diff --git a/docs/changelog-20260710-carve-gua-hang-fix.md b/docs/changelog-20260710-carve-gua-hang-fix.md
new file mode 100644
index 0000000..595ddf4
--- /dev/null
+++ b/docs/changelog-20260710-carve-gua-hang-fix.md
@@ -0,0 +1,48 @@
+# Changelog 2026-07-10 -- DOCFIX-181: carve_gua subnet-enumeration hang + harness watchdog
+
+**Context.** After the Stage-1 commit, the full `scripts/run-tests-all.sh`
+gauntlet was seen to HANG on `tests/dc-dc-prefixes-import/`. Investigated per
+operator request ("check into this now so it's not a problem later"). Root cause
+is a real bug in the target script, not an environment quirk -- and the harness's
+own claimed "40/40 PASS" was never actually reached (it was hanging).
+
+## Root cause
+
+`netbox/dc-dc-prefixes-import.py::carve_gua()` built
+`list(dc_gua_prefix.subnets(new_prefix=64))` -- materializing EVERY /64 in the
+GUA prefix, then returning only the first. D-101's own GUA example is a `/40`
+(`2602:f3e2:1000::/40`), which has `2**(64-40) = 16,777,216` /64 subnets, so the
+`list()` allocates ~16.7M `IPv6Network` objects -> effective hang / OOM. This is
+NOT test-only: a real import run with a realistic GUA prefix would hang
+identically. (`carve_ula` is safe -- it carves /48->/56->/64, bounded at 256.)
+
+Diagnosed with `faulthandler.dump_traceback_later`, which pointed straight at
+`carve_gua` line 306 inside `ipaddress.subnets()`.
+
+## Fix
+
+- **`netbox/dc-dc-prefixes-import.py::carve_gua`** -- take the first /64 LAZILY
+  with `next(dc_gua_prefix.subnets(new_prefix=64))` (O(1)) instead of
+  `list(...)[0]`. Same result, no enumeration.
+- **`tests/dc-dc-prefixes-import/test_logic.py`** -- added a
+  `faulthandler.dump_traceback_later(30, exit=True)` watchdog at import time, so
+  any FUTURE blocking regression in this Python test self-aborts after 30s with a
+  stack trace (non-zero exit) rather than hanging the whole gauntlet silently.
+
+## Verification
+- `bash tests/dc-dc-prefixes-import/run-tests.sh` -> `ALL PASS (40 checks)` in
+  ~0.05s (previously: hung indefinitely, never completing).
+- `bash scripts/repo-lint.sh` -> 0 fail.
+- Full `scripts/run-tests-all.sh` gauntlet now runs to completion.
+
+## Revert
+- `git checkout netbox/dc-dc-prefixes-import.py tests/dc-dc-prefixes-import/test_logic.py`
+  to the pre-DOCFIX-181 revision, plus
+  `git rm docs/changelog-20260710-carve-gua-hang-fix.md`.
+  (Reverting reinstates the hang -- do not, without replacing the fix.)
+
+## Note
+- The pre-existing ledger claim of "dc-dc-prefixes-import 40/40" was optimistic:
+  the end-to-end path had been hanging, so those checks never actually ran to a
+  green count until this fix. The watchdog prevents that class of false-green
+  (a hang read as "still running") from recurring.
diff --git a/docs/session-ledger.md b/docs/session-ledger.md
index a86fde7..735ab46 100644
--- a/docs/session-ledger.md
+++ b/docs/session-ledger.md
@@ -1601,8 +1601,22 @@
   init/required_providers + Step-9 -input=false and 13-resource plan. Changelog
   `docs/changelog-20260710-phase0-runbook-as-executed.md`. repo-lint 0 fail.
 - **Numbers after DOCFIX-180:** DOCFIX next-free 181 (re-scan before assigning).
-- **STAGE 1 CLOSED. Deliverables DOCFIX-178/179/180 ready to commit** (operator
-  ruled: commit). Next: Stage 2 (dc-dc-phase1-office1-standup) when directed.
+- **STAGE 1 CLOSED + COMMITTED.** Branch `dc-dc-stage1-phase0-first-exec`
+  (340ac58): DOCFIX-178/179/180. NOT pushed. Git identity set repo-local
+  (JANeumatrix/jesse.austin@neumatrix.com, matching prior commits) -- this host
+  had none.
+- **DELIVERED -- DOCFIX-181: `carve_gua` subnet-enumeration hang FIXED.** The full
+  `run-tests-all.sh` gauntlet was HANGING on `tests/dc-dc-prefixes-import` (its
+  long-claimed "40/40" was never actually reached -- it hung). Root cause:
+  `netbox/dc-dc-prefixes-import.py::carve_gua()` did
+  `list(prefix.subnets(new_prefix=64))` -- ~16.7M /64 objects for a /40 GUA --
+  when it only uses the first. Fixed with `next()` (O(1)); added a
+  `faulthandler.dump_traceback_later(30, exit=True)` watchdog to `test_logic.py`
+  so any future hang self-aborts with a traceback instead of stalling the
+  gauntlet. Harness 40/40 in 0.05s; full gauntlet now completes green.
+  Changelog `docs/changelog-20260710-carve-gua-hang-fix.md`. Next-free -> 182.
+- **Next: Stage 2** (`dc-dc-phase1-office1-standup`) when directed -- watch gap
+  #17 (per-site ISP-uplink/WAN net; `wan` is now a candidate model).
 
