Measure output capture allocations for chunked writes

docs/internal/gotool.md

@@ -17,8 +17,14 @@ needed by the caller, such as compiler identification. After the child stops,
 the capture's backing bytes transfer to the caller without a second copy. A
 failed output command returns both those bytes and an error containing the
 diagnostic text. The capture remains in memory for the duration of the child;
-an 8 MiB forwarded capture currently allocates about 8.39 MB per operation,
-with the returned 8 MiB slice owned by its caller. Failed output also formats
+the component benchmark compares one 8 MiB write with the same output in
+32 KiB writes, forwarding to `io.Discard`. Smaller writes incur buffer-growth
+allocations. The [workload-specific results](../roadmap/implementation.md#output-chunking-follow-up)
+record total allocated bytes per operation, excluding subprocess overhead and
+diagnostic strings. These totals count all allocations, including superseded
+buffers. The returned slice retains the final buffer holding the complete output.
+Peak live memory depends on buffer growth, garbage collection, and other command
+work and is not measured by allocation totals. Failed output also formats
 diagnostics into the error, so the returned bytes and diagnostic string can
 coexist. Disk-backed diagnostics could reduce large failure peaks, but add file
 lifecycle and cleanup work and remain a follow-up option.