chore(ci): consolidate the 3-shard test matrix into one unsharded validate-tests run

codecov.yml

@@ -11,21 +11,15 @@ codecov:
   # Don't post a verdict until the CI run that produced the report has finished.
   require_ci_to_pass: true
   notify:
-    # The 3 backend test shards (validate-tests matrix, ci.yml) each upload their own lcov.info
-    # directly (flags: shard-N) -- additive by design, but Codecov re-evaluates and re-posts the
-    # status check after EVERY individual upload, not just the last one. Without this, codecov/patch
-    # can report a wildly wrong verdict (as low as ~20% "patch coverage") after only 1-2 of 3 shards
-    # have landed, before self-correcting once the rest arrive -- require_ci_to_pass above only checks
-    # the GH Actions run's own conclusion, it says nothing about upload completeness. Waiting for all
-    # 3 coverage uploads (JUnit test_results uploads are a separate stream and don't count here) before
-    # posting a status removes that premature-fail/premature-pass window entirely.
-    #
-    # Stays 3, not 4, even though review-enrichment adds a `rees` upload on REES PRs: 3 is the count that
-    # ALWAYS lands whenever validate-tests runs (the minimum floor), while the `rees` upload only exists on
-    # REES PRs. The `rees` report is produced by validate-code, which finishes its REES steps in seconds and
-    # so uploads well before any ~10-minute shard -- it is already merged in by the time the 3rd shard trips
-    # this threshold, so no premature window opens for the review-enrichment diff either.
-    after_n_builds: 3
+    # The count that ALWAYS lands whenever validate-tests runs: since the 2026-07-24 unsharding, the
+    # backend suite produces ONE whole-suite lcov upload (flags: backend) instead of the former 3 shard
+    # uploads this threshold was sized for. It must stay 1, not 2, even though review-enrichment /
+    # control-plane add their own flag uploads on PRs that touch them -- those uploads only exist on such
+    # PRs, and a floor above the guaranteed minimum would leave codecov/patch permanently un-posted on
+    # every other PR. The narrow premature-window this reintroduces (a rees/control-plane upload landing
+    # and posting before the ~25-minute backend run finishes) self-corrects on the backend upload, and
+    # require_ci_to_pass above still holds the final verdict to the run's own conclusion.
+    after_n_builds: 1
 
 coverage:
   status: