docs(testing): record capture aliases, preview ranges and the PR B follow-ups

TESTING.md now states that case and Unicode spellings are aliases, that
the preview serves byte ranges inside the capture pin, where the
cancellation tests live, and two tracked follow-ups: the legacy batch's
ungated cleanup unload under its own last inference, and the three files
over the 800-line ceiling (split py/autotag.py first).

TESTING.md

@@ -1427,6 +1427,22 @@ window completes there with a digest of the copied bytes; POSIX and Windows on
 Vocabulary rename, merge and delete bump the `tag_revision` of every image set
 they change (and `image_index_revision`), so a Tag dialog opened before the
 change gets `tag-conflict` on Save (`tests/test_pair_tag_maintenance.py`).
+A case or Unicode spelling of a listed name (`A.PNG` for `a.png`, an NFD name)
+is an alias too: each path part must be spelled as its directory lists it, so a
+case- or normalization-insensitive filesystem (macOS, Windows) cannot store a
+second locator. The capture preview answers one byte range with 206 (416 for
+an unsatisfiable or multi-range header) inside the capture's pin, and a
+cancelled preview, observe or Generate still closes its handle and ends its pin
+or capture (`tests/test_api_annotations.py` `TestCancellation`,
+`tests/test_model_gate.py`).
+
+Follow-ups (tracked, not accepted): the legacy Auto-tag batch's cleanup
+`unload_model()` in `py/api/autotag_routes.py` is not gated against the
+batch's own in-flight inference when the batch coroutine is cancelled (other
+owners are kept out; the thread may log an error); and `py/autotag.py`,
+`py/api/images.py` and `database/operations.py` are over the 800-line ceiling
+(all three were before #249 PR B), with a split of `py/autotag.py` into
+backends and service planned first.
 
 Budgets: `test_filter_work_is_bounded` always runs. It asserts that a plain first
 page makes 1 link SELECT and a plain cursor page none, that every filter shape