diff --git a/packages/runs/README.md b/packages/runs/README.md
index 8fd78082c..9718bed4d 100644
--- a/packages/runs/README.md
+++ b/packages/runs/README.md
@@ -72,7 +72,10 @@ printed them.
 
 `list` and `show` print exactly what they printed before this package
 existed, for any data root with no link out of it, no run document that
-is JSON but not an object, and no unreadable directory.
+is JSON but not an object, no `result.json` with a field of the wrong
+type (a `status` or `taskId` that isn't a string, or a `workspace` or
+`session` that is neither a string nor `null`), and no unreadable
+directory.
 `agents/rocko/work/queue-56/byte-check.sh` checks that byte for byte
 against a seeded data root. Where those conditions don't hold, the
 output changes on purpose:
@@ -82,6 +85,7 @@ output changes on purpose:
 | run directory or `result.json` linked out | read through the link | `list`: `unknown`; `show`: refuses (run directory) or `result.json: (missing or unreadable)` |
 | `runs/` linked out | read through the link | `list` and `show` refuse, exit 4 |
 | `result.json` is `5` or `[]` | `list` crashed; `show` printed `undefined` fields | `unknown`; `(missing or unreadable)` |
+| `result.json` is an object whose `status` or `taskId` isn't a string, or whose `workspace` or `session` is neither a string nor `null` (`{}`, a numeric `status`, a `null` `taskId`) | `list` crashed on a `status` or `taskId` that isn't a string, hiding every run after it, and printed a `workspace` or `session` that is neither a string nor `null` through `String` | `list`: `unknown` for the status, `-` for each other field, and every later run still lists; `show` as before |
 | `task.json` or `mission.json` is JSON but not an object | `show` printed its snapshot line | snapshot line omitted |
 | run is a regular file | `show` crashed | `run not found`, exit 4 |
 | `runs/` unreadable | `list` printed nothing | refuses, exit 4 |
diff --git a/packages/runs/tests/task-cli.test.mjs b/packages/runs/tests/task-cli.test.mjs
index ed13ecde6..a7c1caed3 100644
--- a/packages/runs/tests/task-cli.test.mjs
+++ b/packages/runs/tests/task-cli.test.mjs
@@ -32,6 +32,34 @@ test("list prints each run in the established format", (t) => {
     `${B}  unknown    task=-                  ws=-          session=-\n`);
 });
 
+test("list prints a damaged result.json as unknown and keeps listing the runs after it", (t) => {
+  const { dataRoot } = scratch(t);
+  const M = "r-20260101T000050Z-mmmmmm";
+  write(path.join(dataRoot, "runs", A, "result.json"), { ...RESULT, workspace: "ws1", session: "s1" });
+  write(path.join(dataRoot, "runs", M, "result.json"), {});
+  write(path.join(dataRoot, "runs", B, "result.json"), { ...RESULT, taskId: "t-two", workspace: ":run" });
+  const out = task(t, dataRoot, "list");
+  assert.equal(out.status, 0, out.stderr);
+  assert.equal(out.stdout,
+    `${A}  succeeded  task=t-one              ws=ws1        session=s1\n` +
+    `${M}  unknown    task=-                  ws=-          session=-\n` +
+    `${B}  succeeded  task=t-two              ws=:run       session=-\n`);
+});
+
+test("list prints each result field that isn't a string as unknown or -", (t) => {
+  const { dataRoot } = scratch(t);
+  const runs = [
+    ["r-20260101T000000Z-status", { status: 5 }, "unknown    task=t-one              ws=-          session=-"],
+    ["r-20260101T000001Z-taskid", { taskId: null }, "succeeded  task=-                  ws=-          session=-"],
+    ["r-20260101T000002Z-worksp", { workspace: 7 }, "succeeded  task=t-one              ws=-          session=-"],
+    ["r-20260101T000003Z-sessin", { session: { name: "s1" } }, "succeeded  task=t-one              ws=-          session=-"],
+  ];
+  for (const [runId, damage] of runs) write(path.join(dataRoot, "runs", runId, "result.json"), { ...RESULT, ...damage });
+  const out = task(t, dataRoot, "list");
+  assert.equal(out.status, 0, out.stderr);
+  assert.equal(out.stdout, runs.map(([runId, , line]) => `${runId}  ${line}\n`).join(""));
+});
+
 test("show prints the run in the established format", (t) => {
   const { dataRoot } = scratch(t);
   const dir = path.join(dataRoot, "runs", A);
diff --git a/scripts/mosaic-task.mjs b/scripts/mosaic-task.mjs
index cf8399a0a..fc4e38450 100755
--- a/scripts/mosaic-task.mjs
+++ b/scripts/mosaic-task.mjs
@@ -470,18 +470,19 @@ function readRuns(read) {
 function listRuns() {
   const resolved = loadConfig();
   for (const { runId, result } of readRuns(() => listRunRecords(resolved.dataRoot))) {
-    // An incomplete or unreadable run record (result null) reports as unknown.
+    // An incomplete or unreadable run record (result null) reports as unknown,
+    // and so does each field of a damaged one that isn't a string.
     let status = "unknown";
     let taskId = "-";
     let workspace = "-";
     let session = "-";
     if (result) {
-      status = result.status;
-      taskId = result.taskId;
-      workspace = result.workspace ?? "-";
-      session = result.session ?? "-";
+      if (typeof result.status === "string") status = result.status;
+      if (typeof result.taskId === "string") taskId = result.taskId;
+      if (typeof result.workspace === "string") workspace = result.workspace;
+      if (typeof result.session === "string") session = result.session;
     }
-    process.stdout.write(`${runId}  ${status.padEnd(9)}  task=${taskId.padEnd(18)} ws=${String(workspace).padEnd(10)} session=${session}\n`);
+    process.stdout.write(`${runId}  ${status.padEnd(9)}  task=${taskId.padEnd(18)} ws=${workspace.padEnd(10)} session=${session}\n`);
   }
 }