add workaround for river wm rotation issue

CLAUDE.md

@@ -76,6 +76,32 @@ pixels. `render_output()` allocates a device-pixel buffer of `width * scale` and
 shorter output dimension (`att_grid()`), which is what makes rotation and arbitrary aspect ratios
 work with no special cases.
 
+**Output resize / rotation** — the surface size comes from `configure` and *only* from `configure`:
+ext-session-lock makes a buffer that does not match the acked size a `dimensions_mismatch` error,
+which kills the client and leaves the session locked with nothing drawing on it. So the locker can
+never resize itself on its own initiative.
+
+That matters because not every compositor reconfigures. River 0.4.5 configures a lock surface once,
+when it is created, and never again (`LockSurface.create()` is the only `configure()` call site, and
+nothing in `Output.zig` re-issues one), so rotating or re-moding an output used to leave the locker
+painting at the old size, clipped to the overlap. `att_lock` therefore watches `wl_output`
+(`mode`/`geometry`/`scale`), and if the output changed shape but no configure arrives within
+`RESIZE_GRACE_MS`, `recreate_lock_surface()` destroys the lock surface and makes a new one for the
+same output, which forces a fresh configure at the current size. The lock object is untouched, so
+the session stays locked across the swap.
+
+Two guards keep this from misfiring, and both matter:
+
+- The change detector compares `wl_output` values against a snapshot of `wl_output` values taken at
+  the last configure (`cfg_*`), never against the configured surface size. On a fractionally scaled
+  output the integer `wl_output.scale` cannot reproduce the logical size, so those two would never
+  match and every idle moment would look like a pending resize.
+- `retry_*` records the geometry a recreate was already attempted for, so a compositor that ignores
+  the recreate is nagged once instead of being put in a destroy/create loop.
+
+A compositor that does send a configure never reaches any of this: by the time the grace period
+expires the snapshot matches again and `outputs_recheck_geometry()` does nothing.
+
 **Pattern model** (`src/pattern.c`) — a sequence of dot indices (`row * 4 + col`). `pattern_add()`
 implements the Android rule that unvisited dots lying exactly on the straight line between the
 previous and new dot get captured first, using the gcd of the row/col delta. `pattern_to_string()`