Fix test coverage merging: seed from test_coverage.json on first run

test_results.json is git-ignored (local to each machine). When a new
contributor ran tests, their empty file caused export_web_coverage() to
overwrite test_coverage.json with only their results, erasing other
testers' data.

Now load_results() seeds from the committed test_coverage.json when
test_results.json is missing or empty, so the next export merges
results from all contributors. Same fix applied to show_matrix.py.

tests/run_tests.py

@@ -216,8 +216,55 @@ def check_json_report_plugin() -> bool:
 
 
 def load_results() -> list[dict]:
+    """Load past results from test_results.json, seeding from test_coverage.json if needed.
+
+    test_results.json is git-ignored (local to each machine).  When a new
+    contributor runs for the first time, their file is empty — but the
+    committed test_coverage.json contains the matrix from other testers.
+    We import those entries so the next export *merges* instead of
+    overwriting.
+    """
     if RESULTS_FILE.exists():
-        return json.loads(RESULTS_FILE.read_text())
+        try:
+            data = json.loads(RESULTS_FILE.read_text())
+            if data:
+                return data
+        except (json.JSONDecodeError, ValueError):
+            pass
+
+    # Seed from the committed web coverage file so we don't lose other
+    # contributors' results on first run.
+    if WEB_COVERAGE_FILE.exists():
+        try:
+            coverage = json.loads(WEB_COVERAGE_FILE.read_text())
+            entries = coverage.get("matrix", [])
+            if entries:
+                # Convert matrix entries back to results-like dicts.
+                # The matrix has: os, robot, suite, browser, status,
+                # passed, failed, total, date.  We synthesise a
+                # timestamp from the generated_at field so the
+                # "latest per combo" logic still works.
+                generated = coverage.get("generated_at", datetime.now(timezone.utc).isoformat())
+                seeded = []
+                for e in entries:
+                    seeded.append({
+                        "timestamp": generated,
+                        "os": e["os"],
+                        "robot": e["robot"],
+                        "suite": e["suite"],
+                        "browser": e.get("browser"),
+                        "passed": e.get("passed", 0),
+                        "failed": e.get("failed", 0),
+                        "errors": 0,
+                        "total": e.get("total", 0),
+                        "status": e.get("status", "pass"),
+                        "returncode": 0,
+                    })
+                print(f"Seeded {len(seeded)} entries from {WEB_COVERAGE_FILE.name}")
+                return seeded
+        except (json.JSONDecodeError, ValueError):
+            pass
+
     return []
 
 

tests/show_matrix.py

@@ -122,15 +122,48 @@ def print_catalog(catalog: list[dict]) -> None:
         print()
 
 
-def main() -> None:
-    if not RESULTS_FILE.exists():
-        print(f"No results file found at {RESULTS_FILE}")
-        print("Run tests first: python tests/run_tests.py")
-        sys.exit(1)
+def load_results() -> list[dict]:
+    """Load results from test_results.json, falling back to test_coverage.json."""
+    if RESULTS_FILE.exists():
+        try:
+            data = json.loads(RESULTS_FILE.read_text())
+            if data:
+                return data
+        except (json.JSONDecodeError, ValueError):
+            pass
 
-    results = json.loads(RESULTS_FILE.read_text())
+    # Fall back to the committed web coverage file
+    if WEB_COVERAGE_FILE.exists():
+        try:
+            coverage = json.loads(WEB_COVERAGE_FILE.read_text())
+            entries = coverage.get("matrix", [])
+            generated = coverage.get("generated_at", "2025-01-01T00:00:00+00:00")
+            return [
+                {
+                    "timestamp": generated,
+                    "os": e["os"],
+                    "robot": e["robot"],
+                    "suite": e["suite"],
+                    "browser": e.get("browser"),
+                    "passed": e.get("passed", 0),
+                    "failed": e.get("failed", 0),
+                    "errors": 0,
+                    "total": e.get("total", 0),
+                    "status": e.get("status", "pass"),
+                    "returncode": 0,
+                }
+                for e in entries
+            ]
+        except (json.JSONDecodeError, ValueError):
+            pass
+
+    return []
+
+
+def main() -> None:
+    results = load_results()
     if not results:
-        print("No test results recorded yet.")
+        print("No test results found.")
         print("Run tests first: python tests/run_tests.py")
         sys.exit(1)