docs(lane): the GPU latch is unreachable; record what replaced L2

L7b and the GPU work, and one finding the next session should not have
to rediscover: the framing's L2 is offered as the GPU's manual-authority
witness and cannot be one. The origin survives a height-only resize with
manual_left_authority never read anywhere in that frontend, because
Q#F6's painted-before policy skips the follow whenever the caret is off
screen --- and when the caret is on screen it is inside the viewport,
where follow_left is a no-op. Both branches leave the latch unreachable.

The real gap was clause 3's clamp, and it is recorded with the number
that shows it: 960px past the maximum after a widen, most of the
viewport blank.

The entry marks L2's wording as owed to the FRAMING rather than the
code, and says explicitly that deleting the GPU's four inert writes
versus giving them a reader is a framing decision. Recording it as owed
rather than settling it in passing is the point --- an approved contract
does not get amended by whoever notices it is wrong.

docs/active-work.md

@@ -319,7 +319,7 @@ Framing
 this base, the panel-replay prerequisite recorded as DISCHARGED by #243,
 and the both-axis effect witness still owed.
 
-**Landed so far** (latest verified code head `deb3f0b`)**:** B1's per-target fractional
+**Landed so far** (latest verified code head `ec6444e`)**:** B1's per-target fractional
 wheel residual (the producer), B2's daemon-side horizontal panel leg,
 B3/B7's shared `scroll_window_columns` with its saturated bound and wrap
 pin, B4's middle-click PRIMARY paste, **B6's minimap wheel routing**,
@@ -430,9 +430,36 @@ assertion that looked strict and was not:
   origin, which is exactly the state the row claims cannot
   discriminate. The probe requires `col < last_content_cols`.
 
-**Still owed on this axis: L7b (content shrink), and the GPU's entire
-read side with L2 and L5's GPU leg.** The GPU's four writes remain
-inert until something consults them.
+**L7b landed at `feda851`** — clause 3's content half, the shrink that
+lowers `widest − viewport` with the viewport untouched, asserted on the
+exact new bound and firing on both the release mutation and an
+off-by-one.
+
+### The GPU's latch is unreachable, and its real gap was the clamp
+
+`ec6444e`. **The framing's L2 cannot witness what it is offered for.**
+It proposes wheel-sideways then a height-only resize as the GPU's
+manual-authority row. Measured before anything was added: the origin
+survives that resize with `manual_left_authority` **never read anywhere
+in the frontend**. Q#F6's painted-before policy is what preserves it —
+`resize` runs `ensure_caret_painted` only when the caret was painted,
+and a caret scrolled off screen is not painted, so the follow that
+would snap the origin back never runs. When the caret IS painted it is
+inside the viewport, where `follow_left` returns the origin it was
+given. **The latch is unreachable on this frontend by either branch.**
+
+What the GPU actually lacked was clause 3's clamp, for the same reason:
+nothing brought the origin DOWN when the maximum fell, because the only
+code that would is the follow that is skipped in that state.
+**Measured: scroll to the right bound at 640px, widen to 1600px, and
+the origin stayed 960px past the new maximum** — most of the viewport
+blank, the text off its left edge. `clamp_code_scroll_left` now sits at
+`reshape`'s tail, beside B5's icon hook and for the same reason.
+
+**Owed to the framing, not to the code: L2's wording**, which promises a
+witness this frontend cannot provide. The GPU's four `manual_left_authority`
+writes are still read by nothing; whether they should be deleted or given
+a reader is a framing decision, not one to take in passing.
 
 **Landed but NOT yet witnessed:**