diff --git a/src/domain/process/processCaptureValidation.ts b/src/domain/process/processCaptureValidation.ts
index 02d0b8157a..a222a47a69 100644
--- a/src/domain/process/processCaptureValidation.ts
+++ b/src/domain/process/processCaptureValidation.ts
@@ -140,17 +140,39 @@ const validateCoverage = (
     hasCaptureTruncation(
       details,
     ), "truncation_details", "aggregate truncation must match producer coverage");
-  for (const [name, retention, count] of [
-    ["raw_terminal", details.raw_terminal, capture.frames.length],
+  for (const [name, retention, count, bytes] of [
+    [
+      "raw_terminal",
+      details.raw_terminal,
+      capture.frames.length,
+      capture.frames.reduce(
+        (total, frame) =>
+          total + Buffer.byteLength(frame.raw_data ?? frame.data),
+        0,
+      ),
+    ],
     [
       "rendered_terminal",
       details.rendered_terminal,
       capture.rendered_frames.length,
+      capture.rendered_frames.reduce(
+        (total, frame) =>
+          frame.lines.reduce(
+            (sum, line) => sum + Buffer.byteLength(line),
+            total + Buffer.byteLength(frame.serialized_state),
+          ),
+        0,
+      ),
     ],
   ] as const) {
+    // Whole frames are retained or omitted, so retained bytes are exactly the
+    // retained frames' bytes, and nothing is unretained when no frame was omitted.
     require(retention.retained_frames === count &&
       retention.observed_frames >= count &&
+      retention.retained_bytes === bytes &&
       retention.observed_bytes >= retention.retained_bytes &&
+      (retention.observed_frames > count ||
+        retention.observed_bytes === retention.retained_bytes) &&
       retention.retained_bytes <=
         retention.budget_bytes, `truncation_details.${name}`, "retained observations and budget accounting do not agree");
   }
diff --git a/tests/boundary/process/processTruncationAdapters.test.ts b/tests/boundary/process/processTruncationAdapters.test.ts
index 7a46e5aab3..00e2c7f5c2 100644
--- a/tests/boundary/process/processTruncationAdapters.test.ts
+++ b/tests/boundary/process/processTruncationAdapters.test.ts
@@ -133,6 +133,30 @@ itWithCaptureCapability.each(["cli", "mcp"] as const)(
     expect(
       processCaptureSchema.safeParse({ ...result, truncated: false }).success,
     ).toBe(false);
+    const withTerminal = (
+      name: "raw_terminal" | "rendered_terminal",
+      change: Partial<typeof details.raw_terminal>,
+    ) =>
+      processCaptureSchema.safeParse({
+        ...result,
+        truncation_details: {
+          ...details,
+          [name]: { ...details[name], ...change },
+        },
+      }).success;
+    // Byte totals must match the retained frames, and with no omitted frame
+    // nothing observed can be missing from retention.
+    expect(withTerminal("raw_terminal", { retained_bytes: 0 })).toBe(false);
+    expect(
+      withTerminal("raw_terminal", {
+        observed_bytes: details.raw_terminal.observed_bytes + 1,
+      }),
+    ).toBe(false);
+    expect(
+      withTerminal("rendered_terminal", {
+        retained_bytes: details.rendered_terminal.retained_bytes - 1,
+      }),
+    ).toBe(false);
   },
   20_000,
 );