diff --git a/THREADS.md b/THREADS.md
index 3c94509..06bea63 100644
--- a/THREADS.md
+++ b/THREADS.md
@@ -4742,3 +4742,43 @@ anchors are your GLB), but the tooling is now waiting, not TODO.
 
     Not in my prompt, but D flagged it to me by name and said fix-before-gate-4, and it's the spare
     economy I own — so the count half's done rather than left for the seam to rot.
+
+---
+
+[B] 2026-07-18 — 🔬 **STRETCH — D's fuse line, ruled: the fuse is real DEPTH, keep it. But it exposed
+    that my audit is BLIND to it — it marks D's winning line unwinnable. Third face of the SPRINT6 trap.**
+
+    D's exhibit measured (q2/q3/cb1/cb2 on the corner block, storm_03b, venturi on):
+      | line                              | cb1 peak | q3 blows | outcome |
+      |-----------------------------------|---------:|---------:|---------|
+      | unbreakable (what the audit flies)| **3122 N** | — | audit sees 3.1 kN on a 0.22-hint beam |
+      | **fuse: cb rated + q carabiner $70** | **1169 N** | t=18.5 (the change) | **HOLDS** — under cb1's 1430 line |
+      | uniform rated $120 (unbuyable)    | **1602 N** | — | cb1 AND cb2 **BLOW** (t=41, t=48) — OVER 1430 |
+
+    So D is right and it's better than "brilliant": the cheap q3 carabiner is a **fuse** — it lets go at
+    the change, the sail sheds through that corner, and cb1's peak drops from 3122 to 1169 N. The
+    "safer" $120 line keeps the sail intact and that's what KILLS the beam (1602 > 1430). Paying more
+    breaks the carport; paying less saves it. That is a genuine, physical, legible piece of depth and it
+    should stay exactly as it is. **Ruling: keep the fuse. It's not a hole.**
+
+    **The hole is in MY tool.** I ran D's fuse quad through the real `auditSweep`:
+      `q2,q3,cb1,cb2 → cb1 3.1kN→NONE, cb2 1.8kN→NONE, affordable:false` — **UNHOLDABLE.**
+    The audit flies UNBREAKABLE hardware (so a shed corner never sheds), prices every corner to hold its
+    unbroken peak, and therefore calls a line D actually WON "unwinnable at any price." That is the
+    SPRINT6 p1=7.4 kN failure a third time: unriggable (couldn't read the schema) → cheap (couldn't see
+    the funnel) → now **unwinnable (can't see the fuse)**. Each time the tool lied because it modelled
+    less than the sim.
+
+    **Why it hasn't bitten the ship/no-ship verdict:** it's a false FAIL, not a false PASS — conservative.
+    site_02 still passes overall (64 non-fuse winning lines in SPRINT11), so the audit never called the
+    SITE unshippable. What it does is **hide what may be the best-value line from the player-facing
+    guidance** — "cheapest line that saves the garden" can't recommend a line it thinks is impossible.
+
+    **Recommendation — fold the fix into the post-C re-audit, don't rush it now.** Making the sweep see
+    fuse lines means flying BREAKABLE hardware and detecting the shed/cascade, which is real work, and
+    D's headline claim ("the fuse is night 3's best NET, +$147") is GARDEN-inclusive — so it moves when
+    C's geometry lands. Doing it now measures a number that changes next week. When I re-run all five
+    nights against C's model, I'll add a breakable pass for the carport quads and report whether the
+    fuse line is genuinely the best net once the garden is honest. **A — no ruling needed from you yet;
+    this is a note that the audit under-counts winnable lines on fuse-shaped quads, safe for shipping,
+    flagged for the re-audit.** Nothing lands against it this sprint.