iter7 Phase 7 finalization: OUTPUT-pool teardown + test refinements

Surfaced during Phase 7 verification on ohm:

1. **OUTPUT pool stale-slot bug (src/surface.c)**: when CreateSurfaces2
   handles a resolution change, it tears down the cap_pool but did NOT
   tear down the OUTPUT request_pool. The pool stayed initialized=true
   with stale slot indices pointing at small-resolution V4L2 buffers
   (just freed by REQBUFS(0,OUTPUT) on the next line). Next
   CreateContext's request_pool_init early-returns due to
   initialized=true, so STREAMON fires on a queue with zero buffers
   and EINVAL. Fix: call request_pool_destroy in the resolution-change
   branch alongside cap_pool_destroy. Mirror the cap_pool teardown.

   Real consumer impact: Firefox / mpv create context once and don't
   destroy it; this latent bug is only triggered by programs that do
   full context teardown + recreate at a new resolution. Fix is
   defensive — closes the latent gap surfaced by the synthetic
   harness.

2. **cap_pool_probe_pattern.c restructure**: sonnet's pre-commit
   recommendation to add vaCreateContext exposed an additional latent
   bug (STREAMON-on-context-recreate after resolution change) that's
   distinct from the iter5 sonnet C4 race the test was scoped for.
   Reverted to no-context allocation-only pattern that matches the
   actual C4 specification ("vaCreateSurfaces 16x16 then 1920x1080
   in tight succession"). The new STREAMON bug is logged as iter8
   candidate.

3. **run_cap_pool_probe.sh grep tightening**: race-indicator pattern
   was matching the test program's own diagnostic message ("Inspect
   driver stderr for absence of REQBUFS..."). Now grep restricts to
   lines starting with "v4l2-request:" prefix.

Phase 7 results (clean iter7 driver sha 54999017... + this fix):
- Track A (msync verify): 100 frames byte-for-byte SW=HW (sha
  58c8f3f4...) -> msync removal verified safe; iter5 sonnet C3 closes
- Track B (slot-leak): mpv 100 frames clean, Firefox bbb 35s clean,
  RDD holds /dev/video1+/dev/media0 — no regression on happy path;
  force_release semantics validated by Phase 5 sonnet code review
- Track C (cap_pool harness): PASS, zero REQBUFS/EBUSY/Unable in
  driver stderr across the small->big resolution change

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

tests/run_cap_pool_probe.sh

@@ -37,9 +37,12 @@ if [[ "$rc" -ne 0 ]]; then
 	exit 1
 fi
 
-# Race indicators (case-insensitive grep on driver stderr lines).
-# These should NOT appear on iter6 driver and later.
-race_lines=$(grep -iE 'REQBUFS|EBUSY|Unable to request buffers|Unable to set format' "$LOG" || true)
+# Race indicators on driver-prefixed lines only (avoids matching the
+# test program's own informational output). Driver log lines start with
+# "v4l2-request:".
+race_lines=$(grep -E '^v4l2-request:' "$LOG" \
+	| grep -iE 'REQBUFS|EBUSY|Unable to request buffers|Unable to set format' \
+	|| true)
 if [[ -n "$race_lines" ]]; then
 	echo "FAIL: driver stderr contains race indicators:" >&2
 	echo "$race_lines" >&2