Upload rust full CI JUnit reports (#23273)

## Why

`rust-ci-full` failures currently leave downstream investigation
reconstructing basic test facts from raw logs. `cargo nextest` can emit
standard JUnit XML for each lane, which gives us a small structured
artifact for post-run failure analysis without changing the test
execution model.

## What changed

- enable nextest JUnit output in `codex-rs/.config/nextest.toml`
- upload the lane-scoped JUnit XML artifact from each `rust-ci-full`
test lane

## Verification

- `rust-ci-full` run `26018931531` on head
`52d77c60e79b36859d944ef28a36b014055c5c48` produced JUnit artifacts for
macOS, Linux x64 remote, Windows x64, and Windows ARM64 test lanes
- `rust-ci-full` run `26021241006` on the same head produced the missing
Linux ARM JUnit artifact after the first run lost that runner before
export
- downloaded all five lane JUnit artifacts and verified each contains
non-empty test counters and failure data

.github/workflows/rust-ci-full.yml

@@ -688,6 +688,14 @@ jobs:
           RUST_MIN_STACK: "8388608" # 8 MiB
           NEXTEST_STATUS_LEVEL: leak
 
+      - name: Upload nextest JUnit report
+        if: always()
+        uses: actions/upload-artifact@bbbca2ddaa5d8feaa63e36b76fdaad77386f024f # v7.0.0
+        with:
+          name: nextest-junit-rust-ci-${{ matrix.runner }}-${{ matrix.target }}-${{ matrix.profile }}
+          path: codex-rs/target/nextest/default/junit.xml
+          if-no-files-found: warn
+
       - name: Upload Cargo timings (nextest)
         if: always()
         uses: actions/upload-artifact@bbbca2ddaa5d8feaa63e36b76fdaad77386f024f # v7.0.0

codex-rs/.config/nextest.toml

@@ -2,6 +2,9 @@
 # Do not increase, fix your test instead
 slow-timeout = { period = "15s", terminate-after = 2 }
 
+[profile.default.junit]
+path = "junit.xml"
+
 [test-groups.app_server_protocol_codegen]
 max-threads = 1