diff --git a/IMPROVEMENT_LOG.md b/docs/archive/IMPROVEMENT_LOG.md
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+++ b/docs/archive/IMPROVEMENT_LOG.md
@@ -1,3 +1,5 @@
+> **Historical (archived 2026-09-28):** a log of an automated improvement loop's PRs from April–May 2026, on the earlier `quantumclaw/clawhdf5` PR numbering (not today's). Superseded by [`CHANGELOG.md`](../../CHANGELOG.md) and `git log`.
+
 # Improvement Log -- clawhdf5
 
 | Date | Loop | PR | Changes | Status |
diff --git a/IMPROVEMENT_SCAN.md b/docs/archive/IMPROVEMENT_SCAN.md
similarity index 82%
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@@ -1,3 +1,5 @@
+> **Historical (archived 2026-09-28):** one automated scan's notes (2026-05-04), describing changes long since merged. Superseded by [`CHANGELOG.md`](../../CHANGELOG.md) and `git log`.
+
 # Improvement Scan -- clawhdf5
 
 **Date:** 2026-05-04
diff --git a/docs/superpowers/plans/2026-06-29-filter-codecs.md b/docs/archive/plans/2026-06-29-filter-codecs.md
similarity index 98%
rename from docs/superpowers/plans/2026-06-29-filter-codecs.md
rename to docs/archive/plans/2026-06-29-filter-codecs.md
index 9f44186..8a78d49 100644
--- a/docs/superpowers/plans/2026-06-29-filter-codecs.md
+++ b/docs/archive/plans/2026-06-29-filter-codecs.md
@@ -1,3 +1,5 @@
+> **Historical (archived 2026-09-28):** a pre-work plan, implemented in `d6c4d4f` (2026-06-30). Superseded by the code (`crates/clawhdf5-format`), [`CHANGELOG.md`](../../../CHANGELOG.md) and [`ROADMAP.md`](../../../ROADMAP.md); not an open task list.
+
 # Filter Codecs Implementation Plan
 
 > **Status (2026-08-03):** Implemented — shipped in commit `d6c4d4f` (2026-06-30), with FFI/constant fixes in `cb0b0e9`/`e91f7fc`. This doc was authored 2026-06-29 as the pre-work plan and committed to the repo retroactively on 2026-08-03; checkboxes below have been marked complete to match. Treat this as a historical record, not an open task list.
diff --git a/docs/superpowers/plans/2026-06-29-format-write-extensions.md b/docs/archive/plans/2026-06-29-format-write-extensions.md
similarity index 99%
rename from docs/superpowers/plans/2026-06-29-format-write-extensions.md
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--- a/docs/superpowers/plans/2026-06-29-format-write-extensions.md
+++ b/docs/archive/plans/2026-06-29-format-write-extensions.md
@@ -1,3 +1,5 @@
+> **Historical (archived 2026-09-28):** a pre-work plan, implemented in `d6c4d4f` (2026-06-30) and on 2026-08-03. Superseded by the code (`crates/clawhdf5-format`), [`CHANGELOG.md`](../../../CHANGELOG.md) and [`ROADMAP.md`](../../../ROADMAP.md); not an open task list.
+
 # Format Write Extensions Implementation Plan
 
 > **Status (2026-08-03):** Implemented. Tasks 1–3 (external links, VDS mapping serialization, VDS `FileWriter` API) shipped in commit `d6c4d4f` (2026-06-30). Tasks 4–5 (superblock v4 read/write) were not part of that commit and were completed separately as part of this cleanup pass (2026-08-03) — see `Superblock::parse_v4`/`serialize` and `FileWriter::with_page_size` in `crates/clawhdf5-format`. This doc was authored 2026-06-29 as the pre-work plan and committed to the repo retroactively; checkboxes below have been marked complete to match current state. Treat this as a historical record, not an open task list.
diff --git a/docs/superpowers/plans/2026-06-29-mpi-io-vol-backend.md b/docs/archive/plans/2026-06-29-mpi-io-vol-backend.md
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--- a/docs/superpowers/plans/2026-06-29-mpi-io-vol-backend.md
+++ b/docs/archive/plans/2026-06-29-mpi-io-vol-backend.md
@@ -1,3 +1,5 @@
+> **Historical (archived 2026-09-28):** a pre-work plan. Its goal of *collective* MPI-IO is not what shipped: `MpiVol` (`d6c4d4f`) is root-read + broadcast and gather-to-root writes (see [`crates/clawhdf5-io/README.md`](../../../crates/clawhdf5-io/README.md)); collective I/O is an open item in [`ROADMAP.md`](../../../ROADMAP.md).
+
 # MPI-IO VOL Backend Implementation Plan
 
 > **Status (2026-08-03):** Implemented — shipped in commit `d6c4d4f` (2026-06-30), with FFI/constant fixes in `cb0b0e9`/`e91f7fc`. This doc was authored 2026-06-29 as the pre-work plan and committed to the repo retroactively on 2026-08-03; checkboxes below have been marked complete to match. Treat this as a historical record, not an open task list.