fix: a file view states its pin once, so the axis holds still

`set_data_pin()` takes a range and `pin_event_window()` a pre/post
split; the file view handed the split to both. On a recording whose
stamps start before zero that stored a pin that no longer held the
data, so every second frame found the pin wrong and stated it in full
again -- rewriting the group's x range and discarding the user's
gesture with it. The view alternated between the file's span and the
corrupted one at the frame rate: a flicker in which no pan, zoom or
click survived. `[drop-probe]` now reports the view and the count of
pin statements, which must stay at two for a whole run.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

docs/claude/probe-readings.md

@@ -997,7 +997,7 @@ configuration that carries settings, is the defect this exists for — a saved h
 ## `[drop-probe]`
 
 ```
-[drop-probe] signals=4 channels=4 rows=4 slots0=[sine|||]
+[drop-probe] signals=4 channels=4 rows=4 slots0=[sine|||] view=[-3.999690..15.999670] repins=2
 [drop-probe] dropped signal 0 -> 1 slots=[sine|sine||]
 [drop-probe] dropped signal 1 -> 1 slots=[sine|sine|square|]
 ```
@@ -1007,6 +1007,8 @@ configuration that carries settings, is the defect this exists for — a saved h
 | `rows` | the column count, capped at `RowSet::kMaxRows` — one row per trace | rows sized four signals to one row: the only row fills and *every* drop is refused ("plot 1 already holds four signals"), which reads as a scope that cannot plot anything |
 | `dropped … -> 1` | 1, and the row gains that trace | a drop that cannot find a free slot, or a signal with no channel to bind |
 | `channels` | one per signal | a file whose columns did not become channels, so nothing can be plotted at all |
+| `view` | the file's own span, or whatever the user last zoomed to — never a *sub-range of it the user did not ask for* | a pin that no longer holds the data: `view=[3.999690..15.999670]` against a file spanning `[-4..16]` is the pin written as a pre/post split where a range belongs |
+| `repins` | **2**, for the whole run, however long | the file view stating its pin per frame instead of refreshing its numbers. Each statement writes the group's range, so the axis alternates between the file's span and the pin's and no gesture survives: `repins=116` at three seconds is one per frame, and it reads on screen as a flicker in which nothing can be clicked |
 
 ## `[events]`