ci: Log df during tmt runs and at the end of jobs

To help us debug out of space failures.

Assisted-by: OpenCode (Claude Sonnet 4.6)
Signed-off-by: Colin Walters <walters@verbum.org>

Author: cgwalters

.github/workflows/ci.yml

@@ -296,6 +296,14 @@ jobs:
 
           just clean-local-images
 
+      - name: Disk usage summary
+        if: always()
+        run: |
+          echo "### Disk usage" >> "$GITHUB_STEP_SUMMARY"
+          echo '```' >> "$GITHUB_STEP_SUMMARY"
+          df -h >> "$GITHUB_STEP_SUMMARY"
+          echo '```' >> "$GITHUB_STEP_SUMMARY"
+
       - name: Archive TMT logs
         if: always()
         uses: actions/upload-artifact@v7
@@ -350,6 +358,14 @@ jobs:
       - name: Run upgrade test
         run: just test-upgrade
 
+      - name: Disk usage summary
+        if: always()
+        run: |
+          echo "### Disk usage" >> "$GITHUB_STEP_SUMMARY"
+          echo '```' >> "$GITHUB_STEP_SUMMARY"
+          df -h >> "$GITHUB_STEP_SUMMARY"
+          echo '```' >> "$GITHUB_STEP_SUMMARY"
+
       - name: Archive TMT logs
         if: always()
         uses: actions/upload-artifact@v7

crates/xtask/src/tmt.rs

@@ -659,6 +659,10 @@ pub(crate) fn run_tmt(sh: &Shell, args: &RunTmtArgs) -> Result<()> {
         )
         .run();
 
+        // Log disk usage after each test run to help diagnose "no space left on device" failures
+        println!("Disk usage after plan {}:", plan);
+        let _ = cmd!(sh, "df -h").run();
+
         // Clean up VM regardless of test result (unless --preserve-vm is set)
         cleanup_vm();