 <!-- END: jumphost -->
 
diff --git a/netbox/dc-dc-prefixes-import.py b/netbox/dc-dc-prefixes-import.py
index 9bf69db..999aa84 100644
--- a/netbox/dc-dc-prefixes-import.py
+++ b/netbox/dc-dc-prefixes-import.py
@@ -302,9 +302,13 @@
 
 
 def carve_gua(dc_gua_prefix: ipaddress.IPv6Network) -> dict:
-    # Only provider-public carries GUA in the current family matrix.
-    gua_64_candidates = list(dc_gua_prefix.subnets(new_prefix=64))
-    return {"provider-public": str(gua_64_candidates[0])}
+    # Only provider-public carries GUA in the current family matrix. Take the
+    # FIRST /64 LAZILY: a realistic GUA prefix (D-101's own example is a /40)
+    # has 2**24 = ~16.7M /64 subnets, so list(...subnets(new_prefix=64)) would
+    # materialize them all and hang/OOM. next() over the generator is O(1).
+    # (DOCFIX-181 -- found by the harness hanging on the /40 test input.)
+    first_64 = next(dc_gua_prefix.subnets(new_prefix=64))
+    return {"provider-public": str(first_64)}
 
 
 # -----------------------------------------------------------------------------
diff --git a/tests/dc-dc-prefixes-import/test_logic.py b/tests/dc-dc-prefixes-import/test_logic.py
index 13821a5..67f489e 100644
--- a/tests/dc-dc-prefixes-import/test_logic.py
+++ b/tests/dc-dc-prefixes-import/test_logic.py
@@ -20,6 +20,15 @@
 import os
 import sys
 
+import faulthandler
+
+# Watchdog: self-abort WITH a traceback after 30s instead of hanging the whole
+# run-tests-all.sh gauntlet if any test ever blocks. This is exactly how the
+# carve_gua /40 subnet-enumeration hang (DOCFIX-181) was diagnosed; now a future
+# blocking regression fails loudly (non-zero exit + stack dump) rather than
+# stalling the gauntlet indefinitely.
+faulthandler.dump_traceback_later(30, exit=True)
+
 HERE = os.path.dirname(os.path.abspath(__file__))
 REPO_ROOT = os.path.dirname(os.path.dirname(HERE))
 STUB_SYSPATH = os.path.join(HERE, "stub_syspath")