Expose nextest failure tail in CI

Co-authored-by: Codex <noreply@openai.com>

.codex/flaky-test-triage.md

@@ -78,3 +78,4 @@ Older failures also appeared on Linux, but the repeated cross-PR signal is stron
 | `c3b8a0ebf` | Correct Windows popup selection assertions | full pass | Full PR CI passed on run `23081835533`, including both Windows `Tests` jobs and Bazel. The Windows-only initial-selection assertions now expect `Read Only` when the unelevated popup opens on Windows. This restarts the passing streak at 1 of 5 after the intervening failed commits. |
 | `9835ec89d` | Record validation pass 1 | full pass | Full PR CI passed on run `23082212165`, including the rerun of `Tests — windows-arm64 - aarch64-pc-windows-msvc` on job `67054619213`. The branch now has 2 consecutive full-suite green commits after `c3b8a0ebf`. |
 | `b6e18d2e8` | Record validation pass 2 | failed | Run `23083106021` isolated a new failure in `Tests — ubuntu-24.04 - x86_64-unknown-linux-gnu` while both Windows `Tests` jobs and all Bazel/lint checks passed. The GitHub CLI log download hit EOFs on both `results-receiver.actions.githubusercontent.com` and the signed Azure blob URL again, so the follow-up commit adds CI annotations and step-summary output for parsed nextest `FAIL`/`LEAK` lines. |
+| `761363008` | Annotate nextest failures in CI | failed | Run `23083522224` flipped to a new `Tests — windows-x64 - x86_64-pc-windows-msvc` failure while `Tests — windows-arm64 - aarch64-pc-windows-msvc` and every non-test job passed. The new annotations proved this failure did not emit a parsable nextest `FAIL`/`LEAK` line, so the next follow-up extends the annotations to the last 80 log lines and requests explicit final failure output from nextest. |

.github/workflows/rust-ci.yml

@@ -629,13 +629,35 @@ jobs:
                 tail -n 200 "$log_file"
                 echo '```'
               } >> "$GITHUB_STEP_SUMMARY"
-              echo "::error::nextest failed without a parsable FAIL/LEAK line; inspect the tail in the step summary"
+              echo "::error::nextest failed without a parsable FAIL/LEAK line; the last 80 log lines were emitted as annotations"
+
+              mapfile -t tail_lines < <(tail -n 80 "$log_file")
+              chunk=""
+              chunk_index=1
+              for i in "${!tail_lines[@]}"; do
+                line=${tail_lines[$i]//%/%25}
+                line=${line//$'\r'/%0D}
+                line=${line//$'\n'/%0A}
+                if [[ -n "$chunk" ]]; then
+                  chunk="${chunk}%0A${line}"
+                else
+                  chunk="$line"
+                fi
+
+                if (( (i + 1) % 10 == 0 || i + 1 == ${#tail_lines[@]} )); then
+                  echo "::error title=nextest failure tail ${chunk_index}::$chunk"
+                  chunk=""
+                  ((chunk_index++))
+                fi
+              done
             fi
           fi
 
           exit $status
         env:
           RUST_BACKTRACE: 1
+          NEXTEST_FAILURE_OUTPUT: final
+          NEXTEST_FINAL_STATUS_LEVEL: fail
           NEXTEST_STATUS_LEVEL: leak
 
       - name: Upload Cargo timings (nextest)