[Test] (Retrace): make a retrace under MOBILEGL_PIPE_VERIFY prove it armed, and give the lane a label

- A retrace that exports MOBILEGL_PIPE_VERIFY=1 at a library configured without
  -DMOBILEGL_PIPE_VERIFY=ON is a no-op: the frames still match their goldens and the
  case reports green having compared nothing. run_trace_case.cmake now demands the
  evidence whenever the variable is set to anything but 0/false - mobilegl.log must
  exist, must carry "MGPipe: verify armed", and must carry neither
  Fatal{PipeVerifyDiffer nor Fatal{UnmigratedPipeInput. With the variable unset the
  script is byte-for-byte the old one.
- The Fatal scan is not redundant with the replay's exit status:
  MOBILEGL_PIPE_VERIFY_FATAL=0 is the supported triage configuration, and there a
  divergence is logged and counted rather than aborted, so the run would finish 0
  with its own report sitting unread in the log.
- LABELS retrace on both registrations: the lane was selectable only by regex, so
  `ctest -L retrace --no-tests=error` - the spelling that reds a lane which
  registered nothing - could not be written at all.
- "verify": true on eight cases (the five 180s cases plus minecraft-1.21.4-in-world,
  minecraft-1.21.4-fabric-sodium-in-world and improved-transparency-minecraft-26.3),
  and --format github-verify-matrix over that subset: 16 entries, against the full
  lane's 77. The verify build compares at every verb boundary and again at every
  accessor read, which the design budgets at 5-10x, so the per-push job runs the
  subset and the full sweep is a phase-exit / workflow_dispatch run.
- The flag is validated in the manifest loader, not at the matrix, so a non-boolean
  or a verify case excluded from CI is a loud error in every consumer instead of a
  subset that is quietly one case short.

tools/trace_replay/trace_cases.py

@@ -26,6 +26,16 @@ def load_trace_case_manifest(path=TRACE_CASES_JSON):
         for key in ("trace_archive", "trace_file", "golden", "target_call", "width", "height"):
             if key not in merged:
                 raise ValueError(f"{key} is required for {name}")
+        # "verify" opts a case into the MOBILEGL_PIPE_VERIFY retrace subset. It is checked here
+        # rather than where the matrix is built so that a typo is a loud manifest error in every
+        # consumer (the cmake emitter included) instead of a subset that is quietly one case short.
+        verify = merged.get("verify", False)
+        if not isinstance(verify, bool):
+            raise ValueError(f"verify must be true or false for {name}")
+        if verify and not merged.get("ci", True):
+            raise ValueError(
+                f"{name} is marked verify but excluded from CI, so the verify matrix would drop it"
+            )
         cases.append(merged)
     return {"defaults": defaults, "cases": cases}
 
@@ -72,6 +82,16 @@ def ci_trace_cases(cases):
     return [case for case in cases if case.get("ci", True)]
 
 
+def verify_trace_cases(cases):
+    """The subset the third CI mode retraces.
+
+    The verify build compares two state models at every verb boundary and again at every accessor
+    read, which the design budgets at 5-10x, so the per-push lane runs a named subset and the full
+    79-case sweep happens at the phase exit and on workflow_dispatch.
+    """
+    return [case for case in cases if case.get("verify", False)]
+
+
 def ci_backends(case):
     backends = case.get("ci_backends")
     if backends is None:
@@ -98,6 +118,10 @@ def github_test_matrix(cases):
     }
 
 
+def github_verify_matrix(cases):
+    return github_test_matrix(verify_trace_cases(cases))
+
+
 def github_apk_matrix(cases):
     backends = {
         "DirectGLES": {"name": "DirectGLES", "gpu": "software"},
@@ -158,6 +182,7 @@ def parse_args():
         choices=(
             "names",
             "github-test-matrix",
+            "github-verify-matrix",
             "github-apk",
             "github-apk-matrix",
             "fixture-files",
@@ -177,6 +202,8 @@ def main():
         print(json.dumps([case["name"] for case in cases], separators=(",", ":")))
     elif args.format == "github-test-matrix":
         print(json.dumps(github_test_matrix(cases), separators=(",", ":")))
+    elif args.format == "github-verify-matrix":
+        print(json.dumps(github_verify_matrix(cases), separators=(",", ":")))
     elif args.format == "github-apk":
         print(json.dumps([github_apk_case(case) for case in cases], separators=(",", ":")))
     elif args.format == "github-apk-matrix":