine/hooks/spreadsheet-completeness-guard/claude_stop_check.py
@@ -0,0 +1,10 @@
+#!/usr/bin/env python3
+from __future__ import annotations
+import os
+import sys
+sys.path.insert(0, os.path.join(os.path.dirname(os.path.dirname(os.path.abspath(__file__))), "_sdk"))
+from detect import detect  # noqa: E402
+from runtime import run_hook  # noqa: E402
+
+if __name__ == "__main__":
+    run_hook("spreadsheet-completeness-guard", "claude", detect, "Stop", json_error_stderr=False)
diff --git a/engine/hooks/spreadsheet-completeness-guard/codex.hook.json b/engine/hooks/spreadsheet-completeness-guard/codex.hook.json
new file mode 100644
index 00000000..447e5ad2
--- /dev/null
+++ b/engine/hooks/spreadsheet-completeness-guard/codex.hook.json
@@ -0,0 +1,5 @@
+{
+  "hooks": {
+    "Stop": [{"matcher": "*", "hooks": [{"type": "command", "command": "python3 $HOME/.codex/hooks/spreadsheet-completeness-guard/codex_stop_check.py", "timeout": 10}]}]
+  }
+}
diff --git a/engine/hooks/spreadsheet-completeness-guard/codex_stop_check.py b/engine/hooks/spreadsheet-completeness-guard/codex_stop_check.py
new file mode 100644
index 00000000..dd667ce5
--- /dev/null
+++ b/engine/hooks/spreadsheet-completeness-guard/codex_stop_check.py
@@ -0,0 +1,10 @@
+#!/usr/bin/env python3
+from __future__ import annotations
+import os
+import sys
+sys.path.insert(0, os.path.join(os.path.dirname(os.path.dirname(os.path.abspath(__file__))), "_sdk"))
+from detect import detect  # noqa: E402
+from runtime import run_hook  # noqa: E402
+
+if __name__ == "__main__":
+    run_hook("spreadsheet-completeness-guard", "codex", detect, "Stop")
diff --git a/engine/hooks/spreadsheet-completeness-guard/cursor.hook.json b/engine/hooks/spreadsheet-completeness-guard/cursor.hook.json
new file mode 100644
index 00000000..8705fc89
--- /dev/null
+++ b/engine/hooks/spreadsheet-completeness-guard/cursor.hook.json
@@ -0,0 +1,5 @@
+{
+  "hooks": {
+    "stop": [{"command": "python3 $HOME/.cursor/hooks/spreadsheet-completeness-guard/cursor_stop_check.py", "timeout": 10}]
+  }
+}
diff --git a/engine/hooks/spreadsheet-completeness-guard/cursor_stop_check.py b/engine/hooks/spreadsheet-completeness-guard/cursor_stop_check.py
new file mode 100644
index 00000000..d586b3f5
--- /dev/null
+++ b/engine/hooks/spreadsheet-completeness-guard/cursor_stop_check.py
@@ -0,0 +1,10 @@
+#!/usr/bin/env python3
+from __future__ import annotations
+import os
+import sys
+sys.path.insert(0, os.path.join(os.path.dirname(os.path.dirname(os.path.abspath(__file__))), "_sdk"))
+from detect import detect  # noqa: E402
+from runtime import run_hook  # noqa: E402
+
+if __name__ == "__main__":
+    run_hook("spreadsheet-completeness-guard", "cursor", detect, "stop")
diff --git a/engine/hooks/spreadsheet-completeness-guard/detect.py b/engine/hooks/spreadsheet-completeness-guard/detect.py
new file mode 100644
index 00000000..62b6b32d
--- /dev/null
+++ b/engine/hooks/spreadsheet-completeness-guard/detect.py
@@ -0,0 +1,55 @@
+"""Stop completion claims for spreadsheet work without a coverage receipt."""
