docs(wasm-viewer): package size re-measured after openUrl; round-trip costs

The size table predated openUrl (it said so). Re-measured on tank at
9b5803f with `bash examples/wasm-viewer/build.sh`, then `wc -c` and
`gzip -9 -n -c`: the wasm is 1,384,607 B (378,485 gzipped), was 627,501
(191,639); the glue 40,711 (8,181), was 21,826 (4,487); remote.js 9,326
(3,448). 476,062 B of the wasm is the function-name section. opt-level z
(CARGO_PROFILE_WASM_RELEASE_OPT_LEVEL=z) is now 1% smaller gzipped than
the profile's s; 3 is larger. h5wasm rows unchanged.

Also adds the measured cost of listing a large group and reading one
dataset by URL (passes / requests / bytes, from CHANGELOG, 2026-09-27).

Co-Authored-By: Claude Opus 5.5 (1M context) <[email protected]>

examples/wasm-viewer/README.md

@@ -79,6 +79,30 @@ for a deep one) and one batch of requests for its chunks. Every answer is
 checked — a `206` with exactly the bytes asked for, from the same file
 (ETag or Last-Modified, and length) — or the call fails.
 
+What that costs, counted on tank on 2026-09-27 (`CHANGELOG.md`, "Remote
+files in the browser: fewer round trips"), on an h5py file of 3000
+datasets of 16384 `f32` in one group (198 MB, h5py 3.16 / HDF5 2.0), as
+passes / requests / bytes fetched, with
+`CLAWHDF5_WASM_LIST_FILE=<file> CLAWHDF5_WASM_READ=/d1500 cargo test
+--release -p clawhdf5-wasm --test lazy listing_cost_of_a_given_file --
+--nocapture`:
+
+| file (`libver`), block size | `list('/')` | open + read one dataset |
+|---|---|---|
+| earliest, 1 MiB | 4 / 68 / 192.5 MB | 6 / 5 / 5.2 MB |
+| earliest, 64 KiB | 5 / 530 / 35.3 MB | 8 / 7 / 0.52 MB |
+| latest, 1 MiB | 5 / 86 / 196.5 MB | 7 / 7 / 6.7 MB |
+| latest, 64 KiB | 6 / 454 / 30.5 MB | 8 / 8 / 0.58 MB |
+
+Listing reads every child's object header, and h5py spreads those through
+the file, so a listing of a group this large fetches most of it at 1 MiB
+blocks; a smaller `blockSize` fetches far less at the cost of more
+requests. Reading one dataset does not list the group. In the test suite's
+200 MB file (`WASM_BIG_MB=200 bash examples/wasm-viewer/test/run.sh`),
+listing the root, reading two small datasets, a group's attributes, the
+large dataset's shape and a 10-value window of it took 5 requests and
+6 MiB.
+
 `data` is the typed array of the stored width (`Float64Array`,
 `Float32Array` also for `f16`, `Int8Array` ... `BigInt64Array`,
 `BigUint64Array`), or an array of strings for fixed- and variable-length
@@ -155,25 +179,39 @@ browser).
 
 ## Size
 
-Measured 2026-09-26 on tank (rustc 1.98.1, wasm-bindgen 0.2.129, gzip 1.14,
+Measured 2026-09-28 on tank at `9b5803f` (rustc 1.98.1, wasm-bindgen
-`gzip -9 -n`), after `bash examples/wasm-viewer/build.sh`. The package is
+0.2.129, gzip 1.14): `bash examples/wasm-viewer/build.sh`, then `wc -c` and
-larger now and the table has not been re-measured: the reader has grown
+`gzip -9 -n -c FILE | wc -c` of each file in `pkg/`. The opt-level `z` and
-since, and `openUrl` (2026-09-27) made the facade's range-read path
+`3` rows are the same build with `CARGO_PROFILE_WASM_RELEASE_OPT_LEVEL=z`
-reachable from JavaScript and added promise glue and `remote.js`.
+(or `3`) and the same `wasm-bindgen --target web` step.
 
 | | raw | gzip -9 |
 |---|---:|---:|
-| `pkg/clawhdf5_wasm_bg.wasm` (profile `wasm-release`, opt-level `s`) | 627,501 B | 191,639 B |
+| `pkg/clawhdf5_wasm_bg.wasm` (profile `wasm-release`, opt-level `s`) | 1,384,607 B | 378,485 B |
-| `pkg/clawhdf5_wasm.js` (wasm-bindgen glue) | 21,826 B | 4,487 B |
+| `pkg/clawhdf5_wasm.js` (wasm-bindgen glue) | 40,711 B | 8,181 B |
-| same wasm at opt-level `z` | 693,068 B | 192,550 B |
+| `pkg/snippets/.../js/remote.js` (the HTTP side of `openUrl`) | 9,326 B | 3,448 B |
-| same wasm at opt-level `3` | 544,035 B | 198,803 B |
+| same wasm at opt-level `z` | 1,533,772 B | 374,765 B |
+| same wasm at opt-level `3` | 1,184,889 B | 394,569 B |
 | h5wasm 0.10.3: wasm embedded in `dist/esm/hdf5_util.js` | 3,544,184 B | 907,096 B |
 | h5wasm 0.10.3: `dist/esm/hdf5_util.js` as shipped | 4,150,134 B | 986,699 B |
 
-h5wasm figures: `npm pack [email protected]` (npm reports
+The previous measurement (2026-09-26, before `openUrl`) was 627,501 B /
-`dist.unpackedSize` 14,731,385 B for the whole package), wasm extracted from
+191,639 B gzipped for the wasm and 21,826 B / 4,487 B for the glue. The
-the `binaryDecode` literal in `hdf5_util.js`. h5wasm is the whole of libhdf5
+package roughly doubled since. `openUrl` made the facade's `Storage` read
-(writing, every datatype, plugins), so this compares download size, not
+path reachable from JavaScript (it was compiled out before) and added the
-equal functionality. No `wasm-opt` pass was applied (binaryen is not
+lazy cache and the promise glue (`CHANGELOG.md`, M4); the growth has not
-installed on tank). opt-level `s` is used because it is the smallest
+been broken down per change. Of the
-compressed.
+wasm's 1,384,607 bytes, 476,062 are the `name` custom section (function
+names, which wasm-bindgen keeps; `wasm-bindgen --remove-name-section` or a
+`wasm-opt` pass would drop them); code is 816,244 and data 83,431. Without
+the name section the wasm is 908,541 B, 329,854 B gzipped (section removed
+with a script, not a supported build option yet). At
+opt-level `z` the gzipped wasm is now 1% smaller than at `s`, which the
+profile still uses.
+
+h5wasm figures (2026-09-26, unchanged): `npm pack [email protected]` (npm
+reports `dist.unpackedSize` 14,731,385 B for the whole package), wasm
+extracted from the `binaryDecode` literal in `hdf5_util.js`. h5wasm is the
+whole of libhdf5 (writing, every datatype, plugins), so this compares
+download size, not equal functionality. No `wasm-opt` pass was applied
+(binaryen is not installed on tank).