iter2 Fix 1: invalidate format cache on DestroyContext + REQBUFS(0) on CAPTURE in resolution-change path

Fix 1 of iteration 2 per phase4_iter2_plan.md.

Adds surface_reset_format_cache() exposed from src/surface.h. Called
from RequestDestroyContext after the dual REQBUFS(0). Without this,
multi-video Firefox sessions on mozilla.org corrupted the next
session's CAPTURE format query: the kernel reset to defaults but
our LAST_OUTPUT_WIDTH/HEIGHT cache still said 'already 1920x1088,'
so the next G_FMT returned 48x48 and the exported descriptor
encoded wrong pitch/offset.

Also adds REQBUFS(0) on CAPTURE in the resolution-change path of
RequestCreateSurfaces2 (Sonnet Phase 5 review iter2 9.1). The
existing code only did REQBUFS(0) on OUTPUT before re-S_FMTting;
hantro derives CAPTURE format from OUTPUT format, so leftover
CAPTURE buffers from the prior resolution would also block the
implicit format change. Pre-existing bug surfaced by Sonnet's
audit; Fix 3 pool refactor would have exposed it more often.

Limitation noted in surface.h docblock: the LAST_OUTPUT_WIDTH/
HEIGHT cache is a static process-global, so concurrent multi-
context use still races (Sonnet 7.3 / 9.6). Iteration 2 only
addresses sequential sessions. Multi-context safety is iteration 3+.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/surface.h

@@ -126,4 +126,24 @@ VAStatus RequestExportSurfaceHandle(VADriverContextP context,
 				    VASurfaceID surface_id, uint32_t mem_type,
 				    uint32_t flags, void *descriptor);
 
+/*
+ * Iteration 2 Fix 1: invalidate the LAST_OUTPUT_WIDTH/HEIGHT cache used
+ * by RequestCreateSurfaces2 to skip redundant v4l2_set_format calls.
+ *
+ * Must be called when the kernel's CAPTURE format state is no longer
+ * guaranteed to match what we last set on OUTPUT — at minimum, on
+ * RequestDestroyContext after REQBUFS(0). Without this, Firefox
+ * playing a multi-video page (mozilla.org with 864-wide intro
+ * videos at varying resolutions) corrupts the next session's CAPTURE
+ * format query: the cache says "already 1920x1088" while the kernel
+ * has reset to defaults, our subsequent G_FMT returns 48x48, and the
+ * exported descriptor encodes wrong pitch/offset.
+ *
+ * Limitation (Sonnet Phase 5 review 7.3 / 9.6): the cache is a
+ * static process-global, so concurrent multi-context use still races.
+ * Iteration 2 only addresses sequential sessions. Multi-context
+ * safety is iteration 3+ scope.
+ */
+void surface_reset_format_cache(void);
+
 #endif