+from __future__ import annotations
+
+import re
+import sys
+from pathlib import Path
+
+sys.path.insert(0, str(Path(__file__).resolve().parents[1] / "_sdk"))
+from finding import Finding  # noqa: E402
+
+RULE_INCOMPLETE = "spreadsheet-completeness-guard.incomplete"
+SPREADSHEET_RE = re.compile(r"\b(?:spreadsheet|google sheet|google sheets|workbook|raw tab|aggregation table|chart)\b", re.I)
+COMPLETION_RE = re.compile(r"\b(?:complete|completed|done|filled|populated|regenerated|ready|all competitors)\b", re.I)
+RECEIPT_RE = re.compile(r"SPREADSHEET_COVERAGE\s*:\s*PASS\b", re.I)
+FAIL_RE = re.compile(r"SPREADSHEET_COVERAGE\s*:\s*FAIL\b", re.I)
+
+
+def claims_completion(message: str) -> bool:
+    return bool(SPREADSHEET_RE.search(message or "") and COMPLETION_RE.search(message or ""))
+
+
+def has_receipt(message: str) -> bool:
+    return bool(RECEIPT_RE.search(message or ""))
+
+
+def decide(payload: dict) -> Finding | None:
+    message = str(payload.get("last_assistant_message") or payload.get("message") or "")
+    if not claims_completion(message) or has_receipt(message):
+        return None
+    try:
+        retry_count = int(payload.get("spreadsheet_retry_count") or 0)
+    except (TypeError, ValueError):
+        retry_count = 0
+    retry_count = max(0, min(retry_count, 3))
+    if FAIL_RE.search(message):
+        return Finding(
+            rule_id=RULE_INCOMPLETE,
+            subject="spreadsheet coverage failure",
+            message="Coverage failed after the bounded retry loop. Do not generate or declare the table/chart complete; list the unresolved entity/period keys.",
+            evidence=f"SPREADSHEET_COVERAGE: FAIL; retry {retry_count}/3",
+        )
+    return Finding(
+        rule_id=RULE_INCOMPLETE,
+        subject="spreadsheet completion claim",
+        message=(f"Do not declare spreadsheet data complete until the expected-entity coverage "
+                 f"validator has passed. Run source collection retry {min(retry_count + 1, 3)}/3; "
+                 "add source-backed rows or state unresolved entity/period keys. "
+                 "Only SPREADSHEET_COVERAGE: PASS permits completion."),
+        evidence=f"completion claim without a coverage receipt; retry {retry_count}/3",
+    )
+
+
+def detect(event: dict[str, object]) -> list[Finding]:
+    finding = decide(event)
+    return [] if finding is None else [finding]
diff --git a/engine/hooks/spreadsheet-completeness-guard/tests/test_hooks.py b/engine/hooks/spreadsheet-completeness-guard/tests/test_hooks.py
new file mode 100644
index 00000000..375deda3
--- /dev/null
+++ b/engine/hooks/spreadsheet-completeness-guard/tests/test_hooks.py
@@ -0,0 +1,38 @@
+import os
+import sys
+import unittest
+
+sys.path.insert(0, os.path.dirname(os.path.dirname(os.path.abspath(__file__))))
+import detect  # noqa: E402
+
+
+class SpreadsheetCompletenessTests(unittest.TestCase):
+    def test_blocks_completion_without_coverage_receipt(self):
+        finding = detect.decide({"last_assistant_message": "The spreadsheet is complete and all competitors are populated."})
+        self.assertIsNotNone(finding)
+        self.assertEqual(finding.rule_id, "spreadsheet-completeness-guard.incomplete")
+
+    def test_stays_silent_with_pass_receipt(self):
+        finding = detect.decide({"last_assistant_message": "SPREADSHEET_COVERAGE: PASS — the workbook is complete."})
+        self.assertIsNone(finding)
+
+    def test_stays_silent_for_non_spreadsheet_completion(self):
+        self.assertIsNone(detect.decide({"last_assistant_message": "The README edit is complete."}))
+
+    def test_requests_bounded_retry_when_coverage_is_missing(self):
+        finding = detect.decide({
+            "last_assistant_message": "The spreadsheet is complete.",
+            "spreadsheet_retry_count": 1,
+        })
+        self.assertIn("retry 2/3", finding.message)
+
+    def test_keeps_blocking_after_three_failed_retries(self):
+        finding = detect.decide({
+            "last_assistant_message": "SPREADSHEET_COVERAGE: FAIL — the spreadsheet is complete.",
+            "spreadsheet_retry_count": 3,
+        })
+        self.assertIn("after the bounded retry loop", finding.message)
+
+
+if __name__ == "__main__":
+    unittest.main()